Understanding PCB Assembly

When constructing a PCB there are 5 steps that are usually followed: pasting, pick & place, cooking, inspection and testing. Below is a simple overview of the PCB assembly procedures that are carried out once a manufacturer has all the information they need.

First, solder paste must be applied to the blank board. There are a few ways to handle this but it is common to use a solder screen. The screen is created using the files provided by the designer and contains holes delineating the location of each component on the PCB Assembly. Paste is then pushed through the screen onto the board surface where the solder pads will later hold each component to the board.

After paste is applied to the board, the next step is to place components on the board with a process called “pick and place.” In this procedure, a machine, programmed with the PCB design specifications, picks each component from a dispenser of some type and places it in the correct location on the board. Paste keeps the board compnents stuck the surface until they are permanently attached in the next process.

Once all components are in place, the board is ready to be “cooked.” This essentially entails placing the board into an oven, which heats the PCB enough to permanently solder the components in place without damaging them. Other processes can be used if the components are too delicate to be soldered in this way.

Once this is done, the PCB has to go through an inspection process to be sure it is working to specifications. Commonly, this is done by putting the board in a machine that checks all connections and confirms locations for every component. Some machines can even detect instances in which components are accidentally switched by the pick and place machine.

Lastly, each board must be tested. Oftentimes this is called the “burn in” process. It is where the PCB Assemblywill be set in the device it is meant for, and seeing if the board is functioning properly.