There have been several posts recently asking about white residue on PC boards. It has been variously identified in the posts as lead oxide and here as "proteinaceous material." From past experience I doubt that it is either. White residue is often the result of delayed cleaning of printed circuit boards after soldering using a rosin based flux. There was a workshop on this problem several years ago at China Lake. The outcome of the workshop was that the exact nature of the white residue remained an unknown but that it showed structural similarities to the abietic and pimaric acid components of rosin based flux. These similarities can be seen using FTIR. Typically, lead could be detected chemically or by x-ray fluorescence. The condition is agravated by prolonged exposure to heat and by delayed cleaning. A few words on FTIR. While it is a wonderful technique for identifying pure materials and if coupled other techniques such as gas chromatography can be used effectively to identify the constituents of a solution. It is virtually impossible to identify the components of a complex solid solution using FTIR. What you can do is show that certain bands are similar to those obtained from certain molecular groups such -OH or -COOH. Unfortunately, there is enough overlap of bands that if you have any preconceived notion of what should be in a sample, you will probably think you see it. _______________________________________________________________________________ Subject: White residue between soldered leads From: [log in to unmask] at Internet Date: 5/7/96 2:31 PM I have a white residue problem that is becoming all to common. The white residue appears between and behind soldered leads on the polyimide substrate. It does not appear on or inside of soldered-through holes. On some boards I can find it between all the leads. On others I see it only between a few leads. I have analyzed this residue many times with FTIR. Everytime, I get proteinaceous matter (protein). I see no evidence of rosin-based or water-soluble flux, but at times I see cellulose fibers mixed in with the proteinaceous matter. What is this stuff? We have considered: 1. skin residue (dandruff) 2. debris from camel hair brushes 3. fungus There appears to be far too much residue to consider 1. and 2. The problem appears after the final cleaning/rinsing step. Any ideas would be greatly appreciated. Thank you. --Phil