Sorry Mike, as the question is ambiguous, so is your answer! Simply, 
IMHO, it is not an issue.

Brian

On 07.06.2013 00:17, Mike Fenner wrote:
> Answer yes.
>
> Melting the object you are joining is welding. Soldering is dissolving.
> When you make solder joints to SN plated/coated surfaces they do not melt in
> the solder. The plating dissolves rapidly and goes into solution. (The usual
> analogy is sugar into coffee). The underlying or base metal is now exposed
> to solder but dissolves very slowly.  Naturally we don't wait for that
> process to complete :). So on freezing there is a transitional zone which is
> neither pure solder nor base metal but a mixture. (usually referred to as
> intermetallic layer)
>
> Sn/2.5Bi can be regarded as a tin plating. The small amount of Bi is added
> to control Tin whisker growth. A smaller amount of lead has the same affect.
> Ceramic devices have had a tin plate - with the lead - for donkey's years
> without a mention for the most part. Now under Pb-free legislation some
> people need to know what their BoM is and the added content information is
> causing everyone to look into things more closely.
>
> Best Wishes
>
>
>
> Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerald Bogert
> Sent: Thursday, June 06, 2013 9:19 PM
> To: [log in to unmask]
> Subject: [TN] Soldering to SMD device wth Sn98Bi2.5 leads using Sn63Pb37
> solder
>
> June 6, 2013
>
>
>
> We have an OM who soldered surface mount Opto-couplers with Sn98/Bi2.5
> leads using Sn63Pb37 solder.  The reflow solder profile used was the
> traditional one for Sn63 solder with a measured peak temperature in the
> range of 209 to 215C.  The actual amount of Bi by weight that wound up
> in the completed solder joint was calculated to be about 0.19%.  Based
> on this, there is no issue with a low temperature alloy forming with the
> combination of Bi and Pb.
>
>
>
> However, since the melting point of the Sn98/Bi2.5 solder is around
> 223-231C, the reflow profile used will not result in melting of the
> solder on the part terminations.  Is this an issue or will the Sn63
> properly bond to the solder on the part terminations to form an
> acceptable solder joint?
>
>
>
> [log in to unmask]
>
>
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