Hello Tracy - you characterized the concerns with electroplate tin finish very well. Just a couple of comments: - Tin whiskers can be prevented by "poisoning" the tin bath with a very small percentage of another element. There have been numerous papers in the industry on the subject. Bismuth, antimony, lead, etc. can all be used to prevent the whiskering. I suggest you talk with your plating supplier and check on what they use to poison their bath. - I believe that you will have fewer problems with oxidation of electroplate tin than HASL, that has been my experience with pwbs we process. We have done quite a bit of SERA solderability testing and the oxides (SnO and SnO2) that develop can be removed with the fluxes we are using. There was a paper published within the last year by Urmi Ray of AT&T on immersion tin that may interest you too (IEEE Transactions on Components, Packaging, and Manufacturing Technology - part A, Vol. 18, No.1, March 1995). David Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Tin electroplate finish for PCBs Author: [log in to unmask] at ccmgw1 Date: 4/17/96 8:42 PM I want to evaluate the possibility of converting to a 100% tin electroplate finish on PCBs that requires a tin or tin-lead for contact pads. Primarily 72 pin SIMM memory modules which are destined for use in tin or tin-lead (usually high tin content 90/10 - 95/5 tin-lead alloy). Overall thickness is an issue with SIMM products (.050" + .004" -.003"). The HAL process results in a adequate finish most of the time, however this process can not be tightly controlled and is a root cause for thickness rejects and contact rel problems. I've a couple of goals: 1) Improve quality and performance of our product by improving contact reliability. 2) Give our PCB suppliers a way to improve yields for overall thickness. There are other pluses (for us and the PCB suppliers) associated with a conversion to tin that I won't bring up. I'm primarily concerned with overcoming any potential quality or reliability problems. Here are some of my concerns: 1) Tin whisker growth. Dependent on stress induced during electroplating. Low/no stress plating is critical. Whisker growth begins at ~50 'C. Spacing between contact pads on a 72 pin SIMM is .010" so whisker growth has to be eliminated. Whiskering is not a problem with lead present. Test conditions: High temperature storage, 150 'C unbiased. Length ? 1080 hrs 125 'C high temp operating life, biased. 85/85 APB T&H 2) Tin undercut must be minimized to prevent tin slivers. 3) Solderability, tin-oxides form readily at room temperature. This problem exists with HAL, but to a lesser same extent. 4) Copper-tin intermetallic growth, tin should be a minimum of 200 microinches thick. Again, this problem exists with HAL. Test conditions: Same as in #1. ************************************************************ My question is, has anyone experience with a tin electroplate finish in a similar application? Any potential problems I've overlooked? All comments are appreciated. Thanks in advance. Tracy Tennant ([log in to unmask]) ph (208) 368-5963