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34 SMT Magazine • July 2017 ture content (MAMC) level, which is typically between 0.1% and 0.5% moisture weight to res- in weight. The document also states "Baking is not rec- ommended for OSP coatings, as it deteriorates the OSP finish. If baking is deemed necessary, the use of the lowest possible temperature and dwell time is suggested as a starting point." Organic solderability preservative (OSP) coatings are among the leading surface finish options in lead free soldering because they pro- vide an attractive combination of solderability, ease of processing and low cost. Compared to alternatives, however, they tend to be the most prone to oxidation. The cause for this lies in the pure copper surface protected only by the OSP coating layer. Under normal climatic con- ditions in a manufacturing process, after only a few minutes there will be a separation of a wa- ter film at the surface (3–5 atom layers). This then starts a diffusion process which leads to a vapor pressure balance through the OSP coat. Baking also accelerates solid diffusion between metals, and increases intermetallic growth. This can lead to a "weak knee" or other solderabil- ity issues if the intermetallic layer reaches the surface and oxidizes. Effects upon other finishes (immersion tin, immersion silver, ENIG) are fur- ther detailed in the guidelines. Just as with components, 125°C bak- ing temperatures degrade the solderability of PCBs. 1601 warns that as little as 4–6 hours at that temperature can render HASL finished boards unsolderable. Over the decades that passed since the J-STD-033 standard was cre- ated, new technologies were developed and proven to safely reset component floor life us- ing low temperatures and ultra-low humidity without requiring extensive time. These 40– 60°C and <1% methods were first adopted in Europe, and their recognition and use has now spread to North America. The same methods were applied to PCBs, and engineers from the company SMT and Hy- brid GmbH published their findings in "Produc- tion of Printed Circuit Boards and Systems" 1 . PCBS ARE MSDS Figure 1: Chart and legend QFP.