What is PCB Board Assembly Manufacturing?
PCB Board Assembly Manufacturing
The process of pcb board assembly manufacturing turns a static, bare circuit board into an electronic device that performs designated tasks. The most captivating aspect of this process is its transformation from a purely mechanical to a functional piece of technology.
As the name implies, this PCB manufacturing step involves assembling all the necessary components to convert the bare PCB into a fully functioning, working electrical circuit. This is accomplished through soldering, a process that uses melting and cooling to create a reliable, durable joint between the components and the board itself.
First, the bare PCB is prepped for assembly by cleaning it with an acid solution to remove any contaminants and to ensure that the surface is smooth enough for soldering. It then undergoes a wash cycle that maintains the water temperature at 144 degF and applies a pressure of 45 pounds per square inch. This washing helps prevent corrosion in the future and also removes any excess flux that might cause shorting during the soldering process.
Afterward, the fabricated PCB goes through an inspection. The board’s silkscreen and solder mask layers get scanned with a computer-controlled laser that matches the digital image to a customer’s provided Bill of Materials (BOM) file. Then, the patterned layers are separated from the base with an epoxy or phenolic adhesive. The fabricator drills registration holes for vias and leaded components on the inner layer of the board. The drills also cut raised ends of copper, known as “fingers.” These extending fingers help maximize the available contact area for soldering and component mounting. They may also constrain the flow of solder during assembly, preventing shorts between closely spaced pads or traces.
What is PCB Board Assembly Manufacturing?
Next, the fabricator lays down a thin coating of solder paste on the bare circuit board. This solder paste is a mix of copper and tin, which is what will be melted and cooled in the soldering process. This solder paste is then inspected for quality, consistency, and thickness. If there are any defects, the manufacturer will re-tinker with the paste formulation or use another type of soldering material.
Once the solder paste is inspected, the components are inserted into their appropriate through-hole locations using a pick and place machine. This step is largely automated for high volume production. Humans get fatigued and suffer from eye strain when handling tiny parts, so it’s better to let machines handle this labor-intensive task.
The populated PCB then gets passed over a wave of liquid solder, coating the exposed leads and pads to form durable solder joints. The reflow process can cause movement between the exposed components and the PCB, which might result in poor connection quality or even a short. To minimize this risk, the reflow is conducted in a nitrogen-blanketed environment, which protects the components from oxidation and facilitates wetting of the solder.
Once the soldering is done, the assembled PCBs are inspected by both manual and automatic optical inspection (AOI) machines. AOI machines use multiple high-powered cameras arranged at different angles to “see” the PCBs, looking for quality solder connections and highlighting areas of concern. This process is faster and more accurate than manual microscopic inspection, which requires highly trained technicians.