METHODS AND APPARATUS FOR REMOVAL OF EDGE BEADS IN SPUN POLYIMIDE FILMS
Original Publication Date: 1995-Oct-31
Included in the Prior Art Database: 2004-Apr-07
Xerox Disclosure Journal
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.