Patterned array of metal balls and methods of making

Abstract

The present invention relates to a method for making an array of metal balls. The method includes the step of generating a first pattern on a metal foil which includes a plurality of foil projections. The method also includes the step of generating a second pattern on a carrier substrate. The second pattern includes a plurality of carrier recesses that are arranged and configured to correspond with the foil projections of the first pattern. The method further includes the steps of placing the metal foil and the carrier substrate together such that the foil projections of the metal foil fit within the carrier recesses of the carrier substrate, and melting the metal foil such that the foil projections form metal balls positioned within the carrier recesses of the carrier substrate. The invention also relates to metal ball arrays constructed via the above method.

What is claimed is:  
     
         1 . A method for making an array of metal balls comprising the steps of: 
 generating a first pattern on a metal foil, the first pattern including a plurality of metal foil projections;    generating a second pattern on a carrier substrate, the second pattern including a plurality of carrier recesses arranged and configured to correspond with the foil projections of the first pattern;    placing the metal foil and the carrier substrate together such that the foil projections of the metal foil fit within the carrier recesses of the carrier substrate; and    melting the metal foil such that the foil projections form metal balls positioned within the carrier recesses of the carrier substrate.    
     
     
         2 . The method of    claim 1   , further comprising the step of coating the metal foil with a fluxing agent after the metal foil and the carrier substrate are placed together.  
     
     
         3 . The method of    claim 1    wherein the opposing surfaces of the metal foil and carrier substrate are in intimate contact with one another prior to melting the metal foil.  
     
     
         4 . The method of    claim 1   , wherein the opposing surfaces are bonded together by means of an adhesive prior to melting the metal foil.  
     
     
         5 . The method of    claim 1   , wherein the exposed side of the metal foil includes a plurality of ridges, and the ridges comprise portions of the metal foil that are removed or displaced to partition the projections into discrete sections prior to complete melting of the metal foil to form balls.  
     
     
         6 . The method of    claim 5   , wherein the portions of metal foil are displaced by compressing the metal ridges with a die.  
     
     
         7 . The method of    claim 5   , wherein the portions of metal foil are removed via abrasion.  
     
     
         8 . The method of    claim 5   , wherein the portions of the metal are displaced via melting.  
     
     
         9 . The method of    claim 8   , wherein the melting occurs in a temperature gradient applied so that the metal at the ridges of the exposed side of the foil are the hottest and the metal in the recesses against the carrier substrate are the coolest.  
     
     
         10 . The method of    claim 1   , wherein the first and second patterns are generated by concurrently embossing both the carrier substrate and the metal foil with an embossing tool.  
     
     
         11 . The method of    claim 1   , wherein the first pattern is generated on the metal foil by: 
 pre-generating the second pattern on the carrier substrate; and    depositing a metal foil on the patterned surface of the carrier substrate.    
     
     
         12 . The method of    claim 1   , wherein the second pattern is generated on the carrier substrate by: 
 pre-generating the first pattern on the metal foil;    placing a flowable backing material over the patterned metal foil such that the foil projections of the first pattern are substantially covered by the backing material; and    hardening the backing material on the metal foil such that the hardened backing material forms the carrier substrate, wherein first pattern on the metal foil generates the second pattern on the carrier substrate.    
     
     
         13 . The method of    claim 1   , wherein the metal foil comprises solder.  
     
     
         14 . The method of    claim 1   , wherein the carrier substrate comprises a carrier tape.  
     
     
         15 . A method for making an array of metal balls comprising the steps of: 
 generating a pattern on a carrier substrate, the pattern including a plurality of carrier recesses;    placing a metal foil against the patterned surface of the carrier substrate;    heating the metal foil while pressing and confining the metal foil and carrier substrate between two rigid dies such that the foil melts to form molten metal segments positioned within the carrier recesses of the carrier substrate;    releasing the pressure between the dies and removing the carrier substrate from between the dies to form metal balls positioned within the carrier recesses of the carrier substrate.    
     
     
         16 . The method of    claim 15    in which the rigid dies are in the form of opposing rollers.  
     
     
         17 . The method of    claim 15   , further comprising the step of coating the metal foil with a fluxing agent before the metal foil and the carrier substrate are placed together.  
     
     
         18 . The method of    claim 15   , further comprising the step of placing a liner between the metal foil and the adjacent die.  
     
     
         19 . A method for making an array of metal balls comprising the steps of: 
 providing a metal foil;    providing an embossing tool having a pattern which includes a plurality of recesses;    providing a carrier substrate having a front surface and a back surface and wherein the thickness of the carrier substrate is less than the depth of the recesses in the embossing tool;    placing the back surface of the carrier substrate against the patterned tool;    placing the metal foil in contact with the front surface of the carrier substrate;    pressing the metal foil and carrier substrate against the embossing tool by means of a rigid die while applying sufficient heat and pressure to form recesses in the front surface of the carrier substrate in conformity to the recesses of the patterned embossing tool and further melting and partitioning the molten metal into sections which are confined within the recesses of the carrier substrate;    releasing the pressure and removing the rigid die from contact with the molten metal to allow the segments of molten metal to form metal balls positioned within the carrier recesses of the carrier substrate.    
     
     
         20 . The method of    claim 19    further comprising the step of placing a liner between the metal foil and the rigid die.  
     
     
         21 . The method of    claim 19   , further comprising the step of coating the metal foil with a fluxing agent before the metal layer and the carrier substrate are placed together.  
     
     
         22 . The method of    claim 19    in which the embossing tool and the rigid die are in the form of opposing rollers.  
     
     
         23 . A method for making an array of metal balls, the method comprising the steps of: 
 providing a metal foil having a front side and a back side;    providing a temporary supporting tape adhered to the front side of the metal foil;    patterning and partitioning the metal foil such that the back side of the metal foil forms a plurality of foil projections, the foil projections being partitioned into a plurality of discrete sections;    placing a flowable backing material over the back side of the metal foil such that the foil projections are substantially covered by the backing material; and    hardening the backing material on the metal foil, the hardened backing material forming a carrier substrate having a plurality of carrier recesses containing the foil projections.    
     
     
         24 . The method of    claim 23   , further comprising the step of removing the temporary supporting tape from the front side of the metal foil.  
     
     
         25 . The method of    claim 24   , further comprising the step of melting the metal foil such that the foil projections form metal balls positioned within the carrier recesses.  
     
     
         26 . The method of    claim 25   , further comprising the step of coating the front side of the metal foil with a fluxing agent before the metal layer is melted.  
     
     
         27 . A method of making an array of solder preforms comprising the steps of: 
 providing a sheet of backing material with a solder foil adhered to one side by means of a deformable adhesive material; and    patterning the solder foil against an embossing tool such that the solder foil is partitioned into discrete sections with each section having a rounded apex that projects outward from the sheet of backing material, the sections being secured to the backing material by the deformable adhesive material.    
     
     
         28 . The method of    claim 27   , wherein the apexes lie on a common plane.  
     
     
         29 . A solder preform apparatus comprising: 
 a carrier tape containing a plurality of discrete solder sections adhered to a backing tape by means of an adhesive, the solder sections being sized and shaped to project outward from the backing tape to form projections, wherein each solder section projection has an apex which lies in a common plane with apexes of the other solder section projections.    
     
     
         30 . The apparatus of    claim 29   , wherein the solder section projections are generally pyramid-shaped.  
     
     
         31 . The apparatus of    claim 29   , wherein the apexes are rounded.  
     
     
         32 . A method for using a solder preform apparatus comprising: 
 providing the solder preform apparatus including an array of discrete solder sections adhered to a backing tape, the solder sections projecting outward from the backing tape and having apexes aligned along a common plane;    placing the array of solder section in contact with a corresponding array of electrical circuit pads;    melting the solder sections such that the solder sections are transferred to the electrical circuit pads; and    removing the backing tape from the solder sections.    
     
     
         33 . A metal ball array apparatus comprising: 
 a carrier tape defining a plurality of carrier recesses; and    a plurality of metal balls, each metal ball being individually contained within one of the carrier recesses.    
     
     
         34 . The apparatus of    claim 33   , further comprising a fluxing agent located within the recesses, the fluxing agent being constructed and arranged for maintaining the metal balls at precise locations within the carrier recesses.  
     
     
         35 . The apparatus of    claim 33   , wherein each carrier recess has a generally pyramidal shape with rounded apexes.