Thanks for your comment, James. I have heard of reports not recommending ENIG for BGA applications, but haven't found any to read them myself. Can anyone help? Recommendations vary depending on application, I find, but what thickness of Gold do you think would be appropriate? Our assembly house was more concerned about the thickness of the Nickel than they were about the Gold before we conducted solderability tests and found it was OK. Our application is Military Avionics, subject to the usual thermal cycling for such equipment and also some substantial, (relatively) low-frequency vibration. Board finishes like HASL, even with very good tolerences on the leveled solder height, do not seem to be as good as the Gold over Nickel in terms of flatness. Flatness for BGA's equals most even joint heights, which in turn means most even distribution of stresses (or minimising stress focal points) and this in turn leads to greater joint reliability under conditions of temperature extremes and vibration. If not Gold over Nickel as a board finish for this application (recommended by Cadence), then what do my learned TNagers suggest instead? Pete Duncan James-Kester <jameswang@KEST To: [log in to unmask] ER.COM.TW> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Sent by: Subject: Re: [TN] PCB surface finishes TechNet <[log in to unmask] G> 07/12/01 10:15 AM Please respond to "TechNet E-Mail Forum."; Please respond to James-Kester Dear Mr. Duncan , I think your gold is too think when applied in soldering . Basically , what Zhangshoukai said is correct , there are some report , such as Hp , has studied such problem and didn't recommend to use ENIG on BGA application . James Wang Assistant Product Manager Litton - Kester Solder , Taiwan -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of <Peter George Duncan> Sent: Thursday, July 12, 2001 8:20 AM To: [log in to unmask] Subject: Re: [TN] PCB surface finishes Hi, Shou Kai, We had a CPU card designed and made for us in the States, and it carries BGA's - 256 and 388 pin devices. This board has an ENIG finish to provide adequate flatness for the BGA's - the finish is 4.5 microinches hard gold over 150 microinches Nickel on a 12 layer FR4 board - quite a thick Nickel layer, I think, but that's what the designers specified. Soldering was a concern to me too, with visions of high melting point solder with silver content and risks of frying dies trying to achieve a good soldering temperature. But we tried a eutectic solder paste (63/37) specially formulated for fibre optics work and it worked very well. Wetting was good, solder joints were properly formed. Peak soldering temperature was 218 deg C for about 16 seconds, bringing the centre pins of the BGA's up to 205 deg C. If your board is in good condition, you should have no problems. Pete Duncan Shoukai Zhang <skzhang@HUAW To: [log in to unmask] EI.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Sent by: Subject: [TN] PCB surface finishes TechNet <[log in to unmask] ORG> 07/11/01 05:27 PM Please respond to "TechNet E-Mail Forum."; Please respond to Shoukai Zhang Dear TechNetters: As we know that the preferred metal surface finishes are HASL, EN/IG (Electroless Nickel and Immersion Gold, and OSP etc. It's reported that EN/IG(also called immersion gold) suface may lead unreliable solder joint for BGA component, and suggest do not use immersion gold for designs that have BGAs. Please give your advices. Thanks with best regards, Zhangshoukai, PE, Huawei Technologies. ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) 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 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------