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Written by Dr. Davide Di Maio
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Wednesday, 31 December 2008 19:00 |
Thermal shock testing can avoid plating adhesion problems.
 The microsection images (Figures 1 and 2) show through-hole copper plating pulling away from the laminate surface. Copper separation from the hole is uncommon, or at least, it has been for many years. Yet, it has been seen in recent years with Pb-free and new laminate materials.
Recent use of higher Tg laminates that require modification in the plating process to successfully key copper to the hole wall have been experienced. The occurrence of poor or lack of adhesion would increase under the higher soldering temperatures and moisture content typical of Pb-free assembly. It is necessary to work with the PCB supplier and examine the testing conducted for different laminate materials. Thermal shock testing on samples and microsectioning are the simplest test methods to consider as means to prove any improvement in the copper plating adhesion. Thermal shock testing is best conducted with a sand bath rather than a solder bath, as it makes the lack of copper adhesion easier to identify. In solder baths, solder can fill the plated through-hole during the test, and tends to support the copper.
These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defect database. The database (defectsdatabase.npl.co.uk), which is available to all Circuits Assembly readers, allows engineers to search and view countless defects and solutions, or submit defects online.
Dr. Davide Di Maio is with the National Physical Laboratory Industry and Innovation division (npl.co.uk);
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Last Updated on Friday, 02 January 2009 08:10 |
