Abstract:
The present invention relates to a contact clip which may be attached to a ceramic or other type substrate and which may be plugged into a PCB and thereby provide electrical connections between the substrate and the conductive traces on the board. More particularly, the clip includes a receptacle for receiving the edge of a substrate for mechanical retention and electrical contact, a spring arm which protects the substrate from thermal and mechanical stresses, a low force pluggable pin section for insertion into a board&#39;s plated-through hole, and means establishing redundant short electrical paths between the pad on the substrate and the traces on the PCB.

Description:
BACKGROUND OF THE INVENTION 
     1. The Field Of The Invention 
     The present invention relates to electrical devices useful for interconnecting circuitry between an active device substrate and a printed circuit or wiring board. 
     2. The Prior Art 
     The present invention is a novel improvement and a departure from at least the following: 
     
         ______________________________________Patent No.    Patentee Class/Subclass______________________________________3,479,634     Pritulsky                  339/173,764,955     Ward     339/65______________________________________ 
    
     Solid state electronic chips such as microprocessors are generally mounted on a substrate of ceramic material. Metalized lines on the substrate provide electrical paths from the very small terminal areas on the electronic chip to larger size pads on the edges of the substrate. The larger size pads more easily facilitate the electrical connections to be made between the substrate and the conductive paths or &#34;traces&#34; on a printed circuit board. The aforementioned prior art patents disclose two connectors for making such electrical connections. In Pritulsky, although the connection is made between a PCB and wires attached to a radio or TV receiver, the connector disclosed can, with little modification, be used to electrically and mechanically connect a substrate to a PCB. The connector of conductive material includes two spaced apart arms bent to provide facing surfaces between which an edge of a PCB is received. The lower member contacts a trace or circuitry on the board edge. Legs integral with the members are adapted for insertion into an aperture on a board of insulative material secured to a radio chassis. Means are included in the connector to receive and terminate wires through which signals are sent to and received from the PCB. 
     Ward discloses a device specifically designed for holding a substrate and electrically connecting the pads thereon to traces on a PCB. Two spaced apart ears on the device are bent in towards each other and then back in parallel to provide two surfaces between which the edge of the substrate is received. A post integral with the ears is adapted for insertion into a plated-through hole in a PCB to complete the electrical connection. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a stamped and formed conductive contact clip having a receptacle for receiving and holding an edge of a substrate and insertion means whereby the clips may be plugged into plated-through holes on a PCB. Further, the clip has a spring arm of considerable length which provides stress-absorbing capabilities. Means are provided on the spring arm so that select soldering techniques may be used to solder the clip to the substrate. 
     The insertion means on the lower end of the clip adapted for being plugged into a board&#39;s plated-through hole preferably includes a pin having three spring members. The pin can be plugged in with relatively low insertion force while still providing excellent electrical contact with the PCB. 
     With circuit speeds being in nanoseconds, it is imperative that the electrical path between the substrate and board be as short as possible. Accordingly, the contact clip of the present invention includes redundant means which provides a very short path without sacrificing other novel and desirable features noted above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a substrate having contact clips of the present invention attached thereto to form an assembly which is shown plugged into a PCB; 
     FIG. 2 shows the assembly of FIG. 1 being inserted into the board; 
     FIG. 3 is a perspective view of the contact clip of FIG. 1; 
     FIG. 4 is a side view of the contact clip of FIG. 1; and 
     FIG. 5 shows the steps of stamping and forming the contact clip of FIG. 1. 
    
    
     DESCRIPTION OF THE INVENTION 
     In FIG. 1 an active device substrate 10 is mechanically held and electrically connected to PCB 12 by a plurality of contact clips 14 made in accordance with the present invention. The clips electrically connect conductive pads (not shown) on the underside of substrate 10 to traces 16 on the PCB. These traces extend from plated-through holes 18 into which the clips have been inserted. 
     All or at least the majority of substrates are made from a ceramic material which is susceptible to breakage by mishandling. Accordingly, a scissor-like hand tool 20, shown in FIG. 2, provides a means for inserting an assembly 22 which includes the substrate with the required number of contact clips secured thereto. Tool 20, preferably molded from plastic, has two arms 24 with each arm terminating in a toothed front end 26. The two arms are pivotally hinged together intermediate the front and back ends 28. The front ends are biased towards each other so that the tool is self adjusting. The biasing means may be a coil spring (not shown) positioned between the arms behind the hinge line indicated by reference numeral 30. Alternatively, the tool may be molded as one piece with the distance between the toothed front ends being slightly less than the width of assembly 22. The front ends are opened by squeezing in on the two back ends 28. In this embodiment, separate biasing means are not needed nor are the means to pivotally connect the two arms together. 
     FIGS. 3 and 4 are drawings of a much enlarged contact clip 14 so as to illustrate the details thereof clearly. 
     The contact clip is an elongated length of conductive material such as 0.008 inch (2.03 mm) thick copper-based alloy. 
     Functionally and structurally the contact clip has three sections: top section 32, intermediate section 34, and lower section 36. 
     The top section includes upper arm 38 and two, spaced-apart depending first fingers 40. The upper portion of arm 38 is curved to provide a convex surface 42 facing downwardly. The lower end of the top section consists of the two fingers. 
     The intermediate section consists of a spring having the form of a non-symmetrical nose 44. The nose has an upper limb 46, lower limb 48 and a rounded bight 50 connecting the two limbs. The nose is attached at one end to the top section in between first fingers 40 and at the other end to strap 51 which forms the top of lower section 36. The lower limb 48 of the nose is relatively horizontal or tilted slightly upwards while the upper limb 46 is at an angle of about thirty degrees relative to the lower limb. The attitude of the two limbs given above are preferred; other configurations may be used; e.g., both limbs may be at a forty-five degree angle. 
     Upper limb 46 has a curved portion 52 adjacent its connection to arm 38. An upwardly facing knob 54 is located next to the curved portion. Knob 54 is the contact point for engagement with a pad on substrate 10 and may be plated with gold, silver, or other suitable plating materials. 
     Curved portion 52 provides a location for placement of a solder ring if the clips are to be soldered to the substrate. 
     Strap 51 carries two, upwardly extending second fingers 56, both of which are generally S-shaped but in opposite orientations. These fingers are in registration with first fingers 40 with the apex of the upper curved segment 58 making contact therewith, one segment bearing against one side of a first finger and the segment on the second bearing against the opposite side of the other first finger. The lower and much larger curved segments 60 of the second fingers pre-load the upper segments 58 so that they exert firm, constant pressure against the first fingers for good electrical contact. 
     The width of strap 51 extends beyond second fingers 56 and the pin portion of the lower section so that there are upwardly facing shoulders 64 and downwardly facing shoulders 66 on both sides. These shoulders provide support for insertion tool 20. 
     The free end of lower section 36 constitutes a pin portion. This pin portion has three spring members so designed that a low force is sufficient for insertion into hole 18 on the PCB but yet good electrical contact therewith is achieved. Two of the three spring members, indicated by reference numeral 68, are connected at one end to strap 51 at spaced apart locations. They extend downward therefrom converging together to form bevelled tip 70. The third spring member 72 is attached to tip 70 and extends upwardly with its unattached, free end 74 being adjacent strap 51. All three spring members are bowed with the bow orientation on members 68 being opposite that on member 72. 
     One method of manufacturing contact clips 14 is by stamping and forming them from strip stock metal as a continuous strip. Steps A through G shown in FIG. 5 illustrate the several stages in blanking out and forming up a clip. Carrier strip 76 guides the clips through the dies (not shown) plating lines, reeling, and further, provides a convenient means for gang insertion into a PCB. It is easily broken off at the juncture with upper arm 38. 
     In step A the clips have been blanked out from the strip of metal (not shown) and the excess material removed. Further, all the cuts have been made as indicated by the lines. Reference numeral 78 indicates two such cut lines. Forming begins with step B where the three spring members on lower section 36 are formed. In step C, the first compound curve is made towards forming upper arm 38 and is completed in step D. The curved portion 52 and knob 54 are formed in step E. Note that this stage also results in defining first fingers 40. The further forming of nose 44 takes place in step F where limb 48 and bight 50 begins to take shape. Limb 46 is now defined. Second fingers 56 are also formed in this step. In step G the final forming of clip 14 occurs by bringing lower section 34 in under and then up towards fingers 44. The free ends of second fingers 56 point outwardly so as they are brought up from below, the curvering portions guides the second fingers up the proper side of the first fingers. 
     If one or more contact points; i.e., knob 54, curved portions 58, first fingers 40, and spring members 68, 72 are to be plated, the preferred method would be to strip-plate the contact points or areas between steps A and B. Pre-plated stock could also be used. 
     Assembly may be made by forcing individual contact clips 14 onto the substrate edges with knobs 54 engaging the pads (not shown) on the underside and the convex surface 42 on upper arms 38 positioned on the topside. The dimensions must be so that there is an interference fit. Alternatively, a length of clips connected together by carrier strip 76 can be loaded onto an edge simultaneously. The carrier strip remains with the assembly while it is being inserted into the PCB as shown in FIG. 2. After insertion the strip is broken away. 
     As is well known, printed circuit boards are subject to mechanical and thermal stresses. Warpage of a board is a common occurrance and can cause non-functioning and even breakage of electronic components on the board. Also, the heat from the electronic device on a substrate can induce thermal stresses into the substrate. 
     One of the novel features of the present invention; i.e., the elongated nose 44, provides a means for preventing damage to the substrate by absorbing the aforementioned stresses. This spring has a high degree of flexibility so that it can dissipate the stress energies harmlessly. 
     Another novel feature of the present invention is the short and redundant electrical paths provided by first and second fingers 40 and 56. The signals do not have to follow the elongated nose 44 in getting through the clip. 
     Still another novel feature of the present invention lies in the adaptability of the clip to be soldered to the substrate. 
     Yet another novel feature of the present invention lies in lower section 36 and its three spring members. Since a low force is sufficient to plug the pin portion into a plated-through hole, the substrate is not subjected to mechanical stresses in that respect. Further, and not withstanding the low insertion force requirements, the pin portion makes good electrical connection with the PCB. 
     The present invention may be subject to many modifications and changes without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive of the scope of the invention.