Hello George, I'm curious, have you performed conformal coating on immersion silver surface finish to improve reliability? Thanks a lot. Best Regards Charming Chan -----Original Message----- From: Wenger, George M. <[log in to unmask]> To: [log in to unmask] Sent: Thu, Oct 1, 2009 1:20 am Subject: Re: [TN] Immersion Silver for Class 3 Boards Most everyone who knows me realizes that I am a strong proponent of immersion ilver surface finish for several reasons. Many of you may have heard me state he main reason but not believed what I had to say. So I'll repeat it again; we se immersion silver surface finish as a solderability indicator that our PCB abricator didn't have a problem with incomplete tin strip or leave a solder ask residue on the PCB features and they should be solderable. For a several ear period when fine pitch components were beginning to appear on products I as assigned to work for an extremely large PCB fabricator and we were being ushed by our assembly factory customers to provide a flatter surface PCB urface finish for fine pitch assembly. Our logical choice was to use Imidazole SP because we had up and running in the factory and our customers were using it or old technology wave solder product. When we switched to Imidazole for fine itch surface mount boards everything looked okay for a while be every now and hen one of the assembly customers would complain that there were features on heir boards that weren't solderable. After a lot of evaluations it was ealized that in any large fabrication operation processes don't run with 100% erfect yield. Checking back on boards used for previous non-fine-pitch roducts we realized that the HASL boards being supplied to customers were olderable because every feature on the boards had solder on them. The reason e knew that was because we did 100% inspection at the end of the HASL line and f we saw any features on an 18"x24" panel with exposed copper (it's amazing how asily a non-solder-coated copper feature on a panel with thousands of features an be detected with the naked eye) the panel was put back through the HASL achine again hoping that the cleaning or micro etch or hot air leveling fusing luid or the hot molten solder would clean off or burn off any incomplete tin trip or solder mask residue and the feature would accept solder. If it didn't he second time we'd run it a third time and a fourth or fifth time in necessary efore we knew better and limited reruns to only three. When we switched from ASL to Imidazole we no longer had the visual confirmation that all the surface ount features were free of incomplete tin strip or solder mask residue because hose contaminates were so thin the features appeared to be copper and after midazole they still looked like copper. During that time period we also articipated on the five year NCMS PCB Surface Finishes and Pb-Free efforts ooking at new surface finishes for fin-pitch and Pb-Free assembly. Yes there as lots of doubt that a surface finish better than HASL could be found. ENIG ooked like a better choice at that time (Black Pad issues weren't publically isclosed at that time) than immersion tin because evaluations showed immersion in had shelve life issues and exposure to temperature and humidity degraded its olderability. We decided to run an evaluation using ENIG boards because we know t provided a flat surface and after ENIG plating we believed we could tell the ifference between a gold colored ENIG pad and a copper pad that hadn't accepted NIG plating. At the time when the evaluation was being planed AlphaLevel mmersion silver was being introduced so it was decided to include it along with NIG. The evaluation didn't reveal any obvious problems with either surface inish but on some of the environmentally stressed boards the solder didn't flow ut to the full extend on some on the ENIG features. All of our experience up o this point (i.e., HASL and OSP) was with solder joints made to copper not ickel. After extensive internal evaluations was decided to use immersion ilver surface finish. The reasons were simple: 1. It provided a visual indication before boards were assembled that there were o non-immersion-silver plated copper features indicating that incomplete tin trip or solder mask residue wasn't there and the features should be solderable. 2. Solder joints were being made to copper not nickel. . No reliability issues were found in our extensive testing. . It worked. Participation on the IPC-3-11g committee confirmed everything we had determined n our internal testing. In my mind the decision we made to use immersion ilver surface finish was the correct decision because in 12 years we have no ocumented reliability issues associated with the use of immersion silver urface finish. Granted our products are only Class 2 telecommunications roducts but they are deployed throughout the world in all kinds of environments nd now in the 3G & 4G wireless world were service providers have having to eploy more active electronics at the tops of towers rather than in base tations they are viewing the reliability of the products as Class 3. As I'm sitting here at my desk typing the long email I look up every now and hen and I see a picture hanging next to my monitor that I took on July 26, 005. It is a photograph of my grandson sitting in front of a TV in my son's ouse in Friendswood, TX. He is pointing to a person on the TV who is the lead pace shuttle robotics engineer standing up in the NASA JSC Mission Control who s talking to an astronaut during a space walk. That person is his father (my on) and my grandson is saying "that's my dad and I want to be just like him". y son has an ambition to some day be an astronaut and so does my grandson. You ight ask what does this have to do with immersion silver. The answer is simple o me. With my FMA and reliability experience associated with immersion silver would feel more comfortable if my son or grandson every because astronaut nowing that they were in space vehicles with electronics that used immersion ilver surface finish that other options like ENIG or immersion tin. My apology again for such a long response. egards, eorge eorge M. Wenger ndrew Solutions enior Principal FMA/Reliability Engineer 0 Technology Drive, Warren, NJ 07059 908) 546-4531 (Office) (732) 309-8964 (cell) [log in to unmask] -----Original Message----- rom: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin ent: Wednesday, September 30, 2009 11:32 AM o: [log in to unmask] ubject: Re: [TN] Immersion Silver for Class 3 Boards Good point about the environmental issues. There are also recommendations I ave seen that state ImAg is primarily a solderable surface protectant, and not he best selection as a final surface finish that may be exposed in the pplication. In that case, the usual recommendations (that I have seen) are NIG or HASL. Kevin Glidden anufacturing Engineer uminescent Systems Inc. -----Original Message----- rom: Thayer, Wayne - IIW [mailto:[log in to unmask]] ent: Wednesday, September 30, 2009 11:22 AM o: [log in to unmask] ubject: Re: [TN] Immersion Silver for Class 3 Boards People panic about silver migration, which is not really an issue. However, there apparently is a very serious problem that can occur on uncoated oards in high sulfur environments, where somehow the silver acts to atalytically cause the copper to redeposit in random directions. Doesn't even eed a voltage to cause this phenomenon! A paper on this was brought up to this forum several months back. If you search he archives on ImAg you should be able to find it. The growths are nice black endrites. Wayne Thayer -----Original Message----- rom: TechNet [mailto:[log in to unmask]] On Behalf Of Harner, Chester ent: Wednesday, September 30, 2009 11:03 AM o: [log in to unmask] ubject: [TN] Immersion Silver for Class 3 Boards The revised Immersion Silver IPC spec (4553A) indicates that Immersion ilver is not recommended for Class 3 boards. There is no stated reason. have been looking into Immersion Silver for all the same reasons as veryone else, to replace HASL for flatness etc. It looked very good ntil the Class 3 problem. Does anyone know why IAg would not be recommended for Class 3 boards? Chet Harner Sr. Engineer Crane Hydro-AirePO Box 7722 Burbank Ca - 1510 818-526-2600 x3557 ------------------------------------------------------------------------------- e value your opinion! How may we serve you better? lease click the survey link to tell us how we are doing: ttp://www.craneae.com/ContactUs/VoiceofCustomer.aspx our feedback is of the utmost importance to us. 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