Prevention and control of intermetallic alloy inclusions that form during reflow of Pb free, Sn rich, solders in contacts in microelectronic packaging in integrated circuit contact structures where electroless Ni(P) metallization is present

Abstract

In using Ni(P) and Sn-rich solders in Pb free interconnections, the prevention and control of the formation of intermetallic compound inclusions, can be achieved through a reaction preventive or control layer that is positioned on top of an electroless Ni(P) metallization, such as by application of a thin layer of Sn on the Ni(P) or through the application of a thin layer of Cu on the Ni(P

1 . In the fabrication of integrated circuit interconnection structures 
 wherein stacked layers of metal for different purposes are caused to fuse together by subjecting said layers to a fusion temperature excursion,    a process for inhibiting a potential undesirable interaction of first and second adjacent layers during said fusion temperature excursion comprising the steps of: 
 exposing a surface of said first of said potential interacting layers,  
 applying a protective layer of a metal having, during said fusion temperature excursion, at least one inhibiting property for said interaction, over said exposed surface of said first of said potential interacting layers,  
 applying said second layer of said first and second potential interacting layers over said protective layer, and,  
 subjecting the assembly stack of said first, said protective and said second layers to said fusion temperature excursion.  
   
   
   
       2 . The process of  claim 1  wherein said first layer is of electroless Ni(P) metallization, said protective layer is a metal taken from the group of Sn, and Cu, and said second layer is a further layer of the interconnection.  
   
   
       3 . The process of  claim 1  wherein said first layer is of electroless Ni(P) metallization, said protective layer is a metal taken from the group of Sn, and Cu, in a thickness range of between 0.1 and 5 micron and said second layer is a further layer of the interconnection.  
   
   
       4 . The process of  claim 1  wherein said first layer is of electroless Ni(P) metallization, said protective layer is a metal taken from the group of Sn, and Cu, in a thickness range of between 0.1 and 5 micron, said second layer is a further layer of the interconnection, and said temperature exursion is up through 250 degrees C.  
   
   
       5 . The process of  claim 1  wherein said first layer is of electroless Ni(P) metallization, said protective layer is a metal taken from the group of Sn, and Cu, in a thickness range of between 0.1 and 5 micron, said second layer is a further layer of the interconnection, and said temperature exursion is up through 250 degrees C.  
   
   
       6 . The process of  claim 1  wherein said first layer is of electroless Ni(P) metallization, said protective layer is a metal taken from the group of Sn, and Cu, in a thickness range of between 0.1 and 5 micron, and said second layer is a layer of Sn-rich Pb-free solders of a material taken from the group of pure Sn, Sn-3.5% Ag, Sn-0.7% Cu, Sn-3% Bi, Sn-3.5%-0.7% Cu, Sn-3.5% Ag-3% Bi, Sn-8%-Zn-3% Bi, Sn-3.5% Ag-0.7% Cu-0.5% Sb, and Sn-2.5% Ag-0.5% Cu.