US 3850499 A
A contact strip for printed circuit boards, of the type having a row of blade contacts embedded in a plastic strip, each blade contact being provided with a contact leg extending beyond the periphery of the printed circuit board and a connector leg projecting substantially perpendicular to the contact leg and making contact with drilled or stamped contact pads on the printed circuit board. In accordance with the invention there is provided a contact strip, wherein each blade contact is formed in its central area into an approximately semi-circular transition section, the connector leg being substantially tangent to the semi-circular transition section, while the contact leg extends approximately perpendicular to a tangent to the semi-circular transition section.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 Bauerle et a1.
[ 1 Nov. 26, 1974 1 1 CONTACT STRIP  Assignee: Bunker Ramo Corporation, Oak
 Filed: June 1l, 1973 ] App]. No.: 368,632
 Foreign Application Priority Data June 12, 1972 Germany 6722190  US. Cl 339/156 R, 339/17 E, 339/218 M  Int. Cl H0lr 13/50  Field of Search 264/275-277; 339/94 R, 94 M, 102, 154-157, 218, 198 E, 17 LC, 17 E  References Cited UNITED STATES PATENTS 2,864,977 12/1958 Witt et a1 339/17 LM 3,111,352 11/1963 Theodoseau 339/30 3,208,026 9/1965 Ruehlemann 339/17 LC 3.315.217 4/1967 Bauerle et a1 "33 /176 MP 3,330,004 7/1967 Cloyd ct a1. 264/275 3,539,974 11/1970 Berg 339/157 R 3,649,957 3/1972 Baluck 339/17 LC 3,742,427 6/1973 Ballard 339/61 M FORElGN PATENTS OR APPLICATlONS France 339/157 R Primary ExaminerPaul R. Gilliam Assistant Examiner-Lawrence J. Staab Attorney, Agent, or FirmNort0n Lesser; F. M. Arbuckle  ABSTRACT A contact strip for printed circuit boards, of the type having a row of blade contacts embedded in a plastic strip, each blade contact being provided with a contact leg extending beyond the periphery of the printed circuit board and a connector leg projecting substantially perpendicular to the contact leg and making contact with drilled or stamped contact pads on the printed circuit board. In accordance with the invention there is provided a contact strip, wherein each blade contact is formed in its central area into an approximately semi-circular transition section, the connector leg being substantially tangent to the semicircular transition section, while the contact leg extends approximately perpendicular to a tangent to the semi-circular transition section.
7 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a contact strip for printed circuit boards, of the type having a row of blade contacts embedded in a plastic strip, each blade contact being provided with a contact leg extending beyond the periphery of the printed circuit board and a connector leg projecting substantially perpendicular to the contact leg and making contact with drilled or stamped contact pads on the printed circuit board.
2. Description of the Prior Art Contact strips are known in which both legs of the blade contact are straight sections joined at a right angle so that the resulting edge is only slightly rounded, if at all. Further, only a relatively short section of the blade contact is embedded in the plastic material of the strip. This results in a relatively small area at which the plastic material bears against the contact. Consequently, relatively high load forces are produced when the contact strip is inserted. This, in turn, may break off pieces of plastic material, particularly when the contacts are not inserted in precise alignment along the longitudinal direction of the contact strip. Of course, longer blade contacts could be used with an associated expansion of the'dimensions of the plastic strip. However, serious weight, space and cost problems would be encountered utilizing such a design.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an improvement over the prior art contact strips, and in particular to provide a simple contact strip of the above-described type, in which blade contacts are easily embedded and firmly secured to the embedded portions of the plastic strip.
In accordance with the invention, each blade contact has a contact leg for external connection and a connector leg for connection to the printed circuit board, the two legs disposed at approximately semi-circular transition section. In a preferred embodiment, the connector leg is substantially tangent to the semi-circular transition section, while the contact leg is bent away from the semi-circular transition section at an obtuse angle.
The bent transition section formed as indicated above increases the area over which the contact is embedded in the plastic material and provides contact surfaces extending in continuously changing directions to anchor the blade contact firmly in place. This configuration is advantageous for transferring the load from the blade contact to the connector body when the contact strip is inserted in a mating connector means. Further, such configuration also eliminates sharp angles in the blade contact and surrounding plastic so as to prevent cracking at the joints of the legs and to prevent protrusions at the plastic strip from being torn off when the contact leg is inserted in inclined position or when the contact leg experiences vibratory loads. In addition, the semi-circular transition section facilitates embedding of the contacts in the plastic strip, since the plastic material easily flows into the arcuate inner section of the contact.
The angle between the transition section and the contact leg is preferably obtuse. In contradistinction to a prior art blade contact having a connector leg bent at right angles to the contact leg, the configuration of the present invention provides an inclined contact area between the blade contact and the plastic strip within the area which sustains the axial or almost axially directed insertion pressure (pressure initially exerted upon the contact leg.) Because of the increased area about the contact, the load is resolved into longitudinal and transverse components and, hence, distributed over the plastic body.
In some embodiments of connector strips, it is desirable to design the blade contact having a connector leg with a thickness and/or width differing from that of the contact leg. In accordance with the present invention, such embodiments are easily accommodated by arranging the transition regions of the blade contact to lie within the embedded portion of the connector strip. Thus, an additional advantage of the present invention lies in the feature that areas prone to shearing or rupture are embedded in the plastic material and, hence, are supported by the same. Moreover, the additional length of contact embedded in the plastic improves the support rendered to the blade contacts by the plastic strip.
The dimensional changes in size of the blade contacts between the transition region and the connector leg and contact leg can be effected in simple fashion, namely, providing abrupt shoulders at the desired transition areas. Such transition areas also function to aid in attachment of the blade contact with the plastic strip near the entry or exit points of a leg.
The blade contact in accordance with the invention is embedded into a plastic contact strip having a substantially T-like cross-section in the support area of the blade contact. One arm of the T and the central stem of the T are enlarged in cross-sectional dimension so as to accommodate the transition portion of the blade contact. The other arm of the T and the lower part of the T stem are reduced in cross-section in order to conserve materials and lower the weight of the connector strip. The contact leg of the blade contact extends perpendicular from approximately central of the thick arm of the T, while the connector leg extends substantially perpendicular to the thickened portion of the stem of the T. The entire transition section of the blade contact, including the points of dimensional changes on the blade contact, is therefore everywhere surrounded by thickened plastic material. This eliminates the need for a heavy plastic strip in all dimensions, thus reducing weight and avoiding excessive unnecessary costs of raw material.
BRIEF DESCRIPTION OF THE DRAWING The invention willnow be described in detail with reference to the accompanying drawings representing preferred embodiments of the contact strip according to the present invention. In the drawings:
DESCRIPTION OF THE PREFERRED EMBODIMENTS The contact strip, generally denoted by 1, consists of a plastic body or strip 2 and blade contacts 3 embedded in the plastic strip. The cross-section of plastic strip 2 can be inferred from FIG. 2. The cross-section of the strip itself is shown in the general form of an inverted T-like member having two arms 2c, 2d and a stem 2a. At the bottom of the stem 2a of the T, the plastic strip defines a transverse protrusion 2b which aids in providing structural support for the strip. The stem 2a comprises a reduced section 7 and a thickened section 8, while the arms of the T are defined by a relatively thin arm 20 and a relatively thick arm 2d. The stem 2a and the arms 20 and 2d form elongate narrow transverse walls with each wall having a major cross-sectional dimension transverse to the major cross-sectional dimensisn of the other wall and plurality of spaced blade contacts 3 are embedded in the plastic strip longitudinally of the same.
Each blade contact 3 is provided with a contact leg 4, a connector leg 5, and a semi-circular transition section 6. The contact leg 4 may end in a knife-like tip 4a. Connector leg 5 may be tapered at its free end 5a.
As can be inferred from FIG. 2, contact leg 4 has a greater thickness than connector leg 5 or has a crosssectional dimension different from the corresponding cross-sectional dimension of leg 5. Moreover, as can be inferred from FIG. 3, contact leg 4 is wider than connector leg 5 or has a second cross-sectional dimension different from the second cross-sectional dimension of leg 5. Transition section 6 has the width of the contact leg 4 and the thickness of the connector leg 5. The dimensional changes occur at transition regions or junctions between the two legs 4, 5 and in the transition section 6, as denoted at points 10 and 11 on the contact 3. Transition region 10 accommodates a change in width of the blade contact 3, while transition section 1 l accommodates a transition in thickness between the contact leg 4 and the transition region 6.
Connector 5 converges into transition section 6 in the form of a tangent to the semi-circular configuration of transition section 6, whereas the contact leg 4 and the adjacent portion of the transition section 6 enclose an obtuse angle. Each blade contact 3 is embedded in plastic strip 2 along the entire transition section 6 and at the junctions of the transition section with the two legs. The embedded portion of the transition section is continuously embedded in the walls defined by stem 2a and arms 2c and 2d, as may be seen in FIG. 2 and the transition section extends along an are having a portion following the major cross-sectional dimension of each wall so that it is entirely situated within the thickened portion 8 of the stem of the T-shaped member and within the thick arm 2d of the T to distribute a portion of the forces occurring on insertion of the blade contact legs in respective socket contacts along the major cross-sectional dimension of each wall. The thickened arm 2d of the T, as shown in FIG. 2, protrudes in the same direction as the connector leg 5.
The arrangement of blade contacts 3 within the plastic strip 2 allow for a close proximity of the plane of contact leg 4 and the plane of the printed circuit board. FIG. 2 clearly illustrates this point and also shows the alignment of the contact leg 4 along the inner edge of the end walls 9 of the connector strip. Such an arrangement is not possible with prior art blade contacts having simple right angle configurations.
From the foregoing, it can readily be realized that this invention can assume various embodiments. For example, the blade contacts 3 can have uniform dimensions or additional dimensional changes than those shown in the drawings and described in the above description. Depending upon the particular application to which the connector strip is applied, the cross-section of the plastic strip can vary within wide limits, as long as sufficient space for embedding the transition section is taken into account. Thus, it is to be understood that the invention is not limited to the specific embodiments described herein, but is to be limited only by the appended claims.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
l. A contact strip for use with a plurality of socket contacts carried by a printed circuit board comprising:
a plastic body having a pair of integrally formed elongate transverse narrow walls with each wallhaving a minor cross-sectional dimension and a major cross-sectional dimension with the major crosssectional dimension of one wall extending in a respective direction transverse to the major crosssectional dimension of the other wall;
a plurality of spaced blade contacts, each of said blade contacts including an integrally formed contact leg at one end of the respective blade contact with each contact leg extending in one direction from one wall of said body;
a connector leg integrally formed at the other end of each blade contact extending in another direction substantially perpendicular to the respective contact leg and from the other wall of said body;
and a substantially semi-circular transition section extending along an are having a portion following the major cross-sectional dimension of each wall and integrally formed between the connector leg and contact leg of each blade contact with each transition section continuously embedded in each wall of said body between the respective legs to enable the simultaneous receipt of a respective leg of each of said blade contacts in a respective socket contact without fracturing one of said walls.
2. The contact strip as claimed in claim 1, wherein said connector leg extends substantially tangentially from one end of said transition section.
3. The contact strip as claimed in claim 2, wherein said contact leg projects angularly away from and at the other end of said transition section at an obtuse angle.
4. The contact strip as claimed in claim 1, wherein each connector leg has a cross-sectional dimension drffering lrom 2L corresponding cross-sectional dimension of the respective contact leg, the dimensional change between the corresponding crosssaid transition section has a radius of curvature of about 2 mm.
7. The contact strip as claimed in claim 1, wherein protrudes from the top of the T and extends perpen dicular to the top of the T, while said connector leg -protrudes from the stem of the T and extends perpendicular t0 the stem of the T.