Subject: | |
From: | |
Date: | Mon, 14 Oct 96 08:20:09 cst |
Content-Type: | text/plain |
Parts/Attachments: |
|
|
Hi!
In response:
" Is this still a valid test and are there other tests used to verify bareboard
solderability?"
* The test you describe is called the "use" test by many people. There is a wave
solder use test in JSTD-003 (PWBS) but no surface mount test as yet - something
for the IPC committees to think about. A use test is a valid test provided that
your PWB supplier and you have agreed on how the test is run and what the
acceptable requirements should/will be. As part of the current revision effort
on JSTD-002 (components) there is a "use" test for surface mount components. The
second draft of both 002 and 003 is hitting the streets right now and will be
discussed at the IPC Naples FL meeting.
"Does the three, six or 12 months periods still apply if the boards are stored
properly?"
* Maybe, maybe not. A tremendous amount of effort has been put forth by the
electronics industry attempting to correlate a conditioning procedure with a
storage time. IPC-TR-464 and its Addendum summarizes a lot of the accelerated
aging work. Steam aging was thought to accelerate surface finishes to an aged
condition but additional IPC work has shown steam aging is applicable to tin and
tin/lead finishes with no "prediction" of storage time. How long can you store
your boards? What type of flux are you using, what is the soldering process, how
good is your storage conditions, how thick of solder coating is on the boards -
a number of other variables are part of the storage time question.
Should I find solderability problems, one corrective action is to return the
bareboards to the supplier for re-soldering and hope the extra thermal cycle
does not affect the board further.
*Sorry, but resoldering the boards will probably not solve a poor solderability
problem. An extra thermal pass with grow the intermetallic layer(s) and stress
the board. More active fluxes may provide you some help but there are risks
involved with those from a corrosion standpoint.
Good Luck
Dave Hillman
Rockwell Collins
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: fab: Solderability
Author: [log in to unmask] at ccmgw1
Date: 10/10/96 6:37 PM
Address,
I have several boards types and part numbers that are older than 18
months. They are SMOBC with SnPb coated pads, SMT both sides. Based
on observation two types have been Horizontal HAL and One Vertical HAL
at an angle. Without an XRF, I going to assume 100 microin. on large
pads (>.025 pitch & caps) and 500~800 microin. on smaller pads (.020
pitch). From past experience and several Round Robin Studies these
boards should have a minimum solderability shelf life of 6 months (a
year in some cases). To validate this, I am going to apply solder
paste to the component side, via solder paste stencial, and run
through reflow as if a production panel. If solderability has been
degradated by copper migration or similar through the thin SnPb layer,
there should be signs of dewetting and/or no wetting.
My question: Is this still a valid test and are there other tests
used to verify bareboard solderability? Does the three, six or 12
months periods still apply if the boards are stored properly?
Should I find solderability problems, one corrective action is to
return the bareboards to the supplier for re-soldering and hope the
extra thermal cycle does not affect the board further.
Please advise. Thanks in advance.
p.s. Jack Crawford; I need your new email or will someone pass it
along.
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to: *
* [log in to unmask] with <subject: unsubscribe> and no text. *
***************************************************************************
|
|
|