Patent GB-1338159-A (GB)
Title: Method and means for forming electrical joints
IPC: H05K3/34
Filed: 1971-07-30
Abstract: 1338159 Soldering WELLS ELECTRONICS Inc 30 July 1971 35919/71 Heading B3R A method of soldering spaced parts of an elongated, flexible, wire or ribbon, conductor (e.g. of copper, silver, nickel) to selected spaced conductive elements of an electrical assembly (e.g. a circuit board) wherein solder is carried by either or both of the conductor or conductive elements, comprises the steps (a) mounting the electrical assembly on a support and threading the conductor through an apertured tip part, (b) bringing the tip part and support together to press a first conductor part against a first selected conductive element, (c) heating the first conductor part to melt the solder, (d) cooling; and thereby solidifying, the solder, (e) moving the tip part and support apart and shifting them relatively so that the conductor is drawn through the tip part, and repeating as required, steps (b)-(e) in respect of second and subsequent conductor parts and selected conductor elements. Where the conductor is coated with a heat-strippable insulation, the heating step (c) also strips the conductor. The heating may be effected by a separate heated member or, as shown, by heating of the tip part. The soldering may be effected without or, preferably, with flux, the latter being provided as a coating on solder pads or in solder. As shown, a printed circuit board 114, having solder pads 120, 120<SP>1</SP> on copper circuit paths 119, is clamped on to a table 12 movable longitudinally and transversely by stepping motors 28 through lead screws (Fig. 2, not shown). A conductor 94 provided with a heat-strippable insulating coating is drawn from a reel 92 and threaded through an aperture in a tip part 16. The latter is supported by and electrically connected to mutually insulated conductor members 44 which are carried by a block 34 vertically movable by a double-acting compressed air cylinder 60. The piston 62 of the cylinder 60 acts downwardly on the block through a spring 70 determining the tip part/table pressure. In operation, a taped operation sequence is inserted into a control unit which first actuates the motors 28 to position a selected solder pad 120<SP>1</SP> below tip part 16 and then engages a reversible valve 110 to energize the cylinder 60 to clamp a part 95 of the conductor 94 between the tip part and the solder pad, whereupon a trip arm 132 on the piston 62 closes a switch 130 to activate a timer 106. This causes an A.C. or D.C. power source 88 to heat the tip part through leads 86 and the conductor members 44, to strip the conductor insulation and melt the solder pad. When the timer 106 times out it deactivates the power source 88 and activates a timer 108 which opens a valve 112 to direct cooling gas (air or inert) from a source 12 on to the solder to cool same. When the timer 108 times out it closes valve 112 and activates the valve 110 reversely to retract the tip 16 from the soldered joint. Control unit 104 then activates motors 28 again to position another solder pad under the tip part and in so doing causes a portion of the conductor 94 to be drawn through the tip part. The sequence is then repeated as required. Additionally, the cooling gas (when inert) may be directed about the joint area during melting of the solder pad to reduce oxidation. If desired, any one or all the steps of the method may be performed manually. The solder may be cooled atmospherically. As shown, the tip part 16 comprises a V- shaped strip of conductive material (e.g. molybdenum, tungsten or stainless steel) having an apertured flat base 78 and tabs 76 secured to the conductor members 44 as by screws. In Fig. 10 (not shown) the base 78 is circular. In Fig. 8 (not shown), the tip part comprises a frustoconically ended cylindrical body provided with an insulating insert; and in Fig. 9 (not shown), the cylindrical part of the body is slotted so as to direct the current through the end of the tip part. Reference has been directed by the Comptroller to Specifications 995,853 and 1,269,602.