Charming, I ditto Dave's answer. In my previous telecommunications company we shipped lots of telecommunication products with immersion silver surface finish and for the past 10 years our primary surface finish for wireless communications products is immersion silvers. These products are deployed all over the world in many harsh environments and we have not had any issues associated with immersion silver corrosion or migration. We've also provided amplifiers with immersion silver surface finish to a customer to be put into a base station and for the base station subjected to Battelle MFG testing. The base station had issues but our amplifiers did not. Besides base station electronics many of our products are tower mounted electronics they do have immersion silver surface finish PCBA's without conformal coating. With the introduction of sophisticated hand held mobile devices (e.g., iphones and Blackberry's)the telecommunications operators around the world are being forced to do better utilization of bandwidth and they are having to deploy much more sophisticated electronics not in base stations but at the tops of towers and they are all worried about survivability and reliability of the electronics. While 96 hr and 14 day salt fog testing of outdoor products has typically been used to determine the effect of harsh outdoor environments, many of the telecommunication operators have been specifying 30 day salt fog testing. We're routinely using 30 day salt fog testing as part of our product qualification program and haven't seen any issues with our products that use immersion silver surface finish on PCBA's. Regards, George George M. Wenger Andrew Solutions Senior Principal FMA/Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 (Office) (732) 309-8964 (cell) [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman Sent: Thursday, October 29, 2009 12:25 PM To: [log in to unmask] Subject: Re: [TN] Immersion Silver for Class 3 Boards Hi! I guess I would disagree with the statement that immersion silver may not be suited for harsh environments. I have seen all of the industry pwb surface finishes fail a Battelle mixed flowing gas test. One portion of the equation on the survivability of any pwb surface finish is the type and robustness of the electronics enclosure. Rockwell Collins uses immersion silver surface finishes in a number of "harsh" environments very successfully and has done so for over 10 years. General statements on the environmental robustness of pwb surface finishes tend to blind folks on possible applications of a specific pwb surface finish that they may have been able to utilize. There are many inputs to the robustness assessment - just need to look at all of the issues with due diligence. Dave Hillman Rockwell Collins [log in to unmask] Charming Chan <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 10/29/2009 11:17 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask] To [log in to unmask] cc Subject Re: [TN] Immersion Silver for Class 3 Boards Hello George, Thanks for your input. If so, most of telecom products need to work in harsh even severe outside environments as well, I'm not sure if immersion silver is robust enough to survive. Some papers show that immersion silver without conformal coating get failed in Mixed Flowing Gas Test of NEBS. Immersion Silver works in the well controlled and protected environments while it may not work in harsh and severe outside environmentals. Best Regards Charming Chan -----Original Message----- From: Wenger, George M. <[log in to unmask]> To: [log in to unmask] Sent: Wed, Oct 28, 2009 11:12 pm Subject: Re: [TN] Immersion Silver for Class 3 Boards Charming, We try to avoid conformal coating whenever possible because of many issues ssociated with manufacturing and repair. We did have one product that goes in n outdoor cabinet and during initial deployment had an issue with water ngress, which has subsequently been corrected, that we put conformal coating on ne board. We'd like not to use the conformal coating but every now and then omething happens were a customers contractor forgets to close the cabinet door o we've left the conformal coating on that one PCBA. That PCBA is a small ower input interface at the back of the cabinet which is the first location ater would touch if the equipment was improperly installed. The other PCBA's in the system are not conformal coated. Regards, 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]<mailto:[log in to unmask]> _______________________________ rom: [log in to unmask] [mailto:[log in to unmask]] ent: Wednesday, October 28, 2009 10:29 AM o: [log in to unmask]; Wenger, George M. ubject: Re: [TN] Immersion Silver for Class 3 Boards Hello George, I'm curious, have you performed conformal coating on immersion silver surface inish to improve reliability? Thanks a lot. Best Regards harming Chan ----Original Message----- rom: Wenger, George M. <[log in to unmask]> o: [log in to unmask] ent: Thu, Oct 1, 2009 1:20 am ubject: Re: [TN] Immersion Silver for Class 3 Boards Most everyone who knows me realizes that I am a strong proponent of immersion silver surface finish for several reasons. Many of you may have heard me state the main reason but not believed what I had to say. So I'll repeat it again; we use immersion silver surface finish as a solderability indicator that our PCB fabricator didn't have a problem with incomplete tin strip or leave a solder mask residue on the PCB features and they should be solderable. For a several year period when fine pitch components were beginning to appear on products I was assigned to work for an extremely large PCB fabricator and we were being pushed by our assembly factory customers to provide a flatter surface PCB surface finish for fine pitch assembly. Our logical choice was to use Imidazole OSP because we had up and running in the factory and our customers were using it for old technology wave solder product. When we switched to Imidazole for fine pitch surface mount boards everything looked okay for a while be every now and then one of the assembly customers would complain that there were features on their boards that weren't solderable. After a lot of evaluations it was realized that in any large fabrication operation processes don't run with 100% perfect yield. Checking back on boards used for previous non-fine-pitch products we realized that the HASL boards being supplied to customers were solderable because every feature on the boards had solder on them. The reason we knew that was because we did 100% inspection at the end of the HASL line and if we saw any features on an 18"x24" panel with exposed copper (it's amazing how easily a non-solder-coated copper feature on a panel with thousands of features can be detected with the naked eye) the panel was put back through the HASL machine again hoping that the cleaning or micro etch or hot air leveling fusing fluid or the hot molten solder would clean off or burn off any incomplete tin strip or solder mask residue and the feature would accept solder. If it didn't the second time we'd run it a third time and a fourth or fifth time in necessary before we knew better and limited reruns to only three. When we switched from HASL to Imidazole we no longer had the visual confirmation that all the surface mount features were free of incomplete tin strip or solder mask residue because those contaminates were so thin the features appeared to be copper and after Imidazole they still looked like copper. During that time period we also participated on the five year NCMS PCB Surface Finishes and Pb-Free efforts looking at new surface finishes for fin-pitch and Pb-Free assembly. Yes there was lots of doubt that a surface finish better than HASL could be found. ENIG looked like a better choice at that time (Black Pad issues weren't publically disclosed at that time) than immersion tin because evaluations showed immersion tin had shelve life issues and exposure to temperature and humidity degraded its solderability. We decided to run an evaluation using ENIG boards because we know it provided a flat surface and after ENIG plating we believed we could tell the difference between a gold colored ENIG pad and a copper pad that hadn't accepted ENIG plating. At the time when the evaluation was being planed AlphaLevel immersion silver was being introduced so it was decided to include it along with ENIG. The evaluation didn't reveal any obvious problems with either surface finish but on some of the environmentally stressed boards the solder didn't flow out to the full extend on some on the ENIG features. All of our experience up to this point (i.e., HASL and OSP) was with solder joints made to copper not nickel. After extensive internal evaluations was decided to use immersion silver surface finish. The reasons were simple: 1. It provided a visual indication before boards were assembled that there were no non-immersion-silver plated copper features indicating that incomplete tin strip or solder mask residue wasn't there and the features should be solderable. 2. Solder joints were being made to copper not nickel. 3. No reliability issues were found in our extensive testing. 4. It worked. Participation on the IPC-3-11g committee confirmed everything we had determined in our internal testing. In my mind the decision we made to use immersion silver surface finish was the correct decision because in 12 years we have no documented reliability issues associated with the use of immersion silver surface finish. Granted our products are only Class 2 telecommunications products but they are deployed throughout the world in all kinds of environments and now in the 3G & 4G wireless world were service providers have having to deploy more active electronics at the tops of towers rather than in base stations 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 then and I see a picture hanging next to my monitor that I took on July 26, 2005. It is a photograph of my grandson sitting in front of a TV in my son's house in Friendswood, TX. He is pointing to a person on the TV who is the lead space shuttle robotics engineer standing up in the NASA JSC Mission Control who is talking to an astronaut during a space walk. That person is his father (my son) and my grandson is saying "that's my dad and I want to be just like him". My son has an ambition to some day be an astronaut and so does my grandson. You might ask what does this have to do with immersion silver. The answer is simple to me. With my FMA and reliability experience associated with immersion silver I would feel more comfortable if my son or grandson every because astronaut knowing that they were in space vehicles with electronics that used immersion silver surface finish that other options like ENIG or immersion tin. My apology again for such a long response. Regards, George George M. Wenger Andrew Solutions Senior Principal FMA/Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 (Office) (732) 309-8964 (cell) [log in to unmask]<mailto:[log in to unmask]> -----Original Message----- From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of lidden, Kevin Sent: Wednesday, September 30, 2009 11:32 AM To: [log in to unmask]<mailto:[log in to unmask]> Subject: Re: [TN] Immersion Silver for Class 3 Boards Good point about the environmental issues. There are also recommendations I have seen that state ImAg is primarily a solderable surface protectant, and not the best selection as a final surface finish that may be exposed in the application. In that case, the usual recommendations (that I have seen) are ENIG or HASL. Kevin Glidden Manufacturing Engineer Luminescent Systems Inc. -----Original Message----- From: Thayer, Wayne - IIW [mailto:[log in to unmask]< mailto:[log in to unmask]>] Sent: Wednesday, September 30, 2009 11:22 AM To: [log in to unmask]<mailto:[log in to unmask]> Subject: 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 boards in high sulfur environments, where somehow the silver acts to catalytically cause the copper to redeposit in random directions. Doesn't even need a voltage to cause this phenomenon! A paper on this was brought up to this forum several months back. If you search the archives on ImAg you should be able to find it. The growths are nice black dendrites. Wayne Thayer -----Original Message----- From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of arner, Chester Sent: Wednesday, September 30, 2009 11:03 AM To: [log in to unmask]<mailto:[log in to unmask]> Subject: [TN] Immersion Silver for Class 3 Boards The revised Immersion Silver IPC spec (4553A) indicates that Immersion Silver is not recommended for Class 3 boards. There is no stated reason. I have been looking into Immersion Silver for all the same reasons as everyone else, to replace HASL for flatness etc. It looked very good until 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 - 91510 818-526-2600 x3557 -------------------------------------------------------------------------------- We value your opinion! How may we serve you better? 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