Device and Method for Connecting a Printed Circuit Film

The present invention pertains to a connecting assembly and method of connection for a printed circuit with a flexible carrier film on which strips are applied as conductors or resistors and, in particular, to such connecting apparatus where the film conductors are connected to a terminal strip connector and are connected through a resistor to a voltage supply.

A keyboard matrix is described in ELEKTRONIK, 1979, pp. 39, 40. All column conductors are connected to terminals and a supply voltage is applied to them via resistors. It is thus provided that the column conductors are under the supply voltage when the keys are not actuated. This circuit can be realized in different ways. For example, the resistors through which the voltage is supplied can be arranged on a separate carrier plate and be connected with the terminal strip. This would be expensive, because the circuit of the key matrix or the circuit of the resistors would have to be separately prepared and the two separate parts of the circuit would each have to be connected to the common terminal strip. Further, it would be undesirable to integrate the resistor circuit on the carrier of the key matrix, because crossings would occur.

The object of the present invention is to provide connection apparatus for a flexible printed circuit film which is easy to prepare, and which enables connecting a resistor circuit part to a conductor circuit part without crossings, while at the same time enabling the conductors of the conductor part to be connected to a terminal output element.

It is another object to provide an improved method of supplying voltages to conductors on a printed circuit film of the type used in keyboards, which method also enables connecting such conductors to output connections pins, the method achieving the desired connections without any crossings on the printed circuit.

The above objects are achieved by a flexible carrier film, or equivalent printed circuit, the film having a first part containing a plurality of conductor strips and a second integral part which contains a plurality of resistor strips for supplying voltages to the conductors. A grid of connection strips, preferably also resistor strips, is positioned between and connected to the conductor strips and the resistor strips, the grid having the same spacing as a grid of connection clamps on a terminal connector. A score line is provided through the connection strips, enabling the film to be folded upon itself and inserted into the terminal connector so that each connection strip is clamped on both sides of the same line. The clamps are in electrical connection with connection pins. A common conductor line leads from the resistor strips to another connection strip on the score line which is also clamped and thus connected to a pin, whereby a supply voltage can be provided. There is thus achieved a simple but efficient manner of providing electrical connection of a plurality of conductors on a film to free ends of connecting pins mounted in a terminal element, as well as providing a supply voltage through the same terminal element.

Both parts of the circuit can be applied on the same side of the film without crossing, in a simple manner. Due to the folding of the film, connection points which are located between the parts of the circuit become accessible for insertion into the terminal element.

In the preferred embodiment of the present invention, a straight score line is located in a zone in which the connection strips extend at an angle of 90.degree. to the score line. The terminal strips preferably extend over both parts of the film, i.e., to each side of the score line. Uncertain contacts due to possible defects in the strips at the bend are thus avoided.

In a preferred embodiment of the present invention, the connector strips comprise resistor strips, and the score line intersects these resistor strips so that the part of each said resistor strip located on one side of the score line has approximately the same length as the part which is located on the other side of the score line. It is thus achieved that the terminal element, or terminal strip, contacts resistor strips rather than conductor strips. This is favorable, because the resistor strips are more resistant to the conditions occurring during the operation.

In an improved variant of the present invention, the connection resistor strips and the resistor strips joining them on one part of the film consist of the same resistor material. Thus, in practicing the method of the invention, it is possible to prepare all resistor strips in a single printing operation. The connection resistor strip and the second resistor strip can form a continuous resistor strip in this case, such that there are no conductors between the resistor strips. To prepare the circuit of this invention, in which a supply voltage is applied to the connecting strips via the second resistor strips, according to the present invention, the poles of the second resistor strip which are remote, or distal, from the connection strip are connected with a common conductor strip which also leads to the terminal strip.

The preferred embodiments of the present invention are illustrated by the following drawings:

FIG. 1 shows a perspective view of the connection apparatus of this invention.

FIG. 2 shows details of the printed film, the film being non-bent.

A flexible carrier film 1 is printed with conductor strips 2 through 8. A first group of connection strips comprising resistor strips 9, 10, and 11 are located between the conductor strips 2 and 5, 3 and 6 and 4 and 7 respectively. A second group of resistor strips 12, 13, and 14 are connected to connection strips 5-7 respectively, and at their opposite ends to common conductor strip 8. The conductor strip 8 is led to a connection strip 15, also preferably a resistor strip. The resistor strips 9 through 15 are printed in a single printing operation using the same resistor paste.

The resistor strips 9, 10, 11, and 15 are parallel to each other and have the same spacing as the connection pins 16 of a terminal strip 17. The conductor strips 2, 3, and 4 lead to connection points (not shown) of a matrix keyboard.

The carrier film 1 is bent by 180.degree. in the direction of the arrow P (FIG. 2) along a score line 18, as seen also in FIG. 1. The score line 18 extends centrally through the resistor strips 9, 10, 11, and 15 and is preferably at an angle of 90.degree. to the longitudinal extension of the resistor strips.

The connection pins 16 are provided with clamps 19 held in the terminal strip 17, which said clamps hold the strips 9, 10, 11, and 15 on both sides of the score line 18. The clamps 19 bridge over the score line 18, providing mechanical and electrical contact on each side. The free ends of pins 16 are available for connection as desired.

As illustrated, two film parts 20 and 21 are formed by bending the film 1. The circuits of these film parts can be electrically connected to the resistor strips 9, 10, 11, and 15 via the connection pins 16. As is apparent, this does not require any crossing of the conductor strips or resistor strips.

Simple contacting by insertion of the bent film into the terminal strip 17 is possible due to the fact that the conductor strips 2 through 8 and the resistor strips 9 through 15 on the film parts 20 and 21 are located on the outside, i.e., on the sides of the film parts 20 and 21 turned away from each other. It is thus seen that a simple but efficient means and method is provided for connecting the conductors to the terminal strip, and for connecting voltage through resistors to each of the conductors. It is to be understood that the invention as illustrated shows the preferred geometry of the conductors, strip resistors, and score line, but that variations may be utilized within the scope of the invention.