Yes, you are probably correct on that. Do you know if there is a fabrication or plating issue that would cause nickel skips in the annular rings? If there were no nickel at all, I would imagine there would be oxidized copper under the gold dewetting into the solder. The thing that puzzles me is why they are having difficulty soldering to through-hole vias/pads, but apparently the SMT pads are soldering up ok. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M. Sent: Wednesday, March 21, 2007 4:15 PM To: [log in to unmask] Subject: Re: [TN] Solderability problems on through holes only. On this one I'll have to disagree and side with Rudy. Richard, On this one I'll have to disagree and side with Rudy. I'm not a metallurgist but it is my understanding that solid state diffusion of copper through nickel is extremely slow. Even if it did migrate to the surface of the nickel what problem would it cause? Certainly not a solderability problem. It is my understanding that most fluxes were formulated to reduce copper oxide not nickel oxide. The flux chemistry should certainly work better on the copper oxide on the surface than if there was nickel oxide. From my old hybrid integrated circuit days I was lead to believe that the people doing wire bonding wanted thick nickel and thick gold. Their reasoning was that the nickel is a leveling agent and provided a "hard" surface as will as prevented a diffusion barrier. There is certainly lots of published work indicating that thick nick was advantageous for wire bonding but I have not seen any that has shown you need thick nickel to get good soldering. There is certainly lots of published work indicating that you need a good quality gold coating to protect the underlying nickel from oxidizing. Regards, George George M. Wenger Andrew Corporation Wireless Network Solutions Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [Office] (732) 309-8964 [Cell] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Wednesday, March 21, 2007 4:40 PM To: [log in to unmask] Subject: Re: [TN] Solderability problems on through holes only. The nickel barrier may be too thin, allowing copper to migrate through. This would lead to poor solderability. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak Sent: Wednesday, March 21, 2007 3:29 PM To: [log in to unmask] Subject: Re: [TN] Solderability problems on through holes only. I would suspect quality of gold plate. If the gold plate was light, and therefore porous, the Nickel under the gold might oxidize during the SMT, and become unsolderable? Rudy Sedlak RD Chemical Company Peter Wong <[log in to unmask]> wrote: Hi Technetters, We are having a solderability problem confined to only through hole locations where we need some help or advice. We are soldering a no-clean SAC305 alloy to an ENIG finished board. All SMT solder joints (both sides) are fine. During hand soldering in our dedicated lead free area, we are having problems with solder wetting to some of the annular rings and barrels of through hole locations, not all holes. The assembly is an 0.062" thick 4 layer 1"x1" board so it is not thermally challenging. We've built thousands of these in the past without this particular problem. The time lag between smt and through hole assembly is 1-2 days. We've tried using a more aggressive flux such as OA flux with no improvement. The only way that we can get solder to wet is to mechanically scrape the annular rings with a pick. Has anyone seen this before? Why would this only occur on some of the through hole locations and not on smt pads? We have isolated this to a specific lot code of boards and are waiting for some advice from our board vendor as well. 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