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.        *
***************************************************************************