Printed Circuit Boards Assembly (PCBA) Process

Electronics are an integral part of our daily lives. Everything from our smart phones to our cars includes electronic components. At the heart of these electronics is the printed circuit board, also known as a PCB.

Most people recognize printed circuit boards when they see them. These are the small green chips covered in lines and copper parts you'll find at the heart of gutted electronic devices. Made with fiberglass, copper lines and other metal parts, these boards are held together with epoxy and insulated with a solder mask. This solder mask is where that characteristic green color comes from.

However, have you ever observed those boards with components solidly stuck on? Never regard them as just decorations of a PCB board. An advanced circuit board won't be able to give its functionality until components are mounted on it. A PCB with components mounted on is called an assembled PCB and the manufacturing process is called PCB assembly or PCBA for short. The copper lines on bare board, called traces, electrically link connectors and components to each other. They run signals between these features, allowing the circuit board to function in a specifically designed way. These functions range from the simple to the complex, and yet the size of PCBs can be smaller than a thumbnail.

Prior to assembly of electrical components, a circuit board is known as a prototype circuit board (PCB). Printed circuit board assembly, or PCB board assembly (PCBA), is the process of soldering paste on the PCB or printed circuit board and the assembly of various components like integrated circuits, resistors, and capacitors.

Here is a step-by-step process of PCB board assembly:

Step 1: Apply solder paste to the circuit board

Place the thin, stainless steel stencil over the board using a mechanical fixture. Solder paste should be applied evenly to the circuit board in the exact locations needed.

Step 2: Pick and place the machine

SMDs, or surface mount components, should be placed on a prepared PCB by a robotic device. Then, the components need to be soldered onto the circuit board surface.

Step 3: Let the solder paste solidify

In order to adhere the components to the PCB, the solder paste needs to reflow and remain in place for an extended period of time.

Step 4: Inspect the PCB assembly

After the reflow process is complete and the mount components are soldered into place, comes the PCB inspection. The assembled board should be tested and inspected for functionality. Ways to check the PCBA for quality control include:

Manual checks: A visual inspection done in person by a designer to ensure the quality of a PCB.

Automatic optical inspection: An inspection method more appropriate for larger batches of PCBAs. An automatic optical inspection machine, or AOI machine, uses high-powered cameras, set at different angles to view the solder connections.

Xray inspection: An inspection used for more complex PCBs by examining the layers of the PCB and identifying potential problems

Step 5: Insert the plated through-hole component

A plated through-hole, or PTH, component is a hole in the PCB that is plated through the board. Rather than soldering paste, more specialized soldering method is required for PTHs.

Manual soldering: A manual, through-hole insertion.

Wave soldering: The automated version on manual soldering where a wave of molten solders all the holes in the bottom of the board at once.

Note: A solder paste applier, pick-and-place machine, high-speed chip shooter, and infrared oven inserted in a conveyor configuration can apply solder, pick-and-place, and solder 50,000 parts or more in an hour.

Step 6: Complete a final inspection

Once the soldering process of the PCB board assembly is complete, it is time to do a final inspection and functional test. Run power and simulated signals to test the PCBs electrical characteristics. A sign that the PCB has failed is when it shows the fluctuation of electrical signals during the test. If the PCB fails the final inspection, it should be scrapped. And the process begins all over until a successful PCB is produced.