PCB Assembly Process Steps
Steps Involved in PCBA Process
The assembly of a printed circuit board (PCB) consists of many steps that should proceed in an orderly to achieve an exemplary PCB assembly (PCBA). One step must work in synergy with the previous one. In addition to this, the input should receive feedback from the output, which makes it easier to track and resolve any errors in the early stages. Let Venture introduce you to what steps are involved in the PCB assembly process.
Step1: Adding Solder Paste
This is the initial stage of the assembly process. In this stage, technicians add solder paste to the component pads in all areas where soldering is required. They place the solder paste on the pads correctly with the solder screen’s help. They make this screen from a PCB file with holes.
Step2: Placement of Components
After adding the solder paste to the component pads, it is time to place the elements. The PCB passes through a machine that puts these components precisely on the pads. The tension provided by the solder paste will hold the assembly.
Step3: Reflow Oven
Now, the solder paste and surface mount components are in place. We will cure the solder paste to the correct specifications critical for proper adhesion of the PCB components. That is the relevant part of the PCB assembly process – reflow soldering. As a result, assemblies with solder paste and elements pass through an industrial reflux furnace on a conveyor belt. The heater in the oven will melt the solder in the solder paste. Once the melting process is complete, the assembly will again move through the conveyor and be exposed to a series of more excellent heaters. The purpose of these coolers is to cool the melted solder and allow it to cure.
Technicians should inspect the PCB to check its functionality after the reflow process. This stage helps to identify poor quality connections, misplaced components, and shorts due to the continuous movement of the board during the reflow process. Venture uses several inspection steps. For example:
- Manual inspection.
- Automatic optical inspection.
- X-ray inspection.
To check the board’s functionality, identify low-quality solder, and locate potential pitfalls. Once the inspection is complete, the assembly team will make critical decisions. Usually, they will scrap the circuit board with several functional errors. On the other hand, they will rework the board if there are more minor errors.
Step5: Through-hole Component Insertion
Certain types of PCBs require the insertion of through-hole components and conventional SMD components. This component is only available for this stage of insertion. For this purpose, the signal is passed from one side to the other with the help of PCB components to create plated through-hole.
Step6: Final inspection
Next, we will proceed to the second level of examination. First, we perform a functional test on the assembled board or a thorough review of the PCB to see its electrical characteristics, including voltage, current or signal output, and other vital data. Today’s manufacturers utilize various advanced test equipment to help determine the success or failure of the finished board.
By this step, all soldering processes are complete. A large amount of flux residue is formed around the solder joint during the soldering process. As the name implies, this step involves cleaning the flux residue. We scour the flux residue with deionized water and solvent. That completes the PCB assembly. Subsequent stages will ensure that the assembly is assembled correctly.
About 13 Common PCB Assembly Problems Summarized By The Venture Team
As a PCB and PCBA manufacturer, Venture has many years of assembly experience. Our excellent assembly team has summarized eight common PCB assembly problems:
- Bill of Materials (BOM) issues: Component availability: Certain parts are out of stock or no longer in production.
- Incorrect PCB packaging: PCB packages can create multiple DFM issues if not built correctly, including poor solder joints, mismatched pins, or lack of physical space. It is important to use industry or manufacturing specifications when building CAD package models and make sure they correctly match the part numbers in the schematic.
- Component placement errors: Components that violate DFM rules by being too close together can cause difficulties with automated assembly systems. For best results, SMT machines, wave, and reflow soldering require minimal spacing. Manual rework also requires adequate component spacing. It can be challenging to fit a soldering iron into an area when another significant part covers the component. Attempting to suit the tool into a tight space near an element may also be subject to collateral damage.
- Solder defects: Violation of DFM rules can also produce a variety of solder defects in the printed circuit board. The following are examples of situations that can occur.
- Solder bridging: When solder forms a connection or short circuit between two metal conductors that are not intended to be connected, it is called a solder bridge. This defect can occur if the assembly team doesn’t place the wave solder component correctly. If they don’t design the solder resist layer correctly, it may result in too much solder on the pad or a design or alignment problem with the solder stencil.
- Shading: Larger parts replacing smaller parts into the wave solder may shade the more minor elements and rob them of the solder; they need to make a good connection.
- Bad solder joints: In through-hole components, this is usually due to insufficient heat sink pads causing excessive heat to be taken away from the connection during soldering.
- Tombstone effect: In small two-pin surface mount components, too much metal on one pin can cause a thermal imbalance, causing the solder on the other pin to melt faster and pull the part off the colder pinpoint.
- Recessed joints: Through-hole pins that are too large for their pinpoints may not hold as much melted solder as they should, resulting in an incomplete connection.
- Heat dissipation problems: Boards with asymmetrical stacks may warp and twist due to the heat applied during soldering operations. These same thermal problems may also adversely affect thermally sensitive components that technicians must assemble manually later.
- Lack of testability: PCB manufacturers use board testing to verify the assembly process and ensure that each component pin has a good connection to its associated network. If technicians are not fully covering the test points according to the design for test (DFT) rules placed, the test can not be fully completed, requiring a manual verification process.
- Inadequate silkscreen markings: Accurate silkscreen markings (such as reference markers and polarity indicators) are critical for assembly verification, rework, and testing. In the absence of these markings, test technicians encounter the more time-consuming and challenging task of finding the right place on the board to work.
- Assembly documentation is incomplete or unclear: The assembly documentation needs to be complete and up-to-date for boards that technicians built. Drawings need to be readable, and all necessary data and information files need to accompany the design for manufacturing.
As you can see, many potential PCB assembly problems can occur due to how technicians designed the board. However, with the help of the Venture team, they can resolve many of these issues. Our talented engineers will work with you throughout the assembly process, verify your BOM before assembly, and provide you with current and up-to-date DFM and DFT rules and constraints. We welcome your quotes and trial orders to test our services!