Miniaturized Contact Spring

Abstract

This invention provides a solution to increase the yield strength and fatigue strength of miniaturized springs, which can be fabricated in arrays with ultra-small pitches. It also discloses a solution to minimize adhesion of the contact pad materials to the spring tips upon repeated contacts without affecting the reliability of the miniaturized springs. In addition, the invention also presents a method to fabricate the springs that allow passage of relatively higher current without significantly degrading their lifetime.

1 . An electrical contactor, comprising: 
 at least one electrically conductive elastic core member, said core member comprising an anchor portion attached to a substrate and electrically connected to at least one electrically conductive through-via disposed in said substrate, and a free portion, having a tip portion at an end thereof, said free portion initially attached to said substrate which portion, upon release, extends to a tip lift height away from said substrate due to an inherent stress gradient in said core member; and    at least one first metal layer electroplated on all non-anchoring surfaces of said core member;    wherein said free portion has a total thickness of between about 4 μm and about 35 μm.    
     
     
         2 . The electrical contactor of  claim 1 , said metal layer having a thickness of at least one half the thickness of said core member.  
     
     
         3 . The electrical contactor of  claim 1 , wherein said free portion is substantially tapered having a width that gradually decreases towards the tip portion over a substantial length of the free portion.  
     
     
         4 . The electrical contactor of  claim 1 , wherein said free portion is substantially trapezoidal in shape.  
     
     
         5 . The electrical contactor of  claim 1 , further comprising: 
 at least one second metal layer selectively electroplated to said tip portion subsequent to electroplating of said first metal layer to said core member, said second metal layer forming a contact button on said tip portion.    
     
     
         6 . The electrical contactor of  claim 1 , wherein any of said first and said second metal layer is selected from the group of materials comprising any of nickel, platinum group materials which comprise any of palladium, platinum rhodium, ruthenium, osmium, iridium, and, gold, silver, copper, cobalt, tungsten, and any of their alloys.  
     
     
         7 . The electrical contactor of  claim 1 , wherein the smallest cross-sectional thickness of said core member after electroplating with said first metal layer is greater than twice the thickness of said core member.  
     
     
         8 . The electrical contactor of  claim 1 , wherein said core member comprises any of Mo, Cr, Ti, W, Zr, Ti—W, and Mo—Cr.  
     
     
         9 . The electrical contactor of  claim 1 , wherein said core member is electroplated with at least one metal layer, without using a mask, to cover all surfaces of said core member including said free portion.  
     
     
         10 . The electrical contactor of  claim 1 , said electrically conductive through-via comprising: 
 a metallized through-via which is electrically connected to a corresponding core member anchor portion.    
     
     
         11 . The electrical contactor of  claim 10 , wherein said through-via provides electrical contact to said core member from a substrate side opposite the side on which the core member is located.  
     
     
         12 . The electrical contactor of  claim 1 , said core member having all exposed surfaces enveloped by said first metal layer without any discontinuity, said metal layer having a thickness greater than that of said core member and balanced internal stresses, wherein lift height variations among a plurality of core members are minimized.  
     
     
         13 . The electrical contactor of  claim 1 , wherein said first metal layer is formed using said through-via in said substrate to establish electrical contact to said core member from a substrate side opposite the side on which the core member is located.  
     
     
         14 . The electrical contactor of  claim 1 , wherein said first metal layer increases spring constant of said core member.  
     
     
         15 . The electrical contactor of  claim 1 , wherein said second metal layer increases conductivity of said core member.  
     
     
         16 . An electrical contactor, comprising: 
 at least one electrically conductive elastic core member, said core member comprising an anchor portion attached to a substrate and electrically connected to at least one electrically conductive through-via disposed in said substrate, and a free portion, having a tip portion at an end thereof, said free portion initially attached to said substrate which portion, upon release, extends to a tip lift height away from said substrate due to an inherent stress gradient in said core member; and    at least a first electroplated metal layer electroplated covering all non-anchoring surfaces of said core member, such that the cross-sectional thickness of said core member after electroplating with said first metal layer is greater than twice the thickness of said core member.    
     
     
         17 . The electrical contactor of  claim 16 , wherein said core member comprises any of Mo, Cr, Ti, W, Zr, Ti—W, and Mo—Cr.  
     
     
         18 . The electrical contactor of  claim 16 , further comprising: 
 at least one second metal layer selectively electroplated to said tip portion subsequent to electroplating of said first metal layer to said core member, said second metal layer forming a contact button on said tip portion.    
     
     
         19 . The electrical contactor of  claim 16 , wherein any of said first and said second metal layer is selected from the group of materials comprising any of nickel, platinum group materials which comprise any of palladium, platinum rhodium, ruthenium, osmium, iridium, and, gold, silver, copper, cobalt, tungsten, and any of their alloys.  
     
     
         20 . The electrical contactor of  claim 16 , said electrically conductive through-via comprising: 
 a metallized through-via which is electrically connected to a corresponding core member anchor portion.    
     
     
         21 . The electrical contactor of  claim 20 , wherein said through-via provides electrical contact to said core member from a substrate side opposite the side on which the core member is located.  
     
     
         22 . The electrical contactor of  claim 16 , wherein said first metal layer is electroplated using said through-via in said substrate to establish electrical contact to said core member from a substrate side opposite the side on which the core member is located.  
     
     
         23 . The electrical contactor of  claim 16 , wherein said core member is electroplated with at least one metal layer, without using a mask, to cover all surfaces of said core member including said free portion.  
     
     
         24 . The electrical contactor of  claim 16 , said core member having all exposed surfaces enveloped by said first metal layer without any discontinuity, said metal layer having a thickness greater than that of said core member and balanced internal stresses, wherein lift height variations among a plurality of core members are minimized.  
     
     
         25 . The electrical contactor of  claim 16 , wherein said first metal layer increases said core member spring constant.  
     
     
         26 . The electrical contactor of  claim 16 , wherein said second metal layer increases said core member conductivity.  
     
     
         27 . An electrical contactor, comprising: 
 at least one electrically conductive elastic core member, said core member comprising an anchor portion attached to a substrate and electrically connected to at least one electrically conductive through-via disposed in said substrate, and a free portion extending away from said substrate, said free portion having a tip portion extending from the end of said free portion toward said anchor potion; and    at least one photolithographically defined metal layer covering a least a portion of said tip portion of said core member, said metal layer forming a contact button on said tip portion of said core member.    
     
     
         28 . The electrical contactor of  claim 27 , wherein said core member comprises any of Mo, Cr, Ti, W, Zr, Ti—W, and Mo—Cr.  
     
     
         29 . The electrical contactor of  claim 27 , wherein said contact button is selected from the group of materials comprising any of nickel, platinum group materials which comprise any of palladium, platinum rhodium, ruthenium, osmium, iridium, and, gold, silver, copper, cobalt, tungsten, and any of their alloys.  
     
     
         30 . The electrical contactor of  claim 27 , said electrically conductive through-via comprising: 
 a metallized through-via which is electrically connected to a corresponding core member anchor portion.    
     
     
         31 . The electrical contactor of  claim 27 , wherein said through-via provides electrical contact to said core member from a substrate side opposite the side on which the core member is located.  
     
     
         32 . The electrical contactor of  claim 27 , wherein said contact button is electroplated using said through-via in said substrate to establish electrical contact to said core member from a substrate side opposite the side on which the core member is located.  
     
     
         33 . The electrical contactor of  claim 27 , wherein said contact button comprises at least one electrically conducting material that does not have strong adherence to an opposite contact pad or terminal.  
     
     
         34 . The electrical contactor of  claim 27 , wherein said substrate comprises any of ceramic, glass, quartz, silicon, and organic material.