Greg, typically the laser does not scribe directly into the plastic of the
package body because it does not create enough contrast.  The surface of
the package is usually coated with a thin film and it is this material that
is scribed by the laser.  Unfortunately, I do not know the chemical
composition of these coating materials, but I suspect that this is what you
are having trouble adhering to. 
 
Regards, 
 
Marshall 
 
On Jun 06, 1996 13:22:40, '"Greg Bartlett" <[log in to unmask]>' wrote: 
 
 
>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,
perha=  
>ps?) 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 
>[log in to unmask] 
> 
>-------------------------------------- 
>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 
>[log in to unmask] 
>