Conductive sidewall for microbumps

Abstract

Electromigration in microbump connections causes voids in the microbumps, which reduces the lifetime of an integrated circuit containing the microbump, Electromigration lifetime may be increased in microbumps by forming a copper shell around the solder. The copper shell of one microbump contacts the copper shell of a second microbump to enclose the solder of the microbump connection. The copper shell allows higher current densities through the microbump. Thus, smaller microbumps may be manufactured on a smaller pitch without suffering failure from electromigration. Additionally, the copper shell reduces shorting or bridging between microbump connections on a substrate.

What is claimed is: 
     
         1 . A method, comprising:
 forming an opening in a sacrificial layer on a contact pad of a substrate;   depositing a first conductive layer covering sidewalls of the opening and a bottom of the opening; and   depositing a second conductive layer inside the first conductive layer, the second conductive layer having a lower melting point than the first conductive layer.   
     
     
         2 . The method of  claim 1 , in which depositing the first conductive layer comprises electroplating copper and/or nickel. 
     
     
         3 . The method of  claim 1 , in which depositing the second conductive layer comprises electroplating tin and/or silver. 
     
     
         4 . The method of  claim 1 , further comprising depositing an underbump metal (UBM) layer on the contact pad before depositing the first conductive layer, the first conductive layer partially covering a surface of the UBM layer. 
     
     
         5 . The method of  claim 4 , further comprising depositing a passivation layer on the substrate, prior to depositing the UBM layer. 
     
     
         6 . The method of  claim 1 , in which forming the opening comprises: patterning the sacrificial layer;
 depositing a seed layer; and   etching back the seed layer.   
     
     
         7 . The method, of  claim 6 , in which the seed layer comprises titanium and/or copper. 
     
     
         8 . The method of  claim 1 , further comprising heating the second conductive layer while not reflowing the first conductive layer. 
     
     
         9 . The method of  claim 1 , further comprising bonding the second conductive material to a third conductive material of another substrate. 
     
     
         10 . The method, of  claim 1 , further comprising integrating the substrate into a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and/or a fixed location data unit. 
     
     
         11 . A method, comprising:
 selecting a first substrate with a first plurality of microbumps having a first conductive material and a second conductive material substantially contained within the first conductive material;   selecting a second substrate with a second plurality of microbumps having a first conductive material and a second conductive material substantially contained within the first conductive material;   aligning microbumps of the first plurality of microbumps with microbumps of the second plurality of microbumps; and   forming a bond between microbumps of the first plurality of microbumps and microbumps of the second plurality of microbumps such that the first conductive material of the first plurality of microbumps contacts the first conductive material of the second plurality of microbumps.   
     
     
         12 . The method of  claim 11 , in which forming the bond, comprises forming a thermo compression bond. 
     
     
         13 . The method of  claim 11 , in which the selected second substrate is symmetric with the selected first substrate. 
     
     
         14 . The method of  claim 11 , further comprising integrating the first and second substrates into a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and/or a fixed location data unit.