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April 2008

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Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Wed, 2 Apr 2008 18:39:01 +0100
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IF you are using vacuum to reduce voids, you might be better off pulling it
on the adhesive before use, you will need to decant or dispense it into a
container with at least 3x the volume of adhesive being degassed. A
cartridge like those used for paste is ideal and you can get a little gizmo
from the cartridge supplier to back fill regular syringes. This will get
gross air out. The rheology maybe affected by doing this so you may need to
adjust application parameters. 
You can see from this procedure why pulling a vacuum on assembly may not be
such a good idea. A better alternative would be to specify de-aired material
to your supplier.
It might be better to adjust your application procedures, deposit shape,
ramp rate, pressure etc. 
For example if your bond area is square then an x shaped adhesive dot is
preferred. On warming the adhesive viscosity will fall before it rises with
cure (assuming you can get ramp rate suitably adjusted) and with a little
pressure the adhesive will wet out to fill the square. After this "degassing
"stage ramp quickly to peak cure temp to get good cross linking. During this
time you might want to pull a small vacuum.
The x allows evolution of any volatiles and as the adhesive flows to fill
square it will sweep any trapped air in front of it. Hopefully you can
intuit bead shapes for different geographies from the above.

Hope this helps.





Regards 

Mike Fenner 
Indium Corporation 

T: + 44 1908 580 400 
M: + 44 7810 526 317 
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Chandler
Sent: Wednesday, April 02, 2008 3:01 PM
To: [log in to unmask]
Subject: [TN] Vacuum Assembly

Anyone have experience with using vacuum assembly to attach a flex circuit
to a concave surface using adhesive without voids? Any insight into this
process would be appreciated.

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