SOLDERING APPARATUS

Abstract: An apparatus for soldering printed circuit boards moving along a predetermined path of travel, comprises an upwardly extending nozzle member having an opening at its top end from which molten solder is caused to overflow to form an overflowing molten solder with which the underside surface of the printed circuit board is contacted, and an adjustable outlet member rotatably disposed in the opening to define an outlet extending in the direction transverse to the path of travel, so that by adjusting the angular position of the outlet member the orientation of the outlet may be varied for adjustment of the direction and height of the overflowing solder.

Description: This invention relates to an apparatus for soldering printed circuit boards. There have thus far been proposed various kinds soldering apparatus for printed circuit boards. When applied to printed circuit boards bearing chip type electric parts such as resisters and condensers, however, the known apparatus invariably gives rise to problems of soldering failures due to the recesses defined between adjacent chip type parts or behind the chip type parts as seen in the direction of travel of the boards. Such recesses or spaces can block the molten solder from flowing thereinto and can trap gases therein, causing incomplete deposition of the solder. Air bubbles which are once trapped in the recesses are difficult to remove even if the molten solder is poured over the printed circuit board over a long period of time. To cope with this problem, there is proposed in US-A-4,465,219 a wave soldering apparatus capable of adjusting the direction and height of the solder wave so as to provide optimum contact between molten solder and printed circuit boards. An embodiment of this prior art apparatus is shown in Fig. 7 of the accompanying drawings, in which the reference numeral 3 denotes an upwardly converged nozzle member having an overflow outlet 4 extending in the direction perpendicular to the direction shown by the arrow A along which a printed circuit board 1 bearing temporality mounted chip parts 2 travels. A molten solder 5 is caused to overflow from the outlet 4 to form thereover a solder wave 5a. The front plate of the nozzle member 3 has an L-shaped plate 6 mounted on a V-shaped plate 7 which in turn is mounted on a stationary plate 9. The position of the L-shaped plate 6 is adjustable horizontally in the direction parallel to the direction A of the travel of the printed circuit board 1 while the position of the V-shaped plate 7 is adjusted vertically, so that the orientation and size of the area of the overflow outlet 4 may be varied for the adjustment of the direction and height of the overflowing solder wave 5a. One problem associated with this prior apparatus is that it is troublesome and time consuming to vary the position of the plates 6 and 7. In particular it is very difficult to control the orientation of the overflow outlet 4. In IBM Technical Disclosure Bulletin, Vol. 18, No. 5, October 1975, pages 1335-6, there is disclosed an apparatus for soldering printed circuit boards or the like moving along a predetermined path of travel, which apparatus comprises: an open-topped tank for containing a molten solder; an upwardly extending nozzle member having its lower end in flow communication with the tank and its upper end defining an opening extending laterally in the direction transverse to the predetermined path of travel of the printed circuit boards; solder feed means operable for supplying molten solder in the tank to the nozzle member to cause the molten solder to overflow from the opening, with the under surface of the printed circuit board being contacted by the overflowing molten solder; and outlet means disposed in the upper opening of the nozzle to define a laterally extending outlet, the outlet means being rotatable about an axis oriented transversely to the predetermined path of travel of the printed circuit boards so that by adjusting the angular position of the outlet means the orientation of the outlet may be varied for adjustment of the direction of the overflowing solder; and the width of the laterally extending outlet being adjustable for adjustment of the height of the overflowing solder. The object of the present invention is to provide a soldering apparatus which can provide various shapes of soldering wave such as thin solder waves having a high flowing speed suitable for soldering printed circuit boards bearing small outline integrated circuits. In accordance with the present invention there is provided an apparatus for soldering printed circuit boards as set forth in Claim 1. Preferred embodiments of soldering apparatus according to the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional, elevational view diagrammatically showing one embodiment of the soldering apparatus according to the present invention; Figs. 2 through 4 are partial, elevational, cross-sectional views schematically showing various solder wave forms produced by the apparatus of Fig. 1; Figs. 5 and 6 are views, similar to Figs. 2 through 4, illustrating a further embodiment of the present invention; and Fig. 7 is a cross-sectional, elevational view schematically showing a conventional solder overflowing nozzle member. Referring to Figs. 1 and 2, the reference numeral 12 denotes a tank which is generally a rectangular in shape and which is open on the top side thereof. The tank 12 contains a molten solder or melt 13 which is maintained at a suitable temperature by a heating element (not shown). The melt 13 is applied to printed circuit boards by solder applicator means generally indicated by a reference numeral 11. Disposed within the tank 12 is an upwardly extending nozzle member 14, the lower end of which is connected to one end of a conduit 17. At the other end, the conduit 17 is provided with a molten solder supply hole 18 which is opened toward the bottom of the tank 12. Consequently, the lower portion of the nozzle member 14 is in flow communication with the tank 12. The nozzle member 14 is formed in a substantially rectangular shape in section and has a sectional area gradually reduced from its middle portion toward its upper tip end. More specifically, of the two pairs of opposing walls which define the configuration of the nozzle member 14, the side plates are disposed substantially parallel with each other but the front and rear plates are converged toward the upper end of the nozzle member 14. A feed means is provided in the tank 12 for continuously supplying the molten solder 13 in the tank 12 to the nozzle member 14. The feed means preferably includes a propeller assembly 15 which is disposed in the conduit 17 adjacent to the opening 18. The propeller 15 is provided with a shaft which is connected to drive means including a motor 16, so that it is rotated about the shaft upon actuation of the motor 16 to supply the molten solder 13 in the tank 12 continuously to the nozzle 14. The supplied molten solder flows upwards through the nozzle 14, overflows from its upper end 19 to form an overflowing wave or layer 13a and, then, returns to the tank 12. The opening 19 which is defined at the upper end of the nozzle 14 extends laterally in the direction transverse to a direction A along which a printed circuit board 1 bearing chip type electric parts 2 temporarily attached to its underside by means of an adhesive or solder paste is fed by operation of ordinary transfer means. In this instance, it is preferred that the printed circuit board 1 travel in a rearwardly inclined posture and along a similarly inclined path of travel at an angle of ϑ₁ with respect to a horizontal plane so that excess molten solder applied to the board 1 can drop in a facilitated manner. As the printed circuit board 1 passes over the nozzle 14, its lower side is brought into contact with the overflowing molten solder 13a for soldering the electric parts 2 on the underside of the printed circuit board 1. Provided within the opening 19 at the upper end of the nozzle 14 is an outlet means 20 to reduce the area of the size of the opening 19 and to define a laterally extending outlet 32 (Fig. 2). The outlet means 20 in this embodiment includes a curved plate 30 which has a connecting plate 36 at one end. The connecting plate 36 is rotatably supported by a shaft 34 fixed to a side plate of the nozzle member 14. The other end of the curved plate 30 is connected to a connecting plate (not shown) to which a shaft (not shown) is secured. The shaft is rotatably received by a bore in the side wall of the nozzle 14. Of the two pairs of the side walls constituting the nozzle 14, the front side wall has an elongated upper portion 33 curved in the direction of the arrow A. Between the upper portion 33 and the curved plate 30 is defined an overflow outlet 32. The orientation and the width of the outlet 32 may be varied by adjusting the angular position of the curved plate 30. When the curved plate 30 is positioned to provide a wide width for the outlet 32, as shown in Fig. 2, there is formed a solder wave suitable for performing flow dip soldering of printed circuit boards which bear electric components having lead wires depending from the underside of the boards. The reference numeral 27 designates a guide plate on which a running layer 13a of the overflowing molten solder is supported. To the rear end of the plate 27 is fixed a dam plate 28 by means of screws 29. The position of the plate 28 is vertically adjustable for controlling the height of the solder layer 13a. The molten solder in the tank 12 (Fig. 1) is fed to the nozzle 14 and is passed to the overflow outlet 32. The overflowing solder forms the layer or wave running on the plate 27 in the direction parallel with and opposite to the direction A along which printed circuit boards 1 carrying electric parts 2a travel. The printed circuit boards 1 are brought into contact with the solder wave 13a to effect dip soldering. When soldering printed circuit boards bearing chip parts by dip soldering, the overflow outlet 32 is narrowed and is oriented upward as shown in Fig. 3 to form a protruded wave 13b. The printed circuit boards (not shown in Fig. 3) are contacted with the apex portion of the protruded wave 13b. As shown in Fig. 4, by further narrowing the width of the outlet 32, which has the effect of orienting the outlet toward the direction opposite to the direction A of the travel of the printed circuit boards, there is formed an overflowing wave 13c extending in the direction opposite to the direction A. Such an overflowing solder wave 13c is effective in preventing the formation of "bridges" and "icicles" of the solder. A further embodiment is shown in Figs. 5 and 6, in which the same reference numerals designate similar component parts. Outlet means 20 in this embodiment includes a curved plate 40 having a structure similar to that of the embodiment shown in Figs. 2 through 4. The inwardly curved portion 33 of Fig. 2 is removed and replaced by an outwardly extending guide plate 43. When the curved plate 40 is positioned to provide a wide width for the outlet 42, as shown in Fig. 5, there is formed a layer 13a of molten solder similar to that of Fig. 2. As shown in Fig. 6, by narrowing the width, a thin wave 13c is formed in the same manner as in Fig. 4. The solder wave applicator means 11 described in the foregoing are suitably used as one of the two solder applicators of a dual-stage soldering apparatus in combination with another solder applicator capable of forming a laterally moving progressive wave.

Claims: An apparatus for soldering printed circuit boards (1) moving along a predetermined path of travel (A), said apparatus comprising: an open-topped tank (12) for containing a molten solder (13); an upwardly extending nozzle member (14) having its lower end in flow communication with said tank (12) and its upper end defining an opening (19) extending laterally in the direction transverse to said path of travel (A); solder feed means (15,17,18) operable for supplying said molten solder (13) in said tank (12) to said nozzle member (14) to cause said molten solder (13) to overflow from said opening, with the under surface of the printed circuit board (1) being contacted by the overflowing molten solder (13a,13b,13c); and outlet means (20) disposed in said opening (19) to reduce the area of said opening (19) and to define a laterally extending outlet (32;42); said outlet means (20) being rotatable about an axis (C) oriented transversely to said path of travel (A) so that by adjusting the angular position of said outlet means (20) the orientation of said outlet (32;42) may be varied for adjustment of the direction of said overflowing solder (13a,13b,13c); and the width of said laterally extending outlet (32;42) being adjustable for adjustment of the height of said overflowing solder (13a,13b,13c); characterized in that said outlet means includes a longitudinally curved plate (30;40) rotatably disposed about said axis (C) and defining said outlet (32;42) between an upper tip of said nozzle member (14) and said plate (30;40) whereby by adjusting the angular position of said curved plate (30;40) the orientation and the width of said outlet (32;42) may both be varied sufficiently to change the direction of said overflowing solder (13a,13b,13c) between a first flow direction which is generally opposite to said predetermined path of travel (A) of said printed circuit boards and a second flow direction which is generally in the same direction as said predetermined path of travel (A). Apparatus as set forth in Claim 1, wherein said guide plate includes an upwardly extending plate (28) at its end remote from said opening (19) for controlling the height of the overflowing solder (13a,13b) on said guide plate (27). Apparatus as set forth in Claim 2, wherein the height of the upwardly extending plate (28) is vertically adjustable.

Inventors: KONDO, KENSHI
Applicants: NIHON DEN-NETSU KEIKI CO., LTD.
Application year: 1987
Main classification: B23K3
IPC codes: B23K3