RE>ASSY: Laser Ash?                          6/6/96

Funny that you should mention this, Norm.  I believe that we're seeing a related problem.  While we're not seeing a white residue, we are seeing a problem with laser etched devices.  We use thermally-screened devices on certain products.  Our screening house uses a yellow epoxy dot on the corner of the device to signify successful screening, but these dots have been falling off of the laser etched parts.  We suspect that the laser is modifying the surface of the devices somehow (redeposition of carbon, perhaps?) to cause this.  

Any thoughts on how to either clean the device surface or come up with an alternative, inexpensive way to mark these devices?

Greg Bartlett
Mercury Computer Systems
Chelmsford, MA
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From: Dill, Norm J

     After cleaning (soap & water) soldered assemblies, has anyone had a 
white residue problem that was traced back to the laser etched characters on 
plastic DIP's?
     We currently have a white residue problem under investigation where the 
initial evidence indicates the source to be a certain brand of DIP IC.  The 
top of the DIP has laser etched character markings that appear to leach a 
chemical component(s) that combines with the rinse (tap) water to form a 
white residue after drying.  The residue is easily removed with a cotton 
swab and alcohol.
      At this point the complaint is only visual and easily corrected by 
hand cleaning but the concerns are what is actually being deposited on the 
board surface and is it being completely removed.
      Any inputs on this will be greatly appreciated.

     Norm Dill
     Harris RF Communications
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