Primary Components Involved in Circuit Board Assembly
A circuit board must contain various components to function. These include resistors, diodes, capacitors and transistors. Technicians must know each component’s functionality and proper placement on the board for optimal operation.
The first step in circuit board assembly is the creation of a schematic diagram. This serves as a blueprint for the layout of the parts and their connections. This is an essential part of the process and must be done correctly. Failure to follow the design of a circuit board may lead to poor performance or even electrical failure in the final product.
Printed circuit boards (PCBs) consist of flat sheets of insulating material with layers of copper foil laminated to them. Chemical etching divides the copper into separate conducting lines called tracks or circuit traces, pads for connecting components, and features like solid conductive areas for electromagnetic shielding and other purposes. The insulating material of the substrate may be made from different materials such as woven fiberglass, nonwoven polyester, glass fibers, or paper. The most common is FR-4, an epoxy-based resin composite with a layer of fiberglass or other filler.
What Are the Primary Components Involved in Circuit Board Assembly?
In addition to the etching process, some PCBs are manufactured using an additive process. This is a variation of the subtractive process where the unpatterned substrate has a thin layer of copper applied to it, then a reverse mask is applied and the exposed copper is then plated with tin-lead to make a conductive path for the circuit traces. This process allows higher component density and miniaturized designs to be produced more efficiently than a subtractive board.
After the etching and masking steps are complete, a layer of solder paste is added to the surface of the PCB. Solder paste is a grayish substance that includes tiny metal balls (96.5% tin, 3% silver and 0.5% copper) and a special liquid that contains flux, a chemical designed to help the solder melt and bond to a surface. Technicians use a pick-and-place machine to apply the solder paste to the locations on the PCB where components will be placed.
When the PCB is ready for assembly, it moves to the preheat zone where the temperature gradually rises to a level that activates the flux in the solder paste. Next, the board goes through a ramp-up zone that quickly brings the temperature up to reflow temperature. During the reflow soldering phase, the melted solder flows and connects the components to the conductive traces on the PCB. Once the reflow soldering is complete, the board enters a cooling zone to prevent thermal stress and allow the solder joints to fully solidify.
The finished circuit board then undergoes post-reflow inspection. This is typically performed with automated optical inspection (AOI) and X-ray inspection to ensure quality. To get a quote for circuit board assembly, most companies that specialize in PCB fabrication will require the design file and any other notes and specifications that you may have. They will also conduct a design for manufacturability check, or DFM check to identify any issues that could affect the function of your finished product.
