Minimizing whisker growth in tin electrodeposits

Abstract

The present invention relates to a method for reducing tin whisker formation in tin deposits by plating on an underlying metal tin deposits which are essentially free of compressive stress or are predominantly in a predetermined crystal orientation that essentially matches that of the underlying metal in order to inhibit tin whisker growth. The deposits preferably exhibit no compressive stress or exhibit a tensile stress. Also, the most preferred crystal orientation is one that is the same as that of the underlying metal. The deposit preferably contains at least 95% tin and optionally at least one alloying element of silver, bismuth, copper or zinc in an amount of 5% or less.

1 . A method for reducing tin whisker formation in a tin deposit by providing upon an underlying metal a plated tin deposit that is essentially free of compressive stress.  
     
     
         2 . The method of  claim 1 , wherein the tin deposit either exhibits no compressive stress or exhibits a tensile stress.  
     
     
         3 . The method of  claim 1 , wherein the tin deposit is provided in a crystal orientation that is compatible with the underlying metal in order to further inhibit tin whisker growth.  
     
     
         4 . The method of  claim 3 , wherein the crystal orientation of the tin deposit essentially matches that of the underlying metal.  
     
     
         5 . The method of  claim 3 , wherein the underlying metal is present as a substrate or as a deposit upon a substrate.  
     
     
         6 . The method of  claim 1 , wherein the underlying metal comprises copper or a copper alloy.  
     
     
         7 . The method of  claim 1 , wherein the tin deposit contains at least 95% tin and optionally at least one alloying element of silver, bismuth, copper or zinc in an amount of 5% or less.  
     
     
         8 . The method of  claim 1 , wherein the tin deposit is provided during electroplating from a solution comprising an acid, a tin salt, and a surfactant.  
     
     
         9 . The method of  claim 8 , wherein the acid is a sulfonic acid, sulfuric acid, a halide ion acid, a fluoborate or mixtures thereof.  
     
     
         10 . The method of  claim 8 , wherein the solution includes an alkylol sulfonic acid or solution soluble salt thereof in an amount sufficient to improve deposit appearance.  
     
     
         11 . The method of  claim 8 , wherein the surfactant comprises a solution soluble organic compound having 2 to 4 joined rings, a total of 6 to 24 ring members, and at least one oxygen or nitrogen atom present in or attached to at least one of the rings, a condensation compound of an alkylene oxide, or block copolymer.  
     
     
         12 . A method for reducing tin whisker formation in a plated tin deposit, which comprises plating the tin deposit onto the underlying metal from an electroplating solution comprising an acid, a tin salt, a surfactant in an amount sufficient to assist in providing a tin deposit directly on an underlying metal such that the deposit is essentially free of compressive stress in order to inhibit tin whisker growth in the tin deposit, and, optionally, a solution soluble salt of at least one alloying element, wherein stress of the tin deposit is determined to confirm that it is essentially free from compressive stress, thus reducing tin whisker formation in the deposit.  
     
     
         13 . The method of  claim 12 , wherein the underlying metal is a substrate or a deposit upon a substrate.  
     
     
         14 . The method of  claim 12 , wherein the tin deposit either exhibits no compressive stress or exhibits a tensile stress.  
     
     
         15 . The method of  claim 12 , wherein the tin deposit is provided in a crystal orientation that is compatible with the underlying metal in order to further inhibit tin whisker growth.  
     
     
         16 . The method of  claim 12 , wherein the crystal orientation of the tin deposit essentially matches that of the underlying metal.  
     
     
         17 . The method of  claim 12 , wherein the underlying metal is present as a substrate or as a deposit upon a substrate.  
     
     
         18 . The method of  claim 12 , wherein the underlying metal comprises copper or a copper alloy.  
     
     
         19 . The method of  claim 12 , wherein the tin deposit contains at least 95% tin and optionally at least one alloying element of silver, bismuth, copper or zinc in an amount of 5% or less.  
     
     
         20 . The method of  claim 12 , wherein the tin deposit is provided during electroplating from a solution comprising an acid, a tin salt, and a surfactant.  
     
     
         21 . The method of  claim 20 , wherein the acid is a sulfonic acid, sulfuric acid, a halide ion acid, a fluoborate or mixtures thereof.  
     
     
         22 . The method of  claim 20 , wherein the solution includes an alkylol sulfonic acid or solution soluble salt thereof in an amount sufficient to improve deposit appearance.  
     
     
         23 . The method of  claim 20 , wherein the surfactant comprises a solution soluble organic compound having 2 to 4 joined rings, a total of 6 to 24 ring members, and at least one oxygen or nitrogen atom present in or attached to at least one of the rings, a condensation compound of an alkylene oxide, or block copolymer.  
     
     
         24 . A method of manufacturing an electronic component which comprises plating a tin deposit onto metallic portions of the electrical component so that the tin deposit is essentially free of compressive stress in order to inhibit tin whisker growth thereon.  
     
     
         25 . A method of reducing environmental contamination resulting from plated components which comprises plating metallic portions of the components with a deposit of tin or a tin alloy containing at least 95% tin and that is essentially free of compressive stress in order to inhibit tin whisker growth, thus avoiding the need to plate the components with metals or alloys comprising one or more environmentally harmful elements.