Method for depositing solder material on an electronic component part

Abstract

A method for accurately depositing a required volume of solder material on a specific area of a lead frame, substrate or other part ( 4 ) of an electronic component to be bonded by reflow of solder material to another part into a reliable, void-free connection during a subsequent assembly step comprises the following steps. Minute particles ( 3 ) of solder material whose cumulative volume corresponds to the total volume to be deposited are loaded into a cavity ( 2 ) cut into a fixture ( 1 ) made from a material such as graphite. The cavity delineates the specific area of deposit. The part ( 4 ) is then laid upon the fixture and immobilized thereon by a cover ( 7 ) made from a material such as graphite. The fixture and its enclosed part are then subjected to solder material melting temperature under a controlled atmosphere in a furnace. The cavity is patterned and dimensioned to accommodate the right number of uniformly dimensioned particles necessary to precisely create the desired deposit of solder material.

1 . A method for accurately depositing a metered volume of solder material of a given melting point on a delineated area of an electronic component part, said method comprising the steps of:
 providing a fixture having a top surface shaped and dimensioned for intimate contact with said area, and a melting temperature substantially higher than said melting point;   carving into said top surface a cavity shaped to be congruent with said area;   placing into said cavity a number of particles of said solder material;   positioning said part against said top surface and said particles in contact with said area; and   exposing said fixture and part to a temperature at least equal to said melting point;
 whereby the material of said particles melts and adheres to said area. 
   
   
   
       2 . The method of  claim 1  which further comprises securing said part upon said fixture with a cover. 
   
   
       3 . The method of  claim 1 , wherein said fixture is made of a material comprising high density graphite. 
   
   
       4 . The method of  claim 1 , wherein said solder material comprises a metal alloy selected from the group consisting of gold alloys, tin alloys, lead alloys, copper alloys, and silver alloys. 
   
   
       5 . The method of  claim 1 , wherein said solder material comprises a metal alloy selected from the group consisting of AuSn, AuGe, AuSi, AuAgCu, AgCu, and PbSnAg. 
   
   
       6 . The method of  claim 1 , wherein said delineated area comprises an electronic package lead frame. 
   
   
       7 . The method of  claim 1 , wherein said delineated area comprises a marginal, peripheral area of a microelectronic package lid. 
   
   
       8 . The method of  claim 1 , wherein said cavity is segmented into a plurality of ditches. 
   
   
       9 . The method of  claim 8 , wherein two of said plurality of ditches are differently dimensioned. 
   
   
       10 . The method of  claim 1 , wherein said particles are laid in a single row into said cavity. 
   
   
       11 . The method of  claim 1 , wherein said particles are substantially uniform. 
   
   
       12 . The method of  claim 1 , wherein said particles are laid in a plurality of rows into said cavity. 
   
   
       13 . The method of  claim 1 , wherein said particles are symmetrical, and have calculated dimensions. 
   
   
       14 . The method of  claim 1 , wherein said particles are spherical, and have a calculated diameter and radius. 
   
   
       15 . The method of  claim 1 , wherein the cumulative volume of said particles is equal to said metered volume. 
   
   
       16 . The method of  claim 14 , wherein said cavity has a constant depth greater than said diameter. 
   
   
       17 . The method of  claim 1 , wherein said step of positioning comprises inverting said fixture and part. 
   
   
       18 . The method of  claim 14 , wherein said cavity has a constant depth lesser than said diameter. 
   
   
       19 . The method of  claim 1 , which further comprises pressing said part against said fixture. 
   
   
       20 . The method of  claim 14 , wherein said cavity has an arcuate bottom of a radius commensurate with the radius of said particles. 
   
   
       21 . The method of  claim 14 , wherein said cavity has a series of spaced-apart bottom separators dimensioned to intimately nest said particles. 
   
   
       22 . The method of  claim 21 , wherein said separators are regularly spaced-apart at a calculated interval.