This invention relates to a flexible printed circuit board with components mounted only on one side of the board.

In particular, it relates to such a flexible printed circuit intended to constitute part of a catheter.

Background

It is difficult to mount components on both sides of a flexible printed circuit board (FPC). The reason is that a complex jig normally is needed for component mounting on the back side after mounting on the opposite side.

When an FPC is used in a catheter, it is usually desirable to have the circuit board as narrow as possible to minimize the diameter of the catheter. In some types of catheters, it is also desirable to mount a large number of sensors while maintaining a small diameter. Normally double sided FPCs are used, i.e. FPCs with conductor lines on both sides and components mounted on one side.

Such a printed circuit board mounted with sensors or other components can be used to manufacture a catheter by pulling the board into a tube with holes in the tube wall. The holes are positioned to align with the sensor positions on the circuit board. This enables the sensors to measure physical quantities in the environment, e.g. pressure and temperature, through these holes. A problem with flexible printed circuit boards in catheters is that the boards need to be very long with a small width in order to fit within narrow diameter lumina of the catheter. A large length and a narrow width is something that is difficult and sometimes impossible for FPC manufacturers to manufacture.

It would therefore be very advantageous if a simple method could be developed for transforming an FPC of a certain width with components mounted on one side into a form with smaller width since it would enable manufacture of catheters with smaller diameters.

One objective of the invention is to provide a flexible printed circuit board with components mounted only on one side, which may be transformed into an element with a smaller width and with components on both sides. A major benefit is that despite having more components mounted on the boards, they could still fit into narrow catheter tubing. Another reason may be that such mounting permits direction sensitive detection of different parameters. These and other objectives are achieved by a flexible circuit board according to the characterizing parts of the independent claim.

Summary

The invention relates to an elongated flexible printed circuit la-b with the wiring pattern 2, 5 on at least one of its sides. Components 3a-d are mounted only on one side of the board and the board la-b is folded along at least one parting line 4a-c so as to form a mainly flat element having a top and a bottom, where the components are situated only on the element's top and bottom. In this fashion, the components may be mounted on one side of the board only, but after folding a double-sided element is achieved.

The circuit board la-c is folded along at least a first dividing line 4a-c, such that it forms an elongated, substantially flat element where further the first dividing line 4a-c extends essentially parallel to the lengthwise extent of the element. The circuit board la-c may be folded along secondary dividing line 4a-c, each of which is parallel to the first dividing line 4a-c,

In one advantageous embodiment, the dividing line 4a-c is provided with fold indications, for example in the form of perforations through the FPC.

In a further embodiment at least one dividing line 4a-c divides the board into two portions, where the two portions are of different length.

The invention further discloses such a flexible circuit board which is intended to form part of a catheter. Typically, the printed circuit board is at one end provided with electrical connector elements 5 used to provide electrical connection between the catheter and other

instrumentation.

Brief description of the figures

Fig. 1 shows a first embodiment of the invention in a flat state Fig. 2 shows a cross section through the first embodiment in a folded position Fig. 3 shows a second embodiment of the invention in a flat state Fig. 4 shows a cross section through the second embodiment in a folded state Fig. 5 shows a third embodiment of the invention in a flat state

Fig. 6 shows a cross section of the third embodiment in a folded state

Fig. 7 shows a catheter with a flexible circuit board according to the invention

Fig. 8 shows a cross section through the catheter along the line A-A according to a first embodiment

Fig. 9 shows a cross section through the catheter along the line B-B according to a first embodiment

Fig. 10 shows a cross section through the catheter along the line A-A according to a second embodiment

Fig. 11 shows a cross section through the catheter along the line B-B according to a second embodiment

Description of preferred embodiments

The embodiments show flexible printed circuit boards provided with copper patterns on both sides. In the figures only the copper pattern on one side of the boards is illustrated, as only one side of the FPC is exposed to the viewer. On the FPCs, components have been mounted only on one side of the flexible circuit boards. All embodiments are depicted with the circuit boards in a position which illustrates that the electronic components are mounted on only one side of the FPC, and in a folded position where the components after folding are directed opposite to each other. Obviously, the boards may comprise only one pattern layer or more than two pattern layers, but the components are still only mounted only on one side of the boards.

Fig. 1 shows a first embodiment of the invention with a circuit board la in a flat position, i.e. layed out on a flat surface for mounting components. The board is provided with a copper pattern 2 forming the electric conductors and solder pads connecting the first end of the board with the components 3a-b, distributed over the board's upper surface, which is facing the viewer of the figure. The board's first end is the most distant from the viewer's perspective, i.e. in the upper right part of the figure, and is the end that connects to different types of measuring instruments or devices that supplies power to or generates control signals to the board. On the board's first end, the conductor lines 2 connect to connector pads 5 of copper or other conductive material that allow easy connection to a suitable connector. The boards also have copper patterns on the rear side of the board, which similarly connects the contact surfaces of the board's first end with components on top of the board by means of via holes, but these are not illustrated in the figure.

On the upper side of the board, two electronic components 3a-b are mounted and connected to the bonding pads on the upper side of the board. On the side of each component facing the board's first end, the component is connected to the bonding pads, which constitute parts of the conductor lines 2 on the upper side of the board. On the side of each component facing away from the board's first end, the component is connected to the bonding pads that by vias are connected to the conductor lines on the bottom of the board, so only viewed from the perspective of the viewer of the figure, these seem not be connected to anything at all, but obviously these are also directly or indirectly connected to contact surfaces on the bottom of board's first end.

The flexible printed circuit board is rectangular and elongated with a dividing line 4 extending parallel to the long side of the board and divides the board into two halves of equal width. The dividing line 4 represents the line along which the board is intended to be folded and can be a completely imaginary line, but the board can of course also be provided with some type of fold indication along this line, for example a series of openings through the board.

Regardless of how the dividing line is embodied, the board is intended to be folded along this line, so that the components 3a-b after folding are facing away from each other. Fig. 2 shows a cross section through the first embodiment in the folded position, which is when the board is folded along the dividing line. The board la is then divided into two halves, which are connected along the folded portion of the board and the board does in cross section have nearly a V-shape. On one of the legs of the V, that in the figure constitutes the upper one, one component 3a is arranged and it extends upwards in the figure, while on the other leg, which in the figure constitutes the lowermost one, the second component 3b is arranged and it extends downwards from the board as shown in the figure, that is opposite of the first component.

The thus folded flexible circuit board with components is for example intended to constitute at least part of a catheter and the components could for example be sensors which measure pressure, temperature, flow rate or others. Since the components faces in opposite directions, the catheter can then carry out measurements in two different directions. The components are also positioned at different locations along the longitudinal extent of the board, so that measurements may also take place at different distance from the first end of the catheter.

Fig. 3 shows a second embodiment of the invention in a flat state. The second embodiment of the flexible circuit board is largely identical to the first embodiment, but differs from it in that the distal portion of the circuit board beyond the electronic component 3 a has been removed. After folding, this reduces the total thickness and makes this part of the folded circuit board more flexible, often a desirable property for catheters.

Fig. 4 shows a cross section through the second embodiment of the circuit board in a folded state, and from the presented view, its looks identical to the cross section through the first embodiment illustrated in fig. 2.

Fig. 5 shows a third embodiment of the invention in a flat state, where the board lb is embodied as if it comprised two boards according to the first embodiments placed along each other, where one is shorter than the other. In total there are three division lines 4a-c in the entire board, separating the board into four elongated portions. The four elongated portions comprise two pairs of portions, where one such portion extends from the end, while the other does not reach all the way to the end. All four portions are contacted to connector pads 5. The arrangement is done in such a way that when the portions are folded, the portion on the top will not block the connector pads on the bottom board. On each of the four portions, components 3a-d are arranged in the same manner as in the first embodiment. They are connected to the bonding pads adjacent to the component and these are connected to the connector pads 5 at the board end. This embodiment too is provided with copper patterns on the lower side of the board, and possibly additional pattern layers if it is a multilayer board, but all components situated only on the upper side of the board, which is the side facing the viewer of fig. 5.

The circuit board is supposed to be folded together in a way that essentially corresponds to the folding procedure for the first embodiment, but three folds in succession are required for this extended board. As seen from the perspective illustrated in fig. 6, each portion is folded n a clock-wise fashion relative to the portion preceding it, such that the board after three folds forms a comparatively flat structure. Fig. 6 shows a cross section through the third embodiment in the folded position, where the four portions form four flat elements, and these are connected to each other along the curved pieces of printed circuit boards which extend along the three fold lines 4a-c. In fig. 6, only two components are shown, one facing upwards and the second facing downwards. The other two components are, from the perspective of the viewer, situated behind each of the component shown and thus face upwards and downwards in a corresponding fashion.

In the illustrated third embodiment, measurement values may be sensed by the catheter at four different distances from the first end of the catheter, with a measurement values sensed on two opposing sides. Components are often distributed in this manner, which makes the number of required conductor lines to increase the closer one gets to the first end of the board, which is beneficial for applications where a large number of sensors or other components are required. The invention solves this in an advantageous fashion.

Further sections can of course be added to the FPC making it successively wider towards the first end but allowing more conductor lines and sensors. The board then has to be folded along a correspondingly larger number of dividing lines, in order to still constitute an essentially flat element with components on the upper and lower sides, despite being produced as a flat element with components on only one side. The limitation is that the total thickness of the folded board cannot be too large and that the structure has to be largely planar.

Fig. 7 shows a simplistic illustration of a catheter 7 internally provided with a flexible circuit board according to the invention. The flexible circuit board is not illustrated, but though holes 8a-d extending from the surface of the catheter to sensor elements mounted on the flexible circuit board are illustrated as dashed circles. The catheter is provided with three electrodes 9a-c that embrace the catheter in a ring-like fashion, and the electrodes are in electrical contact with corresponding sensor elements that sits on the circuit board via the though holes 8a-c.

What in the figure is illustrated as the lowermost sensor element 8d, is constituted by a pressure sensor and no electrode is provided on the catheter here. Cross section through the catheter along a line A-A is shown in figs 8 and 10, and the figure illustrates where in fig. 7 the cross section is taken. Correspondingly, cross section through the catheter along a line B- B is shown in figs 9 and 11, and the figure illustrates where in fig. 7 this cross section is taken. Fig. 8 shows a cross section through the catheter along the line A-A according to a first embodiment. The catheter is provided with a ring electrode 9 and the flexible circuit board lc is arranged in a single lumen inside the catheter, which extends along the length of the catheter. The FPC lc has three conductor lines 2 that are covered by an insulating layer 13 except below the hole 8a-c where the middle conductor has a pad which is exposed and electrically connected to the ring electrode via conducting adhesive 10, e.g. conducting epoxy. The folded flexible circuit board extends from one side of this lumen to the opposite side, which prevents any liquids introduced into the lumen through the hole 8a-c to penetrate to the lower side of the lumen. Flow of liquids in longitudinal directions may be prevented by providing bumps on either side of the conductor pad or by using a glue with sufficiently high viscosity. The adhesive may during production be inserted through the hole 8a-c, the electrode thread onto the catheter to cover the hole 8c and clamped to make electrical contact to the glue and hence to the conductor line.

Fig. 9 shows a cross section through the catheter along the line B-B according to a first embodiment. Here, like in fig. 8, the flexible circuit board extends from one side of the lumen to the opposite, such that fluids may be introduced into the lumen without penetrating into the lowermost half of the lumen. The uppermost part of the lumen is, in a way corresponding that illustrated in fig. 8, filled with silicone 14. The silicone transmits the ambient pressure to a pressure sensor 3d on the upper side of the folded flexible circuit board. In the figure, a second sensor element is illustrated on the lower side of the folded flexible circuit board, which clearly is unaffected by the silicone in the upper half of the lumen.

In cases when a second or more lumens are required in the catheter a second embodiment according to Figs. 10-1 1 can be utilized. Fig. 10 shows a cross section through the catheter along the line A-A of this second embodiment, which differs from the first one illustrated in figs 8-9, in that the lumen 1 1 receiving the folded flexible circuit board is crescent moon shaped, and this leaves room for a second lumen 12, that may be used for purposes other than housing circuit boards. The folded flexible circuit board here also extends between opposite tips of the crescent moon shaped lumen, which gives the same advantages as in the previous embodiment. In a circular lumen, the flexible circuit board may naturally twist along its length, giving problems with angular alignment of the sensor with the hole 8a-d. In the crescent moon shaped lumen, however, the folded flexible circuit board is forced to remain in one give position - rotationally fixed - and the sensor hence aligns perfectly with the hole 8a-d in this respect.

Fig. 1 1 shows a cross section through the catheter along the line B-B according to a second embodiment, where here the sensor element is constituted by a pressure sensor 3d, immersed in silicone. The advantages of the crescent moon shaped lumen are much the same here as those disclosed for the case related to fig. 10.