Improvements in the connection of electrical devices to printed wiring

摘要

1,013,333. Soldering. INTERNATIONAL BUSINESS MACHINES CORPORATION. Aug. 4, 1964 [Aug. 8, 1963], No. 31402/64. Heading B3R. [Also in Division H1] A method of connecting an electrical device to solder-coated printed wiring on a substrate comprises the steps of providing the device with dependent contacts of a predetermined thickness and having a melting point higher than the solder, positioning the device on the printed wiring and heating the substrate so that the contacts are secured by the solder, without the contacts being deformed. The method is described with reference to attaching chip components 25 mils. square to a substrate 0À45 inch square. The component 20, Fig. 2, is a planar semi-conductor device comprising electrodes 34, 36 and a glass layer 26. Metal strips connect the electrodes to openings 24 in the glass layer, a metal film 30 being deposited in the opening before the balls 22 are positioned. The balls are made of 72/25 gold-antimony alloy or other solderable alloy. The substrate, Fig. 3, is made of an insulating material having good thermal conductivity, a low thermal coefficient of expansion and the ability to withstand high temperatures. An example of such a material is one containing 95% alumina. The printed wiring pattern is produced by silk-screen printing and firing, cleaning and tinning. A jig, Fig. 4, is used to position the components relative to the substrate. The flap 206 has locating pins 207 and a spring clip 209, and the flap 204 has apertures 208 to receive the components. The substrate is coated with a sticky flux before being placed in the open jig, so that when the flaps 204, 206 are closed the components adhere to the substrate. Alternatively, the flaps may be brought together with sufficient pressure to form cold-welds between the metals of sufficient strength to aid preventing the components sliding on the solder during subsequent operations. The assembly is then fired to establish the permanent joint. With balls 22 of 75/25 gold-antimony alloy and 90/10 lead-tin substrate solder, twenty-five seconds in a furnace operating at 700‹ C; is sufficient to heat the substrate to 320‹ C., which melts the solder but does not cause deformation of the balls 22. Solder fillets 142, Fig. 6, extend up the sides of the balls. The assembly is aircooled, cleaned and electrically and mechanically tested.