Electrical connector having improved elastomeric contact pressure pad

A high-density electrical connector includes a rigid member having an array of electrical contact pads, a clamp housing attached to the rigid member, and a flexible printed circuit. The flexible printed circuit has a back surface, a front surface and a contact portion having a matching array of electrical contacts protruding outwardly of the front surface of the flexible printed circuit. The contact portion is disposed between the clamp housing and the rigid member and an elastomeric contact pressure pad is disposed between the clamp housing and the flexible printed circuit pressing each of the protruding electrical contacts into one of the electrical contact pads. The elastomeric pad is shaped and resiliently deformed by the clamp housing to provide a substantially uniform contact pressure to the array of electrical contacts.

FIELD OF INVENTION

The present invention relates to electrical connectors and more particularly to electrical connectors employing an elastomeric contact pressure pad to provide good electrical contact pressure between bump or gold dot contacts and their cooperating electrical contact pads.

BACKGROUND OF THE INVENTION

A flexible printed circuit having bump contacts or gold dot contacts is already known from U.S. Pat. Nos. 5,197,184 and 5,207,887 granted to William R. Crumly et al Mar. 30, 1993 and May 4, 1993 respectively.

An electrical connector employing such a flexible printed circuit is also known from U.S. Pat. No. 5,295,838 granted to James R. Whalen et al Mar. 22, 1994. In this electrical connector, the bump contacts or gold dot contacts of the flexible printed circuit are pressed against mating sets of contacts carried by a rigid circuit board by a clamping structure that is bolted to the rigid circuit board. The clamping structure includes an elongated pressure bar that engages the back side of the flexible printed circuit. The pressure bar has a plurality of blind holes aligned with the respective contacts of the flexible printed circuit. Each blind hole receives a compression spring that is compressed between the pressure bar and a pressure bar housing so that the pressure bar presses the electrical contacts of the flexible printed circuit against the mating set of electrical contact pads carried by the rigid circuit board.

“High-density” electrical connectors having raised bump or gold dot electrical contacts on one connector element adjacent a second connector element with electrical contact pads generally require a mechanism for providing compressive force urging the connector elements together to assure that electrical contact is maintained. Among the most successful prior approaches is an approach involving the provision of a spring-type element for maintaining pressure across the contact elements, particularly in combination with some external clamping arrangement as shown for example in U.S. Pat. No. 5,295,838. (Any electrical connector in which the pitch of the electrical contacts is between about 0.020 and about 0.050 mils is generally recognized as a high density electrical connector.)

Recently, the use of an elastomeric pad or layer having individual ridges aligned with each row of raised bumps has been adopted and widely accepted in the high-density connector field. By carefully aligning the ribs with the rows of bumps, reliable engagement force can be assured. A known175way “high density” electrical connector1of this type employing a flexible printed circuit2is illustrated inFIGS. 1 and 2. The flexible printed circuit2shown inFIG. 1thus has 175 closely spaced contacts arranged rank and file with 7 rows of contacts each containing 25 contacts. In this high density electrical connector, an elongated elastomeric contact pressure pad3engages the flexible printed circuit to press the contacts4of the flexible printed circuit against the mating set of contact pads5carried by a rigid printed circuit board6. The elastomeric pad3has twenty-five spaced ribs7that extend laterally across the elastomeric pad. Each rib7is aligned with a short transverse row of contacts and engages the back side of the flexible printed circuit pushing the contacts4against the contact pads5when the flexible printed circuit2and the elastomeric pad3are clamped between a clamp housing8and the printed circuit board6. Clamp housing8is adjusted by machine screws9that screw into attachment portions of the clamp housing8. Screws9pass through aligned locator holes in a stiffener bar9a, printed circuit board6and flexible printed circuit2to align contacts4with contact pads5and the ribs7with the short rows of contacts4.

SUMMARY OF THE INVENTION

This invention provides an electrical connector that has an improved elastomeric contact pressure pad that has been developed specifically for high-density electrical connectors having bump or gold dot type electrical contacts engaging adjacent electrical contact pads.

Particular advantage is provided in bump or gold dot contact electrical connectors where it is desired to provide uniform contact pressure across the array of bump or gold dot contacts.

The elastomeric contact pressure pad preferably includes an arcuate surface on one side engaging the flexible printed circuit providing good contact engagement force without the need for strict alignment of the ribs with the rows of bump-type electrical contacts as in the prior art elastomeric pad discussed above in connection withFIGS. 1 and 2of the patent drawing.

On the opposite side of the elastomeric contact pressure pad, it is also preferable to provide longitudinal ribs having a tendency to increase the forces along the longitudinal rows of bump-type contacts. By placing the longitudinal ribs on the opposite side of the elastomeric pad, greater resiliency is additionally imparted to the overall compression arrangement accommodating a higher degree of shock and/or vibration without causing the electrical contacts to lose their alignment with the electrical contact pads to which electrical connection is desired.

Referring now toFIGS. 3 through 7, a high-density electrical connector10incorporating the invention is disclosed. Electrical connector10comprises a flexible printed circuit12for making an electrical interconnection between an upper printed circuit board14and a lower printed circuit board16.

Printed circuit boards are well known in the art and consequently the printed circuit boards14and16are not shown in detail. Briefly, the printed circuit boards14and16comprise a rigid member or substrate having a pattern of electrical traces that form electrical circuits and electrical contact pads for making electrical connections to the electrical circuits. In this particular instance, the electrical contact pads are arranged in an elongate array of electrical contact pads as best shown inFIG. 3by the electrical contact pads18on the upper surface of lower printed circuit board16. Upper printed circuit board14has a similar array of electrical contact pads on its lower surface (not shown).

Flexible printed circuits are also well known in the art and consequently, the flexible printed circuit12is not shown in detail. Briefly, flexible printed circuit12comprises a flexible ribbon insulator20having a pattern of electrical traces that form electrical circuits and electrical contact pads for making electrical connections to the electrical circuits. In this particular instance, the flexible ribbon insulator20has a front surface22, a back surface24and a contact portion26at each end. Each contact portion26has an elongate array of electrical contacts28that protrude outwardly of the front surface22of the flexible ribbon insulator20, which may be a single layer or a multiple layer laminate as is well known in the art. The protruding electrical contacts28may be bump contacts or gold dot contacts that are described above in the background of the invention.

The two arrays of contacts28may be identical or the arrays may be different. In any event, the elongate array of electrical contacts28at the upper end of flexible printed circuit12always matches the elongate array of electrical contact pads (not shown) on the bottom surface of upper printed circuit board14. On the other hand, the elongate array of electrical contacts28at the lower end of flexible printed circuit (not shown) always matches the elongate array of electrical contact pads18on the upper surface of the lower printed circuit board16.

Electrical connector10includes an adjustable clamp housing30that is attached to the rigid printed circuit boards14and16individually by two sets of machine screws32and34. Clamp housing30has attachment portions36at each end that project vertically in each direction to form upper and lower attachment portions36aand36bfor the respective upper and lower printed circuit boards14and16. The attachment portions36aand36bhave threaded bores to receive machine screws32and34respectively and concentric projecting bosses38aand38bat the outer ends of the threaded bores. As best shown inFIG. 5these bosses project through locating holes40in the contact portions26of the flexible printed circuit12and through locating holes42in the upper and lower printed circuit boards14and16. Thus the projecting bosses38aand38balign the elongate arrays of electrical contacts28of the flexible printed circuit12with the respective elongate arrays of electrical contact pads18of the printed circuit boards14and16when the contact portions26are disposed between the clamp housing30and the respective printed circuit boards14and16as best shown inFIGS. 4 and 6.

Electrical connector10further includes an upper elongate elastomeric contact pressure pad44and a lower elongate elastomeric contact pressure pad46which are made for example of silicone rubber. Upper pad44is disposed between the upper side wall of the clamp housing30(between attachment portions36a) and the contact portion26at the upper end of the flexible printed circuit12pressing each of the electrical contacts28into one of the electrical contact pads18of upper printed circuit board14. Narrow ribs are preferably provided at the longer ends of the upper side wall to locate upper pad44. Lower pad46is disposed in a similar manner between the lower side wall47of the clamp housing30and the contact portion26at the lower end of the flexible printed circuit12pressing each of the electrical contacts28into one of the electrical contact pads18of lower printed circuit board16. Narrow ribs49are also preferably provided at the longer ends of lower side wall47to locate elastomeric pad46.

The typical elongate elastomeric pad46has an arcuate surface48on one side engaging the back surface24of the flexible insulator ribbon20of the flexible printed circuit12and a plurality of longitudinal ribs50on an opposite side engaging the lower side wall47of clamp housing30. The longitudinal ribs50are substantially parallel and the arcuate surface48has an apex52that is substantially parallel to the longitudinal ribs50as best shown inFIGS. 4 and 7. The upper elastomeric pad44has the same shape.

Electrical connector10is assembled by abutting the longitudinal ribs50of elastomeric pad46with the lower side wall47of clamp housing30between attachment portions36bwith the elastomeric pad preferably being located by the narrow ribs49. The lower contact portion26of flexible printed circuit12is then located against the arcuate surface48of pad46by bosses38bengaging in locating holes40. The lower printed circuit board16is then located against the lower contact portion26by bosses38bengaging in its locating holes42. Machine screws34are then screwed into the threaded bores of the lower attachment portions36bof clamp housing30until the elastomeric pad46and the contact portion26of the flexible printed circuit12are clamped securely between clamp housing30and lower printed circuit board16. Electrical connector10may also include an optional stiffener bar54to enhance the rigidity of the lower printed circuit board16in the area behind the elongate array of electrical contact pads.

The position of the clamp housing30with respect to the lower printed circuit board16is adjusted by turning machine screws34. The adjustment is preferably such that the elastomeric pad46is resiliently defomed by the clamp housing30to provide a substantially uniform contact pressure to the elongate array of electrical contacts28of the lower contact portion26that engages the matching elongate array of electrical contact pads18carried by the lower printed circuit board16. This condition is essentially achieved when the arcuate surface48is flattened and the longitudinal ribs50are flattened whereby the opposite sides of the pad46are substantially planar and parallel to each other as best shown in FIG.6. In this regard it should be noted that the outer longitudinal ribs50are initially inside the narrow locating ribs49of clamp housing30as best shown in FIG.4.

The upper elastomeric pad44, upper contact portion26and the upper printed circuit board14are assembled and attached in a like manner by machine screws32. Machine screws32are also used to adjust the position of the upper printed circuit board14with respect to the clamp housing30so that elastomeric pad44is resiliently defomed by the clamp housing30to provide a substantially uniform contact pressure to the elongate array of electrical contacts28of the upper contact portion26that engage the matching elongate array of electrical contact pads carried by the upper printed circuit board14.

It should be noted that the flexible printed circuit engaging surface of elastomeric pad44or46of the invention has an arcuate shape to allow localized force to be distributed down the center portion, at the same time allowing even distribution of forces to be maintained towards the long outer edges of the elastomeric pad, creating an excellent overall electrical connection of the elongated array of contacts to the elongated array of electrical contact pads. The arcuate shape of the elastomeric flexible printed circuit engaging surface allows uniform pressure distribution along the overall region of the perimeter, which allows the flexible printed circuit to maintain an electrical connection whereas the elastomeric pad3of the prior art discussed in connection withFIGS. 1 and 2of the patent drawing, creates heavy forces on the top and bottom ends of the perimeter causing uneven forces aimed towards the center portion

Elastomeric pads44and46are easy to manufacture by extruding, and less costly to produce than the elastomeric pad of the prior art. The elastomeric pads44and46also allow a higher density of electric contacts in flexible printed circuit connections which in turn facilitates providing more input and output contact pads on a printed circuit board in comparison to the prior art electrical connector1discussed above.

The elastomeric pad of the invention eliminates the need for precise location and alignment, unlike the elastomeric pad3of the prior art which relies on direct positioning of ribs under each transverse row of electrical contacts during electrical connector assembly.

The elastomeric pad of the invention reduces connector interface resistance significantly and provides a uniform pattern of contact force distribution for bump or gold dot type contacts because the arcuate flexible printed circuit engaging surface flattens out when compressed causing even distribution of forces. In contrast the type elastomeric pad3of the prior art has a slight dish in each rib, which causes heavier forces in the outer regions and a lighter force located directly down the center region.