PCBs are a crucial component of electronics and circuits that significantly impact our daily lives. Their importance lies in their ability to conduct all electrical functions in a smaller space. That is why PCB assembly is just as important. PCB assembly lines manufacture these circuit boards and assemble them into functional components.

In this blog, we will learn about the assembly process of PCBs. We will start from their fabrication to the end, when they become ready to be used. 

Overview of the PCB Assembly Workflow

PCB assembly is a process used to fit all the necessary components on the circuit board. It involves the following processes:

• DFA (Design For Assembly)
• SMT (Surface Mount Technology)
• Through-hole component placement
• Testing
• Final Inspection

Step-by-Step PCB Assembly Process

It all starts from the fabrication house. They craft the circuit boards according to the DFM guidelines. It is very important to follow these guidelines to prevent any likely manufacturing errors. Here’s how the assembly line will work afterward:

1. DFA (ODB++ and BOM)

Design for assembly, or DFA, is the first step of the PCB assembly process. Following DFA guidelines is extremely important for designers. The DFA engineers will verify the data present in ODB++ and BOM files. The goal of this step is to confirm that there are no potential assembly errors.

2. SMT (Surface Mount Technology)

SMT assembly involves placing and soldering electronic components to the board. This can be done either by a pick-and-place machine or simply using an automated machine. Before mounting the SMDs, they are checked to see if they’re washable or not. Non-washable components are added later on. 

Here are the important steps of SMT:

• Solder paste screening and inspection 
• SMT component placement 
• Reflow soldering 
• Automated optical inspection (AOI)
• X-Ray Inspection 
• Flying Probe Testing (FPT)

All the steps are extremely important for SMT assembly. Afterward, the soldering and surfaces are ready for the next step.

3. Through-Hole Assembly 

This part can be carried out manually or by using an automated machine. There are three types of soldering techniques used for through-hole assembly:

• Wave soldering 

This technique is used for large-scale soldering processes. The parts are placed on the board, and liquid flux is applied to all the component leads. Then the board is pre-heated to a specific temperature and passed through a solder wave, using a conveyor belt.

• Selective soldering 

This process is a rather simple one; only the selected through-hole location on the circuit is soldered. It is done using a robotic solder or a special solder nozzle. 

• Hand soldering 

If there is a lack of automated options, hand soldering can be used to solder the components. It is not as efficient and precise. Flux is used to clean metal surfaces and to prevent any oxidation.

4. Cleaning of Assembled Parts 

After mounting the components, cleaning is the next step in the PCB assembly. Deionized water or a Kaizen solution is used to remove the flux residues or any contaminants. The boards are treated with deionized water at 144°F at high pressure and speed. 

5. Soldering of Non-Washable Components

If there were any non-washable components in the design, they would be placed now. A special type of no-clean flux is used for this process. This flux doesn’t need to be cleaned afterward. This flux has resins and activators that make the solder flow easily and prevent it from oxidizing.

6. Final Inspection and Testing

At this stage, final inspection and testing ensure the boards are ready for use. The manufacturers do their best to ensure no errors are present. But even after ensuring, they keep coming. You can think of this like a final test to remove any missing pieces or errors. If anything does come up, it can be easily fixed at this point.

7. Conformal Coating 

Conformal coating is applied to the circuit board. This creates a barrier between the PCB and the contaminants. It also acts as an insulating layer; this goes a long way in reducing crosstalk, current leakage, and electrochemical migration on the board. This layer usually consists of acrylics, polyurethanes, or epoxy resins. 

These are all the steps required for a PCB assembly. The end product is a PCB that is ready for use in a circuit or electronic device.

Advanced Techniques in PCB Assembly

We will now discuss the various advanced techniques employed in PCB assembly. These techniques have come around in recent years and have proven to be extremely effective.

Lead-Free and RoHS-Compliant Assembly

Electronics also require them to be safe and environmentally friendly. That is why the lead-free and RoHS-compliant assembly is becoming the standard, mostly for building environmentally responsible PCB assembly services. These assemblies should immediately eliminate the use of hazardous substances, such as lead. 

But as we all know, this also presents some other challenges. The biggest one being lead-free solder tends to melt at higher temperatures. It can damage the circuit and important components. These hurdles do tend to slow down the process. Regardless, lead-free and RoHS-compliant assembly is going to be an important factor here.

High-Density and Micro Assembly Trends

Not only that, but the electronics are continuing to go as small as they can. As a result, high-density and micro assembly have become increasingly popular. Wearables, smartphones, and IoT sensors are going to demand that the circuits be small. In order to handle these tiny components, manufacturers are bound to use advanced microelectronics tools and equipment. They use precision pick-and-place machines, laser drills, and automated optical inspection in their PCB assembly process.

Common Challenges in PCB Assembly

As we all know, PCB assembly is a complex process in its own. The problem is that small and large errors keep coming. This is going to compromise the efficiency of the assembly line. Here are some of the important challenges to keep in mind:

1. Component Misalignment & Solder Bridging
2. Moisture-Sensitive Devices (MSDs)
3. PCB Warping & Thermal Stress
4. Preventing Common Defects

All these challenges ultimately halt the assembly process. By keeping them in mind and ensuring they don’t happen, your assembly will work like a charm. 

Quality Standards and Certifications

In PCB assembly services and building, maintaining quality and consistency is extremely important. This is where the industry quality standards and certifications come into play. 

• Key Certifications 

Here are the important certifications you require for industry-standard products:

1. IPC-A-610
2. ISO 9001
3. UL Certification

• Why standards matter in PCB assembly reliability

These standards are an important way to:

1. Ensures a  uniform quality across production batches
2. Improves the product reliability and long-term performance
3. Reducing any rework, defects, and warranty issues
4. Building trust with clients and compliance regulators

Conclusion 

The PCB assembly process is a complex and crucial one. The resultant products will shape electronics and everyday devices. That is why so much thought and care go into this assembly process. A proper assembly will result in a line of reliable products and quality assurance. 

If you’re considering manufacturing PCBs, always consult a trusted manufacturer. Insight PCB is known to offer expert solutions, reliable repairs, and top-notch PCB services.