Dave- I wasn't trying to indicate the iNEMI statements are incorrect so much as incomplete, and verging on misleading. As everyone who has responded so far has pointed out, the data suggests that ImAg deserves a better rating in their table of Hi Rel PCB finishes. The report suggests that ImAg on PCBs is at risk for silver migration in corrosive environments, but the IPC/UL study suggests that it is no more at risk for migration in these environments than most other finishes. Also, they did not choose to list any risk for "black pad" for ENIG, nor a risk of joint embrittlement for electroplated Au. Any reasonable person who is wondering about PCB finishes and picks up that iNEMI paper will conclude the ImAg is a risky finish to use. That appears to be an assumption by the authors of the paper without any convincing data. I know if one of my customers happens to pick this paper up, they'll limit my finish options to exclude ImAg. After all, everyone wants "hi rel" if they can get it without much additional cost. Wayne Thayer >>> [log in to unmask] 12/19/2006 5:14:57 pm >>> Hi Wayne! There is a big difference in the migration behavior of electroplated silver and immersion silver. Some of the differences are due to the specific chemical baths, the nature of the deposition mechanics, the deposit thickness, and the deposit structure. The IPC committee work that George W. described included electroplated silver samples in their testing. And to quote Doug Pauls, the propensity of silver to migrate "depends"! Don Cullen has presented some data on the creep corrosion of immersion silver in a very harsh, high humidity environment. The INEMI statement is not incorrect but there are a number of other use environment dependences (such as a sulfur contaminated atmosphere, etc.) which need to be considered. Many high performance product companies have determined that immersion silver is an applicable finish for their use environments. There will be some information on immersion silver durability in the next revision of Clyde Coomb's Handbook. Dave Hillman Rockwell Collins [log in to unmask] Wayne Thayer <WTHAYER@EVITECHN OLOGY.COM> To Sent by: TechNet [log in to unmask] <[log in to unmask]> cc Subject 12/19/2006 12:29 Re: [TN] Fwd: RE: [TN] iNEMI Hi rel PM Pb-free finish report Please respond to TechNet E-Mail Forum <[log in to unmask]> ; Please respond to Wayne Thayer <WTHAYER@EVITECHN OLOGY.COM> Steve- Thanks for the link. That paper actually increases my questions about the iNEMI recommendations: First, it IS about whiskers grown from silver, not electrochemical migration. The author claims to have seen such whiskers "6-8 cm long and 1mm in diameter"! Second, on page 4, it specifically mentions whiskers also being grown on AgNi alloy, while the iNEMI recommendations list Ag over Ni as one of their preferred finishes for separable contacts. Maybe the plated coatings won't make enough AgNi to matter, but it would probably have been a useful tidbit to add to the recommendations paper. The author, Bella Chudnovsky (Square D circuit breakers), of this paper actually concludes that Tin might be better in some situations for addressing this problem, since it isn't as reactive to the sulfurous environment found within a pulp plant and the whiskers are relatively tiny. She does temper this by recommending the use of Tin alloys which have higher whisker resistance. She reports that thinner platings of silver actually makes the situation worse, but the thinnest she could find data reported on was still 2 microns--much thicker than ImAg. The reasoning is that the base metal, copper, contributes to the reaction (copper was found in the whiskers in single digit percentages). She claims to have solved her problem with a combination of air filtration and circulation to minimize H2S and drop the temperature, contact lube (to form a film to further block sulfur), and regular maintenance solved her issue (circuit breakers failing in a pulp plant). Sounds like it would be an interesting challenge to attempt to grow these structures on PCBs with ImAg. Growth accelerated greatly above 140C, and you want about 1ppm H2S to get the precursors started. Wayne >>> [log in to unmask] 12/19/2006 12:19 pm >>> Wayne writes: "...The UL paper you and I both found suggests that ImAg is no more susceptible to electrochemical migration (I hear you Bev!) than most other finishes. The subject paper contains language which gives me the impression some hydrogen sulfide tests were done with ImAg and the results were of concern, but the only obviously relevant paper in the reference area was 38 Chudnovsky, Bella, "Degradation of power Contacts in Industrial Atmosphere: Silver Corrosion and Whiskers". Proceedings of the 48th IEEE Holm Conference on Electrical Contacts, 2002 which I don't have ready access to, but I suspect it doesn't concern ImAg." Hi Wayne! I found it for you: http://tinyurl.com/oo23f -Steve Gregory- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [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]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [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]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------