Agree, but the solder mask adhesion to gold is not as good as on copper. We had problems with solder mask adhesion during rework, and loosing solder mask around pads on a large ground area or beteen the pad and the via is not much fun when replacing BGA's. Gaby ----- Original Message ----- From: "Tony Steinke" <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, August 27, 2003 3:45 PM Subject: Re: [TN] ENIG--Black Pad > Werner, Bev, > > The soldermask process prior to ENIG plate is very critical(poor vacuum > during exposing, developing, improper cure, poor oven ventilation, > soldermask design, etc) and with my experience is probably a major cause of > the black pad syndrome. We process all ENIG boards as SMOG (soldermask over > gold). This eliminates alot of potential problems(yes, some may argue it is > a band-aid), but we have not experienced 1 panel with the black pad > syndrome. The cost is a bit higher but it certainly out weighs a > dissatisified customer(especially when you are building high end boards). > > Tony Steinke > AIT-Atlanta Inc. > ----- Original Message ----- > From: "Bev Christian" <[log in to unmask]> > To: <[log in to unmask]> > Sent: Wednesday, August 27, 2003 8:44 AM > Subject: Re: [TN] ENIG--Black Pad > > > Werner, > Another theory I have heard espoused for black pad is that it occurs when > there is preferential leaching of nickel into the gold plating bath from > small pads electrically connected via traces and vias (sorry, pun) to larger > pads. The large pads plate out properly, and first, leaving the smaller > ones in contact with the relatively corrosive gold plating chemicals. This > would explain why the process in localized and why the higher phosphorus > concentration. However, I have no clue as to what would cause the potential > difference between the big and small pads. And if people are seeing black > pad with low phosphorus, this theory cannot explain that. > > I agree a technique - non-destructive, quick and inexpensive (where is a > fairy godmother when you need one?) is needed. ENIG is a good surface > finish, but getting bitten, even at the overall average occurrence in the > ppm level is NOT FUN. At a previous company we ended up having to scrap > over 2000 completed circuit packs because of black pad. My problem with the > invitation to participate is that it INITIALLY came from students and there > was no background given in the invitation. Now it did come from Siggi's > e-mail address, but I think we should have got an introduction by him of the > students, if they are really interested in getting people to participate. > If he is on holiday, then it should have been held off until his return. > Siggi, are you there? > regards, > Bev Christian > Research in Motion > > -----Original Message----- > From: Werner Engelmaier [mailto:[log in to unmask]] > Sent: August 27, 2003 8:28 AM > To: [log in to unmask] > Subject: [TN] ENIG--Black Pad > > > Hi TechNetters, > I had hoped to get a response/discussion to my posting repeated below. I > would like to get peoples experiences to see whether the fit into scenario A > or B. > Repeat: > Yes, a method to detect problematic ENIG prior to assembly would be very > useful--my problem is, that I do not know what such a method would be > looking for. > From my experience [but no research other than what other people write], > what > may be happening is as follows [please correct me, if I got it wrong and > compare to your experience]: > 1. during the Ni plating, P is co-deposited, > 2. the amount of P varies with the plating bath/chemistry, > At this point there seems to be some divirging opinions--maybe two different > processes--I split them up into scenarios A and B. > 3A. Ni with too little P is subject to more corrosion during > Au-plating--thus > "Low-Phos" EN is bad--sulfur being dragged into the EN bath by solder mask > also is implicated. > 4A. A "loosely structured" nickel layer enriched in phosphorous is formed > under the Au layer; this is sometimes called black-line nickel (BLN). > 5A. Reflow soldering fails to form a consistent Sn/Ni IMC layer and a good > metallurgical bond. > 6A. "Brittle" interfacial fractures occur when loads are applied. > CONSEQUENCE: The whole PCB surface would have this condition [I have not > seen > this]. > or > 3B. During reflow, the Ni is consumed by the formation of the Sn/Ni IMC > layer > leaving P behind--the higher the P-content in Ni, the more Ni concentration > at the interface between Ni and Sn/Ni IMC--thus "High-Phos" EN is bad. > 4B. The more heat [temperature x time] is available for IMC formation, the > higher the P concentration. > 5B. Nickel phosphide is formed creating a "weak link" adhesion between the > Ni > and the Sn/Ni IMC, even though good wetting has occurred. > 6B. "Brittle" interfacial fractures occur when loads are applied. > CONSEQUENCE: The "Black Pad" condition is worse in high peak reflow profile > areas--thus it is seemingly "localised" on the PCB; and typically the > soldering > pad has a crater-like rim of fractured ductile solder--rather than the > "brittle" interfacial failure, perhaps because the P-concentration is less > at the > pad/ENIG area periphery. [this is more consistent with my observations]. > > In either case, I do not know what one would be looking for on the > as-received PWBs. > > Please give my--and the TechNet--youe feedback as to your observations; in > particular, it would be interesting to get some Fab houses to respond with > their > experience. > > Werner Engelmaier > > --------------------------------------------------- > Technet Mail List provided as a free 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 > 847-509-9700 ext.5315 > ----------------------------------------------------- > > --------------------------------------------------- > Technet Mail List provided as a free 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 > 847-509-9700 ext.5315 > ----------------------------------------------------- > > --------------------------------------------------- > Technet Mail List provided as a free 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 847-509-9700 ext.5315 > ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free 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 847-509-9700 ext.5315 -----------------------------------------------------