What Is PCB Assembly?
PCB Assembly is the process of putting together printed circuit boards (PCB) for new products. It includes everything from stencil preparation and solder paste printing to SMD component placement and bonds formation through wave or reflow soldering.
The first step is component placement, where automated pick-and-place machines orchestrate a dance of precision. They follow design blueprints to place components in their designated spots.
Component Placement
One of the most important aspects of PCB design is logically arranging all components. For example, it is crucial to place connectors (like USB ports and RJ45 sockets) near the edge of the board so they are easier to reach. This also avoids the risk of cables touching other components and causing electrical interference.
Additionally, it’s important to include fiducial marks on the PCB for automated assembly processes like pick and place machines. These are used to locate and align the components during assembly. Finally, it’s important to orient similar components in the same direction to simplify assembly and inspection. This can reduce manufacturing costs by reducing the number of steps required.
Moreover, placing parts with overlapping footprints is another common error in the PCB layout process. If the copper pads of two parts touch in even the slightest amount, then a stream of electricity will pass between them, which may result in unintended short circuits and/or errors during soldering.
It’s also important to include connections for mechanical elements that can’t be moved, such as a screw terminal or ejector handle. These should be placed near the edges of the board so they are easy to access during final system assembly. This will make it faster to route power, ground and signal traces through the board. Keeping these tips in mind will help you create a professional and reliable PCB design.
Soldering
Soldering on PCBs helps to form the electrical connections between tracks and component leads. These connections pass signals and power through the board, and provide adhesion and strain relief. It also allows for the addition or replacement of components on a populated board. It is one of the most important steps in PCB assembly, so working with a manufacturer who has a strong understanding of this process can be beneficial for your business.
The soldering step begins with the application of solder paste, which is a mixture of tiny grains of metal (typically 96.5% tin, 3.0% silver and 0.5% copper) and flux, which is applied PCB Assembly to the areas of the PCB where components are to be placed. On a professional PCBA line, the paste is applied through a stainless steel stencil, and the applicator evenly spreads the paste across every open area of the stencil.
Next, the circuit boards move to a pick-and-place machine, which is a robotic device that places surface mount components, or SMDs, on a prepared PCB. This is the fastest and most precise method of component placement available. Once the placement is complete, the machine moves the board to a specialized conveyor belt that passes through an oven that covers the bottom of the circuit boards with a wave of solder.
The molten solder then melts onto the pads and components to secure them. Once the solder has cooled, it is trimmed with side cutters. Depending on the type of solder used (and whether it is lead-based or lead-free), the assembled PCBs may be subjected to inspection and functional testing.
Inspection
During the assembly process, it’s important that a PCB is properly inspected to ensure that all components are positioned correctly and that they’re in good condition. If any issues are found, the board may not function as expected. This could lead to customer returns and loss of trust in the manufacturer. It’s also possible that the product could be defective or even unsafe to use, which can result in costly warranty claims and lawsuits.
Fortunately, there are many inspection technologies that can be used for PCBs to ensure quality and accuracy during the manufacturing process. These inspection methods can help to identify defects in the final products and allow them to be corrected before they reach the end customer.
For example, an automated machine vision system can check for surface mount devices such as LEDs and microprocessors to make sure they’re present and in the correct position on the circuit board. However, it’s difficult for these systems to detect small changes in appearance that can indicate a misplaced component or even a chip that’s missing from the board altogether. These errors can be caused by slight variations in lighting, changing perspectives and orientation, or glare on metallic surfaces.
Another common inspection method is X-ray imaging, which looks for voids or nodules in metalized vias on a PCB. This technique uses varying X-ray absorptivity to scan the board and find hidden defects such as soldering failures or bridging.
Testing
In the PCB assembly process, we inspect all components on the circuit board to make sure they meet your project specifications. This includes inspection of the tiny apertures that present mounting spots for electrical components. The tiny Smart door lock supplier gaps must be filled with exceptional precision to prevent bridging, which can be a very serious issue that can lead to circuit board malfunctions. These gaps can only be properly filled with state-of-the-art inspection devices.
Using an automated optical inspection (AOI) machine, we can check large batches of PCBs to find defects that affect the quality of the final product. It uses high-resolution cameras that click on different angles and compares them with perfect or imperfect PCB designs stored in a database. The AOI process also detects defects such as component alignment, soldering quality and lifted pins.
For more precise and in-depth electrical testing, we use an in-circuit test (ICT) instrument. It attaches to the circuit board via fixed probes that connect to test points that are predesigned in the board. The test system then tests each circuit against critical values, including short circuits, open circuits, resistance measurements, capacitance measurements and diode/direction of current measurements. If any of these tests fail, the board will be rejected and discarded. This is why it’s important to work with a PCB manufacturer that offers ICT and other quality assurance testing services.
