PCB Soldering Defects

PCB soldering defects are a common issue in PCB assembly. In this blog post, we will discuss the most common soldering defects and their causes. We will also look at how these defects affect the assembly process and the technologies available for minimizing or eliminating them.

Top 10 PCB Soldering Defects

Gaps in Solder Joints

Gaps often occur due to insufficient solder paste on the joint. Other causes include component misalignment, thermal shock, or vibration during soldering.

Solder Balling

This issue is caused by the presence of impurities in the solder paste, such as oxides or contaminants. Solder balling can also be caused by too much heat during soldering.

Cold Solder Joints

This defect occurs when the solder joint is not heated to the proper temperature. Cold solder joints can also be caused by insufficient flux or too much heat during soldering.

Solder Bridging

Bridging is a common soldering defect that occurs when two conductors are connected by a solder bridge. Often, this is caused by too much solder paste on the joint or component misalignment.

Component Shift

This defect occurs when the component is not properly aligned before soldering. A component shift can also be caused by too much heat during soldering, which causes the component to move. While visual inspection can reveal this defect, automated inspection and testing are required to confirm it.

Lifted Pads

Lifted pads often occur due to too much heat during soldering. Other causes include thermal shock or vibration during soldering. This defect can also be caused by a faulty component. Automated optical inspection can be used to detect lifted pads.

Webbing and Splashes

Pollutants can sometimes cause webbing or splashes on the PCB. These defects can be caused by poor solder paste quality, inadequate cleaning, or insufficient flux. The defects will affect the appearance of your printed circuit board and sometimes even cause short-circuit failures.

Sunken Joints

Sunken joints often happen during wave soldering when molten solder wicks up the lead before it can solidify. They can also be caused by too much heat during soldering or insufficient flux.

Tombstoning

Due to a thermal imbalance, discrete components can sometimes stand up on one end during wave soldering. This is called tombstoning, and it can cause a short circuit or an open circuit.

Shadowing

Shadowing also happens during waver soldering when surface-mount components do not make full contact with the solder. The result is an incomplete or poor connection, which can cause electrical problems, and functional testing is required to detect this defect.

How Do These Defects Affect The Assembly Process?

These defects can generate a range of problems during the assembly process from cosmetic issues to functional failures. In some cases, the problem can be fixed with a simple rework.

However, in other cases, the board will need to be scrapped entirely, which causes delays in the assembly process and increases costs.  

How Do the Defects Delay the PCB Assembly Process?

When there is a PCB defect, the board has to be stopped and fixed. The pause causes a delay in the PCB assembly process, and setbacks can range from a couple of minutes to a few hours, depending on the severity of the defect. Additionally, the entire process has to start over from the beginning since the board is scrapped, leading to more delays and significantly increasing the cost of the PCB.

How Do the Defects Increase Assembly Costs?

PCB soldering defects can also increase the cost of assembly. For example, if a board has to be scrapped, the assembly process has to be reset and built with all new parts, significantly delaying the completion time and increasing the cost of the project.

In some cases, the problem can be fixed with a simple rework. However, in other cases, the board will need to be scrapped entirely. This obviously means that more money has to be spent on production.

Technologies and Methods That Help Catch Assembly Mistakes

There are various types of inspection and testing used to catch soldering defects. They include the following, among others:

Electrical Part Verification

This is a process that uses an automated optical inspection system to check for soldering defects.

X-Ray Inspection

This is a process that uses X-rays to inspect the PCB for soldering defects. This is a more expensive method, but it can be used to detect smaller defects like inspecting solder joints for any defects. The images are able to compare the quality in different builds and, thus, are extremely useful when performing a multiboard build. With the x-ray inspection, your board is assured to have every joint at the same level of quality before the rest of the production.

Flying Probe

The flying probe test (FPT) is a testing method that uses probes to test PCBs for electrical continuity and shorts. During its examination, the spring-loaded probes are skimmed along the planes of the pads and traces of the boards, and gravity applies pressure to these parts to test the integrity.

In-Circuit Test 

ICT is another test for PCBs that utilizes a bed of nails fixture; the continuity and electrical characteristics of the nodes are examined for signal strength, voltage levels, resistance, and so on. This test ensures that there are no errors in the assembly of the board during the soldering process.

3D Optical Inspection

This is a more expensive method that uses lasers to scan the PCB and create a three-dimensional image. This image can be used to detect small defects.

Automated Optical Inspection

AOI is a process that uses an automated optical inspection system to check for soldering defects.

Paste Inspection

This is another great PCB assembly inspection method used when looking for defects in the solder paste. It is among the most effective ways to find defects in the solder paste application process.

Design Review

Now, after the design process is complete, it’s time for a design review. This helps to identify any potential problems that could cause soldering defects. Design review includes:

• Design For Manufacturability (DFM) Analysis looks at the design and identifies any areas that could be improved to prevent soldering defects.
• DFX (Design For Excellence) Analysis looks at the design and identifies any areas that could be improved to prevent soldering defects.

Both of these analyses are important in the prevention of soldering defects.

All of these different inspection and testing methods can be used to catch soldering defects. By using these methods, you can improve the quality of your PCBs and prevent soldering defects. PCB manufacturers can use these methods to improve their manufacturing process and create high-quality products.

Final Thoughts

When it comes to PCB soldering defects, prevention is the best cure. By using the different technologies and methods available, you can catch potential defects before they cause issues, and they will save you time and money in the long run. So, don’t wait until there’s a problem; be proactive and prevent soldering defects before they happen.

If you have any questions about soldering defects or how to prevent them, reach out to the experts at Geospace Technologies MFG. We are more than happy to help with all of your PCB project needs.