1. Technical Field of the Invention
This application relates to electrical contacts and, more particularly, to apparatus and a method for making electrical contacts which are bondable to printed circuit boards.
2. Description of the Prior Art
A conventional method for electrically connecting plug-in printed circuit boards to mating backplane connectors utilizes patterned and plated fingers at the board edge. These fingers are usually an extension of the circuit pattern. They are plated with a sequence of metallization layers to provide low contact resistance between the mating parts of the connector over the circuit life.
Another method for providing finger contacts on printed circuit boards is disclosed in H. E. Spooner et al U.S. Pat. No. 3,396,461, issued Aug. 13, 1968. In Spooner et al the contact elements are carried on a common support strip. This strip is positioned over the conductor patterns on the circuit board thereby bringing the contact elements into alignment with the conductor patterns. The contact elements are then bonded to the conductor patterns by welding or soldering after which the common support strip is removed.
Still another method for terminating printed circuit boards utilizes a double-sided piece of adhesive tape to fasten a connector along an edge of the board. This approach to board termination is disclosed in R. D. Nelson, U.S. Pat. No. 3,704,515, issued Dec. 5, 1972. In Nelson the connector contacts are bent at right angles to facilitate engagement with apertures in the printed circuit board. Once the contacts are inserted into the apertures, they are held securely in place by solder.
A somewhat related method for terminating circuit modules is disclosed in C. W. Wallach U.S. Pat. No. 4,044,201, issued Aug. 23, 1977. In Wallach a lead frame assembly includes a pair of spaced-apart, parallel carrier strips with a plurality of collapsible rungs extending between the strips at regular intervals along its length. The rungs are collapsed inwardly to seat against the sides of the circuit module which is positioned between the ends of the leads. After seating, the lead ends are soldered to metallized surfaces on the module. Following bending of the leads, the carrier strips and rungs are cut away.
Apparatus for attaching multiconductor flat cable to an electrical connector is disclosed in W. R. Over et al, U.S. Pat. No. 3,938,246, issued Feb. 17, 1976. The apparatus employs a movable ram which moves through multiple strokes to perform all of the necessary steps. A movable connector holder is utilized so that cables may be attached to opposite faces of the connector by using a single, movable ram. The contacts used in effecting this type of termination are manufactured by punching a thin strip of metal to form individual contacts. Plastic carrier strips are applied to opposite edges of the contacts to provide support after the contacts are severed from their metallic support strip.
None of the aforementioned references addresses the problem of providing protection, support and compliance to the finger contacts during the attachment process and during subsequent handling operations. Moreover, these references do not address the problem of effecting repairs to an individual contact which might be damaged during subsequent usage of the board.
Our invention overcomes these problems because the finger contacts are manufactured separately from the printed circuit board itself. Moreover, our finger contacts can be advantageously mass terminated to a printed circuit board. In addition, the plated contact areas are protected during installation and subsequent handling. By virtue of this approach to solving the aforementioned problems individual finger contacts which may become damaged during subsequent handling or use can be advantageously repaired.
A further aspect of our invention is that finger contacts may be advantageously applied to a printed circuit board at any stage of its manufacture both before and after the components are attached. Further aspects of our invention are that the finger contact strip configuration allows at least two different circuit attachment methods to be employed. In particular, both wave soldering and reflow soldering attachment techniques can be advantageously employed. For wave soldering attachment, the finger contacts are electrically connected to the circuit board during the normal wave soldering operation employed to electrically attach the circuit elements. In addition, the wave soldering option facilitates electrical attachment of finger contacts on both sides of the circuit board even though the printed circuit may appear on only one side of the board. As a result the manufacturing cost of printed circuit boards is significantly reduced.
Another aspect of our invention is that the finger contacts can be advantageously affixed to other areas of a printed circuit board other than along an edge region thereof.