Re; "Lead Fracture"

Did the component lead itself break or did the solder joint between the lead
and the board fracture?

There are some papers in the industry which talk about a fracture at the Ni
interface occasionally, with Ni/Au boards.  We have duplicated this, and
believe we have found a mechanism by which we can turn it on and off.  I am
lobbying our management to allow us to present this in more detail to the IPC
at a future conference.

Component "lead"  fracture  is something we have not at all encountered.  We
have more experiments upcoming looking at solder joint fracture and also at PTH
reliability, and defect impacts (like what happens to the vias when they don't
completely plate with Ni/Au).

"Solderability" at time 0 using standards solderability tests has been
excellent.   So long as the Ni was not allowed to oxidize prior to the Au plate
(using Electroless Ni/Immersion Au) and the Au plate is about 3 microinches, we
haven't seen problems.  Be aware though, that if the Ni/Au is applied BEFORE
solder mask, residues left on the pads by poor expose/develop of solder mask
could interfere with solderability.

6 times thermal shock testing of fully Ni/Au plated vias has not shown any
concerns with embrittlement of the pth or Interplane Separation problems in our
experiments.

I am not aware of any mechanism by which  the Ni/Sn intermetalic of the solder
joint (as opposed to the CuSn intermetalic of an OSP or HASL board)  would
cause a component lead to experience higher than normal stresses, which in turn
could cause the component lead to fracture, under what sounds like a fatigue or
crack propagation mode if I take your wording literally.

Jim Herard
KBL, Product Quality Engineering
IBM Microelectronics Endicott
t/l 857-7026

---------------------- Forwarded by Jim Herard/Endicott/IBM on 07-10-97 06:11 PM
 ---------------------------

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        07-10-97 10:18 AM
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Subject: Electroless Nickle and Immersion Gold

Hi All,
Recently I heard of Solderability issue and lead fracture on fine picth QFP (16
mils or less) during vabiration test on the PWB with Electroless Nickle and
Immersion Gold finish (100u-200u of Nickle and 3u-5u of gold) , couple reason
was mention one being the flux used during the assembly and another was the
Nickle passivation on the PWB before assembly. Is any of you have any
experience with this problem and if you do, what you have done to correct the
problem. Also I am interested on all the good things you can tell me about this
finish type. Thanks.

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