PCB Assembly is an intricate process involving the mounting and soldering of electronic components to transform a bare substrate into a functional Printed Circuit Board. It entails several stages including component placement, reflow soldering, and meticulous inspection.
The first step involves applying a stencil to the PCB with a stainless-steel paste to specific spots where solder pads will exist. This allows automated machines to position components on the PCB according to its design blueprint.
Design for Manufacture (DFM) Check
DFM is an important part of the PCB layout process. It ensures that the design is optimized for electrical performance and can be manufactured easily on a large production scale. It also helps reduce cost, risk and time factors.
The DFM check can be performed manually or with software tools. The tool’s effectiveness depends on several factors, including the experience and expertise of the team that performs it, the availability of advanced software and the speed of communication between engineering and manufacturing teams.
For example, a small change in a design can have significant implications for the manufacturing process. Unnecessary variation in the thickness of a molded component, for example, can greatly increase cooling times and drive up production costs. DFM checks should allow designers to directly understand the impact of their design choices on production concerns.
DFM tools can also be used to optimize material specifications given functional requirements and cost targets. For example, a pin that’s missing a clearance pad on all plane layers could connect to voltage planes and cause shorts. Using DFM tools like PCBflow can help us spot these issues and fix them before they become fabrication or assembly problems.
Printed Circuit Board (PCB) Fabrication
The PCB fabrication process involves converting design output files, such as Gerbers and netlists, into a physical circuit board that can be soldered. This is done by etching the copper layers, applying solder mask, and applying coatings like green solder resist.
Once the PCB is etched, it’s covered with a layer of green solder mask that insulates the copper traces from accidental contact with other conductive materials that could create functional problems. It also helps ensure that solder is applied to the correct locations during assembly.
Next, the assembler stencil prints a layer of solder paste onto the surface of PCB Assembly the circuit board. This is usually made of SnAgCu (Tin, Silver, Copper) alloy with a melting point of 217 to 220 degrees Celsius. Common defects in solder printing include excessive and uneven amounts of solder.
Once the assembler has placed all of the SMCs, they can use a machine called a glue-dosing device to apply a tiny drop of glue to each location on the bottom side of the circuit board where they will mount through-hole components. This will prevent the through-hole components from falling off during the wave soldering process.
Component Procurement
Getting the right components for PCB assembly is critical for quick turnaround time. Getting it wrong can cause costly delays, resulting in lost revenue for the company and its customers. The component procurement process involves identifying potential suppliers and vendors that can provide the required parts for assembly. It also includes evaluating them based on various criteria such as pricing, quality, delivery time, and customer service.
The sourcing cycle can be extended due to factors such as the availability of the desired components, resourcing issues, and delays in delivery. These delays can result in missed delivery dates, and they can also affect the final price of the finished product.
During this stage, the PCBs are washed with deionized water and cleaning chemicals to remove flux residues, stains, and oil fingerprints. The cleaned circuit boards are then dried and packaged before shipping.
Pick-and-Place (P&P)
Pick and Place (P&P) machines are used to precisely position Surface Mount Devices (SMD) components on a PCB. These small, tiny electronic components include resistors, capacitors, ICs, and diodes. They’re critical to the function and reliability of electronic products.
The P&P machine carries the components from their feeder systems — usually tape, tray, or tube feeders – and uses an automated robotic arm to assemble them on the PCB. A “position file” identifies where each component is supposed to be placed on the board. The position files are generated by the KiCad software using the board’s layout.
These position files also identify the x-y rotation and coordinates of each component, so that a machine can correctly position them on the PCB. Most P&P machines use vision systems to verify the orientation and placement of each component. They can also compensate for the inevitable registration errors that occur during the pickup process by adjusting the position of the picking head. The reflow machine sits after the P&P machine and melts the solder to join the PCB and SMT components together.
Soldering
PCB Assembly includes PCB Assembly supplier the mounting and soldering of electronic components on a bare circuit board. This creates a functional printed circuit board that can be used to make an entire electronic product.
The most common method for PCB assembly is surface mount technology (SMT). It is faster and more efficient than thru-hole technology. However, it requires more careful inspection and assembly to ensure quality. The assembler will perform several inspections throughout the process to make sure that all components are correctly attached and that the connections between them are secure.
Another important step is to verify that the solder paste pattern is accurate on the PCB. This can be done using an automated machine called an automatic optical inspection (AOI). The AOI uses cameras positioned at different angles to check for the quality of solder connections on a circuit board. Poor quality solder connections often result in de-wetting, which can cause the solder joints to fail.
After the pick-and-place machine has placed all of the components, they will be soldered to the PCB using a heated process known as reflow. This ensures that all of the connections between the components and the circuit board are secure and will not fail over time.
