George, If you would have asked this question a couple of years ago I would say your asking for trouble. Being open to change has continually opened these eyes. Enthone originally made Entek Cu-56, which is a single pass OSP. Ok for Type I assembly, but crapped out in Type II and III assemblies, unless you take it through all heat excursions within several hours with no dwell times. Then came along Entek 106A which is a multi-pass OSP. This works great for Type I, II and III assemblies. The Cu-106A allows anywhere between 4~6 thermal passes before totally evaporating. Common with both OSPs, they initially evaporate when making contact with solder paste or solder (wave). Providing your paste stencil aperture is less than the land you will have a copper annular ring surrounding the paste following N2, VPR,etc reflow. Again the solder will not wet beyond its aperture. Strick control must be in place for 106A. Long dwell times between heat excursions may eventually leave voids in the OSP coverage, in turn Oxidation may hinder solder wetting properly. The OSP will eventually wear off and then oxidation will manifest itself. You should not experience any functional problems with exposed copper, unless ionic contaminates (salts) or similar are present between SMT or PTH pads. Which brings us to Exposed Copper...... At my last company, we assembled High Storage Devices for Main Frames which a good percentage of our shipments would eventually make their way to Japan (A very high humidity and temperature change environment). We performed Environmental Bareboard Testing to mirror such tropical environments. Our thermal shock (through hole reliability) and humidity (SIR) tests were very extreme and represented 8-10 years of operational life. The power supply cards were single sided, 1 side aluminum thermal clad and 100% SMT. These cards have exposed copper on the component side. So what we have is Exposed copper, eventual oxidation, humidity and so on. Based on our testing, no dendritic shorts or similar were encountered. The cards were relatively clean based on SEC testing. I'm in agreement with DMG Engineering (David Gengaro) that oxidation is a protectant, similar to OSP, but in the Angstroms. Copper oxidation is self limiting and will proprogate no further then the surface. Unless you have surface contaminates (including under soldermask) there is not a concern. If not Bellcore Compliant or otherwise specified, In-Process SEC testing is not required from most end users. So instead of taking the chance of unclean boards with exposed copper, it is frowned upon. Regards, John Gulley Compuroute Inc. Dallas, TX > Date: Wed, 7 Aug 1996 09:56:04 -0500 > To: [log in to unmask] > From: [log in to unmask] (George Franck X2648 N408) > Subject: FAB/ASM: Pressure Fit Entek > Good day! > > We are considering using SMOBC (tented vias) and Entek on a press fit > connector backplane. The assembly process will not coat the Entek with > solder or conformal coat. The boards will go into the field with only > Entek as an oxidation barrier for the copper. > > The use environment is in a non-temperature controlled external buildings > (shacks), ie ambient temperatures and humidity. Installations are expected > in high humidity and in arid areas, near oceans, in both hot and cold > climates, basically any metro area. > > Question: What level of protection could I expect from the Entek in these > environments? Using IPC definitions of Performance Classes (eg > IPC-RB-276), Would yuo use this for class 2 boards?, Class 3? > > Are there any success stories, horror stories, or maybe even data? > > I would not be upset to receive a phone call from an Enthone Techie on the > subject. > > Thanks for your help. > > > ==================================================================== > George Franck > PWB Product Assurance Phone (703) 560-5000 x2648 > Raytheon E-Systems M/S N408 Fax (703) 280-4613 > 7700 Arlington Blvd E-Mail: [log in to unmask] > Falls Church Va 22046 E-Mail: [log in to unmask] > ==================================================================== > > > *************************************************************************** > * TechNet mail list is provided as a service by IPC using SmartList v3.05 * > *************************************************************************** > * To unsubscribe from this list at any time, send a message to: * > * [log in to unmask] with <subject: unsubscribe> and no text. * > *************************************************************************** > > *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************