Defective solder joints on HASL boards

What is possible cause of incomplete soldering after surface mount reflow? The bare circuit boards in question are hot air solder leveled. At the problem areas we notice a yellow stain on the hot air leveled surface of the PCB.

S. Q.

Expert Panel Responses

I would be very worried about either a surface contamination, or a change in surface tension at or around the area which exhibits the "yellow stain". Surface analysis with IR spectroscopy/microscope should give a definitive answer about any chemical changes which would affect the surface chemistry/physics. Hard to give a better answer with the limited info at hand.

Jim Williams
Chairman
Polyonics, Inc.

Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.

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