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March 2003

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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 21 Mar 2003 11:35:52 +0200
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Steve,

Using viscous adhesives with a large polymerised molecule, such as
epoxies, will inevitably create gaps in the magnetic circuit, thereby
reducing the inductance. The object of the exercise is to minimise the
gap. In another life, I used a very liquid cyanacrylate of a type used
by restorers for repairing ceramics. I believe it was made by Eastman
Kodak, if I remember correctly. A tiny microdrop dispensed on each of
the ends of the three arms of the E will do the trick. Almost
instantaneous bonding and minimal loss of inductance.

Brian

Shoda, Steve wrote:
> Does anyone have any experience bonding ferrite cores?  I am working on
> developing a process for bonding an e-core to an i-core. They are 0.8" x
> 1.2" and sandwich the winding in the pwb. So the bond must be done once the
> assembly is populated.   I'm applying a high viscosity epoxy, but it can be
> difficult to control.  I attempted a 0.002" epoxy preform, but the outcome
> was reduced inductance, so we are still using the high viscosity epoxy.  Why
> would they result in such different inductance properties?   In either case,
> the cure time at 250°F is 1 hour and production is requesting a material
> which has a very short cycle time.
>
> Steve Shoda
> BAE SYSTEMS Controls
>
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