Tom,

I've had experience spray coating a couple of materials that may work,
depending on the methods that can be employed with the material:

1) A thermoplastic adhesive from General Chemical called GenTak 230 (at
least, they used to have it - I've not used it in a couple of years).
It is a thermoplastic that can be sprayed on once diluted, and has a
bond temperature 150C (Glass transition temp of ~130C).  This material
would basically be reversible - if you heat it up again, it will become
soft again.

2) SU-8 - this material is effectively a UV curing epoxy that applies
like a photoresist. It has a glass transition temperature at 55C (a
little lower than the 150C you mention).  However, once exposed to UV
and baked at 95C for several minutes, the material becomes a permanent,
hard cured epoxy that is absolutely impervious to any solvent. If the
process can be arranged so that a UV cure can occur after the objects
have been embedded, or if the process can occur quickly enough that the
object can be embedded after UV exposure, and in between glass
transition and full cure during the heating cycle, then this could be a
good method.

In both of these cases, my experience was with spraying via an EVG150
OmniSpray system, which has variants capable of coating flat panel
displays.

Best Regards,
Chad Brubaker


-----Original Message-----
From: Tom Rust
Sent: Monday, November 07, 2005 4:26 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Wax or adhesive sought

I'm looking for some kind of material which could be spray applied to
areas of a few square feet at a time, which when applied would dry to a
non-sticky film of maybe 10-25u thickness, that could then be heated to
say 150C or more and would soften and become tacky and act as an
adhesive. When it cooled it would harden and serve to lock objects
placed over it in place. It need do this only once.
It also must be clear and withstand long term (like 20yr solar exposure)

UV exposure without significant degradation.

I've considered waxes and UV cured epoxies.