Patent Publication Number: US-6905343-B1

Title: Interposer assembly

Description:
This application is a division of U.S. application Ser. No. 09/897,332 filed Jul. 2, 2001 now U.S. Pat. No. 6,730,134. 

   FIELD OF THE INVENTION 
   The invention relates to interposer assemblies of the type which are sandwiched between substrates to form electrical connections between opposed pads on the substrates, and to cantilever contacts for forming electrical connections with contact pads. 
   BACKGROUND OF THE INVENTION 
   Interposer assemblies typically include plastic plates with through passages and contacts in the passages for forming electrical connections between opposed contact pads. 
   Interposer assemblies form electrical connections between contact pads arranged in a very close proximity to each other. The pads may be arranged on a one millimeter center-to-center grid. Each assembly may include as many as 961 contacts with four interposer assemblies mounted in a single frame with a total of 3,844 contacts in the frame. The contacts must establish reliable electrical connections with the pads when the assemblies are sandwiched together between circuit members. Failure of a single contact to make a reliable connection renders the entire frame useless. 
   Contacts in interposer assemblies include contact surfaces which mechanically engage the contact pads and form electrical connections with the contact pads. Conventional interposer assemblies have single surface contacts which engage each pad to form a single electrical connection with each pad. The contact may wipe along the pad to improve the quality of the electrical connection. Impurities, oxides or contaminants on either the contact surface or the pad can impair the single surface electrical connections with the pads. Contacts used in interposer assemblies are typically symmetrical about the center of the insulating plate, each including a separate spring which biases a single contact surface against a pad. 
   Accordingly, there is a need for an improved interposer assembly in which each contact makes redundant contacts with each pad so that when the assembly is sandwiched between overlying and underlying substrates each contact establishes two reliable electrical connections with each pad. The connections should have small contact areas to increase the contact pressure between the contact and the pad. Wiped high contact pressure redundant connections would provide reliable interposer assembly electrical connections. There is also a need for a method of making a contact with spaced contact points from strip stock, which may be very thin and difficult to form. 
   Further, there is need for a spring contact having spaced contact points for engaging a contact pad and forming redundant wiped high pressure redundant electrical connections between the contact and the pad. 
   SUMMARY OF THE INVENTION 
   The invention is an improved interposer assembly including contacts mounted in passages extending through an insulating plate s with each contact having two contact points on each end of the contact. When the interposer assembly is sandwiched between overlying and underlying substrates the pairs of contact points are brought into wiped pressure engagement with overlying and underlying pads and forms redundant electrical connections with the pads. 
   The contact points are formed on rounded edge corners of the contacts and have small contact areas, resulting in high contact pressure and reliable electrical connections despite debris, oxides and surface contaminants on the contacts and pads. 
   Each contact includes two tapered spring arms joined to a central portion. A pair of contact points is formed on the outer end of each spring arm. The points project above and below the plate. The arms are independently deflected during compression of the contact by overlying and underlying substrates. The spring arms may include retention legs extending outwardly from the contact points for engagement with adjacent cam surfaces. Compression of the contacts moves the ends of the legs along the cam surface to further stress the spring and increase contact force. 
   Additionally, the invention relates to a contact having a beam with a mounting end and a contact end carrying a pair of laterally spaced contact points. Movement of a pad against the contact points stresses the beam and moves the contact points laterally along the pad to form wiped high pressure electrical connections between the contact and the pad. The contact points are rounded edge corners and have a very small contact area in order to increase contact pressure and form redundant wiped high pressure electrical connections between the contact and the pad. The contact points are preferably located on opposite sides of the spring arm and stabilize the contact against twisting. 
   Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are five sheets of drawings and two embodiments. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top view, broken away, of an interposer assembly according to the invention; 
       FIG. 1A  is an isometric view of a contact used in the interposer assembly; 
       FIG. 2  is a top view of a substrate with pads for forming electrical connections with the contacts in the interposer assembly; 
       FIG. 3  is a sectional view taken along line  3 — 3  of  FIG. 1 ; 
       FIG. 4  is a view like  FIG. 3  showing the interposer assembly sandwiched between top and bottom substrates; 
       FIG. 5  is an enlarged view of portion of  FIG. 4  showing an alternative construction; 
       FIG. 6  is a view like  FIG. 4  showing the substrates engaging the interposer assembly; 
       FIG. 7  is a view like  FIG. 2  showing wipe traces on the contact pads of the substrate; 
       FIG. 8  is a partially broken away view taken along line  8 — 8  of  FIG. 6 ; 
       FIG. 9  is a contact preform; 
       FIG. 10  is an enlarged view of a portion of the preform of  FIG. 9  showing a pair of wings; 
       FIG. 11  is a sectional view taken along line  11 — 11  of  FIG. 9  showing the wings bent upwardly; 
       FIG. 12  is a sectional view showing tooling used for punch forming the preform from strip stock; and 
       FIGS. 13 and 14  are sectional views showing a cantilever contact related to the interposer contact. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The disclosure relates to the interposer assembly of U.S. Pat. No. 6,176,707, the disclosure of which is incorporated herein by reference in its entirety. 
   The disclosure also relates to the interposer assembly of Neidich, et al. U.S. Pat. No. 6,290,507 the disclosure of which is incorporated herein by reference, in its entirety. 
   The first embodiment interposer assembly  10  includes a flat dielectric plate  12  preferably molded from thermoplastic resin and having a plurality of contact passages  14  extending through the thickness of the plate from plate top  16  to plate bottom  18 . A contact  20  is held in each passage  14 . The height of plate  12  may be as little as 0.048 inches. 
   Passages  14  are elongate in transverse cross section. Each passage includes a wide end  22 , an opposed narrow end  24 , a uniform width portion  26  adjacent the wide end  22  and a tapered, reduced width portion  28  adjacent the narrow end. The uniform width portion  26  has opposed parallel walls extending between the top and bottom of the plate and the reduced width portion has inwardly tapered walls extending from portion  26  to narrow end  24 . 
   As illustrated in  FIG. 3 , a shallow contact-retention projection  30  is formed in each narrow passage end  24 . The projection is defined by flat upper and lower cam surfaces  32  and  34  extending from projection tip  36  to the top and bottom of plate  12  respectively. The tip is located equidistant between the top and bottom of the plate. Both cam surfaces slope away from the tip at a shallow angle of about 12 degrees from the vertical. Flat end wall  38  at wide passage end  22  extends perpendicularly between the top and bottom of plate  12 . 
     FIG. 5  illustrates a modified interposer assembly plate  12   a  similar to plate  12  and having a top cam surface  32   a  and bottom cam surface (not illustrated) which end a short distance  98  inwardly from the plate top side  16   a  and bottom side (not illustrated). The cam surfaces and short, straight end wall surfaces  98  at the top and bottom sides of the plate extend across the narrow end  24   a  of contact passage  14   a.    
   Plates  12  and  12   a  are molded from thermoplastic resin using mold supporting core pins forming passages  14  and  14   a . The tooling supporting the core pins normally extends a very short distance into the mold cavity to prevent the cam surfaces from extending to the top and bottom of the plate. Each straight surface  98  has a vertical extent of about 0.005 inches so that, in practice, the cam surfaces are recessed from the top and bottom of the plate only a very small distance. This recess distance does not effect the operation of the interposer assembly. 
   Contact  20  is formed from thin uniform thickness metal strip stock, which may be a beryllium copper, and is preferably plated with a conductive metal, which may be gold or a gold alloy, to reduce contact resistance and prevent oxidation. Contacts  20  may be made from strip stock having a thickness of 0.0017 inches. This thin stock is difficult to shape accurately. 
   Contacts  20  include a flat central portion or spine  40 , like upper and lower curved and tapered spring arms or beams  42 . Arms  42  extend in opposite directions from spine  40 . Contact noses  44  are located at the upper and lower ends of the spring arms. Short, straight and tapered retention legs  46  extending outwardly from the noses and toward each other to rounded ends  48 . When contacts  20  are unstressed the noses  44  are spaced apart a distance of 0.060 inches, greater than the thickness of plate  12 . Spring arms  42  are bent laterally away from central spine  40  in the same direction so that noses  44  are located between the spine and retention leg ends  48 . Arms  42  have a maximum width adjacent spine  40 . The width of each arm decreases from the spine to nose  44 . Contacts  20  are symmetrical to either side of spine  40 . 
   Each spring arm  42  includes a pair of contact points  50  adjacent nose  44 . The contact points are spaced apart on opposite sides of the spring arm a short distance inwardly from the nose and project above the surface of the arm. As shown in  FIG. 1 , the contact points also are located outwardly from the arms to increase the width of the contact adjacent the nose. 
     FIG. 9  illustrates preform  52  which is stamped from uniform thickness strip stock and shaped to form contact  20 . The preform includes a central portion  54  which forms spine  40  and two, like arm or beam sections  56  extending to either side of the central portion which form arms  42  and legs  46 . The widths of the arm sections decrease from a maximum at the central portion to minimums at ends  58 . Rounded projections or wings  60  extend outwardly from the sides of the arm sections between the central portion  54  and ends  58 . 
     FIG. 12  illustrates tooling used to stamp preform  52  from thin strip stock  62 . The strip stock is positioned on anvil  64  with an overlying pressure plate  66  clamping the strip stock to the anvil. Cutters  68 , located to either side of the plate and anvil and above strip stock  62 , are moved down past the anvil to cut or shear away outer portions  70  of the strip stock from the portion  72  held between the anvil and pressure plate. Sharing forms sheared edges  74  on held portion  72  with rounded upper corners  76  and sharp, drag lower corners  78 . In the drawings, the size of corners  76  and  78  is exaggerated for clarity. 
   Stamped preform  52  includes cut edges  74  extending along the sides of both arm sections  56  and around the wings or projections  60  on the arm sections. Rounded edge corners  76  are located on one side of the preform and drag corners  78  are located on the other side of the preform. 
   Contact  20  is formed from preform  52  by bending the preform about axes parallel to the plane of the preform to form curved spring arms  42 , noses  44 , legs  46  and curved ends  48  at the ends of legs  46 . The preform is bent to locate rounded edge corners  76  on the outside of the contact and drag corners  78  on the inside of the contact. 
   Additionally, during bending of the preform to form the contact, or as an independent step, both projections or wings  60  are bent upwardly relative to the arm sections, around bend lines  80  shown in  FIG. 10 , to form contact points  50  extending above the spring arms  42  adjacent to noses  44 .  FIG. 7  illustrates the bent up wings with rounded corners  76  located above the arm section  56  and with the drag corners  78  located outwardly and below the rounded corners. 
   Contact preform  52  may have a thickness of 0.0017 inches. Metal of this thickness is very hard to handle and shape reliably. The small diameter, rounded corners on the contact points are formed during shearing of the preform from strip stock material without the necessity of physically bending the strip stock. The rounded corners are very small having a transverse radius of curvature of about 0.0006 inches to 0.0010 depending on tool clearance and wear. It would be very difficult to form these small rounded corners by mechanically shaping the preform. The radius of curvature along the length of the corners is about 0.012 inches. 
   After bending of preform  52  to form contact  20  as described, the contact is preferably plated with a conductive metal which may be gold or a gold alloy to form a plating  82  surrounding the contact. 
   Formed and plated contacts  20  are inserted into contact passages  14  in plate  12  by positioning each contact to one side of a passage with a contact nose located adjacent the center of the passage, spring arms  42  adjacent wide passage end  22  and retention legs  46  adjacent narrow passage end  24 . The contact is then moved into the passage to bring spine  40  into engagement with wall  38  and the lead retention leg  46  into engagement with the adjacent cam surface  32  or  34 . This engagement results because the horizontal distance between the spine and curved ends  48  of legs  46  is greater than the minimum spacing between tip  36  and wall  38 . Continued movement of the contact into the passage elastically stresses the contact to move the leg inwardly and permit movement the leg past the projection to the inserted position shown in FIG.  3 . After the leg passes the projection tip the contact returns to the shape shown in FIG.  3 . In this position the contact  20  is unstressed and loose in passage  14 . Projection  30  extends between the ends of the retention legs  46  to prevent dislodgement of the loose contact from the passage. 
     FIG. 3  shows loose contact  20  with the retention legs away from the projection. In practice, gravity will shift the contact down in the passage so that the upper leg  46  rests on upper top cam surface  32 . With contact  20  in passage  14  as illustrated, the upper and lower contact noses  44  are located at the top and bottom of the contact. The contact points  50  are also located at the top and bottom of the contact. Noses  44  extend across the width of the contact. Projections  50  are located on the opposed sides of the contact. 
   In one interposer assembly  10  having a plate  12  with a thickness of 0.048 inches and contact  20  formed from uniform thickness strip stock having a thickness of 0.0017 inches the height of the unstressed contacts from nose to nose is 0.060 inches. When the contact is positioned in a contact passage  14  as shown in  FIG. 3  each contact nose  44  projects a distance 0.006 inches above the top or bottom side of the plate. The contact points  50  are spaced apart across the width of the contact 0.0115 inches. 
   Interposer assembly  10  is used to establish electrical connections between opposed contact pads  84  on substrates  86  located to either side of the assembly.  FIG. 2  illustrates the contact surface of a substrate  86  with pads  84 .  FIG. 4  illustrates the interposer assembly  10  located between substrates  86  with the contact pads  84  lightly engaging the contact noses  44  and contact points  50  on each end of contacts  20  in passage  14  with contact  20  unstressed. 
     FIG. 6  illustrates interposer assembly  10  fully sandwiched between substrates  86  with the contact pads  84  on the substrates engaging the top and bottom plate surfaces and contact  20  collapsed into passage  14 . During movement of the substrates onto the plate each contact nose is collapsed 0.006 inches into the passage, the rounded ends of the retention legs  46  are brought into engagement with the upper and lower cam surfaces  32  and  34  and are moved inwardly along the surfaces to the position shown in  FIG. 3  adjacent tip  36 . As the contact is collapsed, the retention legs  46  and the spring arms  42  are bent laterally elastically to provide high contact pressure between the ends of the contact and the pads  84  and to wipe the points along the pads. The spring arms  42  and central portion or spine  40  form an elastic spring system. In this position, contacts  20  are held in the passages by the substrates. 
   As contact  20  is collapsed into passage  14  the ends of arms  43  rotate and engagement between the outer ends of the arms and pads  84  moves along the arms from noses  44  to the adjacent rounded corners  76  at the tops of the contact points  50 . Compare  FIGS. 4 and 6 . The rounded edge corners  76  at the tops of the contact points  50  wipe along pads  84  to form wipe traces  88  shown in FIG.  7 . Each trace  88  extends from a point of initial contact  90  between a point  50  and the pad to a final contact position  92 . The contact points move along traces  88  in a direction away from passage wide end  22  and toward passage narrow end  24 . The resiliency of the stressed spring system biases the small area rounded corners  76  of points  50  against the contact pads under high pressure as the points are moved along traces  88 . The contact pressure exerted by the spring system is applied to the pads at the small four rounded corners  76  of points  50 , resulting in redundant high pressure electrical connections between the points and pads. The contact pressures are high because the contact areas are low. High pressure wiped engagement between the points  50  and the pads breaks through debris, oxides or other surface contaminants on the points or on the pads. The rounded corners slide along, but do not cut into the pads. The provision of redundant contacts at each end of contacts  20  increases the reliability of electrical connection between contact  20  and pads  84  over conventional single area contacts. 
   During compression of contacts  20  into passages  14  the two contact arms  44  are each bent away from wide passage end  22  independently of each other with contact central portion or spine  40  held on end wall  22 , although the contact may shift vertically a slight distance in the passage to shift the spine up or down along wide end wall  22 . Each arm  42  is stressed essentially independently of the other arm  42  so that the contact pressure at points  50  on one end of the contact is provided by elastic deformation of the adjacent spring arm  42  and retention leg  46 , located to one side of the central portion. Thus, contact  20  includes two like spring contacts each located to one side of the central portion and each including a curved tapered spring arm  42  and a tapered retention leg  46 . The width of retention leg  46  decreases from nose  44  to end  48  to permit ready deflection of the leg by the adjacent cam surface  32  or  34 . Deflection of both the spring arm  42  and leg  46  contribute to the spring force holding projections  50  against adjacent pad  84 . Each of the independent, like spring contacts provides an electrical connection between a contact pad and the spine  40  at the center of contact  20 . 
     FIGS. 13 and 14  illustrate a cantilever spring contact  100  formed from bent uniform thickness strip stock, related to contact  20 . The strip stock may have a desired thickness, which may be other than the thickness of contact  20 . The contact  100  includes a mounting end  102  and a contact end  108 . End  102  is mounted in substrate  104 . A curved, tapered spring arm or beam  106  extends upwardly from the substrate and is bent laterally to one side of the mounting end  102 . The mounting end is connected to a circuit element (not illustrated). Contact  100  connects the circuit element to pad  114  on substrate  112 . 
   Spring arm  106  may be identical to spring arm  42  in contact  20  and is a beam having a tapered width decreasing from a maximum width at mounting end  102  to a minimum width at contact end or end  108 . A pair of contact points  110  having upwardly facing rounded edge corners are formed on the opposite sides of arm  106  at end  108 . Arm  106 , end  108  and contact points  110  may be identical to arm  42 , nose  44  and contact points  50  of contact  20 , previously described. 
     FIG. 13  illustrates substrate  112  located above substrate  104  and carrying contact pad  114 . Pad  114  engages end  108  and points  110  of contact  100  without stressing the contact. 
   Electrical connections are established between pad  114  and contact  100  by reducing the distance between substrates  104  and  112  so that the spring arm  106  is elastically bent laterally and engagement between the contact and the pad shifts from end  108  to the rounded corners of spaced contact points  110 , in the same way redundant contacts are established between the ends of the spring arms  42  in contact  20  and overlying and underlying pads  84 . 
   Elastic bending of the spring arm provides high contact pressure engagement between the points  110  and pad  114 . The points are wiped along the pad to form contact traces on the pad like traces  88  shown in FIG.  7 . The wiped, redundant high pressure contacts between the contact and pad assure reliable low resistance electrical connections are established. The spaced apart contact points  110  support contact  100  on pad  114  to prevent twisting of the contact. 
   Contact  100  does not include a leg and curved end like retention leg  46  and curved end  48  of contact  20 . If desired, contact  130  may be provided with a leg  116  having a curved end  118 , like leg  46  and end  48 , and substrate  104  may be provided with a cam surface  120 , like top cam surface  32  in plate  2 . Leg  116 , end  118  and cam surface  120  are shown in dashed lines in  FIGS. 13 and 14 . During collapse of spring  100  provided with a leg  116  and end  118 , end  118  engages cam surface  120 , leg  116  is elastically deformed and increases the contact pressure between points  102  and pad  114 . The spring arm  110  with arm  116  and end  118  is deformed identically to each half of contact  20  as the overlying and underlying substrates  86  are moved together from the position of  FIG. 4  to the position of FIG.  6 . 
   While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.