Computer‐aided Solderability Testing for Receiving Inspection Available to Purchase

The availability of a wetting balance which can be easily interfaced to a microcomputer has made possible a practical receiving inspection solderability test for component leads that avoids the subjectivity of the present dip‐and‐look test. The wetting balance, in effect, detects the size and shape of the solder meniscus on the lead. Since it is the solder meniscus more than the degree of coverage that is evaluated by inspectors of the completed solder joint, the wetting balance provides a more realistic test of how well the components will perform on the PWA. The software that has been developed for the wetting balance is designed to make it easy for inspection workers to perform the test with a minimum of training. It asks for identification of the part, manufacturer, date code, purchase order number, etc., so that the final results are adequately documented. Use of a computer to present the results means that the wetting force as a function of time can be plotted as a normalised curve (automatically accounting for differences in number and size of leads), and also that the results can be accumulated in a factory computer for statistical quality control. For a given lot of components, there is usually little spread in the observed results. This indicates that a sample size as small as three is sufficient to characterise the lot. With further data accumulation, it should be possible to devise a skip‐lot sampling plan for those manufacturers showing consistently good solderability. Also, the accumulated results of lots from problem manufacturers, coupled with microscopic studies of the causes of poor solderability, can be used as a basis for negotiations. The results are reproducible from one plant to another because they do not require visual interpretation. Judicious application of this method of solderability testing by a component user should allow removal of problem lots (for return or solderability enhancement), and therefore lead to a virtual elimination of solderability‐related defects observed after PWA soldering. Widespread application by component manufacturers (after burn‐in) should lead to a virtual elimination of cases of shipping unsolderable components.