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Due to the unique configuration of DIP package leads having a flat shouldered structure, extra care must be exercised in hole size design and insertion. Too large a hole diameter which results in the shoulder contacting the edge of the PTH, combined with too high an insertion force, could result in fracture of the copper plated layer at this point. Even at normal insertion forces, the localised pressure exerted at the small contact area is increased considerably and could result in failure of the plating. Creating a fissure, or discontinuity of any kind in the plated layer, leaves a path open for laminate degassing during the soldering operation. The result of the degassing is a poorly formed solder joint with voids and blowholes present, the source of which is not clearly evident to the board manufacturer unless careful metallographic work is carried out. Unless precise orientation of the samples and accurate control of polishing is carried out, the source of the problem might very easily be missed when examining the microsections.

In striving to produce higher yields and fault‐free printed wiring assemblies, the PWB processor usually finds solder shorting or bridging to be one of the most difficult faults to eliminate. Finding himself faced with a high incidence of solder bridging, he usually attacks the problem by examining his own process parameters. Fluxing, preheating, solder composition and temperature, conveyor speeds, etc., are all assessed and adjusted so that the problem is minimised as much as possible. But still it appears, though at a lower level of incidence (l‐3%). With nothing else in his arsenal of weapons to attack this persistent problem, the process engineer is left somewhat helpless, wondering what further he can do to aid his course.

With the advent of stricter tolerances and higher reliability requirements on electronic assemblies, PWB contamination has arisen as a significant contributing factor to these performance criteria.