Problems where you only have one or two panels in a particular lot,
     and it comes and goes, sometimes with months in between occurrences,
     are terrible to troubleshoot.

     From what you describe it sounds like it may be organic contaminants
     at the copper solder interface. There are several possible sources; in
     the copper, on the copper, or in the solder. The best way to prevent
     these nagging intermittent problems is to establish thorough process
     maintenance procedures and stick to them. Make sure that you're
     operating at the optimum chemistry conditions and use DI water.


     Andrew P. Magee - Applications Engineer
     Rogers - Circuit Materials Unit
     Tel: (602) 917-5237
     Fax: (602) 917-5256
     E-Mail: [log in to unmask]


______________________________ Reply Separator _________________________________

Subject: plated Tin/Lead adhesion
Author:  Steve Allen::(ALLENSAE) at ~FABRIK
Date:    1/8/96 12:46 AM


From: Steve Allen
Date: Mon, Jan 8, 1996 0:46 AM
Subject: plated Tin/Lead adhesion
To: TechNet
Concerning I.R. reflowed plated Tin/Lead on single and double sided
PCB's.
What can cause poor adhesion of the reflowed Tin/Lead to the plated
copper pad?
Our plating process is : acid copper/h2o rinse /fluorboric
dip/fluorboric Tin/lead plating/ etch/ I.R. reflow.
The "problem" is only seen on one or two panels in a particular lot,
and comes and goes, sometimes with months in between occurances!
Sometimes its detected by a random tape test at pre-mask
inspection...sometimes, "unfortunatly" it's found after the customer
has assembled the PCB.  The solder joints appear to flow very well, but
will seperate from the copper if pressure is applied the component
lead.
No copper is attached to the solder joint that has lifted.
The copper pad below is usually somewhat oxidized.
We have explored many possible causes, including excessive hold time
between steps, etc.
I would appreciate any thoughts on this, if anyone has some ideas...?