Identification of Antistatic Packaging Material as a Source of Circuit Board Contamination

摘要

Circuit boards to be used in satellites were shipped to Sandia in Richmond RCAS 4200 ESD shielding bags. Upon inspection under low magnification, a white fuzzy deposit was observed on many of the solder joints. Preliminary examination using Fourier transform infrared (FT-IR) microspectroscopy identified the material as a metal salt of a long chain aliphatic carboxylic acid. The material was definitively identified as a mixture of lead di(n-octanoate) and tin di(n-octanoate) using mass spectrometry. These compounds were formed by the reaction of octanoic acid with the lead/tin solder. We have demonstrated that the solder is mechanically weakened by the formation of these compounds. Investigation has shown that the Richmond RCAS 4200 ESD shielding bags contain octanoic acid in sufficient quantities to form visually detectable quantities of lead di(n-octanoate) and tin di(n-octanoate) in less than 90 days at room temperature. Ameri-Stat Static Shield and Dow Chemical CHIPLOC ES antistatic bags do not contain carboxylic acids, and solder samples stored in these bags for several months do not exhibit evidence of lead di(n-octanoate) or tin di(n-octanoate) formation. Users of static shielding bags should be aware that the use of static shielding bags can be harmful to solder joints. Steps should be taken to ensure that all antistatic packaging in use is free from carboxylic acid contamination. 3 refs., 6 figs., 1 tab. (ERA citation 14:006197)