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April 1997

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Subject:
From:
"Lang, Michael" <[log in to unmask]> (by way of Patrick Ducas <[log in to unmask]>)
Date:
Tue, 29 Apr 1997 09:56:53 -0400
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Micheal, I'm not able to answer all these questions but I can suggest you
the following:

You might look towards High Frequency Ultrasonic Gold Ball Bonding. It will
allow you to do wirebonding to a PCB at very low temperature. FR-4 material
may be used in that type of packaging.

Regards.
  


I am looking for information regarding Chip On Board (COB) and other 
packaging schemes which rely on wirebonding to a PCB.  If you can, please 
answer the following:

1) Do you currently use COB or other packaging schemes which rely on 
wirebonding directly to a PCB?  If not, is it because of previous bad 
experience or other problems?



2) What temperature is wirebonding to PCB's performed at?



3) How it the heat applied (heated stage of wirebonder, heated N2 blowing on 
site, etc).  If a heated stage, is the PCB placed directly on the stage?



4) What PCB materials can be used for this type of packaging (polyimide, 
Kevlar, FR-4)?  What are the driving characteristics (Coefficient of Thermal 
Expansion in the Z direction leading to barrel cracking, glass transition 
temperature, etc)



5) Can wirebonds survive outside of a hermetic environment (assuming they 
are protected from physical damage)?  Will they survive salt fog, etc.? 
 This question assumes the wirebond is NOT used for connection to a chip, 
but instead to another PCB, I/O pin, etc.





Thanks,


Michael Lang
[log in to unmask] 

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