Jim Herard wrote:
> 
> 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
>  ---------------------------
> 
>         [log in to unmask]
>         07-10-97 10:18 AM
> Please respond to [log in to unmask] @ internet
> 
> To: [log in to unmask] @ internet
> cc:
> 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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Jim
Thank you for clarifying the problem, you are right the fracture occurs at solder joint 
between the component lead and the board.

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