Method for manufacturing a printed circuit board with a connecting cable

Abstract

A method for producing a permanent connection between a printed circuit board (PCB) and a connecting cable (AK) is described, wherein the connecting cable (AK) has a cable sheath (20) and three strands (15), wherein the printed circuit board (PCB) has a width perpendicular to a center line (M) that does not permit the arrangement of three solder joints side by side, comprising the following method features: automatic stripping of three strand ends of equal length of the connecting cable (AK); passing a first of the three strands (15) from a top side of the printed circuit board (PCB) through a hole (50) provided in the printed circuit board (PCB) which lies on the center line (M) of the printed circuit board (PCB), so that the end of the strand (15) protrudes on the underside of the printed circuit board (PCB); soldering of the strand ends of a second and a third strand (15) on the top side at a second and a third solder joint which are located side by side symmetrically to the center line (M);Soldering of the first wire end to a first solder point provided on the opposite underside of the printed circuit board (PCB).

Description

The invention relates to a method for producing a fixed connection between a printed circuit board and a connecting cable.It is known in the art to produce a soldered connection between a printed circuit board and a connecting cable as a fixed connection, in which three soldered points are arranged symmetrically to the center line of the printed circuit board on the upper side of the printed circuit board.In very narrow printed circuit boards, under certain circumstances too little space is to be arranged next to one another around three soldering points. One solution to this problem is to provide the central solder location offset on the center line, see FIG. 1.Such an arrangement of the soldered joints would, however, lead to the problem of differently long strand ends and their insulation-removal in the case of very thin connecting cables with correspondingly thin strands, which can only be realized with great difficulty or not at all in terms of production technology.In addition, in the case of thin connecting cables, the load-bearing capacity of the soldered connection is frequently not sufficient.It is an object of the invention to specify a method for producing a fixed connection between a printed circuit board and a connecting cable, which method overcomes the above-mentioned disadvantages and can be realized in a simple manner from a manufacturing standpoint.This object is achieved by the method specified in claim 1.Advantageous further developments of the invention are specified in the dependent claims.An essential idea of the invention is to provide the soldered joints on different sides of the printed circuit board and to space them apart in such a way that stranded ends of equal length can be used.Further features and advantages of the present invention are explained in more detail below with reference to the figures. The following are shown: FIG. 1 shows a circuit board known from the prior art with three soldering points; FIG. 2 ashows a printed circuit board produced according to the method according to the invention, in an isometric view from below; FIG. 2 bshows the printed circuit board according to FIG. 2 ain a view from above; FIG. 3 ashows the printed circuit board according to FIGS. 2 a, 2 bin a sectional view; FIG. 3 bshows the printed circuit board according to FIGS. 2 a, 2 bin a plan view from below. FIG. 4 shows an embodiment according to the invention with a soldering point at a strand end.FIG. 1 shows a printed circuit board PCB with three solder joints 30 comprising an electronic circuit 60 on at least one upper side, wherein the middle solder joint 30 is arranged offset on the center line M due to the small width B of the printed circuit board PCB. For this arrangement of the solder joints, the strands of the connecting cable AK must be provided and stripped to different lengths. This is possible manually, but from a manufacturing standpoint only with very great expense or in principle not at all. In addition, such a soldered connection would be only of little load-bearing capacity.FIGS. 2 aand 2 b show different views of a printed circuit board PCB produced according to the method according to the invention. The printed circuit board PCB is connected to a lead cable AK. The connecting cable AK has a cable sheath 20 and three strands. The printed circuit board PCB has a width B perpendicular to a center line M, which perceptibly does not allow an arrangement of three solder joints next to one another.FIG. 2 ashows a top view of the underside of the printed circuit board PCB comprising an electronic circuit 60 on at least one top side, where a first strand end protrudes and is soldered at a first solder location. For this purpose, a bore 50 is provided in the printed circuit board PCB, which lies on its center line M.FIG. 2 bshows a top view of the top side of the printed circuit board PCB, where a second and third strand end is soldered at a second and third solder location. The second and third solder joints are located side by side symmetrically to the centre line M of the printed circuit board PCB.FIG. 3 ashows a sectional view according to FIGS. 2 a, 2 b, where a first strand end is deflected by 90° to the connection cable AK and is guided through the bore 50 so that the end of the strand 15 protrudes at the underside of the printed circuit board PCB. By this arrangement, the connection can absorb higher tensile forces, so that the connection cable AK is more firmly connected to the printed circuit board PCB.FIG. 3 bshows a plan view of a bottom side according to FIGS. 2 a, 2 b. The bore 50 lies on the center line M. A stranded end is guided through the bore, which stranded end penetrates the printed circuit board and protrudes at the underside of the printed circuit board PCB. The bore surrounds a solder joint to which the strand end is soldered. The end of the stranded wire is firmly connected to the printed circuit board PCB by the soldering.FIG. 4 shows a further embodiment according to the invention. In this case, the end of the stranded wire which is guided through the bore 50 is not soldered to the printed circuit board PCB on the underside of the printed circuit board PCB, but a soldering point 40 which is greater than the bore diameter is attached to the end of the stranded wire. The solder pad 40 is not soldered to the printed circuit board PCB. This has the advantage that a tensile force acting on the connecting cable AK is initially absorbed by the static friction which exists between the strands and the cable sheath 20, is thereby attenuated, and as a result the strands are subjected to a lower tensile force. Since the soldering point 40 is made larger than the diameter of the bore 50, the soldering point 40 acts like an anchor in the case of a tensile force on the connecting cable AK. As has surprisingly been shown, the assembly with the soldering point 40 at the braid end can absorb a greater tensile force than if the braid end is firmly soldered to the printed circuit board PCB.Before soldering, the end of the first strand must be passed from the top side of the printed circuit board PCB through the bore 50 so that the end of the strand protrudes at the bottom side of the printed circuit board PCB.Subsequently, stranded wire ends can be soldered.Before the first strand is passed through the bore 50, all three strand ends can be laid side by side in parallel in order to make it visible that all three strand ends are of equal length and stripped over the same length.The individual process steps are given below:In a first method step, the three similarly long stranded ends of the connecting cable AK are stripped off in an automated manner. Then, one of the three strands is passed from an upper surface of the printed circuit board PCB through the hole 50 provided in the printed circuit board PCB. The end of this braid projects somewhat from the underside of the printed circuit board PCB. Subsequently, either all three strand ends are soldered, or only the second and third strands 15 on the upper side are soldered.In a further embodiment, the first stranded wire 15 is passed through the bore 50 and is not soldered to the printed circuit board PCB on the underside of the printed circuit board PCB. For this purpose, a soldering point 40 is applied to the end of the stranded wire in a further step, which soldering point is larger than the bore diameter. The solder pad 40 is not soldered to the printed circuit board PCB.The soldering method according to the invention can be carried out in an automated manner.Due to the stranded wire end deflected by 90° and anchored, the soldered connection can be loaded considerably against tension on the cable.List of reference characters15 Strands 20 Cable jacket 30 Soldering point 40 Soldering point 50 Bore 60 Electronic circuit AK Connecting cable B Width of the printed circuit board M Center line of the printed circuit board PCB printed circuit board

Claims

Method for producing a fixed connection between a printed circuit board (PCB) and a connecting cable (AK), wherein the connecting cable (AK) has a cable sheath (20) and three strands (15), wherein the printed circuit board (PCB) has a width perpendicular to a centre line (M) which does not allow an arrangement of three soldering points next to one another, characterized bythe following method features: a.) Automatic stripping of three similarly long stranded ends of the connecting cable (AK); b.) passing a first of the three strands (15) from a top surface of the printed circuit board (PCB) through a bore (50) provided in the printed circuit board (PCB) and lying on the centre line (M) of the printed circuit board (PCB), so that the end of the strand (15) protrudes from the bottom surface of the printed circuit board (PCB); c.) soldering the strand ends of a second and a third strand (15) on the upper side at a second and a third solder location which are located next to one another symmetrically with respect to the center line (M); d.) Soldering the first strand end at a first solder location provided on the opposite bottom side of the printed circuit board (PCB).

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