Issue link: https://iconnect007.uberflip.com/i/1011746
52 PCB007 MAGAZINE I AUGUST 2018 Feature by Richard Heimsch SUPER DRY Guidelines for the proper storage, handling and moisture protection of electronic compo- nents can be found in the standards IPC/JEDEC J-STD-033C. Though these date back to 1999, there were no published standards for storage and moisture protection for printed boards un- til 2010, and their proper handling is still often overlooked. But with the correct storage con- trol and the use of suitable drying methods, considerable manufacturing advantages can be gained: PCBs will remain solderable for much longer and damage during reflow due to mois- ture can be eliminated. Historically, the printed board industry relied on military specifications and guidelines to de- fine the packaging methods used to preserve the quality and reliability of PCBs during ship- ment and storage. Over time, of course, many of these documents became obsolete, were found to be incomplete, didn't address lead- free assembly, or did not provide guidance for newer laminates or final finishes. Additional- ly, the proliferation of alternative final finishes has produced concerns and requirements for printed board packaging and handling to pre- serve the finish and assure good solderability. For instance, IPC-1601A (2016 revision) Printed Board Handling and Storage Guide- lines, states: "Baking is not recommended 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 fin- ish options in lead-free soldering because they provide an attractive combination of solder- ability, ease of processing and low cost. Com- pared 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 climat- ic conditions in a manufacturing process, after only a few minutes there will be a separation of a water film at the surface (3-5 atom lay- ers). This then starts a diffusion process which leads to a vapor pressure balance through the