The alloy of the new pb-free solder is probably not a factor, but the
different flux could be, along with the higher process temperatures
required with the new Pb-free paste. You do not state what type of paste
the old one and the new one are, no-clean or water soluble.
If your previous paste (which I assume was a no-clean, for certain
reasons) did not fail this surface moisture laden contaminate resistance
test, but assemblies soldered with the new paste do, and "nothing has
changed" other than the paste, then go back and verify that by taking
one of the old assemblies and testing it alongside one of the new
assemblies to verify that only the different paste and process is the
root cause. Once that is verified, you need to determine if the new
paste flux residues are the cause, or if something changed due to the
process (higher reflow temp).
I suspect it is a combination of both.
The other possibility: along with a changeover to Pb-free, there is
usually an associated increase in touchup rework, at least initially
until the inspectors/rework operators get their eyeballs recalibrated.
Along with this is more flux from rework, which is never fully activated
by heat. This small amount of conductive flux residue in direct contact
with the condensed dust can lead to additional leakage failures.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: Wednesday, December 12, 2007 8:53 AM
To: [log in to unmask]
Subject: [LF] FW: Environmental testing and Pb free process
I thought I had posted this a week or so ago but due to problems with my
e-mail address it may not have gotten posted. My apologies if this is a
duplicate posting.
________________________________
From: Fleury, Bill [ECB/MSN]
Sent: Monday, December 03, 2007 4:14 PM
To: [log in to unmask]
Subject: Environmental testing and Pb free process
Hi All,
This is a question regarding environmental testing of products
manufactured using lead free process.
Has anyone out there experienced problems with passing the Hygroscopic
Dust portion of Airborne Contaminants testing from Telcordia GR-63-CORE
standard since converting to lead free solder?
Without going into excruciating details, the test consists of coating a
PWB with a surface film of a single-component hygroscopic solution to
lower surface insulation resistance at high relative humidity. The board
is then soaked at a relative humidity (40 - 85%) and tested for
functional performance.
We have always tested our products to these requirements with no issues.
Now, since we have converted to lead free process we have been
experiencing failures during this testing. We are trying to determine a
possible reason for these failures and the only thing that has changed
in our process was switching to lead free. Any insight into this or
others with experiences similar to ours that would be willing to share
this information would be greatly appreciated.
BTW these are low voltage cards; no high voltages involved.
Regards,
Bill Fleury
Emerson Network Power
Embedded Computing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bill Fleury, MIEEE
Senior Compliance Engineer
8310 Excelsior Drive Phone: 608-826-8375
Madison, WI 53717 Fax: 608-831-8844
email:[log in to unmask]
visit us:www.emersonembeddedcomputing.com
<http://www.emersonembeddedcomputing.com/>
Please note my new email address
Consider It Solved
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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