Reactive bonding of a flip chip package

Abstract

An array of bonding pads including a set of reactive materials is provided on a first substrate. The set of reactive materials is selected to be capable of ignition by magnetic heating induced by time-dependent magnetic field. The magnetic heating can be eddy current heating, hysteresis heating, and/or heating by magnetic relaxation processes. An array of solder balls on a second substrate is brought to contact with the array of bonding pads. A reaction is initiated in the set of magnetic materials by an applied magnetic field. Rapid release of heat during a resulting reaction of the set of reactive materials to form a reacted material melts the solder balls and provides boding between the first substrate and the second substrate. Since the magnetic heating can be localized, the heating and warpage of the substrate can be minimized during the bonding process.

What is claimed is: 
     
         1 . A structure for bonding substrates comprising a substrate having an array of bonding pads thereupon, wherein each of said bonding pads comprises at least one unit reactive-material-including stack that includes a set of reactive materials including a first material and a second material that, upon ignition, react spontaneously to form an alloy or a composite of said first material and said second material, wherein a magnetic material is present within each of said bonding pads as said first material, said second material, or an additional metal. 
     
     
         2 . The structure of  claim 1 , further comprising another substrate bonded to an array of solder balls and overlying or underlying said substrate, wherein said array of solder balls is oriented in a direction that faces said array of bonding pads. 
     
     
         3 . The structure of  claim 2 , wherein said array of solder balls contacts said array of bonding pads. 
     
     
         4 . The structure of  claim 2 , further comprising an apparatus for generating a time-varying magnetic field, said apparatus oriented such that a magnetic field is applied to said array of bonding pads when said time-varying magnetic field is generated. 
     
     
         5 . The structure of  claim 1 , wherein said first material is said magnetic material, and said second material is a non-magnetic material. 
     
     
         6 . The structure of  claim 5 , wherein each bonding pad in said array of bonding pads comprises at least one unit reactive-material-including stack that includes a layer of said first material and a layer of said second material. 
     
     
         7 . The structure of  claim 5 , wherein each bonding pad in said array of bonding pads comprises a matrix of said first material and embedding particles of said second material. 
     
     
         8 . The structure of  claim 5 , wherein each bonding pad in said array of bonding pads comprises a matrix of said second material and embedding particles of said first material. 
     
     
         9 . The structure of  claim 5 , wherein said first material comprises Co, Fe or Ni, and said second material comprises Al, Si, or Nb. 
     
     
         10 . The structure of  claim 1 , wherein said first material and said second material are non-magnetic materials, and said magnetic material is said additional metal. 
     
     
         11 . The structure of  claim 10 , wherein each bonding pad in said array of bonding pads comprises at least one unit reactive-material-including stack that includes a layer of said first material, a layer of said second material, and a layer of said additional metal. 
     
     
         12 . The structure of  claim 11 , wherein said layer of said additional metal comprises a matrix of one of said first material and said second material, and embedded particles of said additional metal. 
     
     
         13 . The structure of  claim 12 , wherein sizes of said embedded particles of said additional metal range from 5 nm to 1,000 nm. 
     
     
         14 . The structure of  claim 12 , wherein said embedded particles of said additional metal are arranged into an array of disjoined islands. 
     
     
         15 . The structure of  claim 14 , wherein each island in said array of disjoined islands has a shape comprising a polygon, a circle, an ellipse, or a combination thereof. 
     
     
         16 . The structure of  claim 12 , wherein said embedded particles of said additional metal are arranged into an array of parallel strips, each strip in said array of parallel strips having lengthwise edges oriented along a direction of said time-varying magnetic field. 
     
     
         17 . The structure of  claim 11 , wherein said first material comprises Al or Ti, said second material comprises Ti, Si, Pt or CuOx, wherein x is equal to 0.5, 0.75, or 1.0, said additional metal comprises Fe, Co, Ni or a magnetic rare-earth material.