Methods for forming carbon nanotube thermal pads

Abstract

Methods for forming thermal pads including arrays of vertically aligned carbon nanotubes are provided. The thermal pads are formed on various substrates, including foils, thin self-supporting polished metals, semiconductor dies, heat management aids, and lead frames. The arrays are growth from a catalyst layer disposed on the substrate. Forming the array can include leaving the ends of the nanotubes unfinished, attaching a foil thereto, or coating the ends with a metal layer. The metal layer coating can then be polished to a desired smoothness. The array can be filled with a matrix material, only partially filled, or left unfilled. Where the substrate is a foil, the method can be a continuous process where foil is taken from a roll and fed through a series of formation steps. Where the substrate is a lead frame, heating can be generated by applying an current to a pad of the lead frame.

1 . A method of forming a thermal pad comprising: 
 providing a substrate having a thickness of less than 500μ and a planar surface;    forming a catalyst layer over the planar surface of the substrate; and    forming an array of carbon nanotubes on the catalyst layer such that the carbon nanotubes are generally aligned in a direction perpendicular to the planar surface, the array characterized by a first end attached to the catalyst layer and a second end opposite the first end.    
   
   
       2 . The method of  claim 1  wherein the substrate includes copper.  
   
   
       3 . The method of  claim 1  wherein the substrate includes silicon.  
   
   
       4 . The method of  claim 1  wherein providing the substrate includes supporting the substrate with a frame.  
   
   
       5 . The method of  claim 1  wherein providing the substrate includes feeding a foil from a roll into a guide and using a transport mechanism to move the foil along the guide.  
   
   
       6 . The method of  claim 1  further comprising forming an interface layer on the substrate before forming the catalyst layer.  
   
   
       7 . The method of  claim 6  wherein forming the interface layer includes depositing aluminum oxide.  
   
   
       8 . The method of  claim 6  further comprising forming a barrier layer on the substrate before forming the interface layer.  
   
   
       9 . The method of  claim 1  further comprising infiltrating a matrix material into the array to fill an interstitial space thereof between the first and second ends.  
   
   
       10 . The method of  claim 9  wherein infiltrating the matrix material includes injection molding a polymer to fill the interstitial space.  
   
   
       11 . The method of  claim 1  further comprising forming a base metal layer around the carbon nanotubes at the first end of the array such that an interstitial space of the array between the base metal layer and the second end of the array remains unfilled.  
   
   
       12 . The method of  claim 1  further comprising forming a metal layer on the second end of the array, wherein the carbon nanotubes extend at least partially into the metal layer.  
   
   
       13 . The method of  claim 12  further comprising polishing the metal layer.  
   
   
       14 . The method of  claim 12  wherein forming the metal layer includes coating the ends of the carbon nanotubes at the second end of the array with a wetting layer.  
   
   
       15 . The method of  claim 14  further comprising coating the ends of the carbon nanotubes with a protective layer over the wetting layer.  
   
   
       16 . The method of  claim 1  further comprising attaching a metal foil to the second end of the array.  
   
   
       17 . The method of  claim 16  wherein attaching the metal foil includes forming an attachment layer on the second end of the array.  
   
   
       18 . The method of  claim 1  wherein forming the catalyst layer includes patterning the catalyst layer to form a patterned catalyst layer, and wherein forming the array includes forming bundles of aligned carbon nanotubes on the patterned catalyst layer.  
   
   
       19 . The method of  claim 1  further comprising providing a spacer on the planar surface before forming the array.  
   
   
       20 . The method of  claim 1  further comprising 
 forming a second catalyst layer on a second planar surface of the substrate; and    forming a second array of carbon nanotubes on the second catalyst layer such that the carbon nanotubes are generally aligned in a direction perpendicular to the second planar surface.    
   
   
       21 . A method of forming a thermal pad comprising: 
 providing a lead frame having a die bonding pad;    forming a catalyst layer over the die bonding pad; and    forming an array of carbon nanotubes on the catalyst layer such that the carbon nanotubes are generally aligned in a direction perpendicular to the die bonding pad.    
   
   
       22 . The method of  claim 21  further wherein forming the array comprises heating the die bonding pad by applying a current thereto.  
   
   
       23 . The method of  claim 21  further comprising separating the die bonding pad from the lead frame.