GB832402A - Improvements relating to electrical contact members - Google Patents

Abstract

832,402. Modifying metallic surfaces. SIEMENS EDISON SWAN Ltd. July 21, 1958 [July 30, 1957], No. 24208/57. Class 82(2) [Also in Groups XXII, XXXVI and XXXVII] A contact, particularly for soldering into a printed circuit (see Group XXXVI) has a contact surface coated with a layer of conductive material which resists being wetted by solder, and a connecting surface to which solder will adhere. The contact may be stamped from metal strip which may have the coating formed thereon before the contact is severed therefrom. Fig. 5 shows one method of treating a strip 21. The strip is a copper-base alloy and is silver-plated before passing it through driving rollers 11, 12 which push the strip between rollers 22, 23, rotating in such a direction as to oppose movement of the strip between them. These rollers are spring-pressed into engagement with opposite faces of the strip and dip into a container 27 filled with solder or flux lacquer which is transferred by the rollers on to the strip in the form of a thin layer 29 adjacent one edge. The strip is then treated, e.g. with ammonium sulphide, so that the silver on the uncoated part is converted into silver oxide or silver sulphide, which is not wetted by solder, this part of the strip subsequently forming the contact surfaces. In a modification of the device shown in Fig. 5, rollers 22, 23 are replaced by a drum (Fig. 6, not shown) which drives a pair of conical rollers engaging the central portion only of the strip 21. The position of the strip of coating material thus applied may be altered by changing the relative positions of strip and rollers. A broken strip of coating material may be applied by using rollers as shown in Fig. 7 instead of the conical rollers. Bosses 44 on these rollers, which rotate in the same direction as and at the same speed as the moving strip 21 apply short lengths of coating material. According to a further alternative, the whole of the silver plating on the strip 21 may be converted to the oxide or sulphide and then removed by brushing where it is not required.