We manufacture an IC package using a Cu carrier upon which an Au/Ni/Cu/Ni/Au stack is plated to create wire bond contacts and a die attach pad. The ICs are assembled on the matrix sheet with high temp (150 - 175C) for die attach and wire bonding, followed by transfer molding at about 170-180C, followed by 5 hours of post mold cure at 175C. Then the copper carrier is etched off, and this etching process cleans the exposed Au pads somewhat. Cu diffusion into the Au layer from the Cu carrier is low and has been characterized with scanning Auger depth profiling. Under some conditions the Au pads can develop a darker color, but solderability remains excellent. The solder paste cleans the Au surface of any oxides, rapidly dissolves the Au and any Cu that has diffused into the Au, and wets very nicely to the underlying Ni. The mechanisms described below do not appear sound. Best regards, Leo Director of Applications Engineering ASAT, Inc. 3755 Capital of Texas Highway, Suite 100 Austin, Texas 78704 ph 512-383-4593 fx 512-383-1590 [log in to unmask] www.asat.com The information contained in this electronic message is CUSTOMER/SUPPLIER PRIVILEGED AND CONFIDENTIAL INFORMATION intended only for the use of the individual or entity named above. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution and copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify the sender by electronic mail. Thank you. -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Ryan Grant Sent: Friday, October 14, 2005 9:23 AM To: [log in to unmask] Subject: Re: [TN] Direct Immersion Gold Interesting. Is the brown color the diffused and oxidized copper? Does the high affinity of Tin and Gold lift the oxidized copper atoms within the gold matrix into pseudo solution with the bulk solder? Even if the oxidized copper is not molecularly bound (wetted) to the tin atoms, if it is completely surrounded, it would appear as part of the bulk solder (or at least until it precipitates out). That would turn the exposed copper gold matrix layer into a sacrificial layer. So in other words, even though the solder can't wet to the oxidized copper on top, it would displace that copper by lifting the gold with it and access un-oxidized copper underneath. Is that what is happening? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerard O'Brien Sent: Thursday, October 13, 2005 5:56 AM To: [log in to unmask] Subject: Re: [TN] Direct Immersion Gold Ryan - it has to do with density of the deposit. If you perform a porosity test on DIG, the results mimic that of 30 microinches of gold rather than the 2-4 microinches that is actually there. I have been testing in real time DIG and using a wetting balance have a data set over 900 days of storage - non protected office environment. If I compare my ENIG longterm test to DIG, the DIG solders better at 899 days, wets faster and produces a higher wetting force. The underlying Cu (oxide) I guess is easier to solder to than a partially passivated nickel layer. After 900 days it does not look very nice - rather brown in color but boy does it solder. Regards Gerard O'Brien Photocircuits. -----Original Message----- From: Ryan Grant [mailto:[log in to unmask]] Sent: Wednesday, October 12, 2005 10:34 AM To: [log in to unmask] Subject: [TN] Direct Immersion Gold Hi Techies, Can anyone explain what direct immersion gold is? My supplier gave me samples of several different board finishes, of which two groups were direct immersion gold from two different suppliers. The gold over copper was 5uin and 7uin, which I was surprised the copper hadn't already diffused into the gold. I told him I had no interest in direct immersion gold...but, since he gave me the samples, I might as well test them with the samples that I am interested in (immersion silver). First, I baked the boards at 125C for 48 hours to kill the solderability. Then they were reflowed twice to kill solderability, and checked for wetting. Again, I expected the copper to completely diffuse through the gold, and/or the solderability to be dead. To my surprise, the gold was still there and solderability was still good; whereas immersion tin and OSP showed evidence of dewetting. (ENIG and immersion silver still had good wetting too). So can anyone explain why the copper and gold didn't diffuse into each other? Thanks, Ryan --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------