Patent GB-1248841-A (GB)
Title: Improvements relating to electric switch apparatus for sensing the presence of an object
IPC: H01H13/02
Filed: 1969-02-19
Abstract: 1,248,841. Mechanical switches; rotary interrupters; printed circuits. INTERNATIONAL BUSINESS MACHINES CORP. 19 Feb., 1969 [18 March, 1968], No. 8965/69. Headings H1N and H1R. Electric switch apparatus for sensing the presence of a multiple assembly of an individually detected array of objects C, Fig. 6, on a substrate S, comprises probes 7 engaging each object C when a carrier 24 is successively lowered over the assembly, each probe operating to open a normally closed electric circuit by lifting a cantilever spring blade 41 clear of a common conducting sheet 44. The blades 41 are formed as parts of a printed circuit diagram (see below) on an insulating base 42 which has apertures 43 to expose the conducting sheet 44. Apertures 27 in the base 26 and sheet 44 permit passage of a reduced portion 30 of each probe 7 to engage a head 32 insulated at 33. The apparatus is applied to a sensor for detecting the correct assembly of a transistor C or other components on substrates S in a continuous production line for welding components on printed circuit substrates S as described in Specification 1,147,924. The blades 41 are normally urged against the sheet 44 by coil spring 34 located on pins 66 which limit the upwards movement. Projecting pins 5p under the head 24 provide a reference guide by engagement with the substrates S. Movement of the head 24 is controlled by a cam 18p, Fig. 3, on a drive shaft 20p coupled to the drive of the substrate conveyer (not shown) and operates through roller 19p and push rod 17p to raise and lower pivoted arm 15p. As the head 24 is normally urged downwards by a spring 14p which limits the pressure on the substrate assembly, the arm system operates only to lift the head 24 positively permitting its downward movement under the action of the spring 14p only. Making printed circuit contacts.-The cantilever contact blades 41 are formed as a printed circuit diagram on a substrate of polyethylene terephthalate polymer, glass, paper or paperfilled laminate initially clad on both surfaces with copper or beryllium-copper alloy and coated with photo-resist. One face 54, Fig. 9A, is masked to give the required contact pattern 41A and locating holes 47A and the other face 55 is masked to provide a pattern of apertures 43A, 60, 61 and locating holes 48A. The assembly is then etched to expose the insulating base 53 on both faces. Since the base 53 is required to be removed at the apertures 43A, 48A, 60 and 61, the face 64 is coated with P.V.C. and the assembly exposed to a chemical solvent such as sulphuric acid to remove the exposed parts of the board 53 on that side. The coating of P.V.C. is then removed by a solvent such as methylethyl ketone. A second application of photo-resist is then applied and exposed and masked, whereby the remainder of the cladding 55 is removed while the now exposed underside of the contacts 41B, Fig. 9D, are protected by by the photoresist. The arrangement is such that on assembly, the contacts 41 may be pressed through the apertures in the board to engage the conducting sheet 44 on the underside. In a modification, the lower cladding face 55 may be retained in the process to form the lower sheet contact.