Hi, Steve
You are wise to question that.
Many of the Pb-free parts are just the old part with a new finish, and
no other changes except bumping up the MSD rating and print notes. They
may or may not work as well when soldered with the higher lead-free
process temperatures. Many are finding this out the hard way. Two
examples from my consulting work:
A relay that used to switch freely when soldered at 220 deg. C max. no
longer does so when reflowed at 245 deg. C. The part print was changed
to update the terminal finish, and they INCREASED THE SUGGESTED SOURCE
POWER to make it switch if reflowed at higher temperatures, but failed
to mention that in the ECN of the part. However, the physical change in
the housing (plastic deformation) from the hotter process causes the
relay not to switch even at the higher voltage. The print used to state
that the parts could be subjected to 220 deg. C. for up to 60 seconds.
The SMT lead-free version of the component says it can stand up to 250
deg. C. for no more than 10 seconds. How do you reflow that?
Some parts of course were changed to withstand Pb-free processing and
make them RoHS-compliant, and those changes are manifested in different
performance issues. An example of this is removing a hex. chromium
spring switch inside of a component and replacing it with a stainless
steel switch, which cannot pulse fast enough at the higher end of its
specified range. The result for the unhappy customer is that he no
longer has a part that works in his design, and he needs to alter the
design and completely re-qualify it.
Example like this are happening every day.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, September 18, 2006 1:28 PM
To: [log in to unmask]
Subject: Re: [TN] Lower temp soldering pass of lead-free boards
Hi Ioan!
Are you sure that things are really different between the "Leaded" and
"Lead-free" parts besides the plating? We were in a situation where we
had to build a consigned material assembly which is in the process of
becoming "compliant". However, our customer had purchased quite a number
of digital video devices and did not want to throw them away because
they weren't PB free...the assemblies that we were building weren't
going to the EU.
But we were using PB free solder paste and had some concerns about
whether or not the leaded parts would be able to withstand the lead-free
temperatures. So we called the manufacturer of the device inquiring if
the part could take the heat, and was told "unofficially" (like if we
repeated what he said he would deny it) that the only difference between
the lead-free and leaded part was the plating on the leads...nothing had
changed internally.
I wonder how many PB free parts REALLY have something different about
them besides the lead plating?
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Monday, September 18, 2006 11:26 AM
To: [log in to unmask]
Subject: [TN] Lower temp soldering pass of lead-free boards
Hi Technos,
I have a lead-free board, but some nasty leadless comps are only
available leaded, so not supporting 240C.
I am thinking what about soldering everything that works at lead-free
temps and then make another soldering pass at about 210C with these
comps only. Will this affect the reliability of the lead-free joints,
since the solder will get almost pasty? Did anybody try this?
I agree with the ones that will say: "what the heck, they cannot give
you compliant parts, don't do it", but it is an important project, the
customer knows what this means, but they want to risk.
Btw, I have to make sure the original reliability of the lead-free
joints, as good as it is, will not be latered, it is a high-rel
application.
Thanks,
Ioan
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