Dennis, You're probably going to get many answers some indicating OSP aren't as solderable as other finishes, doesn't have a long enough shelf life, doesn't have a low enough surface resistance for applications that require good contact or EMI and shielding requirements. However I have a different take on OSP coating. I think one of the fundamental reasons users stated to move away from OSPs is because OSP coatings don't change the color of the copper features that they coat. What I mean by that is that PCB fabricators just like any manufacturer, don't have perfect controlled processes that provide 100% yield. They sometimes leave an extremely thin tin residue (or solder if they use solder as an etch resist) behind on features after tin-strip process. They can also leave behind an extremely thin solder mask residue on features during the solder mask operation. Although these thin residues will cause soldering problems, the residues aren't thick enough to change the color of the copper feature so you don't know they are there until you try to solder the product. Many PCBs are made as SMOBC (solder mask over bare copper) and the finial surface finish is applied after solder mask. It really doesn't matter what metallic surface finish you use (e.g., ENIG, ISn, IAg, HASL) they all change the color of the copper features. The color change makes it easy to look at a board and tell if the PCB fabricated had a tin-strip or solder mask problem. If you see features with a copper color the surface finish didn't plate or wet the copper feature because there was. All of the HASL operations I've seen have an inspector looking at panels as they come off the HASL process looking for features that didn't coat with solder. These PCB fabrication defects are therefore caught during fabrication and don't reach the end user. With OSP boards the fabricator doesn't know if there are features that have a process residue. The way the user finds out is to screen solder paste, place components, and reflow. The large telecom company I retired from converted many of there PCB codes to OSP in the early 1990's because it was a flat surface finish for fine pitch components and the supply chair people said great because it was cheap. Well by the end of the 1990's they began switching away from OSP as fast as they switched to it initially. They reason was because the assembly people were finding all of the PCB fabrication defects that their fabricators used to find. You find out quickly that saving a few pennies or even a few dollars per board doesn't offset the expense of scrapping populated boards that cost hundreds to thousands of dollars. Regards, George George M. Wenger, Andrew Corporation Reliability / FMA Engineer Base Station & Subsystems Group 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Manowski Sent: Friday, January 14, 2005 1:57 PM To: [log in to unmask] Subject: [TN] OSP Board Finish Does anyone know why the use of SMT PCB's with OSP finish has dropped off as much as it has ? --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- ------------------------------------------------------------------------------------------------ This message is for the designated recipient only and may contain privileged, proprietary, or otherwise private information. 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