Metallurgical Evaluation of Steam Aged LCCC Devices following Solderability Testing

Abstract

Solderability testing, according to Military Standard 883, has evolved through four sets of different test conditions during the past ten years. These relate to the duration of artificial steam ageing and the utilisation of either mildly activated or pure rosin flux. The European Space Agency (ESA) has experienced few solderability problems with leadless ceramic chip carriers (LCCCs) supporting tin‐lead finished castellations. However, similar packages having gold on nickel plated finishes will only produce satisfactory solderability results when activated flux is applied to samples exposed to steam ageing for eight hours. A reason for poor solderability is given, based on an evaluation of test samples and metallography. It is concluded that tin‐lead finished devices should be subjected to eight hours of steam ageing followed by solderability testing with pure rosin flux. An ESA prerequisite for soldering is that all gold finishes must be removed, possibly with the aid of RA type fluxes. For this reason it is recommended that RA flux is permitted (when necessary) during the standard solderability test.