I am betting on the concentration of P.     I will let the fab guru's now
speak.


Kerry McMullen
Principal New Product Mfg. Engineer
LTX Corporation
50 Rosemont Road
Westwood, MA 02090-2306
(T) 781-467-5468



"Arbour, Michel" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/08/2005 09:47 AM
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"Arbour, Michel" <[log in to unmask]>


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Subject
[TN] Solderability issues with ENIG finish






> Hi ,
> We've been having some solderability problems with one of our supplier.
A
> populated PCB was sent for elementary analysis and we got the results
back
> from the lab.
> Before going further in the corrective action process i would like to
know
> if some of you agree and support the conclusions of the report based on
> the following data.
>
> - The board sent to analysis was populated , one half of a smt pad  did
> not wet with solder the other half wetted properly
> - The problem was noticeable on approx. 2% of the lot of PCB. 2-3 pads
per
> board
> - The pad could not be soldered using an iron pen
> - Solder paste is standard Sn63, Pb37
>
> Two area on the pad were analyzed, one that was wetted , the other was
> not.
> Concentrations of element found  were the following
> - On the wetted area of the pad ALIAS : "AREA B"
> 5.40% C
> 2.04% N
> 0.81% O
> 45.32% Sn
> 2.45% Ni
> 3.67% Cu
> 40.31% Pb
>
> On the unsolderable area of the pad ALIAS "AREA A"
> 6.08% C
> 9.08% P
> 9.55% Sn
> 66.62% Ni
> 3.47% Cu
> 5.20% Au
>
> The conclusion of the report states :
> Area A is a fracture surface at the intermetallic boundary while Area B
is
> a fracture surface at or near the bulk solder.  No mud cracking is seen
at
> Area A which indicates that black nickel was most likely not present.
The
> fact that there is a fairly large gold peak at area A indicates that
there
> may not have been sufficient time to adequately form the solder joint as
> the gold may not have had time to diffuse into the bulk solder.
>
> I can post a picture of the pad if you can point me to a location
>
>
> Michel Arbour
> Kontron Canada Inc.
>

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