Ask the Experts
June 16, 2010 - Updated
June 14, 2010 - Originally Posted

Advantages Using OSP Surface Finish

What are the advantages using OSP surface finish? What precautions should we take when using circuit boards supplied with OSP finish?

S. B.

Expert Panel Responses

The biggest advantage of an OSP finished board is the price. OSP boards tend to be cheaper than those fabricated with other surfaces such as HASL, Immersion Tin, Immersion Silver or ENIG. Another advantage that OSP has, particularly as compared to HASL finished boards, is the flatness of the pads. The primary drawbacks are related to solderability, shelf life, re-use of misprinted boards, and multiple heating cycles. The solderability/shelf life issues are connected; if the OSP degrades through shelf life (typically less than 1 year), the Copper underneath oxidizes fairly easily and prevents the board from being generally easy to solder. The re-use of misprinted boards can also be an issue with OSP since alcohol and other solvents used to clean misprinted boards will also remove the OSP, leaving the Copper surface very easy to oxidize. Misprinted boards that are cleaned need to be sent back through the print/place/reflow processes quickly to avoid this issue. Finally, OSP boards can be susceptible to solderability problems when subjected to multiple heating cycles; this occurs as a result of the OSP itself being degraded by the heating processes. There are new OSP materials that can overcome all of these issues, so consult your board suppliers to see what they can offer.

Brian Smith
General Manager - Electronic Assembly Americas
DEK International
Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.

The big advantage with OSP as a surface finish is that it is coplanar unlike Hot Air Leveling. OSP is also relatively inexpensive when comparing to ENIG. The issue in the past with OSP was that the coating didn't hold up well to multiple heat cycles. Over the past 10 years or so we have seen an improvement in this area but I believe you still need to be careful with storage of your PCB's.

Mike Scimeca
FCT Assembly
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.

Flatest surface for SMT placement. No possible contamination from Bareboard assembly chemicals interfering with long term reliability. Shelf life should ideally be twelve months from application but not all OSP's are the same so check manufacturers instructions

Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
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