Hi Paul! Yes, I have started to experience the same issue. We recently had
one component fabricator offer "white bronze" as a possible solderable
component lead finish option (just the metal alloy, no surface finish).
White bronze is a copper/tin/zinc alloy and I am guessing that its
JSTD-002 solderability response would be less than happy without using an
active flux material. Also, without a barrier plating, a component using
white bronze could have a issue with dezincification which degrades the
solder joint integrity.
And if I included "it depends" in my response, I would have to pay Doug
another Diet Mt. Dew. : - )
Dave
Paul Edwards <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/02/2011 11:56 AM
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Re: [TN] Recommended Reflow Peak Temperature Using Sn63Pb37 Solder and
SAC305 Finished Component Leads?
Dave,
I concur in most cases but I am starting to see new RoHS lead frame
material that doesn't appear to have any surface finish on it that only
wet with more heat on longer soak times...
Again "it depends"...
Paul
Paul Edwards
Process/Quality Engineering
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, March 02, 2011 8:00 AM
To: [log in to unmask]
Subject: Re: [TN] Recommended Reflow Peak Temperature Using Sn63Pb37
Solder and SAC305 Finished Component Leads?
Hi Dick! The introduction of lead-free soldering technology sometimes
messes with everyone's thought processes and your question is one that I
have seen asked multiple times by lots of folks. The typical tin/lead SMT
soldering process has a maximum board reflow temperature in the 215C -
225C range (and yes, there are always exceptions). With a Sn63Pb37 solder
alloy melting temperature of 183C, that means we are reflow any components
with a eutectic tin/lead surface finish. However, other components with
surface finishes such as gold, silver, nickel/palladium/gold and
palladium/silver, the solder joint formation is the result of dissolution
so we have technically been soldering a number lead-free component surface
finishes for years. The industry is now seeing the introduction of tin,
tin/bismuth and various other lead-free surface finishes such as the SAC
alloy family you mentioned. Formation of solder joints using these
lead-free surface finishes will be accomplished by dissolution in the same
fashion as gold, silver, etc in a tin/lead reflow process. Depending on
which lead-free surface finish you are dealing with, you may want to
slightly slow down the conveyor speed or tweak the reflow temperature a
few degrees higher (if possible, some components have max reflow
temperatures around 225C) to allow for more complete dissolution and
solder joint formation. Some of the rules of thumb we use when soldering
to nickel plating can be applied here (see Werner's past TechNet responses
on soldering to nickel). I have conducted a number of lead-free component
and tin/lead solder process reflow trials and found minimal impact to the
overall reflow profile times/temps. Having a well characterized reflow
profile is the key parameter.
Dave Hillman
Rockwell Collins
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"Richard D. Krug" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/02/2011 08:30 AM
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"Richard D. Krug" <[log in to unmask]>
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Subject
[TN] Recommended Reflow Peak Temperature Using Sn63Pb37 Solder and SAC305
Finished Component Leads?
What should the peak reflow temperature be when using Sn63Pb37 solder
paste when some component lead finishes are now an undefined Pb-free
finish? Based on comments from the component manufacturer, I suspect a
SAC alloy.
Can I solder to SAC solder or do I need to reflow the lead finish?
Dick Krug, CSMTPE
SMT Process Engineer
Sparton Corporation
30167 Power Line Road
Brooksville, FL 34602-8299
p (352) 540-4012 (Internal Ext. 2012)
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