Hi Russ -
     
You are one of the first folks I have heard that are using a palladium finish on
QFP - there is a wide distribution of SOIC components (Texas Instruments) with a
palladium finish in the industry. Two issues with palladium that may be of 
assistance to you: (1) flux dependency, (2) dissolution rate. The testing I have
completed shows that my ability to form a good solder joint with a palladium 
finish is highly dependent on the specific flux activator. Having an inert 
atmosphere (either vapor phase or nitrogen) was not a significant factor. 
Palladium has a slower dissolution rate into solder than other metallics you 
typically deal with (i.e. silver, gold) which means you may have to alter your 
soldering profiles to allow for more soldering time. How thick is the palladium 
finish? Some recent published data shows two camps of thought - palladium can 
cause a solder joint to crack and palladium won't cause a solder joint to crack.
Also how are you testing the solderability? The next revision of JSTD-002 will 
include a surface mount simulation test method which has been show to be more 
applicable to SMT components than the dip and look test. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]


______________________________ Reply Separator _________________________________
Subject: assembly
Author:  [log in to unmask] at ccmgw1
Date:    4/10/97 10:06 PM


Hello Technet,
Is anyone out there experiencing solderability problems (dewetting) on QFP 
fine pitch devices that are Palladium plated or coated over nickel (copper 
lead frames)?  The parts in question are 4 - 6 months old. Storage is open; 
Parts are baked at 125C for 24 hours prior to placement. Paste used is RMA 
390 DH3. Reflow is forced convection (BTU  VP98).
Any help on this issue would be greatly appreciated!!
     
Russ Vertefeuille
Mfg. Eng.
Honeywell
     
     
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