Blow Holes and Pin Holes in Solder Joints and How to Prevent Them

blow hole solder

What is a blow hole / pin hole in PCB, and is it something you should worry about? Blow holes are caused by gas being released due to poor plating in a plated through hole, excess flux or moisture during soldering, or poor solderability in component leads or boards. Generally, seeing this discrepancy is a process indicator for the PCBAs. Poor solder joints can result in faulty boards which then end up failing during test or worse, in the field. It is crucial to perform a root cause analysis so that the issue does not propagate over an entire set of boards or products.

Excess Flux or Moisture Causing Blow Holes

The first cause of blowholes we are going to dive in to is excess flux and moisture. When solvents get trapped in the flux inside of the holes of a PCB, blow holes can occur. The solvent boils, expands, and blows solder out of the hole. When blowholes happen, moisture is often to blame. Non-plated areas on a bare PCB that expose the internal laminate are more vulnerable to moisture.

To eliminate this problem, a manufacturer can try to bake the boards to draw all the moisture out. A better solution would be to keep all boards vacuum sealed until absolutely necessary.

Low Quality Bare Boards

Another cause of blow holes and pin holes in PCBs is a poor manufacturing process for the bare boards. Drilling of plated through holes during fabrication could be a culprit. The drilling process can potentially leave gaps between the plating and the laminate. The concern with that is that air can get caught in these traps. When the board is heated up during soldering/assembly, the trapped air can expand and thus push through the thin layer of plating. Improved drilling processes can help with this problem. It is important to only use trusted bare board fabricators who have a track record of quality boards. Vinatronic has a network of bare board fabricators across the world that consistently produces quality PCBs.

Are Blow Holes / Pin Holes Okay for Use

blow hole / pin hole pcb

PCBAs with Blow Holes and Pin Holes may still work but pose a risk in terms of reliability. IPC-610 details criteria for solder fill as shown above.

If you continue to have issues with blow holes or pin holes, please reach out to us. Our engineers are experts at root cause analysis and our PCB fabrication shops have been proven to provide quality bare boards. We’d love to help out in any way that we can.

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