Methods for improving adhesion of aluminum films

Abstract

The described embodiments relate generally to aluminum films and pretreatments for improving the adhesion of aluminum films on substrate surfaces. Methods involve providing three-dimensional adhesion surfaces on the substrate that promote adhesion to a subsequently deposited aluminum film. The methods can avoid the use of strike materials, such as nickel and copper, used in conventional adhesion-promoting treatments. According to some embodiments, methods involve providing an aluminum oxide adhesion layer on the substrate prior to depositing aluminum. According to some embodiments, methods involve providing a zincating layer on the substrate prior to depositing aluminum. According some embodiments, methods involve roughening the surface of the substrate prior to depositing aluminum. Some embodiments involve a combination of two or more substrate pretreatments. Described methods can be used to provide more flexibility in subsequent anodizing processes. In some embodiments, methods involve anodizing the aluminum film and a portion of the substrate.

1 . A method of forming a protective coating on a surface of an aluminum substrate, the method comprising:
 forming an adhesion-promoting layer on a surface of the aluminum substrate, the adhesion-promoting layer having a plurality of cavities having side walls oriented substantially normal to the surface of the aluminum substrate, wherein the adhesion-promoting layer is chemically compatible with a subsequent anodizing process; and   depositing an aluminum layer on the adhesion-promoting layer, the aluminum layer having a plurality of anchor portions disposed within corresponding cavities of the adhesion-promoting layer, wherein the anchor portions engage with the side walls of the adhesion-promoting layer resisting a shearing force applied to the aluminum layer securing the aluminum layer to the adhesion-promoting layer.   
     
     
         2 . The method of  claim 1 , further comprising:
 converting at least a portion of the aluminum layer to an aluminum oxide layer using an anodizing process.   
     
     
         3 . The method of  claim 2 , wherein substantially the entire aluminum layer is converted to the aluminum oxide layer. 
     
     
         4 . The method of  claim 3 , further comprising:
 during the anodizing, transcending a boundary between the adhesion-promoting layer and the aluminum substrate converting a portion of the aluminum substrate to a second aluminum oxide layer.   
     
     
         5 . The method of  claim 1 , wherein the aluminum substrate makes up at least a portion of an enclosure for an electronic device. 
     
     
         6 . The method of  claim 1 , wherein the adhesion-promoting layer is substantially free of copper or nickel. 
     
     
         7 . The method of  claim 1 , wherein the aluminum oxide adhesion layer has a thickness of about 3 micrometers or less. 
     
     
         8 . The method of  claim 1 , wherein forming the adhesion-promoting layer comprises:
 forming an aluminum oxide adhesion layer on the surface of the aluminum substrate, the aluminum oxide adhesion layer having a plurality of pores defined by a plurality of corresponding pore walls, wherein the plurality of pores have an average pore size sufficiently large to allow anchoring portions of the aluminum layer to form therein during the subsequent aluminum layer depositing process.   
     
     
         9 . The method of  claim 8 , wherein the aluminum oxide adhesion layer has a thickness of about 3 micrometers or less. 
     
     
         10 . The method of  claim 1 , wherein forming the adhesion-promoting layer comprises:
 forming a zincate layer on the aluminum substrate, the zincate layer having a crystalline structure having the plurality of cavities.   
     
     
         11 . The method of  claim 10 , wherein the zincate layer has a thickness of less than about 0.5 micrometers. 
     
     
         12 . The method of  claim 1 , further comprising:
 prior to forming the adhesion-promoting layer, roughening the surface of the aluminum substrate.   
     
     
         13 . The method of  claim 12 , wherein the aluminum substrate is comprised of an aluminum alloy. 
     
     
         14 . The method of  claim 1 , wherein the aluminum substrate is comprised of an aluminum alloy. 
     
     
         15 . A method for forming an aluminum layer on a substrate, the method comprising:
 forming an aluminum oxide adhesion layer on the substrate, the aluminum oxide adhesion layer having a plurality of pores defined by a plurality of corresponding pore walls;   during the forming, controlling an average pore size of the aluminum oxide adhesion layer by simultaneously allowing growth of the pore walls and dissolving the pore walls and dissolving that the average pore size is sufficiently large to allow aluminum material to form therein during a subsequent aluminum layer depositing process; and   depositing the aluminum layer on the aluminum oxide adhesion layer, wherein during the depositing, anchoring portions of the aluminum layer form within at least a portion of corresponding pores, wherein the anchor portions engage with the pore walls resisting a shearing force applied to the aluminum layer and securing the aluminum layer to the aluminum oxide layer.   
     
     
         16 . The method of  claim 15 , wherein the substrate is comprised of an anodizable material, the method further comprising:
 converting substantially the entire aluminum layer to an aluminum oxide layer and converting a portion of the substrate to an oxide layer.   
     
     
         17 . The method of  claim 15 , wherein the substrate is comprised of an aluminum alloy. 
     
     
         18 . The method of  claim 16 , wherein the substrate is comprised of an aluminum alloy. 
     
     
         19 . The method of  claim 15 , wherein the aluminum layer is comprise of substantially pure aluminum. 
     
     
         20 . The method of  claim 15 , wherein the aluminum substrate makes up at least part of an enclosure for an electronic device. 
     
     
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