Thanks for the input Rick, I totally agree with you. Makes sense since the two swipe thing would be totally inefficient (costly) as I would have to mask of the footprints for the leaded parts, put the non leaded parts in after the first Pbfree swipe and then wave in th SnPb. Now for my next question.
Here's a real life scenario that I am living with. I now have a board that is populated with SnPb parts, the component supplier has converted the BGA to lead free. I had the choice to
a) change my process to high temp SnPb solder at smt (and adjust oven to higher temp and assume I am still within scope of thermal limits of all components on board) to help ensure joint reliability or
b) convert the whole smt process to lead free paste and subsequently adjust ovens to even higher temp, (at this point not sure if thermal limits on all parts can withstand the potentially 20 Deg C adjustment) for this product.
I opted to go with
c) ran the BGA in my current process with no adjustments.
We have completed all functional testing with no failures, but, I have sent samples to a lab for xray and cross sectioning and comparison evaluations to determine long term reliability.
I haven't received the results back yet.
What would you have done?
Carol
-----Original Message-----
From: Smith, Rick [mailto:[log in to unmask]]
Sent: December 07, 2004 10:39 AM
To: [log in to unmask]
Subject: Re: [LF] Transition questions, Pb to Pbfree wave soldering ??
Team,
?Maybe this is just another duh Rick? If so, you can slap me later at
APEX.
Suggest soldering everything on SnPb wave. LF parts typically solder
fine with SnPb so that will cure all since you won't be LF anyways.
Better to do in one swipe?
The amount of contamination to a LF wave may be insignificant to RoHS,
but maybe not, if the wave has a 1200 lb pot, it currently costs about
$15000.00 to run a pure tin purge and re-fill, so maybe best to leave it
alone until enough data is available to determine how much contamination
could happen??
My thoughts..
Save your wave for the pure stuff
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of MA/NY DDave
Sent: Tuesday, December 07, 2004 11:26 AM
To: [log in to unmask]
Subject: Re: [LF] Transition questions, Pb to Pbfree wave soldering ??
Hi Pratap, Carol, IPC LF Listservers,
<If you have to run mixed parts, FIRST run with PbFree parts on PbFree
wave solder and THEN run with Tin/Lead parts on SnPb wave solder.
Tin/Lead being lower temperature will not flow and therefore will not
contaminate PbFree pot.>
Pratap I think I understand what you are striving to do above, yet I
believe you made a slight error in the soldering temperature heirarchy
or
your process description. Even changing the heirarchy the pot
temperatures
kind of overlap pasty regions so I don't think this will work. YET
reversing the order and doing SnPb component insertion and solder
afterwards is interesting.
Please correct me, as appropriate
Yours in Engineering, Dave
YiEngr, MA/NY DDave
Yours in
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