GB1260468A - Improvements in or relating to the formation of connections on microelectronic circuits - Google Patents

Abstract

1,260,468. Welding by pressure. NATIONAL RESEARCH DEVELOPMENT CORP. 26 March, 1969 [28 March, 1968], No. 15028/68. Heading B3R. [Also in Divisions C1, H1 and H2] In forming connections to metallic conductors of a microelectronic circuit pattern on a substrate, an apertured mask is located over the pattern, metallic particles thicker than the mask are placed in apertures in the mask in contact with the conductors, the particles are pressed against the conductors to bond them thereto and the mask is removed to leave connection pillars bonded to the pattern. A substrate 1 of alumina has a pattern of conductors 2 formed thereon by screen printing or by vacuum deposition through a photo-resist mask, the conductors being at least surfaced with gold, and over the pattern a perforated mask 4 is held, gold spheres 8 being brushed over the mask to occupy the perforations. The spheres protrude above the mask which may be of foil not containing lead, e.g. aluminium or phosphor-bronze or plastics sheet and large perforations may be filled with several spheres side by side. With the substrate on a platen 6 a movable steel platen 7 is pressed on to the spheres to deform them to fill the perforations and pressure bond them to the conductors. The platens 6, 7 are preferably heated and the substrate may be heated to 150-250‹ C. The mask is peeled away leaving upstanding pillars on which inverted integrated circuit chips may be thermocompression bonded. An insulating layer may be formed on the substrate about the pillars before the chip bonding to protect the conductors by applying a colloidal suspension of powdered glass frit in a volatile liquid, e.g. isopropyl alcohol in ethyl acetate and heating to fuse the glass. Instead of mounting chips on the pillars which extend above the insulating layer, the pillars are ground to be flush with the layer and a further pattern of conductors is formed thereon. The process may be repeated to form a multilayer microelectronic circuit with interconnecting pillars. Instead of a glaze an epoxy resin insulating layer may be used possibly containing alumina particles or in a multilayer circuit a series of glazes of progressively lower fusion temperatures or a glaze containing refractory oxide particles may be used.