Patent GB-1225380-A (GB)
IPC: H01L23/66
Filed: 1968-06-13
Abstract: 1,225,380. Etching. R.C.A. CORPORATION. 13 June, 1968 [17 July, 1967], No. 28160/68. Heading B6J. [Also in Divisions C1 and H1] A plurality of electrical component mounting assemblies 1, Fig. 3, each comprising a supporting laminate 2 comprising layers 24, 23, 22, 21, 25, 26 of gold, nickel, copper chromium, nickel and gold respectively a U-shaped glass layer 3, and laminates 27, 28 each comprising layers 29, 30, 31, 32 of chromium, copper, nickel and gold respectively, (see Division H1), are formed by an etching and plating process set out below. (1) A selectively etchable, photosensitive glass slide is cleaned on both major surfaces, a mask having a pattern of U-shaped opaque areas each corresponding to the shape of the layer 3 of the assembly 1 is placed on one surface of the slide, the slide is exposed to active ultraviolet radiation through the mask, the slide is developed by increasing the etchability of the exposed areas by heating in a light-proof furnace, and the slide is cleaned by sand-blasting and optically ground and polished. (2) The slide is immersed in a protective lacquer, having the edges unprotected, which edges are etched with hydrochloric acid so as to be able to serve as reference edges for subsequent masks. The lacquer is removed by immersing in acetone and then with sodium hydroxide and trisodium phosphate. The slide is chemically cleaned by immersion in trichlorethylene, followed by ultrasonic agitation in water and a detergent, and immersion in a chromic-sulphuric acid solution. (3) The slide is heated in a vacuum chamber and chromium deposited on both surfaces, and then copper is evaporated on to the chromium. A photoresist is applied to one copper surface (upper surface of Fig. 3) and photo-etched to remove from the U-leg areas. Nickel is plated 1 micron thick with a Watts bath on to the copper in the leg areas, and gold 3 microns thick with a Temperox solution on to the nickel, and the resist removed by the same process as the lacquer was removed. Before applying the photoresist, whenever this is done in the process, the slide is immersed in a copper cleaner to remove copper oxides and stains, in ammonium persulphate to micro-etch the surface, in acetone, and in isopropyl alcohol, and is then baked. The product at this stage is shown in Fig. 5. (4) Lacquer is applied to the lower surface of the slide, and the upper surface is etched with ferric chloride to remove the copper except on the legs, and then with hydrochloric acid to remove the chromium except on the legs. The lacquer is removed from the lower surface, lacquer is applied to the upper surface an additional copper lacquer is plated to a thickness of 1 mil. on the lower surface, and the lacquer is removed. Photo-resist is applied to the slide, the lower surface is photo-etched to re-expose the U- shaped light-exposed areas of the glass, and said areas are electroplated with additional copper 3 mils thick nickel 1 micron thick and gold 3-5 microns thick in succession the copper plating solution being "Udylite". The product at this stage is shown in Fig. 6. (5) The product is immersed in hydrofluoric acid to remove the exposed parts of the glass and then in hydrochloric acid to remove the underlying chromium. Phot-resist is applied to the upper surface and photo-etched to expose the U-shaped areas, which are cleaned with a copper cleaner. Lacquer is applied to the lower surface, and the exposed areas are plated with nickel 1 micron thick and then with gold 3 microns thick. The product at this stage is shown in Fig. 7, the various assemblies 1 being connected only by the copper layer 22a. (6) The product is immersed in ferric chloride to remove the interconnecting copper.