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PCB-Nov2014

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42 The PCB Magazine • November 2014 by Michael Carano omG eleCtroniC ChemiCals Lead-Free Compatible OSPs: What Does This Really Mean? C o l u m n trouble iN your taNk Introduction The setting: early 2008. Many fabricators and EMS providers are continuing to push pro- grams for RoHs compliance. This, of course, requires electronic assemblies to be, among other things, free of lead-bearing materials. In order to adopt such a program, the surface fin- ish, component finish and the solder used in assembly must be lead-free. While the ques- tions surrounding these issues are many, one in particular appears more frequently: How do we know that a particular finish is truly lead-free soldering compatible? This particular question is being addressed by one of the IPC standards writing committees responsible for developing an industry standard specification of organic solderability preservatives (OSP). The Nature of the Beast The IPC committee made up of a cross-sec- tion of suppliers, PWB fabricators, OEMs and EMS companies is working to complete the development of IPC-4555 (standard for OSP). This committee is developing a protocol to test OSP coatings for lead-free (high-temperature) compatibility. The protocol requires that cop- per coupons coated with the OSP would be subjected to three lead-free reflows, then tested for wettability with an appropriate wetting bal- ance instrument. It should be noted that after the coupons are processed through the OSP solution, the coupons shall be rinsed with DI water and dried at 105°C. Following the proto- col of the ANSI-JSTD-003B, the samples shall be fluxed using the standard 0.5% activated flux

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