Gary,
"we don't call out what type of solder process needs to be used." That
seems like an odd statement. If you don't, how do you know if you are
not cooking components not rated for lead free reflow? How would you be
sure you were even melting SAC alloy if you are using a low end tin/lead
reflow profile?
And the answers you get will be predicated on the type of circuit packs
being produced (how big) and the Class of product.
Our company builds Class II products (We like to think high end class
II.) and the circuit packs do not have a lot of thermal mass. So in the
transition when we started to get lead free array components we went to
a "hot lead" process where we wanted to see good mixing of the solder
paste solder and the ball solder. Dave Hillman and the folks at
Celestica can say a lot more about that. We then had a lead free process
with some remaining leaded components. Same thing but easier, since all
suppliers were by then producing components that for sure could take
more heat. Of course now we are 100% lead-free - well using every
applicable exemption allowed.
Bev
RIM
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Gary Koven
Sent: Friday, June 26, 2009 12:08 PM
To: [log in to unmask]
Subject: [LF] Reflow profiles for mixed Pb status boards
For those of you who subscribe to the IPC DesignerCouncil email forum,
this will be a duplicate topic...
We have a number of PCBAs with both leaded and lead-free parts on them.
Looking over the J-STD-020 reflow profiles on one of the leaded part
datasheets, we saw that its range seemed too restrictive for the
lead-free profile.
Basically the two parameters that interest us are:
(1) Preheat temperature, 100 oC-150 oC for leaded and 150 oC-200 oC for
lead-free
(2) Liquidous temperature, 183 oC for leaded and 217 oC for lead-free.
On our assembly drawings we call out IPC-A-610 Class 2. I understand
that J-STD-002 can also be used together with IPC-A-610 as a note
callout.
Since there is not a RoHS-compliant requirement for these boards, we
don't call out what type of solder process needs to be used.
We're curious about how assembly shops adjust their soldering process
for boards that have both types of parts on them.
We're also wondering whether we need to begin calling out specific
solder processes, but we don't want to add cost to the assembly.
Give me a solution that doesn't add cost to the assembly, but at the
same time satisfies the curious, please.
TIA and Best Regards,
Gary M. Koven, C.I.D.
Dynazign, Inc.
Charlotte, NC, USA
Veteran of the Marsh School
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