Hi Geert, Nice summary :-) The only thing I wouldn't say is that the intermetallic layer is too thin in case of BP. I saw cases when the layer looked pretty much normal, thickness-wise, but oddly shape-wise. Regards, Vladimir -----Original Message----- From: Geert Willems [mailto:[log in to unmask]] Sent: Friday, June 20, 2008 5:05 AM To: [log in to unmask]; Igoshev, Vladimir Cc: Geert Willems Subject: Solder-NiAu interface failure Interesting discussion on the definition of solder-NiAu failures. One I am often confronted with. For what it's worth, my idea of looking at Black Pad and Brittle Fracture at the SnNi IMC-Ni interface. To my opinion the distinction between both is clear when looking at the root cause. It is much less clear if one looks at it from the end result: failing SnNi IMC-Ni interface. Brittle fracture: It seems that the SnNi IMC-Ni interface is intrinsically weak (whatever the concentration of P even for P=0%), at least compared to the SnCu IMC-Cu interface. (Does anybody know why? - Never seen a BF between the SnCuIMC- Cu interface.) The higher the concentration of P in the Ni, the weaker the interface. P detoriates the already weak interface further. (always compared to Cu). Brittle fracture is not limited to ENIG NiAu Black pad: Black pad is related to an immersion Au process problem in which the Au immersion bath attacks the electroless Ni layer. The higher the P bulk concentration in the electroless Ni layer the lower the probability of Black Pad. There are specific signs for Black Pad (according to this definition) which makes it possible to distinguish it from pure Brittle Fracture: - rough Ni surface, "mud-crack"-like look, reduction of Ni thickness along grain boundaries; (BF will show a smooth surface) - Strong P accumulation at the surface but a lower than typical P concentration (7-9%)in the "bulk" of the Ni layer. - Unsoldered PCB: A thicker than typical Au layer. Au is more rapidly deposited under Black Pad conditions which is linked to the high P accumulation seen at the interface. - Soldered PCB: very little or no IMC. Solder does not solder to the corroded Ni. Therefore, with Black Pad you may just pop-off the components if it is wide spread. For BF you will need a bit more force although hitting a heat sink on top of a BGA can be enough. Off course, a low degree of Black Pad can hardly be distinguished from BF. In that case it is just another interface detoriating phenomenon aggravating BF. Interested to read your comments. Geert Willems IMEC --------------------------------------------------- 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 -----------------------------------------------------