The Circuit Board Assembly Process
The circuit board assembly process is where the bare PCB is populated with electronic components according to the function of the finished product. It involves several steps of adherence to industry norms and rigorous quality control measures.
These include a DFM check that reviews a client’s designs for part spacing, pin indications, footprint corroboration among other things. Altest offers this service free of charge.
Layout
Printed circuit boards (PCBs) require careful planning and design to ensure the proper functioning of components. Insufficient consideration can lead to electromagnetic interference, a poor-performing board and production delays and costs.
Front-end engineering involves selecting a layout, netlist import, component placement and routing. During this phase, ECAD software translates schematic diagrams into PCB layout files. The stack-up design is also defined to accommodate plane layers, signal layers and dedicated routing channels.
The layout must conform to industry norms for component footprints, which will enable it to be compatible with automated assembly equipment. Achieving this helps to streamline the assembly process, mitigating assembly difficulties and compliance issues.
The final layout must be able to export to Gerber circuit board assembly format, which is the standard file format for PCBs. Using an accurate PCB layout tool is essential because erroneous Gerber files can cause issues during manufacturing. Sierra Circuits offers Better DFM to check for manufacturability issues in PCB design files before they are used for fabrication. This free tool will highlight any areas of a design that will not adhere to the standard PCB manufacturing rules.
Components
Printed circuit boards are a vital component of electronics. To ensure that the final product meets industry standards, rigorous quality control measures are implemented throughout every step of the assembly process. These include adhering to strict guidelines for components, soldering techniques, and cleanliness standards. This ensures that all finished products deliver reliable and consistent functionality.
The first step in PCB assembly is applying a solder mask to the board. This is done by placing a stencil made of a stainless-steel sheet over the circuit board and applying solder paste to specific areas of the circuit board where the components will sit. The circuit board is then sent on a conveyor belt to robotic pick and place equipment, which adds the surface-mounted components.
For through-hole components, the assembler drills holes into the circuit board and inserts the component leads into these holes. The traces on the copper-clad board then connect to the component leads via soldering. In modern manufacturing, reflow soldering is a popular method for assembling through-hole components. The reflow process involves applying solder paste to the component pads and heating them in a reflow oven, resulting in secure connections that are free from defects.
Soldering
Ongoing technological innovations continue to shape PCB assembly practices, elevating efficiency, precision, and environmental responsibility. These advancements include automated systems for component placement, advanced reflow soldering techniques, and lead-free options that align with industry standards.
Component Verification: Before assembling the circuit board, a careful inspection is conducted to ensure that all of the necessary components are available and in good working condition. This includes a comprehensive inventory check to verify that all resistors, capacitors, diodes, transistors, integrated circuits, and other electrical components are present.
Then, a paste of prealloyed solder and flux is applied to the surface of the board. This is done with a stencil, and the paste is then deposited onto the designated areas where the components will be placed on the board.
Once the paste has been applied, the component leads are inserted into the holes on the PCB using Through-Hole Insertion Technology (THT). This is an older technology than SMT and requires drilling the holes, but it offers a stronger connection between the board and the components. Then, the board is heated in a reflow oven to melt the solder and form strong connections.
Inspection
Component quality is an essential part of the circuit board assembly process. Through meticulous visual inspection and rigorous testing, manufacturers can ensure that all components meet industry standards for functionality, durability, and quality. Adherence to these strict quality control standards is critical for enhancing product reliability and customer satisfaction while minimizing the risk of costly repairs and recalls caused by component-related issues.
Once the layout has been verified, it’s time to begin the actual PCB assembly. Using ECAD software, the next step is to route traces between circuit board custom components. Once the traces have been routed, it’s time to apply the solder paste. This is done with high-speed screen printers, such as Altest’s multiple EKRA and GKG models. These machines use unique 2D and 3D vision systems to verify the correct thickness of the deposited paste.
Once the paste has been applied, the board is moved onto conveyor belts for robotic pick and place equipment to add surface mount components. During this phase, technicians also examine the boards for through-hole components, and solder those parts if necessary.
Packaging
Printed circuit boards play an essential role in most advanced electronics. If you take apart your smartphone, for example, you will probably see one. These small devices are vital to our modern technology, and assembling them requires great concentration and attention to detail.
PCB manufacturers start the assembly process by verifying and stocking up on necessary components, as well as performing a thorough inspection of the board itself for any issues that may impact its functionality. This includes ensuring that the board is ready to receive the plated through-hole (PTH) or surface mount device (SMD) components that it will require.
Next, a stencil is applied to the circuit board to enable assemblers to precisely deposit solder paste in specific areas. These are pads where the components will be placed, and in some cases a special solder paste can be used to fill holes on a PCB that would normally be considered PTH or SMD.
These materials are then laid out by hand or by an automated machine, allowing assemblers to place the components as needed. The assembly is then inspected to ensure it meets all specifications, and it is sealed in an antistatic bag to prevent any damage or contamination.
