Hi Peter - I am a little late to the party but wanted to add on last chunk of information. The TechNet crew gave you some very good possibilities: organic contamination, solderability degradation or improper plating. IMHO, the best "black pad" explanation and discussion is the following journal article "The root cause of black pad failure of solder joints with electroless nickel/immersion gold plating", authors Zeng,Stierman, Abbott, Murtuza, JOM, June 2006, pp. 75-79. Good Luck. Dave Hillman Rockwell Collins [log in to unmask] Peter Wong <[log in to unmask] COM> To Sent by: TechNet [log in to unmask] <[log in to unmask]> cc Subject 03/21/2007 03:17 [TN] Solderability problems on PM through holes only. Please respond to TechNet E-Mail Forum <[log in to unmask]> ; Please respond to Peter Wong <[log in to unmask] COM> 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. Thanks Peter --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 15.0 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 -----------------------------------------------------