you don't have a problem with osp residues building up on test probes on the top side? [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: Exposed Copper on Assem Author: [log in to unmask] at corp Date: 2/23/96 6:46 AM RE>>Exposed Copper on Assemblies 2/23/96 We've been using OSPs on the vast majority of our boards for over two = years with no problems. As Dave Boggs mentions, there is a considerable = amount of data "out there" to show that there are no additional problems = with exposed copper. I've actually seen some data that suggests that = exposed copper is actually *more* reliable than exposed tin/lead under = most typical operating conditions. We did have 1-2 customers question the reliability of exposed copper, but = we were able to successfully address these concerns. Finally, we have not found the need to paste test points, fiducials, or = vias. Greg Bartlett Mercury Computer Systems Chelmsford, MA [log in to unmask] -------- Many OEM users have demonstrated that exposed copper in the assembly does not pose any reliability problems, in fact, this has been going on for over 10 years (with OPSs). Obtaining actual reliability data from these OEMs is more difficult. PCBs have been manufactured for years with electrolytic tin or gold as the surface finish. These boards contain a significant amount of exposed copper along all traces, connectors, etc. The difference is the copper cannot be readliy seen as it is located on the sidewalls and not the board surface. I have several years of experience working with customers converting to the OSP surface finish. There are a number of things that can be done to minimze the exposed copper, such as increasing the solder paste stencil aperture to a 100% opening (most are about 80%), printing paste on test points and vias as you suggested, minimizing through-hole annular ring, etc. I find most customers accept exposed copper as it is not detrimental to the final product. Of course, the product application plays a role. Working with the October Project, I've seen a couple of good articles that may now be available through IPC. One good paper was a study done by Batelle Labs with Digital Equipment Corporation -- it basically concluded that bare copper was more reliable than solder down to a four mil line and space. Dave Boggs Merix Corporation phone (503) 359-9300 EMAIL: [log in to unmask] Kaylor Karl <[log in to unmask]> Wrote: | | | | We are contemplating using OSP's but in doing so will | leave exposed copper | on the final assembly. Specifically, the test points, | fiducials and vias. | We have discussed printing solder paste on the test | points and fiducials | but are not sure how it will affect test and the placement | equipments vision | system. | | What are the long term affects of leaving exposed copper | in these areas? | Does anyone else leave exposed copper on the final | assembly? | What affect will printing solder paste on test points and | fiducials have on | placement and test? | How are assemblers dealing with this issue? | | Any information would be greatly appreciated. | | Karl Kaylor | Thomson Consumer Electronics | [log in to unmask] |