as far as i know you are supposed to check the solderability on as received 
parts and/or after aging which -as i remember does not reach 175C. Never 
heard about a storage temperature so high. Something is not right...
there is the soldering heat resistance test, which is done at these 
temperature for about 10 sec, but it involves solder dipping, and electrical 
test, again, not to be done on the same parts you check for solderability. 
Intermetallics can result at this temperature, and the leads are depleted of 
the solderable tin plating.
Anyway, I am not sure that i understand the test methods you describe.

Gaby
----- Original Message ----- 
From: "- bogert" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, March 02, 2008 3:47 PM
Subject: [TN] Matte Tin Plated Diode Solderability issue


> March 2, 2008
>
> Folks, we have an OEM that purchased axial leaded diodes from On 
> Semiconductor.  Since the diodes were not mil-spec parts, the OEM sent 
> them to a test house for qualification and electrical screening testing. 
> The screening is performed at 175C which I believe is the max storage temp 
> of the part.  They also performed solderability testing which failed (<90% 
> wetting).
>
> The OEM subsequently solder dipped the parts in Sn63 solder and was able 
> to solder them OK.
>
> The part manufacturer indicated the solderability problem was most likely 
> caused by tin migration due to the testing at 175C.
>
> Seems to me that since MIL-PRF-19500 includes electrical screening 
> testing, the parts should have been able to withstand the full screening 
> testing with no solderability failures since the parts most likely were 
> made on the same line and samp processing as mil spec parts.
>
> Any info you can provide on tin migration or on the manuf position that 
> the solderability failure was the result of the testing at 175C would be 
> appreciated.  Have other folks experienced solderability issues for matte 
> tin plated parts?
>
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