Borrowed pcb prototyping system solves major test problems

A circuit board plotter originally purchased for making engineering prototypes is yielding big dividends in the test department at IS0 9001-certified semiconductor manufacturer Supertex Inc., Sunnyvale CA. Test engineers there have been borrowing from their applications engineering department a ProtoMat circuit board plotter system manufactured by LPKF Laser & Electronics to solve some of their most difficult testing problems.

Focused on DMOS, HVCMOS and BiCMOS IC products for use in computer, telecom, medical, instrumentation, defence and consumer-product industries, Supertex designs and manufactures proprietary and industry-standard ICs, and has demonstrated technological leadership in high voltage and mixed signal high voltage semiconductor products.

Supertex applications engineering brought in the plotter to produce prototype boards that are used to demonstrate the company's new high-voltage integrated circuits (ICs). The plotter is now being used to fabricate hundreds of test fixtures as well, yielding big dividends in turnaround time, lower test costs and improved accuracy of test results. The problem that test had is that unreliable test fixtures cause downtime and errors. PCB Assembly Inadequate or unreliable test fixtures had been causing major disruptions to new product introductions at Supertex due to mechanical failures and improper test results.

"We were building typical generic wire-wrap fixtures to adapt our new devices to the dozens of test stations we maintain," Frank Galica, hardware engineer-supervisor, says. "Connectors on the generic fixtures were hard to keep in alignment and always seemed to break down at the worst time, right in the middle of a crunch run."

"As our devices became more sophisticated, other parameters that are difficult to control in a wire-wrap fixture began to affect the measurements themselves," he adds. "Inconsistencies such as improper lead lengths, parasitic inductance and loosening connections forced us to repeat the tests or, at worst, gave us false results that were not caught until much later in the process. Those old fixtures were costing us time and money."

A new semiconductor device is characterized by inserting it into a test fixture that provides support circuitry for power, loads, I/O and other functions and adapts it to instrumentation for measurement of its key parameters. To ensure accurate measurements, the fixture must provide a stable, realistic environment for the device and it needs to withstand repeated insertions and removals without degrading in performance.

"Our fixtures were not keeping up with the demands of the new device technologies," Galica explains, "but we could not let the designs out of our control for pc-board fabrication, since they are proprietary and extremely sensitive."

"Moreover, we do not have the time to wait for an outside vendor to respond. So, we just kept rebuilding and redesigning the fixtures to try to minimize the problems," he adds.

The solution turned out to making custom circuit card fixtures on the spot. Scott Lynch, a Supertex applications engineer showed Galica a prototype circuit board that had just been used to win a design contract. The board had been produced on a newly-installed circuit board plotter and had performed very well in evaluation.

"When I saw the quality of the demo board, I asked Lynch to make us a test fixture board on the same plotter system," Galica says. "The results were excellent: solid performance and mechanical integrity. It was just what we needed, and it only took a couple of hours."

The plotter system downloads files directly from a CAE program and translates them into board layouts. It then automatically produces each board by drilling the through holes and milling the traces from a variety of standard copper-clad FR3, FR4 and G10 laminated materials. Boards are cut to precise sizes and tolerances and most can be produced in a few minutes.

Using the plotter to redesign several other fixtures that had been particularly troublesome resulted in similar results. The plotter provided close control over trace widths and spacing, proper routing of signal paths and optimum placement of parts. Connectors and sockets were precisely aligned and firmly attached for long, reliable lifetimes.

Best of all, the entire process resides in-house, with complete security and instantaneous turnaround. The plotter system is kept in the design lab; no chemicals are used in this process and a built-in vacuuming system keeps the area dust free.

The bottom line is improved performance on the test floor, and it is now time for a second system. Galica had several technicians trained in both CAE design and the board layout programs and they started borrowing Lynch's plotter system on a regular basis. "We have made thousands of boards in the past few years," Galica says. "Our test times are significantly shorter and downtime for broken fixtures is non-existent. We are even making custom test equipment and custom panels for our test stations. Our only problem is that we need to get another system, since demand from the test department has taken over the machine."

LPKF Laser & Electronics is a wholly owned subsidiary of publicly-traded LPKF Laser & Electronics AG of Garbsen, Germany. Founded in 1976, LPKF products target advanced circuit board prototyping and SMD stencil and high-density circuit board designs, eliminating the need for hazardous chemicals. Its MicroLine laser circuit structuring processes are transforming the design of smaller, lower cost, higher-performance products for telecommunications, computing, medical, video and measurement applications, the company says.

LPKF high precision circuit board plotters, multilayer devices and plating systems have become a standard in the industry, with more than 8,000 installations worldwide. The drilling and milling process is simple, safe and economical. High precision tools and superior mechanical design turn circuit designs into holes and traces on a card by removing material.

The ProtoMat C30 plotter provides repetition accuracy of 0.2mil and can produce traces as fine as 4mil with spacing down to 8 mil. A typical card can be produced within one to two hours for US$7 to US$10 in materials and tools.

Plotters handle most demanding RF, microwave circuits Technology breakthroughs have extended the speed, safety and convenience of mechanical pc-board prototyping to the most demanding applications, according to LPKF Laser & Electronics , Wilsonville OR. Unique pneumatic systems control the cutting process far more precisely and gently than with previous methods, making it possible for the first time to create circuits in highly sensitive PTFE (Teflon) substrates such as RT/duroid.

Track width structures as fine as 100-microns with very precise cutting channels and an accuracy of better than 0.2mil ensure the faithful reproduction of fine pitch and higher density circuits. Tool service life and geometric precision electronic assembly are also enhanced through the use of adjustable speed three-phase spindle motors that operate up to 100,000rpm.

The Chemistry of Polychlorinated Biphenyls PCB

IV. EMI: PCB Ground System and Power System

Before you start worrying about the Ground System, all the components should be already placed on the grid to start the PCB layout.

Figure 1: Components Placed on the Grid

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For better understanding, Figure 1 shows the components placed on the grid without traces, a ground system, or a power system. The objective is to place the components as closely as possible to eliminate long traces, and thus reduce electromagnetic noise and interference. Eliminating long traces minimizes internal self inductance, which as already mentioned, is noise. Figure 1 shows one section of the circuitry that will be laid out for the manufacturing purposes for a particular system. Once the components have been laid out, the ground system and power system must be taken into consideration. The power supply trace should run parallel to the ground trace in order to maximize the reduction of electromagnetic noise and interference.

Figure 2: Components with Ground and Power Trace

The above screen shot, Figure 2, shows the power trace (red trace) and the ground trace (green trace). Like I already mentioned, the power and ground traces should run parallel and close together to prevent noise. In my case, I placed the power trace on the top layer (thus red in color) and placed the ground trace on the bottom layer (green denoting the bottom layer).

There are additional measures that can be taken to reduce the noise generated due to the power system and the ground system in a PCB Assembly. One common way to eliminate the noise that is produced due to the ground and power supply traces is to simply use a decoupling capacitor. Basically, all you have to do is place a capacitor between ground and the power supply. It is also important that the capacitor used does not have high impedance. Another important thing to take into account are the pins of the ICs that are unused. It is important to connect the unused pins to a voltage supply with a series resistor, or for a cheaper way (not needing a resistor), just connect the unused input to ground. This will prevent a noise signal to couple to one of the unused inputs and cause a gate to switch when it is not desired. (2)

V. EMI: Placing of Components

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We have discussed some of the techniques that I used to prevent electromagnetic interference (EMI) and noise concerning the ground and power systems when designing a PCB. Additionally, there it is important to take into consideration the noise and EMI from the connections between some components. The connection between oscillators and ICs that they serve should be as short as possible. (2) Also, “to minimize loop area, signal and return paths should be parallel and close together.” (2) The following screen shot is an example of my design taking into account these important notes.

Figure 3: Oscillator and PIC (IC) Connection

In Figure 3, the connections between the PIC and the Oscillator have been minimized and the return paths are close together and in parallel, therefore minimizing the noise in this case. In this example of component placement, mutual and external self inductances have been minimized (to refresh your memory on what these inductances are, please see the section on electromagnetic noise and interference). These inductances were reduced by minimizing the loop area enclosed by current flow. Another technique that should be considered is to make the address, data, and I/O connections as short as possible, with signal and return paths as close as possible, which will again minimize loop area and in turn, minimize mutual and external self inductances. (2) Lastly, the fastest components should be placed on the PCB at a location that is farthest away from external connections as possible. (2) Interestingly, by doing this, the natural loss on the board material will attenuate the noise signals; I find it ironic that this natural loss, in terms of electromagnetic noise and interference, can actually be advantageous.

VI. Conclusion

Electromagnetic interference and noise is an important issue when creating a printed circuit board (PCB). Printed circuit boards are not cheap, so it is imperative that the PCB you design is designed to maximize its capability. To do this, EMI and noise need to be taken into consideration. This document addressed the issues of EMI and noise and in correspondence to PCB development and inductances. In summary, it is

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important to carefully design a PCB having in mind EMI in the following areas: the ground system, the power system, and the placement of components (with respect to each other). I recommend that EMI and noise design techniques be taken into consideration at the start of the PCB development. I learned a lot about EMI after already laying out a lot of my circuitry in Express PCB. To save time, money (so you don’t have to spend additional money, throwing out a PCB that doesn’t work properly because of EMI reasons), and to simply maximize a design, take EMI and noise into consideration while laying out your electronic assembly in the software designing stage.

Tuned Decoupling Tames Noise In Switching Circuits

As printed-circuit boards become more densely populated, the opportunities for "intra-module" interference grows. Similarly, the probability of "inter-module" interference increases. The move to higher switching rates, higher spectral content, and higher power exacerbates these trends. At the same time, engineers struggle with more stringent emissions regulations. Together, these considerations elevate the need to effectively decouple switching circuits.

To achieve effective decoupling, the decoupling source—invariably a good-quality capacitor located close to the switching circuit—must provide the ac content of the switched current. Meanwhile, the main power source—usually located away from the target—must provide the average current and, hence, all of the energy. This confines the high-frequency currents to a small loop in the vicinity of the target, thus minimizing board emissions. In addition, high-frequency currents are kept off the power and ground buses, which minimizes inductively coupled interference. Furthermore, because the ripple voltage across the decoupler (i 1 Z 1 ) appears on the power bus, minimizing this voltage will reduce capacitively coupled interference.

A number of recent papers have considered the effect of both the pc board's bus structure 1, 2 and the characteristics of the decoupling capacitors themselves 3 on suppressing emissions. Here, we mainly investigate the benefits and caveats of using decoupling networks, which suppress specific frequencies. Engineers are often PCB Assembly challenged to suppress one or more clock frequencies and, perhaps, related harmonics or sub-harmonics. In most cases, general decoupler choices do not efficiently address the highly defined suppression targets.

Consider the lumped-parameter model shown in Figure 1. Here, the target (switching) circuit is modeled as an ac current source. V y (f, t) is the ac voltage developed at point y on the power bus, due to the interaction of switching currents and system impedances; i 0 (f, t) is the ac current drawn by the target circuit; i 1 (f, t) is that part of i 0 supplied by the decoupler, and i S (f, t) is the part of i 0 that flows on the power bus. Z is the total impedance of the power bus; Z(y) is the power bus impedance between the decoupler and point y; Z 1 is the impedance of the decoupler; and Z 0 is the impedance between the decoupler and the target. For convenience, we have incorporated the internal impedance of the main power source into Z. The equations are:

Notice that both i S and V y have zeroes at Z 1 = 0 and have poles at Z 1 + Z = 0.

Now, let's consider some familiar decoupler configurations: 1) single-branch, pure (ideal) capacitance; 2) single-branch, capacitance plus inductance; and 3) dual-branch, capacitance plus inductance.

Pure Capacitance

In the good old days, before the advent of modern switching frequencies, it was reasonable to assume pure capacitance for a decoupler. Switching rates were low enough that trace, lead, and connection inductances could usually be ignored. In this case, the model of guides the analysis. From now on, we shall ignore the effect of Z 0 , since doing so does not affect the generality of our analyses. The equations for this configuration are:

where

The frequency response of the relative amplitude, i S /i 0 , has a pole at f = f ? .

The main consideration in such a situation is the selection of C 1 . This value should be such that the amplitude, |i S /i 0 |, is well rolled-off in the frequency range of interest, and f ? is far from this region.

Inductance and Capacitance

Most switching rates are now high enough that pure capacitance has become an untenable assumption for the decoupler. The analysis is better guided by the model of. The equations for this configuration are:

where is a zero of the response, and is a pole.

The existence of a zero at f = f 1 immediately suggests a method of optimally decoupling a specific frequency. That is, choose a decoupling capacitor that just happens to have its impedance anti-resonant at the target frequency. Then, connect this component into a negligible-inductance decoupler branch. At the target frequency, all of the current is provided by the decoupler. None of this current flows in the power bus (or ground bus).

Between the target frequency and the anti-resonant frequencies of the available decoupling capacitors, a sufficiently close match cannot always be found. In this situation, a tuned decoupling can still be achieved by choosing a capacitor with an anti-resonant frequency, f ar , such that f ar > f 1 , where f 1 now designates the target frequency. Let C 1 be, once again, the capacitance of the decoupling component. Then

where l 1 is the intrinsic inductance of the component. Consequently, if external inductance is added to the decoupling circuit, as in

a branch is constructed that maximally decouples the target frequency.

The additional inductance may be inserted in the form of a discrete component. Or, it may be obtained in the form of a pc-board trace electronic assembly of appropriate geometry. For an example of the calculation of trace inductances, see the Rostek article. 4

In some situations, it may be worth considering multiple decoupling branches. For example, tuned circuits have residual, if minor, resistance at the anti-resonant frequency. In order to achieve an even lower response at this frequency, identically tuned decoupling branches are sometimes placed in parallel in the circuit.

When it is a conversation about how the thing offered is received.

The following reply from me to Steve Hays is a friendly attempt to move the conversation along. I have been working on this for a few days now. I have taken the time to put this together because it appears that certain details are causing confusion. While there is a lot Thrust Bearing  I agree with what Steve says below, I just cannot help thinking it all misses the point. We clearly have different concepts of what “offer” is, and what it means to make an offer of something.

What is more, I really think that the attempt to fixate on parsing the word “offer,” to find any and every possible exception really misses the point.

Some introductory thoughts and points:

1) There are two issues. The first issue is basic: Does God make an offer? Does God make a sincere offer? Does God’s offer even need to be sincere? Does God make a well-meaning offer. Does God’s offer even need to be well-meant? When the conversation turns on these sorts of questions, the conversation has gone awry already. It is already turning on Hypercalvinist versus evangelical Calvinist axis points.

The second issue is, on the terms of evangelical Calvinism, can God’s offer of forgiveness to those whom he cannot confer forgiveness be sincere?

Right now, we are bogged down in the first issue. However, I believe that for most folk the issue is pretty straight-forward. That is, it has been our experience that for the most part those who want to challenge the very meaning of constitutes a Needle Roller Bearing sincere offer are generally those who have already made a pre-commitment to Hypercalvinist categories, either tentatively or fully. You can tell these people by the way they get all bent out of shape so quickly. :-)

2) For many, the debate will ultimately come down to these pre-commitments:

If one has affirmed already that God does not by revealed will desire the salvation of all men, then one is already in the Hypercalvinist tradition. This has to be so, because one cannot, on the one hand, deny that God by revealed will desires the salvation of all men and then, on the other hand, meaningfully affirm a well-meant offer.

How does that follow? We know that in terms of the secret will, God desires not to save the non-elect. According to evangelical Calvinism, we also know that in terms of the revealed will God desires to save the non-elect.

So, if we deny that by revealed will that God desires to save the non-elect, and this includes the entailment that the Gospel offer does not express God’s desire to save the non-elect hearers, this means that the criteria which sustains a well-meant offer has now been voided. In the Gospel offer, it would then follow that God only desires to not save the non-elect. Thus, when God makes an appearance of seeking someone’s salvation, he is being insincere. Denial of a well-meant offer is the hallmark of Special Bearing hypercalvinism, if anything is.

For my limited understanding of things, either the gospel offer is well-meant or ill-meant. Non-meant? I don’t think so.

So, a well-meant or a sincere offer cannot be sustained on terms which denies that by revealed will God desires the salvation of the non-elect. A person may speak as if they are positing a well-meant offer, but in actuality, they are not. Therefore, any talk about what constitutes a sincere divine offer of the gospel but yet denies a well-meant offer of the gospel just rings hollow and is antithetical to true Calvinism . For example, no one in the John Calvin, John Murray, John Piper tradition of Calvinism should disagree with this.

So keep in mind, our discussion is properly with non-Hypercalvinist evangelical Calvinists. I know that most of what I say will probably fail to convince anyone already committed to Hypercalvinist assumptions.

3) Regarding the meaning of offer, all one Pressed Bearing needs to do is look up a good dictionary. The OED is one of my favorites.

NSK bearings introduce ES1 Stainless Bearing Steel

NSK bearings Ltd. announced it is commercializing its newest stainless steel, ES1, suited for use manufacturing bearings that will see installation Thrust Bearing in applications where corrosion resistance is paramount.

ES1, originally discussed by NSK in 2000, is a new martensitic stainless that NSK developed with an eye toward carbide size and comparable Rc hardness to 52100 bearing steel. ES1 is essentially 440C with higher nitrogen and Special Bearing lower carbon and chromium. Reducing the chromium and carbon is what helps eliminate the eutectic inclusions. Alloying the nitrogen is what provides superior corrosion resistance.

The most common stainless steel used to manufacture bearings is 440C. However, 440C has a key limitation, which is that is has concentrated chromium coarse eutectic carbide inclusions. Those inclusions lead to three key areas of weakness. First, those inclusions make it virtually impossible to get the best finish on the bearing races, so 440C Pressed Bearing normally run loud, rough, and can run hot. Second, under load, cracks initiating at these inclusions are what usually lead to a 440C bearing failure through flaking and spalling. And third, those inclusions make 440C less corrosion resistant because the chromium is lost in the martensitic matrix.

With no eutectic carbides, NSK ES1 bearings are highly corrosion resistant, have low noise and vibration, and have a longer under-load Needle Roller Bearing fatigue life.Under corrosion testing, ES1 using silicon nitride balls last 5 times longer than 440C. Standard 6203 ES1 ball bearings using silicon nitride balls lasted 25 times longer than 440C.

When it is a conversation about how the thing offered is received.

The following reply from me to Steve Hays is a friendly attempt to move the conversation along. I have been working on this for a few days now. I have taken the time to put this together because it appears that certain details are causing confusion. While there is a lot Thrust Bearing  I agree with what Steve says below, I just cannot help thinking it all misses the point. We clearly have different concepts of what “offer” is, and what it means to make an offer of something.

What is more, I really think that the attempt to fixate on parsing the word “offer,” to find any and every possible exception really misses the point.

Some introductory thoughts and points:

1) There are two issues. The first issue is basic: Does God make an offer? Does God make a sincere offer? Does God’s offer even need to be sincere? Does God make a well-meaning offer. Does God’s offer even need to be well-meant? When the conversation turns on these sorts of questions, the conversation has gone awry already. It is already turning on Hypercalvinist versus evangelical Calvinist axis points.

The second issue is, on the terms of evangelical Calvinism, can God’s offer of forgiveness to those whom he cannot confer forgiveness be sincere?

Right now, we are bogged down in the first issue. However, I believe that for most folk the issue is pretty straight-forward. That is, it has been our experience that for the most part those who want to challenge the very meaning of constitutes a Needle Roller Bearing sincere offer are generally those who have already made a pre-commitment to Hypercalvinist categories, either tentatively or fully. You can tell these people by the way they get all bent out of shape so quickly. :-)

2) For many, the debate will ultimately come down to these pre-commitments:

If one has affirmed already that God does not by revealed will desire the salvation of all men, then one is already in the Hypercalvinist tradition. This has to be so, because one cannot, on the one hand, deny that God by revealed will desires the salvation of all men and then, on the other hand, meaningfully affirm a well-meant offer.

How does that follow? We know that in terms of the secret will, God desires not to save the non-elect. According to evangelical Calvinism, we also know that in terms of the revealed will God desires to save the non-elect.

So, if we deny that by revealed will that God desires to save the non-elect, and this includes the entailment that the Gospel offer does not express God’s desire to save the non-elect hearers, this means that the criteria which sustains a well-meant offer has now been voided. In the Gospel offer, it would then follow that God only desires to not save the non-elect. Thus, when God makes an appearance of seeking someone’s salvation, he is being insincere. Denial of a well-meant offer is the hallmark of Special Bearing hypercalvinism, if anything is.

For my limited understanding of things, either the gospel offer is well-meant or ill-meant. Non-meant? I don’t think so.

So, a well-meant or a sincere offer cannot be sustained on terms which denies that by revealed will God desires the salvation of the non-elect. A person may speak as if they are positing a well-meant offer, but in actuality, they are not. Therefore, any talk about what constitutes a sincere divine offer of the gospel but yet denies a well-meant offer of the gospel just rings hollow and is antithetical to true Calvinism . For example, no one in the John Calvin, John Murray, John Piper tradition of Calvinism should disagree with this.

So keep in mind, our discussion is properly with non-Hypercalvinist evangelical Calvinists. I know that most of what I say will probably fail to convince anyone already committed to Hypercalvinist assumptions.

3) Regarding the meaning of offer, all one Pressed Bearing needs to do is look up a good dictionary. The OED is one of my favorites.

The slewing bearing uses

The slewing bearing uses:

1. The trailer: slewing bearing used in different occasions, one of the most important application in the transportation industry, agriculture trailer, irrigation systems and the airport luggage rack. In the vehicle of the application, transfer of bearing axial load, radial load and torque. In other applications, most of them is to transfer the axial load.

2. The wind power: wind generator bearing usually contains the yaw bearing, change propeller bearing, transmission system (special bearing and the gearbox bearing).

                                                           

The yaw bearing installed in a tower and cockpit, change the connection OARS bearing installed at each leaf roots and hub joint parts. The wind generator per machine with a set of yaw bearing and three sets of change propeller bearing.

3 the solar energy: rotating solar panels is a very good increase energy solutions. Because jinyuan bearing has a very compact design, supply Europe’s largest solar electric field.

4. Medical equipment; high precision, low noise, long service life, high reliability series medical equipment spindle slewing bearings, has been widely used in gamma knife, CT machine, nuclear magnetic resonance (NMR) machine and other large medical equipment.

5. Robot: industrial robots and other facilities. Slewing ring special bearing in the robot joints, the structure can realize part incredible high closely rotation movement.

The slewing bearing uses

The slewing bearing uses:

1. The trailer: slewing bearing used in different occasions, one of the most important application in the transportation industry, agriculture trailer, irrigation systems and the airport luggage rack. In the vehicle of the application, transfer of bearing axial load, radial load and torque. In other applications, most of them is to transfer the axial load.

2. The wind power: wind generator bearing usually contains the yaw bearing, change propeller bearing, transmission system (special bearing and the gearbox bearing).

The yaw bearing installed in a tower and cockpit, change the connection OARS bearing installed at each leaf roots and hub joint parts. The wind generator per machine with a set of yaw bearing and three sets of change propeller bearing.

3 the solar energy: rotating solar panels is a very good increase energy solutions. Because jinyuan bearing has a very compact design, supply Europe’s largest solar electric field.

4. Medical equipment; high precision, low noise, long service life, high reliability series medical equipment spindle slewing bearings, has been widely used in gamma knife, CT machine, nuclear magnetic resonance (NMR) machine and other large medical equipment.

5. Robot: industrial robots and other facilities. Slewing ring special bearing in the robot joints, the structure can realize part incredible high closely rotation movement.

What are the marking requirements for vehicles transporting PCBs?

Vehicles transporting either (1) > 45 kg (99.4 lbs) of liquid PCBs with a concentration >=50 ppm of PCBs or (2) one or more PCB Transformers must be marked on each end and each side of the vehicle.

What is the significance of EPA adding 40 CFR Part 761.40(k)(2) about marking PCB Transformers and PCB Large (Low or High Voltage) Capacitors?

40 CFR Part 761.40(k)(2) requires marking of all equipment containing a PCB Transformer or PCB Large (Low or High Voltage) Capacitor that electronic assembly was not marked at the time of manufacture, distribution in commerce, or removal from use. This means that if the mark falls off or otherwise disappears from a PCB Transformer or PCB Large (Low or High Voltage) Capacitor while in use, the owner/operator is responsible for making sure the equipment is remarked. Prior to this amendment, the responsibility for marking had been put solely on the manufacturer or retailer, and no responsibility for maintaining the mark had been placed on the owner/operator of the equipment.

CAUTION CONTAINS PCBs

A toxic environmental contaminant requiring special handling and disposal in accordance with U.S. Environmental Protection Agency Regulation electronic assembly 40 CFR 761 – For Disposal Information contact the nearest U.S. E.P.A. Office.

In case of accident or spill, call toll free the U.S. Coast Guard National Response Center: 800-424-8802

Are there any other labeling requirements?

Yes. In addition to applying the PCB mark to the required PCB and PCB Items, PCB wastes being stored prior to disposal must also be labeled with a notation indicating the date that the item was removed from service for disposal. If the wastes in storage include drums of PCB-contaminated soil from a remediation activity, the “date removed from service for disposal” would be the date on which the soil was excavated and placed into drums. If the wastes are liquid wastes (e.g., solvents used for flushing or decontaminating PCB Items), the “date removed from service for disposal” is defined as the date that the first batch went into the drum. If PCBs in containers or PCB Items are contaminated with hazardous wastes regulated under the authority of the Resource Conservation and Recovery Act (RCRA), they must be marked in accordance with the applicable RCRA hazardous waste marking requirements, as defined in 40 CFR Part 262, as well as with the applicable TSCA marking requirements.

Impact Crusher

PF series impact crusher is a latest equipment developed by absorbing advanced technologies at home and abroad and referring to domestic sand and stone making industry. It adopts the lasted manufacture technics, unique structures and design, the producd product is of cubic shape without tension and cracks and good grain shape. The max feeding size should not be more than 500mm, and compression resistance should not be more than 350Mpa.

Features of Primary Impact Crusher:Our Impact crushers are powerful in size reduction for crushing of stone, ore, limestone, rock, and refractories. The final products of impact crusher are of good cubic shapes and are fine for railway, road construction and other industries. Our impact crushing equipments are accurate, reliableand and have perfect performance. We manufacture and supply portable, stationary impact crushing plants and equipments.

Various materials(granite, limestone,concrete) of rough, medium fine and super fine quality are available. It is widely used in ore hammer mill crushing, railway, highway, energy, cement, chemistry, construction materials and others to carry out rough, medium fine and super fine crushing, such as limestone, ripe materials, slag coke,coal and so on. Its outlet size can be adjusted, which makes various specifications posible.

1. A large inlet, high crushing chamber which is suitable for materials with high hardness, biger block and less powder;

2. Clearance between impact-plate and plate can be adjust conviniently, which can make effective control of the particle size posible, broken end product is of cubic shape, the grain shape is good;

3. It has compact structure, high machine rigidity, and the rotor has a large inertia;

4. high chrome hammer, impact resistance, abrasion resistance, mechanical wear small, big impact;

5. Using new rotor can increase the impact force;

6. Broken-function is complete, reduction ratio is big, it is of high productivity, low energy consumption, and its overall hammer mill  efficiency is high.

European Hammer Mill

European Hammer Mills are widely used in metallurgy, mining, chemical, cement, coal gangue, construction, sand, refractory material, ceramic and other industry, engaged in breaking and crushing the material in the operation. It is mainly suitable for crushing various soft and hard ore. Whose compression strength is not higher than 320MPa (MPa).

Features of European Hammer Mill:European Hammer Mill is mainly made up of frame, rotor, hammers, grizzly bar and other components. The frame includes upper part and lower parts, which are welded by steel plates after cutting, the remaining parts bolted into one. High manganese steel liners are studded with inside the frame, to facilitate replacement for a new liners after worn; on the main shaft are installed several groups of the spindle distribution of the hammers, which consists of rotor with the axle of hammers and rotary table. The host drives the main shaft through the motor and V-belt driven spindle to rotate the rotor, generating the centrifugal force, and then driving all Hammer Mill stretch around. The bulks of material feed into the crushing chamber will be crushed by the hammers at a high-speed movement. The broken material requested will be passed the grizzly bar at the lower part and discharged, the unbroken rest will be left in the chamber to be crushed repeatedly by the hammers and iron plates until it can reach the requested standard. To avoid clogging, the water content of the material to be crushed should no more than 5%.

1. High production capacity and high crushing ratio.

2. Low power consumption, uniform particle size.

3. Simple, compact and light mechanical structure.

4. Low investment cost, easy management.

Sensor Mounting Techniques

Introduction

While upgrading one of my Mini-Sumo robots, I found that sensor placement and orientation can have a big impact on your final results. This article will discuss the problems I ran into, trouble-shooting, and solutions.

Time to Upgrade

Mini-Spat has competed in 6 PAReX events, as well as several demos at swap meets, high schools, and colleges. In other words, there's a lot of mileage on the little guy. During the Nov. 2003 event it died twice in competition, and in the Nov. 2004 event, there were a few times when it lost it's mind and wandered the ring aimlessly. The original circuit board was a low-profile wire-wrap board. With the extremely short wraps I was concerned about it's reliability and decided to upgrade to a PCB.

Upgrade Woes

The PCB was finished and mounted to the robot. There were no software changes made, except swapping the left and right servos, due to PCB routing issues. Fired up the robot and watched it act just like it did with the old board, in other words, a robot possessed. Since the PCB seemed to be correct, and nothing else had changed, I started looking at what I had done in software, trying to figure out what went wrong.

Basic Trouble-Shooting

The basic problem was the robot was seeing things that weren't there. When Mini-Spat drops, it's suppose to move forward, then start spinning PCB Assembly in a circle looking for the opponent. If there's nothing in range, it should just keep spinning. Most of the time it wouldn't even make one full turn before wandering off in search of a ghost. Other times it would work fine for several runs.

By inserting some breakpoints in the code, I would stop the robot when it thought it saw something, and flash the LED to tell me which sensor was acting up. Turns out the right range sensor, a Sharp GPD012, was at fault. Further investigation showed that two of the three connector pins had broken solder joints! Ahh problem solved!! A quick fix with a soldering iron and it was back on the ring, failing exactly the same way. Insert your favorite expletive here!

Digging Deeper

Well at least I found the intermittent problem. Most Mini-Sumo's don't have a display on them so it can be hard trying to figure out what's going on sometimes. I have a diag routine which can blink an LED to show me an 8-bit sensor value, but you can't use it while the robot is running. I guess the ideal interface would be a wireless link to a PC, then you could receive all kinds of data to see what's going on. Well those links aren't cheap so I fell back on the RS-232 link that I had brought over from the original board. A long 2-wire cable connects the robot to the laptop, but it's still not practical, even on the 30" ring. Since the failure was a range sensor, I did all kinds of tests without the motors running, and the sensor performed perfectly.

Ok, since this is an analog sensor, maybe the motors are generating some electrical noise and hosing things up. Putting the robot on blocks and running the motors during the tests, made no difference, the sensors worked as expected. The only thing left was to monitor the sensors while the robot was running normally. To do this without the cable attached, I would save the sensor readings to RAM, and then connect the cable and dump the data to the laptop.

I had about 250 ram locations to use and as fast as the sensors are updated, it would fill in about 38ms. So I once again set the robot to stop when it saw something and send me the last 250 readings. What I saw was quite interesting, the left sensor read a 0 or 1 the entire log. The right sensor varied from 0x20 to 0x28, before hitting my 0x2C threshold and stopping. The 0x2C is about the length of the ring, so I would "see" things electronic assembly in the ring, but didn't care about what laid beyond. If I did the same test with the motors off I got readings just like the left sensor, nothing greater then 2. If I ran the motors on blocks, again the readings were good. I changed out the sensor and again had no changes. So the actual motion of the robot had something to do with it.

Printed wiring assembly manufacturing

Introduction:

Manufacturing/production of electronic products by its nature involves the assembly of components on a printed circuit board(PCB). The entire assembly is called a printed wiring assembly(PWA). In the electronics industry printed wiring assembly, Printed card assembly(PCA), and circuit card assembly(CCA) are used interchangeably to describe a fully populated and soldered PCB.

In the fast-paced and cost-sensitive world of electronic manufacturing major changes continually take place. Original equipment manufacturers(OEMs) no longer view manufacturing as a core competency or a competitive advantage. They want to focus on technology, product innovation, brand marketing, and sales. So they divested themselves of their manufacturing facilities, selling them to contract manufacturers(CMs)

and established long-term relationships with them. [Contract manufacturers are also referred to as electronic manufacturing service(EMS) providers and contract electronic manufacturers(CEMs). I use these terms interchangeably.] As a result, OEMs have become increasingly dependent on contract manufacturers for some or all of their manufacturing requirements, especially PWA services.

Computer makers were the first to adopt an outsourcing manufacturing model, followed by both telecommunication equipment and wireless(mobile phone) manufacturers, nimbly reacting to instantaneous changes in the marketplace, it is PCB Assembly no longer unusual for a half dozen different brand-name computers to come off a single assembly line. (However, such products are not identical. Each OEM designs products with unique characteristics and specifications, while the EMS provider keeps cuscomer jobs strictly separate to avoid conflicts of interest and other difficulties.)

Outsource manufacturing

When considering outsourcing as a manufacturing strategy, it is important for a company to understand what is driving its need for outsourcing. Is it simply cost? Is it that management feels distracted by having to deal with many functions nad activities it feels are ancillary to its true mission? Is it a strategic decision to not maintain a rapidly changing technology that, when closely examined, is associated with a process that can be deemed as a support or management process?

Manufacturing/Production practices

Outsourcing originally began with the OEMs' need to manage the manufacturing peaks and valleys resulting from volatile, often uppredictable, sales volumes. In order to perform their own manufacturing, OEMs had to fact three difficult choices:

1. Maintain sufficient staff to deliver product at sales peaks, knowing that workload would later drop along with volume.

2. Staff at some compromise level, carefully scheduling and distributing tasks to accommodate peak loads.

3. Hire staff at peak times and lay them off when sales drop.

Obviously, each of these options presented drawbacks. Contract manufacturers provided a solution: they offered to handle these peaks with their production capacity, and as OEMs gained more experience in dealing with them, routine manufacturing also shifted to EMS companies.

Since manufacturing operations are notoriously expensive to build and maintain, OEMs initially got out of manufacturing to reduce costs(reduce fixed assets and people). The inherent unpredictable market demand, sales volumes,product profitability, and resulting financial returns made an OEM's manufacturing operations exceedingly difficult to manage and maintain and thus led many OEMs to outsource that function. They needed to stop a hemorrhaging bottom line because they couldn't control their onw process, they refused or were unable to address deficiencies, they wanted to get rid of a headache, or they just jumped to outsourcing because everyone else was doing so. What initiallly weren't well thought out were the remifications of and support required to manage their outsourcing decision/strategy. They just did it. Many companies climinated assembly line workers and purchasing personnel in a carte blanche manner when they implemented outsource manufacturing, thinking they no longer needed them. The ramifications included lost critical skills, electronic assembly negetive impact on morale of both affected and remaining employees, learning curve loss, inability to both innovate and provide flexbility and fast response to customers, and loss of control of manufacturing quality to a third party. However, the OEMs painfully learned that more(not less) skilled and technically competent workers were required to support the outsource strategy.

The CMs' focus on manufacturing allows them to achieve the lowest product costs and high product quality. The OEMs take advantage of the CMs' strengths to stay competitive in the electronics industry without most of the manufacturing overhead costs. The use of EMS providers adds enormous flexibility to an OEM's arsenal of available tools. Because they make a broad range of products for an equally varied group of customers, EMS providers have accumulated a wider array of knowledge, experience, and expertise than their OEM customers. As a result, EMS providers often suggest other manufacuturing.

PCB Stackup and Reference Planes PCI Express

PCI Express requires no new technology. Generally desktop system boards are designed with 4-layer stackup, whereas server, workstation, and mobile system boards use 6-layer stackup or greater. Add-in cards may use either 4-layer or 6-layer stackup. ½ oz copper plated microstrip and 1 oz copper stripline are used.

An add-in card is required to have overall board thickness of 0.062 inches. A mobile platform can have a thickness of 0.062 inches PCB Assembly or 0.050 inches.

To minimize loss and jitter, the most important considerations are to design to a target impedance and to keep tolerances small. Thicker dielectrics and wider traces will minimize loss. Microstrip differential traces produce greater impedance variation than stripline traces.

A signal pair should avoid discontinuities in the reference plane, such as splits and voids. When a signal changes layers, the ground stitching vias should be electronic assembly placed close to the signal vias. A minimum of 1 to 3 stitching vias per pair of signals is recommended. Never route a trace so that it straddles a plane split.

PCB design for Real-world EMI control

Primary resonance can be moved to a higher frequency(where it is not going affect amissions in the frequency range of concern). It is clear from these simulations that one or two contact points should be avoided, since the resonances are likely to be in the range of the first or second harmornic of the processor clock frequency(where the most energy exists). Eight contact points provided the most significant improvement of all the configurations tested.

PCB reference connection to Chassis reference

If we have a system with a completely enclosed chassis with no I/O cables leaving the enclosure, it makes no difference how, or if, the internal circuits are connected to the

enclosure chassis inside the enclosure. Any internal fields from the PC board are contained within the enclosure. This is seldom the case, however, since most real world products include openings and I/O cables.The most common cause of external emissions in typical

products is unwanted common-mode voltages from unintentional signals on the I/O cables and wires relative to the chassis. From an external point of view, we can consider the enclosure chassis to be reference, and the voltage on the I/O cables to be the feed for an antenna, we might even consider the enclosure and wire(with the source between them) to be a kind of lumpy, irregularly-shaped dipole antenna. PCB Assembly Regardless, the combination of I/O wire and enclosure creates an antenna that will radiate quite effectively at some frequencies.

A low inpedance connection between the PC board and the chassis, when done correctly, can reduce the emissions from these unintentional signals.

I/O Area connection

Consider the case with two I/O wires, such as a signal line and its return(ground),(for example, an audio speaker connection to a persional computer). The return wire is usually connected to the ground-reference on the PC board. Any filtering on the audio signal line is referenced to the ground-reference on the PC board. The reference for the external rediation is the chassis and not the ground-reference on the PC board. Any impedance between the chassis and the PC board gound-reference will allow a voltage to be created between them. This voltage will appear to be source on the I/O reference wire and the I/O signal wire. Figure 4-19 illustrates this problem.

The connection between the PC board reference and the chassis is often accomplished with stand offs and machine screws. The placement of these stand offs is mostly arbitrary and seldom selected for best EMI emissions control. Figure 4-19 shows a connection impedance between the PC board reference and the chassis. This impedance consists of the resistance of the connection and the inductance of the connection. If we consider the loop inductance of the connection between the chassis and the PC board, we will want to keep the loop area as small as possible. Figure 4-20 shows the loop area for the side view and a top view. The total three dimersional loop area is important.

Many I/O connectors have shields that serve two purposes. First, they shield the connector pins from unwanted signals coupling directly onto them from fields inside the enclosure. Secondly, and more importantly for this discussion, they provide a low impedance and low loop area path from the chassis to the PC board. This connector becomes the main connection between the ground-reference plane on the board and the chassis.

PCB Summary

Unfortunately, it is unlikely that the word "ground" is removable from designer's vocabulary. The concept of "ground" is easy to understand and emotionally comforting. Once the frequency range of the signals is above about 10KHZ, however, the "ground" concept is not a good way to think about the physics of the current flow. Consideration to the return current flow path is vital to controlling "ground" currents.

The term "ground" is often misused to mean a number of different reference. It is much better to consider the power-reference, the signal-reference, the chassis-reference. Cable shield-reference,etc. Once these various electronic assembly references are clearly described, then the proper connections can be established, and the return currents controlled.

PCB design for Real-world EMI control

Primary resonance can be moved to a higher frequency(where it is not going affect amissions in the frequency range of concern). It is clear from these simulations that one or two contact points should be avoided, since the resonances are likely to be in the range of the first or second harmornic of the processor clock frequency(where the most energy exists). Eight contact points provided the most significant improvement of all the configurations tested.

PCB reference connection to Chassis reference

If we have a system with a completely enclosed chassis with no I/O cables leaving the enclosure, it makes no difference how, or if, the internal circuits are connected to the

enclosure chassis inside the enclosure. Any internal fields from the PC board are contained within the enclosure. This is seldom the case, however, since most real world products include openings and I/O cables.The most common cause of external emissions in typical

products is unwanted common-mode voltages from unintentional signals on the I/O cables and wires relative to the chassis. From an external point of view, we can consider the enclosure chassis to be reference, and the voltage on the I/O cables to be the feed for an antenna, we might even consider the enclosure and wire(with the source between them) to be a kind of lumpy, irregularly-shaped dipole antenna. PCB Assembly Regardless, the combination of I/O wire and enclosure creates an antenna that will radiate quite effectively at some frequencies.

A low inpedance connection between the PC board and the chassis, when done correctly, can reduce the emissions from these unintentional signals.

I/O Area connection

Consider the case with two I/O wires, such as a signal line and its return(ground),(for example, an audio speaker connection to a persional computer). The return wire is usually connected to the ground-reference on the PC board. Any filtering on the audio signal line is referenced to the ground-reference on the PC board. The reference for the external rediation is the chassis and not the ground-reference on the PC board. Any impedance between the chassis and the PC board gound-reference will allow a voltage to be created between them. This voltage will appear to be source on the I/O reference wire and the I/O signal wire. Figure 4-19 illustrates this problem.

The connection between the PC board reference and the chassis is often accomplished with stand offs and machine screws. The placement of these stand offs is mostly arbitrary and seldom selected for best EMI emissions control. Figure 4-19 shows a connection impedance between the PC board reference and the chassis. This impedance consists of the resistance of the connection and the inductance of the connection. If we consider the loop inductance of the connection between the chassis and the PC board, we will want to keep the loop area as small as possible. Figure 4-20 shows the loop area for the side view and a top view. The total three dimersional loop area is important.

Many I/O connectors have shields that serve two purposes. First, they shield the connector pins from unwanted signals coupling directly onto them from fields inside the enclosure. Secondly, and more importantly for this discussion, they provide a low impedance and low loop area path from the chassis to the PC board. This connector becomes the main connection between the ground-reference plane on the board and the chassis.

PCB Summary

Unfortunately, it is unlikely that the word "ground" is removable from designer's vocabulary. The concept of "ground" is easy to understand and emotionally comforting. Once the frequency range of the signals is above about 10KHZ, however, the "ground" concept is not a good way to think about the physics of the current flow. Consideration to the return current flow path is vital to controlling "ground" currents.

The term "ground" is often misused to mean a number of different reference. It is much better to consider the power-reference, the signal-reference, the chassis-reference. Cable shield-reference,etc. Once these various electronic assembly references are clearly described, then the proper connections can be established, and the return currents controlled.

PCB Design and Layout

5.3 Reference planes

Due to their intrinsic reactance and resonances, tracks, wires, “star grounding”, area fills, guard rings, etc., cannot provide an adequate reference for a PCB except at low frequencies (usually below 1MHz). For example, the rule-of-thumb for the inductance of PCB tracks on their own or single wires, is 1nH/mm. This means that just 10mm of PCB track has an impedance of 6.3 Ω at 100MHz, and 63Ω at 1GHz. For this reason, only unbroken areas of metal conductor can provide an adequate reference up to 1GHz (and beyond), and these are called reference planes. In a PCB these are usually called power, ground, or 0V planes, but it is best to avoid the use of the words “ground” or “earth” in connection with EMC and circuits (reserving them for specific uses associated with safety bonding). As far as most EMC design techniques are concerned, a connection to the green/yellow protective earth conductor can often be more of a problem than a solution.

Reference plane techniques allow dramatic reductions in all unwanted EM coupling when used in conjunction with the other techniques described here. Reference planes are also essential for almost every other PCB EMC design technique to function properly.

5.3.1 Creating proper reference planes

A high-quality high-frequency reference must have a vanishingly small partial inductance, and can be created on a PCB by devoting one layer to an unbroken copper sheet, called a reference plane. A 0V reference plane would be used as the 0V (or “ground”) connection for all its associated circuits, so that all 0V return currents flow in the plane and not in tracks. Power planes are created and used in a similar manner for power connections and their return currents.

0V reference planes must lie under all their PCB Assembly components and all their associated tracks, and extend a significant distance way beyond them. The segregation and interface suppression techniques described above must still be followed even where a common 0V plane is used for a number of circuit areas.

Perforations such as leads, pins, and via holes increase the inductance of a plane, making it less effective at higher frequencies. “Buried via” techniques have been developed for cellphones, allowing interconnections between tracking layers without perforating the reference plane. For less demanding products a rule-of-thumb is that any gaps must have dimensions of 0.01λ or less at the maximum frequency concerned. For a good plane at 1GHz, (e.g. to help meet most of the present EU harmonised EMC standards cost-effectively) this rule implies that plane gaps should have dimensions ? 1.5mm (remembering that the velocity of propagation in FR4 is approx. half of what it is in air). "Sneaking" tracks into a plane layer is not allowed.

Unavoidable gaps in a plane must not merge to create larger ones. PCB design rules should size clearance holes so that for regular hole spacings such as DIL packages, the plane "webs" between holes as shown by Figure 5B.

Tracks, area fills, guard rings, etc. forming part of the reference on signal layers can be used to good effect at high frequencies – but only when bonded to an underlying 0V plane with at least one via hole every 5 to15mm (using a random allocation of spacings).

0V planes should extend well beyond all components, tracks and power planes. [1] recommends “the 20H rule”: 0V planes should extend by at least 20 times their layer spacing. High-speed components (such as digital clocks, processors, and memory) and their signal tracks should always be placed near the centres of their segregated areas, well away from plane edges.

All 0V and power connections must bond immediately to their respective planes to minimise their connection inductance. Leaded components must have their through-plated holes directly connected to planes using thermal-break pads as shown by figure 5B (sometimes called wagon-wheels) to help with soldering. Surface mounted devices (SMDs) for reflow soldering have to compromise the prevention of dry joints or “tomb-stoning” with the need to minimise inductance of plane connections.

Figure 5C shows various methods for connecting reflow-soldered SMDs to planes. Best is to use over-sized pads, tenting the solder-resist over a number of plane vias. Plane connections that do not need to be soldered (typical of the vias for reflow-soldered SMD components) may not need to use thermal-break pads – and using solid plane connections instead will reduce inductance.

Tracks, area fills, guard rings, etc. forming part of the reference on signal layers can be used to good effect at high frequencies – but only when bonded to an underlying 0V plane with at least one via hole every 5 to15mm (using a random allocation of spacings).

0V planes should extend well beyond all components, tracks and power planes. [1] recommends “the 20H rule”: 0V planes should extend by at least 20 times their layer spacing. High-speed components (such as digital clocks, processors, and memory) and their signal tracks should always be placed near the centres of their segregated areas, well away from plane edges.

All 0V and power connections must bond immediately to their respective planes to minimise their connection inductance. Leaded components must have their through-plated holes directly connected to planes using thermal-break pads as shown by figure 5B (sometimes called wagon-wheels) to help with soldering. Surface mounted devices (SMDs) for reflow soldering have to compromise the prevention of dry joints or “tomb-stoning” with the need to minimise inductance of plane connections.

Figure 5C shows various methods for connecting reflow-soldered SMDs to planes. Best is to use over-sized pads, tenting the solder-resist over a number of plane vias. Plane connections that do not need to be soldered (typical of the vias for reflow-soldered SMD components) may not need to use thermal-break pads – and using solid plane connections instead will reduce inductance.

5.3.6 Galvanically isolated planes

The split planes described above are all ultimately powered from the same power rails (0V, at least), so there is a clear need for return current paths to be catered for every conductor (signal or power) that crosses from one plane area to another. It is often assumed that galvanically isolated areas have no return current requirements, but this is not so at high frequencies.

Galvanic isolation devices (opto-isolators, transformers, etc.) suffer from stray internal capacitance. A typical opto has 0.8pF internal capacitance, which provides a shunting impedance of only 2kΩ at 100MHz, or 200Ω at 1GHz, which will clearly prevent signal isolation from being maintained at high frequencies. Transformers (especially in DC/DC power converters) tend to have even larger stray internal capacitances. Common-mode chokes may be used to improve the isolation at high frequencies, but struggle to increase it by an order of magnitude at 1GHz. There are also many other stray capacitances around to compromise isolation. So there is a need, at high frequencies, to provide a local return path for the displacement currents that flow in these stray capacitances, to prevent them from causing common-mode conducted and radiated emissions and immunity problems.

Because we usually only need isolation for low frequencies (usually only 50Hz) we can connect galvanically isolated planes to the main reference plane with a number of low-value capacitors (spread around the gap perimeter), so electronic assembly as to achieve the effect of a single reference plane for high frequencies and provide low-inductance local return paths for stray displacement currents.

Of course, great care may need to be taken with component approvals and leakage currents where safety is concerned.