Worldwide over 1012 soldered joints are made annually in the production of electronics for the consumer, industrial and military markets. About 1/3 of these are made within the Community. With increasing manufacturing automation the cost of identifying and replacing a defective component on a circuit board is often many times that of the actual component. It is thus cost-effective for manufacturers to apply goods-inwards acceptance checks on, say, 0.1 % of a component batch. Currently for solderability this is done visually on component's leads dipped into a pot of molten solder. Such qualitative tests lead to disputes. Attempts have therefore been made to develop so called wetting balances. The project aims to understand the effects of instrumental variables on the results obtained and to develop reference surfaces which will define a solderability scale reproducible to within 5 %.
Tests with wetting balances from the three European manufacturers showed the importance of the thermal mass of the sample holder, the solder bath size and exposed surface area and the timings used when performing solderability determinations. By minor modifications to the instruments results agreeing to better than +/- 10 % were obtained in one laboratory.
An intercomparison was then performed between the three manufacturers using copper specimens, pre-treatment kits, solder and flux provided by the coordinating laboratory. When using benzotriazole passivation and the instrumental modifications suggested, the laboratories were able to achieve the overall goal of a repeatability on any part of the solderability curve to within +/- 8 %, a reproducibility of the mean of +/- 5 % and a reproducibility of a single measurement of +/- 15 % or 0.3 sec. By comparison the participants found some difficulty in using the sulphurization technique given in the AFNOR standard NF C90-551. Although they were in general able to achieve a similar repeatability as obtained with BTA the between laboratory reproducibility was inferior.
Work is continuing to develop an improved reference surfaces which define a complete solderability scale.
Funding SchemeCSC - Cost-sharing contracts
HP2 4RQ Hemel Hempstead
TW11 0LW Teddington