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Polyimide Block Copolymers for Low Stress Coatings

IP.com Disclosure Number: IPCOM000108140D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 54K

Publishing Venue

IBM

Related People

Hedrick, JL: AUTHOR [+6]

Abstract

As the number of polymer layers and overall thickness of thin film structure increases, controlling residual thermal stress developed in the polymer upon curing and subsequent thermal treatments is important. The stress has primarily been controlled by designing rigid polyimides with low thermal expansion coefficients to minimize the mismatch with the rigid substrates. However, this approach is very limited as more function is demanded on the dielectric (i.e., photosensitivity, dielectric constant, etc.) Consequently, we have designed a more generic means of controlling the stress in these structures amenable towards a variety of polymides. Since polyimides are visoelastic materials, a plausible route to a low stress material would be to increase the relaxation rate of the polyimide.

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Polyimide Block Copolymers for Low Stress Coatings

      As the number of polymer layers and overall thickness of thin
film structure increases, controlling residual thermal stress
developed in the polymer upon curing and subsequent thermal
treatments is important.  The stress has primarily been controlled by
designing rigid polyimides with low thermal expansion coefficients to
minimize the mismatch with the rigid substrates.  However, this
approach is very limited as more function is demanded on the
dielectric (i.e., photosensitivity, dielectric constant, etc.)
Consequently, we have designed a more generic means of controlling
the stress in these structures amenable towards a variety of
polymides.  Since polyimides are visoelastic materials, a plausible
route to a low stress material would be to increase the relaxation
rate of the polyimide.  The incorporation of an elastomer is the most
judicious choice, since in most cases elastomers relax simultaneously
with the applied load.  Furthermore, for a given state of strain the
stress is proportional to temperature where the force will decrease
with temperature.  A series of polyimide block polymers were prepared
with coblock Tg's ranging from -123 to 260~C, and above this
transition the coblock behaved as an elastomeric modifier.
Interestingly, the stress above the coblocks transition was
essentially zero, provided high phase purity was achieved.  TEM
investigations showed that the coblocks exist as discrete sphere...