Patent GB-1251501-A (GB)
IPC: H01L23/29
Filed: 1968-10-09
Abstract: 1,251,501. Semi-conductor device handling. WESTERN ELECTRIC CO. Inc. 9 Oct., 1968 [9 Oct., 1967; 10 April, 1968], No. 47871/68. Heading H1K. Pressure is applied between an array of beam lead semi-conductor devices and a pressure sensitive silicone resin or rubber so that the array is held by vacuum resulting from the pressure to a carrier part at least of the surface of which is constituted by said resin or rubber. In the manufacture of beam lead transistors a semi-conductor wafer containing a number of transistor zone configurations is stuck beam leads downwards by wax on a plate of glass, alumina or sapphire and subdivided into individual elements by photoresist and etching steps. The plate is mounted on a pedestal, a metal mesh screen clamped over it and cellulose acetate or nitrate applied to hold the wafer to the screen. After heating to soften the wax the plate is removed and any residual wax removed by immersing in and then spraying with trichloroethylene. Then the exposed face of the wafer is pressed against a pressure sensitive coating of adhesive silicone resin or rubber on a glass disc and the cellulose acetate dissolved in acetone to release the screen. Alternatively water is sprayed on the screen, frozen to clamp the devices thereto and then melted to release the screen. The transistors are individually removable from the disc using tweezers or a vacuum probe. Adhesion may be reduced by using a thinner layer of adhesive or by roughening its surface as by forming a matrix of depressions therein. Devices may be transferred from a less to a more adhesive surface merely by pressing them against the latter and then stripping off the former, the first carrier being stretched if desired, before transfer to space out the transistors. Alternatively a surface of the same adhesive power is pressed on and the adhesion of the first surface reduced by spraying it with trichloroethylene to swell it. This spraying technique may also be used to weaken the adhesion and thus facilitate removal of individual transistors, the reduced adhesion persisting after the solvent has evaporated. In another embodiment the transistors are tested while held by wax on the original substrate, a plastics card with holes punched at the positions of transistors passing the test placed over the substrate and pressuresensitive adhesive applied in a fluid state to form a layer with protrusions contacting the transistors through the holes, and then cured. After dissolving the wax to dislodge the defective transistors a pressure adhesive member is pressed against the remaining transistors and the adherent coating and plastics card peeled off. In yet another arrangement the original support to which the wafer is stuck with wax has a pressure-sensitive adhesive surface. In this case the assembly is held under pressure while the wax is dissolved away to adhere the transistors to the surface. In a modification the original support is a ceramic carrier with frustoconical openings over which the transistor configurations are centred. After attaching the wafer with wax, the wax is locally removed by spraying solvent into the holes and replaced by the pressure-sensitive adhesive material in the fluid state, which on curing forms a sheet with protrusions contacting the transistors through the openings. The transistors are then separated by etching and the remaining wax removed.