TECHNET Archives

June 2008

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Igoshev, Vladimir" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Igoshev, Vladimir
Date:
Fri, 20 Jun 2008 10:15:22 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (89 lines)
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
-----------------------------------------------------

ATOM RSS1 RSS2