Blowholes in PCB Soldering Their Causes and Cures

A blowhole is a defect in a soldered joint on a printed circuit assembly which incorporates plated through‐hole circuitry. Blowholes are caused by volatiles being generated in the through‐hole during the soldering process and it is often thought that these volatiles originate from the flux. Examination of the problem shows this not to be the case; the most likely cause is bad drilling of the hole and/or poor plating. The construction of the glass fabric used in laminate manufacture may be a contributory factor to bad drilling. The incidence of blowholes can often be reduced by baking the boards immediately prior to soldering. If this treatment is successful in reducing blowholes, it merely confirms that the problem is inherent in the boards themselves and not in the soldering process.