What Is PCB Assembly?
PCB Assembly is a crucial step in the electronic manufacturing process. It involves adding components and resistors to the printed circuit board (PCB) and ensuring that it does what it is meant to do.
There are two primary PCB assembly techniques – Through Hole Technology and Surface Mount Technology. This article delves into PCB Assembly the details of both methods, comparing their processes, advantages, and applications.
Design
A PCB’s design can impact its assembly process, so it’s important to consider assembly issues in the early stages of the design phase. For instance, if a board has sensitive traces, it’s important to leave enough room around them to prevent bending during soldering. This is especially true for high-density applications. In addition, it’s a good idea to make sure the layout of your components is compatible with the assembly method you choose.
For example, if your circuit board is going to be hand-soldered, you’ll need to make sure there’s enough space for the soldering tool. Likewise, if your circuit board will be assembled using SMD (surface mount device) components, you should ensure that there’s enough space for these components to fit on the board. You also need to review the location of components that emit heat to ensure there’s sufficient space to avoid thermal damage to other components and traces.
Another assembly-related issue is ensuring that the silkscreen layer on your circuit board has clear and legible reference designators and values. This will help the PCBA manufacturer assemble your circuit boards correctly. For example, it’s important to make sure that the Pin1 indicators and polarity indicators match up with the corresponding component outlines. This way, the expert can quickly and accurately identify these essential instructional markings.
Fabrication
PCB fabrication involves producing the physical structure of a printed circuit board with copper traces and conductive pathways to connect components. The bare substrate material is usually a fiberglass-reinforced epoxy laminate such as FR-4. It can be produced using additive or subtractive methods. The additive method involves coating the bare substrate with a photoresist, which is then imaged by exposure to light to remove the unexposed areas. The exposed areas are then treated to make them capable of bonding metal ions. They can then be plated with copper to form the required pattern of conductors.
After the components have been deposited onto the PCB, it must be cleaned to remove any flux residue and fingerprints. This is a time-consuming process that requires careful attention to detail. PCBs that are dirty are more likely to malfunction.
This step can be done manually or through automated processes such as a pick and place machine. It can also be combined with other automated and manual procedures. The most important thing is to ensure that the components are placed in accordance with the PCB design. If a tiny resistor is not properly placed, it could result in a short-circuit or an electrical failure. A thorough inspection and quality control process is also necessary to ensure that all the components are in working order.
Assembly
PCB assembly is the process of soldering electronic components to the bare circuit board. This results in a fully functional circuit board ready for use. There are two types of PCB assembly: Through-hole and Surface Mount Technology (SMT). Through-hole PCBs have wire leads that run through holes drilled into the PCB and are soldered to copper traces. This method is preferred when mechanical strength is important. Surface mount PCBs have components with smaller leads that are placed on the surface of the circuit board using an automated process called pick-and-place machines.
There are many steps in the PCB assembly process, starting with a Design for Manufacturability check, or DFM, performed by a company that specializes in PCB assembly. This step is designed to look at all of the design specifications and identify any flaws that may affect the functionality of the finished product.
Once the DFM checks are completed, the PCB is sent to an assembly house for populated PCB production. It is then cleaned and shipped to its final destination. During the assembly process, it is vital to ensure that all components are placed correctly and in the correct locations on the PCB. There is a lot of movement during the reflow process, and any misplaced components can lead to shorts or poor quality connections. Often, this movement can be avoided by choosing the right component placement tools early in the design process.
Testing
As PCB designs evolve into higher PCB Assembly supplier density, thinner conductor tracks and laminates, increased quality controls must be used to ensure that these components will perform as designed. Even a single misprocess during the assembly process can result in field failures and other malfunctions that can be costly to manufacturers and consumers alike.
One of the most important steps in ensuring the integrity of your PCB assembly is testing. While many errors can be caught during inspection and the production process, a thorough functional test is the only way to confirm that all components will work together as intended.
Traditionally, this was done with a pair of tweezers, but most manufacturers have switched to automated processes that allow machines to handle the delicate components quickly and without fatigue. These robots can also identify issues that might not be easily visible to human eyes, such as solder bridging or shorts.
During this phase, robotic test probes access the PCB’s test points and check for resistance, capacitance and other electrical parameters. This is usually the final step before the board is shipped. It’s also the time when specialized “no-clean” flux is used to solder surface-mount components. This type of flux contains resins and activators that make it less likely to oxidize during the soldering process. As a result, it’s not necessary to clean the PCB afterward as it would be with conventional non-no-clean fluxes.
