GB1504663A - Large area hybrid microcircuit assembly - Google Patents

Abstract

1504663 Printed circuit component assemblies HUGHES AIRCRAFT CO 9 Feb 1976 [3 March 1975] 04947/76 Heading H1R A hybrid micro-circuit comprises (Fig. 1) a substrate 12 of large area bonded, e.g. by brazing to a mounting plate 14 which carries plural components, e.g. semiconductor chips 16, capacitor chips 18, discrete resistors or capacitors 20, 21, thick film resistors 22, multilayer thick film conductors 24, and other components together with thin film conductors 25 protected in sealed packages located on hermetic sealing areas 48, to which is bonded a lid 64 or a two-part ring frame and cover (Figs. 2a to 2f). The components are interconnected over circuitry 42, connection solder pads 28, terminals 30, pin and socket connectors 32, and wires 34 into an external electronic function (not shown). Plate 14 comprises a block of, e.g. metal or epoxy glass which may be formed as a thermally conductive heat sink with corrugated fins cooled, e.g. by forced air. Substrate 12 of, e.g. alumina is cleaned, and multilevel resistor and conductor patterns are screened and fired thereon together with thick film printed conductors and multiple selective area seals. Via holes are provided to enable interconnection between multiple overlying conductive patterns, and the imposition of the circuit layouts may be computer controlled. A circuit pattern 42 may comprise top level conductors 44 and lower level conductors 46 formed together with hermetic sealing areas 48, to which ring frames 72 may be soldered. The substrate 12 is then bonded to plate 14 by, e.g. silicone adhesive, or brazed to a cooling fin, and discrete components 20, 21 are adhesively fixed and soldered to the substrate, after which jumper wires are soldered to the substrate solder pads 28 thereon, and to connection points, e.g. 30, 33. Chip components are then mounted within frame 72 and wire bonded to points 56 extending outwardly of the sealing areas 48. Pin connector 32 is then adhesively bonded or soldered to plate 14 with leads 34 bonded to pads 28 of the substrate, and the joints are sealed with epoxy adhesive. The thick film resistors may be adjusted by laser trimming. Thereafter covers, e.g. 64, 65 are soldered to the ring frames in nitrogen and leak tested, after which the entire microcircuit is encapsulated in polyurethane plastic. In fabrication of the selective area seals (Figs. 2a to 2f) area 48 is covered with a dielectric ring 66 to insulate leads 44 of the underlying circuit pattern 42, and a metal ring 68, e.g. of platinum and gold, gold, tungsten plated with gold or nickel is screened over ring 66 and tinned with solder at 70. A ring frame, 72, e.g. of iron nickel cobalt alloy, with a pretinned surface 74 is soldered to area 70, and an upper surface 76 is tinned at 78. A similar metal cover 80 flanged at 82 is then soldered to the ring frame, with hermetic sealing by solder closure of hole 84. Alternatively the cover 80 may be soldered directly to substrate 12.