Hi Phil! Which immersion finish is the best" I'll steal Sir Doug's line "it depends"! We have had a number of internal discussions on which of the immersion finishes should be "preferred". The final conclusion we reached is that a pwb designer should have all three in his or her tool box. Immersion tin is low cost, metallurgically matched to tin/lead but quickly oxidizes, has poor thermal exposure robustness and can have tin whiskers issues when improperly produced. Immersion silver has great RF signal characteristics, good thermal exposure characteristics but has corrosion issues under specific use environments (sulfur loaded) and has specific storage requirements. Immersion gold/electroless nickel has great shelf life, handling characteristics, and is widely available but can have "black pad" issues and soldering to nickel can be problematic. All of the finishes have some warts and you need to understand that all immersion tin's or all immersion silver's are not equal -e.g. I have seen some immersion tin that whiskers and some that doesn't. All three immersion finishes are being used in High Performance use environments successfully. The new IPC immersion finish specifications (IPC-4552,4553,4554) will be helpful in getting industry consistency on immersion finishes. Dave Hillman Rockwell Collins [log in to unmask] Phil Nutting <PNutting@KAISERS YSTEMS.COM> To Sent by: TechNet [log in to unmask] <[log in to unmask]> cc Subject 04/14/2005 03:02 Re: [TN] ENIG - no more problems? PM Please respond to TechNet E-Mail Forum <[log in to unmask]> ; Please respond to Phil Nutting <PNutting@KAISERS YSTEMS.COM> Ok, I've been following this whole thread. What I haven't seen is anybody touting the use of Immersion Tin. We do about 98% of our boards as through hole. As we transition to RoHS compliant products we will need to change our board plating. I had thought that Immersion Tin was the best route. Now I'm confused. I need some fog cutters. Baffled in Beverly. Phil Nutting -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker Sent: Thursday, April 14, 2005 3:36 PM To: [log in to unmask] Subject: Re: [TN] ENIG - no more problems? Frank I have been involved in the black pad issue since the middle '90s. I agree with you the occurrence is now much less than eight or nine years ago; however, other than reducing the gold thickness, I have not seen any convincing data of the mechanism or the remedy. Most of what I have experienced are hand waving augments that are void of supporting data and in most cases conflicting. You mentioned "we now have a better understanding of the likely causes". Could you go into some detail both on the likely causes and the supporting data; other than of course reducing the thickness of the gold. Best regards Lee J. Lee Parker, Ph.D. JLP Consultants LLC 804 779 3389 ----- Original Message ----- From: Frank Kimmey<mailto:[log in to unmask]> To: [log in to unmask]<mailto:[log in to unmask]> Sent: Thursday, April 14, 2005 1:47 PM Subject: Re: [TN] ENIG - no more problems? Genny, I hate to argue with folks like Vladimir, Ed and George because I truly respect their opinions and knowledge (they are on my list of who to go to for help). That said, I also need to tell you about the success of ENIG and IAg for replacing Pb. As far as ENIG and Black Pad all the statements of recreating Black Pad are true (I also have never heard of anyone successfully causing it on demand). Also true though is the fact that we (the industry) now has a better understanding of the likely causes and by following corrected processes have seen a large reduction (to the point of elimination in some facilities) of the occurrence of Black Pad. I personally have not had a Black Pad incident in more than 3 years (close to half of our designs are ENIG). We spent 2 years trying to qual IAg and found some finishes better than others (due to thickness of deposit). The result was only one finish (of the 3 available at the time) was qualified for use on our product. Unfortunately some of the finishes resulted in the formation of Cuprous Oxide on the outer surfaces rending the pads unsolderable. From our approved supplier we have seen NO solderability issues in the more than a year we have been using IAG. All rambling aside, we expect to replace Pb HASL with ENIG as drop in for legacy and use ENIG and IAg for designs going forward. Bottom line should be if you have good suppliers then you should be able to confidently make the change from HASL to Pb free finishes. Hope its helped, FNK Frank N Kimmey CID+ Principal PCB Designer Powerwave Technologies Inc Office 916-941-3159 Fax 916-941-3195 Cellular 916-804-2491 -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Lee parker Sent: Thursday, April 14, 2005 9:40 AM To: [log in to unmask]<mailto:[log in to unmask]> Subject: Re: [TN] ENIG - no more problems? Genny If the problem with black pad is resolved, then the suppliers should be able to produce the problem at will and then demonstrate a corrective action that prevents the issue form occurring without any side effects. To the best of my knowledge this is not the case. What has taken place is that most suppliers are now recommending a gold thickness of two micro inches or less based on imperial data; there have been few reported cases of black pad when the gold is restricted to two micro inches or less. Unfortunately, no one has given me a convincing mechanism to explain the phenomena. Also as the gold thickness is reduced the probability of soldering issues is increased. Best regards Lee ----- Original Message ----- From: Genny Gibbard<mailto:[log in to unmask]<mailto:[log in to unmask]>> To: [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:Tec [log in to unmask]>> Sent: Thursday, April 14, 2005 11:54 AM Subject: [TN] ENIG - no more problems? Just listened to a Lead Free presentation by one of our assembly materials suppliers. They tested different pastes on different board finishes using a variety of different patterns, spacings, aperture sizes, etc,... By far and away, ENIG was the best finish for performance, for wetting, defects, voiding, ... The guy making the presentation said that he felt a lot of the initial concerns re ENIG - black pad being the biggest - have been resolved, and that they are no longer a concern, that they have determined what the cause of it is and eliminated it. Anyone want to comment on that? I'm not sure if he is correct, or just out of the loop. It was interesting as well: ImmAg got a very bad rating from them in performance, even though many on this forum really praise that finish. It exhibited dewetting (they printed solderpaste pads on an area with no soldermask, and the solder did not stay and spread where it was printed, it crept together with other pads into a big blob, like you might see a water drop do) and the amount of voiding was impressive!! About 4 years ago I joined this forum, and one of the reasons was because I was looking for info on ENIG. We had done a prototype run of a couple of boards and they failed miserably. They were never analyzed in depth, so it wasn't figured out what exactly caused the failure. It was the excuse we needed to not choose this finish and some of the extra costs associated with it. However, with the Pbfree push now, I don't know if we should re-examine whether to use the finish. For products where we needed a flat finish, we have gone to ImmSn, but we still use HASL wherever possible. Genny "Genius may have its limitations, but stupidity is not thus handicapped" Elbert Hubbard --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto: [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]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto: [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]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto: [log in to unmask]>>: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives<http://listserv.ipc.org/archives<http:/ /listserv.ipc.org/archives<http://listserv.ipc.org/archives>> Please visit IPC web 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