GB1446636A - Treating a printed circuit board so that the conductive areas thereof have a substantially uniform coating of solder thereon - Google Patents

Abstract

1446636 Soldering XEROX CORP 28 Nov 1973 [1 Dec 1972 (2)] 55247/73 Heading B3R In a method of producing a uniform coating of solder on a printed circuit board, the board, coated with solder, is immersed in a heated bath of substance immiscible with the solder and is vibrated in an orbital motion within the bath which is at a temperature such that the solder on the board is flowable for at least part of the duration of the vibration, the board being then removed from the bath. In an embodiment an indexing plate carries outwardly directed arms each of which has a hook on its underside and the plate is rotatably and vertically movably mounted on a vertical shaft around which are arranged a number of tanks. A frame supporting a printed circuit board is hung on one of the hooks and the plate is indexed so that the board is lowered into each of the tanks in turn. The tanks provide (a) a phosphoric or hydrochloric acid solution dip; (b) a cold water spray; (c) a flux dip; (d) preheating to about 250‹F; (e) a solder spray and vibration in solder immiscible liquid; (f) a water rinse at 150‹F (g) a water spray rinse at 120‹F and (h) a drying air flow. In (e) the board in its frame 8, Fig. 4, is lowered between tracks 19, 20 mounted on a plate 21 supported by rods 22, 23 which extend through the wall of the tank 13 and are connected eccentrically to shafts driven by a motor 24. A bath 34 of heated solder, e.g. 63% tin-37% lead is provided in the bottom of the tank and solder is pumped by pump 26 from the bath 34 through pipes 28 providing nozzles 31 directed downwardly. A heated bath 35 of wax, e.g. polyethylene oxide wax or polyethylene glycol wax or an oil, e.g. peanut oil is provided to float above the solder bath 34. As the board is lowered into the tank 13 solder is sprayed upon both sides from the nozzles 31 and when the board reaches the bottom of the channels 19, 20 a switch is operated to cut off the spray from the nozzles. The motor 24 is energised to cause the board to be vibrated in a circular or elliptical orbital path while in the heated bath 35 for 15-20 sees. The orbital motion is stopped and the board is lifted from the tank or alternatively the orbital motion may be continued as lifting proceeds. The board may be wholly coated with solder before it is immersed in the wax bath and the tanks may be arranged in a row.