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Ask the Experts

November 24, 2008 - Updated
November 24, 2008 - Originally Posted

Define Blow Holes

Blow-holes seems to be a daily occurrence in our wave soldering process. Is this a defect? What is the root cause and how can we prevent it?

C. T.

Expert Panel Responses

Yes blow-holes are a defect for class 2 & 3 but not for class 1.

Blow-holes are caused by poor through hole plating or excessive moisture in the board. If the blow-hole is severe enough it will cause the solder joint to be weak and a cause for failure. When the board is over the wave the moisture inside the board turns to steam and builds up pressure till it erupts through the wall of the plated through hole. Poor plating in the holes makes the problem even worse. The only cure is to bake the boards to reduce the amount of moisture in the board. Bake the boards in a oven at 120C for 4 hours then process them through the wave right away. You may have to increase the bake time if you still see some blow-holes.
Blow-holes can also be caused by a component that is capping the top of the plated through hole. This traps the flux and when the PTH is over the wave the flux will out gas and build pressure till it blows the solder out of the PTH. If this is the cause the component must have a standoff the keep it from capping the PTH.

Greg Hueste
Senior Applications Engineer
Speedline Technologies

Greg joined Electrovert in February 1984. Based out of the Electrovert applications laboratory in Camdenton Missouri, Greg has been in the process applications support role since 2000. His primary responsibilities include providing process and machine applications support for the wave soldering lines as well as process, machine and operations training. He also provides applications support for the reflow and cleaner lines. Greg is a PBET certified trainer and holds two patents on wave solder nozzle design.

Blow holes are typically caused by moisture or an organic material trapped in the bare PCB that volatilizes rapidly when the board contacts the wave. The escaping gaseous materials will blow the molten metal out forming a void in the solder joint. Baking the PCBs is an option to remove entrapped moisture.

Karthik Vijay
Technical Manager - Europe
Indium Corp.

Currently with Indium Corporation and responsible for technology programs and technical support for customers in Europe. Over 15 yrs experience in SMT, Power, Thermal & Semiconductor Applications. Masters Degree in Industrial Engg, State University of New York-Binghamton.

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