I believe intermetallic growth and oxidation are separate paths to poor
solderability. It's my understanding that intermetallics are poorly soluble
in solder, whether oxidized or not.
Gregg Temkin
Sr. Manufacturing Engineer
Korry Electronics
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Kane, Joseph E (US
SSA)
Sent: Monday, March 20, 2006 8:01 AM
To: [log in to unmask]
Subject: Re: [LF] Component Long Term Storage
J-STD-033 says that the shelf life of parts dry-packed in moisture
barrier bags must be at least 12 months. Of course, we open
bags older than that all the time, and the HIC still looks good,
so I don't know what the real performance limit is. If you open
the bag after X years and the HIC looks pink, then of course
you can bake.
As for lead finish, we had problems years back with matte
tin. Theory was that the finish was porous and allowed
oxidation of base metal. Hot solder dip almost always
restored solderability. If the problem had been caused by
intermetallic growth, the dipping should have been less effective.
My understanding is that intermetallic only becomes
a problem when it grows out to the surface and oxidizes.
Intermetallic growth might not be a problem with underlying
nickel (slow diffusion rate), or if your copper is covered with a
decent layer of fused tin/lead or hot solder dip. Some parts still
solder perfectly well after 10 years.
Cooling would slow the growth rate of intermetallic, but the
ratio is probably based on degrees K, so it wouldn't help that
much unless you used liquid nitrogen for storage (not recommended).
Leads made of Kovar or Alloy 42 don't seem to last as long,
not sure why. Don't know about nickel/palladium/gold
and some of the newer flavors, I guess we'll see.
Joe Kane
BAE Systems
Johnson City, NY
-----Original Message-----
From: Colin Weber [mailto:[log in to unmask]]
Sent: Sunday, March 19, 2006 11:34 PM
To: [log in to unmask]
Subject: [LF] Component Long Term Storage
Hello Folks,
Could anyone please advise on what realistic long term storage (many
years) can
be achieved, and how to achieve it, for components such as integrate
circuits?
Any articles or guidelines would be helpful.
We are facing some obsolete component issues and do not have resources
to
redesign many boards for incompatible replacements or new devices.
After searching the archives I have ascertained that it seems the
hygroscopic
nature of the packages is not a great problem. J-STD-033 should help
with
determining storage requirements for this issue. Would it be true to say
baking
the components can eliminate any absorbed moisture, even after many
years of
long term storage?
A bigger problem appears to be intermetallic growth on the legs, between
the
coating (tinning) and the actual leg material. The intermetallic can
grow over
time, eventually causing the legs to lose solderability. I suspect the
growth
rate is temperature dependent and could be slowed by cooling.
Regards,
Colin Weber
------------------------------------------------------------------------
-------Leadfee Mail List provided as a service by IPC using LISTSERV
1.8d
To unsubscribe, send a message to [log in to unmask] with following text
in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks
send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
------------------------------------------------------------------------
-------
----------------------------------------------------------------------------
---Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send:
SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
----------------------------------------------------------------------------
---
-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-------------------------------------------------------------------------------
|
