Making and using an ultra-thin copper foil

Abstract

This invention provides a composite foil comprising an organic release layer between a metal carrier layer and an ultra-thin copper foil, and a process for producing such composite foils comprising the steps of depositing the organic release layer on the metal carrier layer and then forming an ultra-thin copper foil layer on said organic release layer, preferably by electrodeposition. The organic release layer preferably is a heterocyclic compound selected from triazoles, thiazoles, imidazoles, or their derivatives, and provides a uniform bond strength which is adequate to prevent separation of the carrier and ultra-thin copper foil during handling and lamination, but which is significantly lower than the peel strength of a copper/substrate bond, so that the carrier can easily be removed after lamination of the composite foil to an insulating substrate. The invention also includes laminates made from such composite foils and printed wiring boards made from such laminates.

What is claimed is:  
     
         1 . A composite foil comprising a release layer uniformly disposed between a metal carrier layer and an ultra-thin copper foil wherein the release layer is an organic compound characterized by: 
 a. containing at least one nitrogen atom;    b. being capable of forming a bond with said copper foil and said metal carrier layer;    c. retaining the ability to bond with copper after exposure to temperatures used in laminating said composite foil to a substrate;    d. having a bond strength to copper which is uniform and lower than the peel strength of said copper foil when laminated to a substrate, thereby permitting the metal carrier to be separated from said copper foil when said copper foil has been laminated to a substrate, and    e. providing a very thin release layer which permits uniform deposition of said ultra-thin copper foil.    
     
     
         2 . A composite foil of  claim 1 , wherein said release layer comprises a heterocyclic compound and at least one member of the group consisting of triazoles, thiazoles, imidazoles, and derivatives thereof.  
     
     
         3 . A composite foil of  claim 1 , wherein said release layer is a triazole or derivatives thereof.  
     
     
         4 . A composite foil of  claim 3 , wherein said triazole is CBTA, CBTA-U, BTA, or mixtures thereof.  
     
     
         5 . A composite foil of  claim 1 , wherein said organic compound retains its ability to bond with copper after exposure to temperatures above 120° C.  
     
     
         6 . A composite foil of  claim 1 , wherein the bond strength between said ultra-thin copper foil and said metal carrier layer is about 0.005-0.3 kgf/cm.  
     
     
         7 . A composite foil of  claim 1 , wherein said metal carrier layer is copper or copper alloy.  
     
     
         8 . A composite foil of  claim 1 , wherein said metal carrier layer is copper-coated aluminum.  
     
     
         9 . A composite foil of  claim 1 , wherein the thickness of said ultra-thin copper foil is less than 12 μm.  
     
     
         10 . A composite foil of  claim 1 , wherein said metal carrier layer has a thickness up to about 5 mm.  
     
     
         11 . A composite foil of  claim 10 , wherein said metal carrier layer has a thickness of about 18-70 μm.  
     
     
         12 . A composite foil of  claim 1 , wherein said ultra-thin copper foil further comprises a nodularization treatment on the exposed copper surface thereof to enhance the peel strength between the ultra-thin copper foil and a substrate.  
     
     
         13 . A composite foil of  claim 12 , wherein said ultra-thin copper foil further comprises a passivated treatment on the exposed surface thereof to prevent oxidation of the surface of the ultra-thin copper foil.  
     
     
         14 . A copper-clad laminate comprising a composite foil of  claim 1  laminated to a substrate.  
     
     
         15 . A copper-clad laminate of  claim 14 , wherein the metal carrier layer has been removed to expose said ultra-thin copper foil.  
     
     
         16 . A printed wiring board comprising the copper-clad laminate of  claim 15 .  
     
     
         17 . A multi-layer printing wiring board formed by laminating on at least one side of an inner layer board on which wiring patterns were previously formed a composite foil according to  claim 1  to obtain a copper clad laminate, separated from the metal carrier layer from the copper clad laminate to expose the ultra-thin copper foil, and forming a wiring pattern on said ultra-thin copper foil, thereby obtaining a multi-layer printed wiring boards.  
     
     
         18 . A multi-layer printed wiring board formed by laminating a plurality of printed wiring boards according to  claim 16 .  
     
     
         19 . A multi-layer printed wiring board formed by laminating a plurality of printed wiring boards according to  claim 17 .  
     
     
         20 . A process for producing a composite foil comprising: 
 a. uniformly applying an organic release layer to a metal carrier layer; and    b. depositing an ultra-thin copper layer on said organic release layer;    wherein said organic release layer is an organic compound characterized by: 
 1. containing at least one nitrogen atom;  
 2. being capable of forming a bond with said copper layer and said metal carrier layer;  
 3. retaining the ability to bond with copper after exposure to temperatures used in laminating said composite foil to a substrate;  
 4. having a bond strength to copper which is uniform and lower than the peel strength of said copper foil when laminated to a substrate, thereby permitting the metal carrier layer to be separated from said copper foil when said copper foil has been laminated to a substrate, and  
 5. providing a very thin release layer which permits uniform deposition of said ultra-thin copper foil.  
   
     
     
         21 . A process of  claim 20 , wherein said organic release layer is applied to said metal carrier layer by dipping said metal carrier layer in an aqueous solution of said organic compound and thereafter rinsing said metal carrier layer in water, leaving a thin layer of said organic compound bonded to said metal carrier layer.  
     
     
         22 . A process of  claim 20 , wherein said organic compound is a heterocyclic compound selected from the group consisting of triazoles, thiazoles, imidazoles, and derivatives thereof.  
     
     
         23 . A process of  claim 22 , wherein said organic compound is a triazole or derivatives thereof.  
     
     
         24 . A process of  claim 23 , wherein said triazole is CBTA, CBTA-U, BTA, or mixtures thereof.  
     
     
         25 . A process of  claim 20 , wherein said organic compound retains its ability to bond to copper after exposure to temperatures above 120° C.  
     
     
         26 . A process of  claim 20 , wherein said ultra-thin copper layer is deposited on said organic release layer by electrodeposition.  
     
     
         27 . A process of  claim 26 , wherein said electrodeposition employs an electrolytic bath which is substantially free of acid.  
     
     
         28 . A process of  claim 27 , wherein said electrolytic bath is a copper cyanide or copper pyrophosphate bath.  
     
     
         29 . A process of  claim 27 , wherein said electrodeposition is used to deposit at least 0.5 μm of copper on said organic release layer.  
     
     
         30 . A process of  claim 26 , wherein said electrodeposition employs a first electrolytic bath containing copper pyrophosphate to deposit a first layer of copper, followed by further electrodeposition using a second electrolytic bath containing copper sulfate and sulfuric acid to deposit a second layer of copper on said first layer.  
     
     
         31 . A process of  claim 29 , wherein said first layer is at least 0.50 μm thick and the thickness of said first and second layers is up to about 12 μm.  
     
     
         32 . A process of  claim 20 , further comprising the step of applying to said ultra-thin copper layer a nodularizing treatment to improve adhesion of said ultra-thin copper layer to a substrate.  
     
     
         33 . A process of  claim 32 , further comprising the step of applying a passivation treatment to said nodularized ultra-thin copper layer to prevent oxidation of said ultra-thin copper layer.  
     
     
         34  A process of  claim 33 , wherein said passivation treatment comprises depositing at least one member of the group consisting of zinc, zinc chromate, nickel, tin, cobalt and chromium to said nodularized ultra-thin copper layer.