This doesn't add up, can you check your numbers/typing/data? On the info
given a peak oven temp of 285C would be an adequate explanation for weak
joints.
All the 90 something lead alloys are in the 290-310C region or thereabouts.
According to my alloy chart the liquidus of 5Sn/95Pb is 312C, solidus 308C
giving a peak requirement of around 340C. At these temps you will need a
specially formulated flux and probably nitrogen inerting. Regular fluxes
degrade around 280-300C in air and at best become hard to remove.

Kind Regards

Mike Fenner

Applications Engineer, European Operations
Indium Corporation
 T: + 44 1908 580 400
M: + 44 7810 526 317
 F: + 44 1908 580 411
 E: [log in to unmask]
W: www.indium.com
Leadfree: www.Pb-Free.com



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of
[log in to unmask]
Sent: Thursday, May 16, 2002 3:39 AM
To: [log in to unmask]
Subject: [TN] Solder-UBM Separation


Hello Guys?
Can anybody explain the separation of Solder Bump from UBM after the
Assembly Process?

Solder Bump=95Pb5Sn Alloy
It is plated on a wafer with Under Bump Metal (UBM) of TiCuNi. It then
reflowed to form a bump (And is Fluxed).

The bumped wafer then assembled, after assembly there were weak bumps which
some of them separated from the UBM.
Can you explain this phenomena? would this be intemetallic effects? Is it
possible to have this phenomena that is caused by mechanical vibration plus
the heat applied?
By the way the reflow profile had a peak temp of 285 C.

I can't figure out yet why this happened?
Any inputs would lead me to solve this problem

regards

Jonathan

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