GB1177285A - Thin-Film Impedance Arrangement - Google Patents

Abstract

1,177,285. Resistors. HUGHES AIRCRAFT CO. 19 April, 1967 [2 May, 1966], No. 17972/67. Heading H1S. A thin film impedance arrangement comprises a primary resistor 73 on an insulating substrate, e.g. glass or ceramic and a plurality of secondary resistors 80 to 86 with their resistance values increasing in consecutive powers of two connected to the primary resistor. A plurality of fusible highly conductive elements 90 to 96 may be connected to the secondary resistors such that the arrangement can be adjusted to a precise resistance value by selectively connecting or disconnecting appropriate ones of the secondary resistances in circuit with the primary resistance. The resistances may be made by depositing resistive material such as nickelchromium or other metal, alloy or metaldielectric combination, followed by a highly conductive layer of e.g. copper and finally a protective layer of e.g. gold. Unwanted gold, copper and nickel-chromium is then etched away by photo-etching or masking leaving resistors and terminals (Fig. 1, not shown). The secondary resistances may be in parallel with the basic resistor and each other (Fig. 4, not shown); trimming of the arrangement may be by electrically fusing with a pulsed current, handscribing or sandblasting the required fuse portions to provide resistance increments. The fuse portions may be thin-films with restrictions for fusing. A modification (Fig. 7, not shown) describes the use of a shunt (120) of e.g. silver, between secondary resistors. The resistor arrangements may be produced, trimmed and monitored automatically.