Hi Richard, You are absolutely correct—there is always an Ni/P layer between the Ni layer and the Ni-IMC layer. The amount of this Ni/P layer is determined by the original P-concentration within the plated Ni as well as the amount on Ni being dissolved in the Sn leaving the P behind. The 'Black Pad' condition is not an all-or-noting issue, but a gradual one—thehigher the concentration the weaker this layer. Werner -----Original Message----- From: [log in to unmask] To: [log in to unmask]; [log in to unmask] Sent: Thu, 17 Aug 2006 3:56 PM Subject: RE: [TN] LEADFREE BGA ISSUE Thank you for your reply, Werner. If the dissolution rate is not affected by the varying amounts of Pb in the alloy, or at least not significantly, then I suspect that the inability of Sn to dissolve in Ni at higher temperatures seen with Pb-free processing is more likely related to the presence of the varying levels of phosphorus. These are directly affected by temperature. While a small amount of P is needed during plating and is deposited with the electroless nickel to avoid acidic corrosion, too much of a layer of P under the gold after the subsequent immersion gold plating process creates a barrier to soldering to the nickel underneath. During soldering the gold is dissolved into the solder and this leaves the phosphorus barrier exposed which of course does not solder very well. The pad is left de-wetted. The greater the heat excursion, the greater the p-barrier and also the greater the nickel oxide barrier. While it is not necessarily a "Black Pad" in that sense of the word, it is still a barrier that gets worse with an increase in temperature. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier Sent: Thursday, August 17, 2006 1:18 PM To: [log in to unmask] Subject: Re: [TN] LEADFREE BGA ISSUE Hi Richard, I do not know to what extent the Pb-content would affect the dissolution rates, but it stands to reason that they would be lower. I have not seen any evidence that the dissultion rates in SAC solders should be less; qute the contrary, all evidence shows higher dissolution rates as evidenced by Cu dissolutions at PTHs and the dissolution of soldering irons and wave solder machines. Now, the evidence shows that SAC does not wet as well as SnPb, but I do not think-it sure does not seem so-that has anything do to with the dissolution rates per se. The dullness of the surface of the Ni layer under the Ni-IMC layer most liekly has to do with the presence of Ni/P enen though is has not led to a 'Black Pad' problem. Werner -----Original Message----- From: [log in to unmask] To: [log in to unmask]; [log in to unmask]; [log in to unmask] Sent: Thu, 17 Aug 2006 1:55 PM Subject: RE: [TN] LEADFREE BGA ISSUE Don't always assume that just because the finish was ENIG, that it was the root cause. It may have contributed to it, but usually there is no one root cause when this happens. Secondly, even when good wetting does take place on ENIG-finished pads, upon removal the pads often appear dull. This is just the nature of the nickel finish. It does not always indicate a solderability problem with the finish. The problem may have been a reflow profile that was not hot enough, with TALT being insufficient to form a good IMF to the nickel base. It is slightly more difficult to achieve this with standard 63/37 solder on nickel than on copper, and appears to be even more difficult with SAC alloy on nickel than on copper. While the temperature is significantly hotter, the SAC alloy does not seem to form a good IMF with nickel as readily as the 63/37 solder does. Werner, the information on the dissolution rate of nickel into a tin alloy from Klein-Wassink's charts are based on pure tin, not a tin/lead alloy. What is the effect on nickel's dissolution rate when the amount of lead in the solder alloy is varied, say from 37% to 0%? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Colin McVean Sent: Thursday, August 17, 2006 9:34 AM To: [log in to unmask] Subject: Re: [TN] LEADFREE BGA ISSUE <Certain pads were very dull and when solder is applied on it, it seened there was dewetting issue> Sounds like an issue with the solderability of the ENIG rather than the substrate. Check with your PCB fab supplier for their comments. <By the way, such kind of issue happened only to one customer...> It only takes one instance of poor process control on ENIG to see faults occurring. Looks like this is what has happened in this case. Rgds Colin Colin McVean M.Inst.C.T. Production Manager Artetch Circuits Limited Main: 01903 725365 DD: 01903 712926 Email: [log in to unmask] www.artetch.co.uk -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Poh Kong Hui Sent: 17 August 2006 15:24 To: [log in to unmask] Subject: Re: [TN] LEADFREE BGA ISSUE Hi Technetters, Could someone advise me the reasons to following issue. 1. There are total 25 boards for the evaluation purpose. 2. Round 1, we assemble d11 units SAC BGA onto board of ENIG. The result was 10 passed functioonal, 1 piece was not working. There was no signal & power to the BGA unit. 3. Round 2, 4 boards were being assembled, 3 passed, 1 was not working 4. Round 3, 10 boards were biring assembled, 1 was working, 9 not working. The above-stated boards undergo the same temperature profile. At the beginning, we were suspecting the board of ENIG. When 1 BGA was being removed from the failed board, and intend to perform the reballing, we realise the not all BGA substrate pads were able to solder. Certain pads were very dull and when solder is applied on it, it seened there was dewetting issue. My question is, if the failure of the BGA that was due to BGA's substrate or otherwise. By the way, such kind of issue happened only to one customer... Thanks KH Poh --------------------------------------------------- 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 ----------------------------------------------------- ________________________________________________________________________ Check out AOL.com today. Breaking news, video search, pictures, email and IM. All on demand. Always Free. --------------------------------------------------- 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 ----------------------------------------------------- ________________________________________________________________________ Check out AOL.com today. Breaking news, video search, pictures, email and IM. All on demand. Always Free. --------------------------------------------------- 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 -----------------------------------------------------