Flexible Printed Board

Abstract

Flexible printed board, in particular for the spatial connection of electronic components, comprising a carrier foil (1), several bonding surfaces (10) arranged on the carrier foil (1), several soldering surfaces (2) arranged on the carrier foil (1), which soldering surfaces (2) are connected to the bonding surfaces (10) via electrical strip conductors, and a stiffening plate (3) that is inseparably connected to the carrier foil (1), wherein the soldering surfaces (2) and the stiffening plate (3) are arranged on a solder side (4) of the carrier foil (1) and the bonding surfaces (10) are arranged on a bonding side (12) that is arranged opposite the solder side (4).

Description

The invention relates to a flexible printed board, in particular for the spatial connection of electronic components.

Printed boards are known as carriers made of insulating material with firmly adhering conductive connections, wherein a printed board serves to mechanically attach and electrically connect electronic components. It is also known that the freedom of the designing of printed boards can be increased by using a flexible carrier material. So-called flexible printed boards can be arranged in a space-saving manner by folding them in an available limited installation space.

For establishing connections to electronic components, bonding surfaces and soldering surfaces are arranged on a flexible printed board. The bonding surfaces and the soldering surfaces are attached to a top of a flexible printed board in an expensive manufacturing process. The increasing miniaturization of electronic devices and a reduced available installation space for flexible printed boards that results from said miniaturization as well as new mounting and joining methods require flexible printed boards that are designed in such a manner that the top and a bottom arranged opposite the top are contactable.

It is also known that a flexible printed board can be contacted on both sides by bending a flexible printed board contacted on one side by 180° and by subsequent conglutination. Such flexible printed boards are expensive on account of the bending operation and the cold-bonding operation that have to be carried out manually. Furthermore, the durability of the cold-bonded joint in the bent region of the flexible printed board is not guaranteed, particularly under the influence of temperature. A highly reliable flexible printed board contacted on both sides will be achieved by a double-layer design of two flexible printed boards each of them being contactable on one side thereof, wherein a non-contactable surface of the first board and a non-contactable surface of the second board are conglutinated. Such a flexible printed board is expensive since two flexible printed boards each of them being contactable on one side thereof are used for the manufacturing of said flexible printed board.

The object of the present invention is to provide a flexible printed board reliably and cost-effectively in such a manner that electronic components can be contacted on both sides of the flexible printed board.

This object is achieved according to the invention by a flexible printed board with the features indicated in claim 1.

According to the invention it was realized that a flexible printed board can be contacted on both sides when soldering surfaces are arranged on a solder side of a carrier foil of the flexible printed board and bonding surfaces are arranged on a bonding side of the carrier foil, which bonding side is arranged opposite the solder side. Such a design of the flexible printed board enables the flexible printed board to be manufactured cost-effectively and reliably since expensive material and manufacturing as well as a stability-critical bending process can be avoided.

A carrier foil according to claim 2 ensures a protection of an electrically conductive layer by means of covering layers attached to both sides thereof.

A design of a covering layer according to claim 3 allows, on the one hand, a good connection of the covering layer to an electrically conductive layer and guarantees, on the other hand, a sufficient protection of the electrically conductive layer.

A protective layer according to claim 4 can be manufactured in a cost-effective manner.

An electrically conductive layer according to claim 5 is characterized by a high electrical conductivity.

A flexible printed board according to claim 6 allows an improved freedom of the designing of the arrangement of the flexible printed board.

A flexible printed board according to claim 7 allows the connection of electrical contacts that are not arranged level with each other.

A removal of the covering layers according to claim 8 serves to connect a contacting layer to an electrically conductive layer.

A contacting layer according to claim 9 is insensitive to thermal stress and resistant to moisture.

A flexible printed board according to claim 10 facilitates a connection of electronic components to a flexible printed board by means of soldering.

A check of the properties of a flexible printed board is possible by the arrangement of test surfaces according to claim 11.

A flexible printed board according to claim 12 has a symmetric design with respect to its contact surfaces.

In the following, exemplary embodiments of the invention will be explained in greater detail on the basis of the drawing in which:

FIGS. 1 and 2 show perspective views of a flexible printed board; and

FIG. 3 shows a schematic representation of a layer design of a flexible printed board that is contactable on both sides.

FIG. 1 shows a flexible printed board with a carrier foil 1, with several soldering surfaces 2 and with a stiffening plate 3 that is inseparably connected to the carrier foil 1. The soldering surfaces 2 and the stiffening plate 3 are arranged on a solder side 4 of the carrier foil 1. The carrier foil 1 is punched in sections, wherein a hole area 5 and a soldering surface 2 are arranged concentrically with each other and wherein the soldering surface 2 is larger than the hole area 5. The soldering surface 2 and the hole area 5 that is arranged concentrically with the soldering surface 2 form an annular soldering contact surface 6 that has a contacting layer 7. For establishing an electrically conductive connection, the contacting layer 7 of a soldering contact surface 6 is connected to an electrically conductive layer 8 of the carrier foil 1. The carrier foil 1 is essentially rectangular. The soldering surfaces 2 are arranged along a soldering-surface edge 9 of the carrier foil 1, wherein a distance between the soldering surfaces 2 and the soldering-surface edge 9 is as big as the diameter d of the circular soldering surfaces 2. Rectangular bonding surfaces 10 are arranged along a bonding-surface edge 11 that is arranged opposite the soldering-surface edge 9. The bonding surfaces 10 are arranged centrally with respect to the stiffening plate 3 that is arranged on the opposite surface of the carrier foil 1. The bonding surfaces 10 are connected to the soldering surfaces 2 via electrical strip conductors.

FIG. 2 shows a bonding side 12 of the carrier foil 1, which bonding side 12 is arranged opposite the solder side 4. Bonding surfaces 10 and test surfaces 13 are arranged on the bonding side 12 of the carrier foil 1. The bonding surfaces 10 serve to contact a bonding wire on the flexible printed board, wherein the stiffening plate 3 arranged opposite the bonding surfaces 10 ensures a sufficient stability as a result of mechanical action of a bonding process. The test surfaces 13 serve to check the properties of the flexible printed board, wherein a test surface 13 is a bonding surface 10 that is not connected to a soldering surface 2. The bonding surfaces 10 and the test surfaces 13 each have a contacting layer 7. This applies to a contacting layer 7 on a soldering surface 2 as well as to a contacting layer 7 on a bonding surface 10.

FIG. 3 shows a carrier foil 1 that is inseparably connected to a stiffening plate 3 by means of an adhesive layer 14. The carrier foil 1 has a centrally arranged electrically conductive layer 8 as well as an upper covering layer 15 and a lower covering layer 16. Each of the two covering layers 15, 16 comprises an adhesive layer 14 and a protective layer 17, wherein each of the covering layers 15, 16 is connected to the electrically conductive layer 8 by means of the adhesive layer 14. The upper covering layer 15 is removed, in sections, for producing soldering surfaces 2 on a solder side 4, and a lower covering layer 16 is removed, in sections, for producing bonding surfaces 10 on a bonding side 12, thereby enabling a contacting layer 7 to be arranged directly on the electrically conductive layer 8 so that there is an electrical contact between the contacting layer 7 and the electrically conductive layer 8. The contacting layer 7 is preferably made of a nickel-gold compound, wherein the layer thickness of the contacting layer 7 is less than 20 μm, in particular less than 10 μm and in particular less than 5 μm. The electrically conductive layer 8 is a copper foil and has a layer thickness of 50 to 200 μm, in particular of 70 to 100 μm. Polyimide with a layer thickness of less than 100 μm, in particular of less than 50 μm and in particular of less than 25 μm, is used for the protective layer 17. An acryl-based adhesive agent, e.g. Pyralux®, with layer thicknesses of less than 100 μm, in particular of less than 50 μm and in particular of less than 25 μm, is used as the adhesive layer 14. The stiffening plate 3 is made of aluminium or of one of its alloys. The thickness of the stiffening plate 3 is between 1 and 4 mm, in particular between 2 and 3 mm.

Claims

1. Flexible printed board, in particular for the spatial connection of electronic components, comprising a carrier foil (1),several bonding surfaces (10) arranged on the carrier foil (1),several soldering surfaces (2) arranged on the carrier foil (1), which soldering surfaces (2) are connected to the bonding surfaces (10) via electrical strip conductors, anda stiffening plate (3) that is inseparably connected to the carrier foil (1),

2. Flexible printed board according to claim 1, characterized in that the carrier foil (1) has an electrically conductive layer (8) that is surrounded by an upper covering layer (15) towards the solder side (4) and by a lower covering layer (16) towards the bonding side (12).

3. Flexible printed board according to claim 2, characterized in that each of the covering layers (15, 16) has an adhesive layer (14) and a protective layer (17), wherein each of the covering layers (15, 16) is attached to the electrically conductive layer (8) by means of the adhesive layer (14).

4. Flexible printed board according to claim 3, characterized in that the protective layer (17) is a synthetic material, in particular polyimide.

5-12. (canceled)

13. Flexible printed board according to claim 3, characterized in that the electrically conductive layer (8) is a copper foil.

14. Flexible printed board according to claim 1, characterized in that the carrier foil (1) is essentially a rectangle, wherein the soldering surfaces (2) and the bonding surfaces (10) are arranged on two respectively mutually opposite edges (9, 11) of the rectangle.

15. Flexible printed board according to claim 1, characterized in that the carrier foil (1) is not plane.

16. Flexible printed board according to claim 2, characterized in that the covering layers (15, 16) of the carrier foil (1) are removed or missing in sections and that a contacting layer (7) is provided there.

17. Flexible printed board according to claim 16, characterized in that the contacting layer (7) consists of a nickel-gold compound.

18. Flexible printed board according to claim 1, characterized in that the carrier foil (1) is punched in sections, that a hole area (5) and one of the soldering surfaces (2) are arranged concentrically with each other, and that the soldering surface (2) is larger than the hole area (5).

19. Flexible printed board according to claim 1, characterized in that at least one test surface (13) for checking the properties of the flexible printed board is arranged on the carrier foil (1), wherein the test surface (13) is an additional bonding surface (10) that is not connected to a soldering surface (2).

20. Flexible printed board according to claim 19, characterized in that the number of soldering surfaces (2) equals the sum of the number of bonding surfaces (10) and the number of test surfaces (13).