Gold-tin solder suitable for self-aligning applications

Abstract

A tin-rich gold-tin solder is disclosed which is particularly advantageous for self-aligning applications. When utilized with gold-plated bond locations, the out-diffusion of tin from the solder during heating functions to shift the composition of the remaining solder closer to the eutectic value, thus preserving the liquid state of the solder and improving its reflow quality with respect to conventional eutectic solders.

What is claimed is:  
     
       1. An article of manufacture including a device with a conductive surface bonded to a gold-plated submount by a solder consisting essentially of 74-78% by weight gold and 26-22% by weight tin, wherein said submount is gold-plated so as to define a bond pad, said conductive surface bonded directly to said bond pad such that the solder completely covers said bond pad and said device is aligned with the bond pad. 
     
     
       2. An article of manufacture as defined in claim  1  wherein the conductive surface of the device is gold. 
     
     
       3. An article of manufacture as defined in claim  1  wherein the device is a light emitting diode. 
     
     
       4. An article of manufacture as defined in claim  1  wherein the submount is silicon. 
     
     
       5. An article of manufacture including a device with a conductive surface bonded to a submount by a solder consisting essentially of 74-78% by weight gold and 26-22% by weight tin, wherein the submount includes a layer of/titanium plated to said submount surface and a layer of platinum plated to said titanium layer, and a layer of gold plated to said platinum layer so as to define a bond pad, said conductive surface bonded directly to said bond pad such that the solder completely covers said bond pad and said device is aligned with the bond pad. 
     
     
       6. A method of soldering a first component to a second component so as to form a self-alignment of said first component to said second component, the self-alignment method comprising the steps of: 
       a) providing a first component and a second component, each component including a surface layer of gold;  
       b) disposing a Au/Sn solder of the composition Au 80−x An 20+x , 0<x≦6, between the gold surface layers,  
       c) contacting the first and second components such that the Au/Sn solder is in physical contact with both gold surface layers; and  
       d) heating the combination to a temperature sufficient to liquify the Au/Sn solder and result in the self-alignment of said first component to said second component.  
     
     
       7. The method of claim  6  wherein in performing step b), 2<x≦4. 
     
     
       8. The method of claim  6  wherein in performing step d), the combination is heated to a temperature in excess of 280° C. 
     
     
       9. A method of sequentially bonding a plurality of components to a substrate, the method comprising the steps of: 
       a) providing a substrate including a plurality of conventional metallized locations for subsequent placement of components;  
       b) providing a component including an exposed surface region covered with a tin-rich Au/Sn solder compound, wherein tin-rich is defined as Au 80−x Sn 20+x , 0<x≦6,  
       c) aligning said component with a predetermined metallized location;  
       d) heating the combination of said component and said predetermined metallized location to a conventional bonding temperature so as to form a bond with a reflow temperature greater than said conventional bonding temperature; and  
       e) repeating steps b) through d) for each component of the plurality of components, wherein utilization of said tin-rich Au/Sn solder significantly raises the resultant bond reflow temperature so as to prevent reflow of previously formed bonds.  
     
     
       10. The method as defined in claim  9  wherein in performing step d), the conventional bond temperature is approximately 315° C. 
     
     
       11. The method as defined in claim  9  wherein in performing step d), the reflow temperature exceeds 400° C. 
     
     
       12. The method as defined in claim  9  wherein in performing step a), the conventional metallization comprises Ti/Pt/Au. 
     
     
       13. The method as defined in claim  9  wherein in performing step a), the conventional metallization comprises Ti/Ni/Au.