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METHODS AND APPARATUS FOR REMOVAL OF EDGE BEADS IN SPUN POLYIMIDE FILMS

IP.com Disclosure Number: IPCOM000027214D
Original Publication Date: 1995-Oct-31
Included in the Prior Art Database: 2004-Apr-07
Document File: 4 page(s) / 183K

Publishing Venue

Xerox Disclosure Journal

Abstract

It is known that spun films of all fluids deposited on a substrate have a distinct bead at the edge thereof. Such edge beads are a direct result of the forces of surface tension which hold residual fluid at the edge of the substrate where it eventually dries and gives rise to the beads observed. These beads can be 5-10 microns thick depending upon the viscosity of the fluid, the spin speed, and the nature of the substrate. The heater wafer of thermal ink jet devices has two layers of polyimide which are laid down by spinning. Consequently, a reasonably thick bead of polyimide at the edges of these heater wafers is formed. As a result, during the process of mating of the heater wafer to the channel wafer, the laminate is seldom in close contact at the edges compared to main body of the two wafers. This lowers the overall yield of working devices. One possible solution to increase the overall yield of useful devices is to force the two wafer laminates together at the edges by laminating them under hydrostatic pressure. This process, however, leads to cracking of the laminate, particularly the channel wafer in the peripheral region. As a result, the same proportion of dies are lost when the wafers are bonded together under hydrostatic pressure as are lost due to the relative lack of bond between the wafers in the peripheral region when they are bonded together without the application of any pressure.

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XEROX DISCLOSURE JOURNAL

METHODS AND APPARATUS FOR REMOVAL OF EDGE BEADS IN U.S. C1.346/140R SPUN POLYIMIDE FILMS

Proposed Classification

Int. C1. GOlD 15/16

Ram S. Narang
Frederick A. Warner

26

78

XEROX DISCLOSURE JOURNAL Vol. 20 No. 5 SeptembedOctober 1995 423

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METHODS AND APPARATUS FOR REMOVAL OF EDGE BEADS IN SPUN POLYIMIDE FILMS (Cont'd)

It is known that spun films of all fluids deposited on a substrate have a distinct bead at the edge thereof. Such edge beads are a direct result of the forces of surface tension which hold residual fluid at the edge of the substrate where it eventually dries and gives rise to the beads observed. These beads can be 5-10 microns thick depending upon the viscosity of the fluid, the spin speed, and the nature of the substrate. The heater wafer of thermal ink jet devices has two layers of polyimide which are laid down by spinning. Consequently, a reasonably thick bead of polyimide at the edges of these heater wafers is formed. As a result, during the process of mating of the heater wafer to the channel wafer, the laminate is seldom in close contact at the edges compared to main body of the two wafers. This lowers the overall yield of working devices. One possible solution to increase the overall yield of useful devices is to force the two wafer laminates together at the edges by laminating them under hydrostatic pressure. This process, however, leads to cracking of the laminate, particularly the channel wafer in the peripheral region. As a result, the same proportion of dies are lost when the wafers are bonded together under hydrostatic pressure as are lost due to the relative lack of bond between the wafers in the peripheral region when they are bonded together without the application of any pressure.

Two alternate methods of applying a vacuum at the periphery of the wafer to remove excess fluid which deposits thereon during spinning using a vacuum chuck are proposed. In addition, the outer areas of the apparatus are also coated with teflon to provide a low energy surface to which very little fluid adheres. This should, in principle, allow for an even dispersal of the fluid which typically gives rise to the observed edge bead away from the edge before it has a chance to dry.

FIG. 1 illustrates a vacuum chuck 10 having an inner rotating part 12 and an outer stationary part 14. The inner rotating part 12 of the chuck rotates for spinning the fluid while the outer part 14 of the chuck remains stationary. The inner part 12 and the outer part 14 are separated from each other by a ball bearing arrangement 16. An...