A Proposal for a Standard Solderability Testing Method for SMDs

When testing SMDs with a wetting balance, some of the test parameters have a much greater influence on the wetting force and wetting time than others. It was found that the most important parameters were the type of flux, the temperature and the immersion depth. These three parameters were thoroughly studied and finally it was possible to make a suggestion for the values that these parameters should have. To evaluate the wetting curve, different methods were studied. The method chosen was to divide the wetting force by the wettable perimeter and this was called the normalised wetting force, measured in mN/m. All of the acceptable passive components tested had normalised wetting forces over 50 mN/m; for SOT‐23s the figures were over 250 mN/m. The normalised wetting forces were reached within 1.5 s in both cases. The main conclusion drawn from the tests was as follows: it seems possible to define one point for what is to be called good or bad solderability. This point will be 50 mN/m for passive chip components and 250 mN/m for SOT‐23s, to be reached within 1.5 s.