Tin electrodeposits having properties or characteristics that minimize tin whisker growth

Abstract

A method of reducing tin whisker formation by creating a tin deposit which is inherently less prone to tin whisker formation or growth facilitated by oxide presence or corrosion reactions on the tin deposit surface. This is obtained by one or more of: (i) the deposition of a fine-grained tin deposit having an average grain diameter in the range of 0.05 to 5 microns; (ii) a phosphorous compound in the solution that is used to electroplate the tin deposit so that that the deposit incorporates trace amounts of phosphorous which in turn reduces tin whisker formation by preventing surface oxides even when exposed to heat or humidity; or (iii) a phosphorous compound, mercaptan, or organic or organo-metallic compound in a solution that applies a protective coating to the surface of a previously electroplated tin deposit, wherein the protective coating acts to minimize or prevent oxide formation or corrosion of the tin deposit during exposure to heat or humidity. Such tin deposits containing 80% to 100% by weight of tin exhibit minimal to no tin whisker growth.

Description

[0001] This application claims the benefit of U.S. provisional application No. 60 / 698,550 filed Jul. 11, 2005, the entire content of which is expressly incorporated herein by reference thereto.FIELD OF INVENTION [0002] The present invention relates to a method for depositing tin in a manner to reduce, minimize or prevent tin whisker growth from such deposits, as well as to electroplated components formed by such a method. More particularly, the invention relates to a modification or treatment of the deposit to render it less prone to whisker growth. In particular, prevention of oxide formation and / or corrosion reactions on the tin deposit surface or post treatment of the deposit surface has been found to be effective for this purpose. BACKGROUND OF THE INVENTION [0003] The use of a tin or tin alloy electroplated deposit has become increasingly important in fabricating electronic circuits, electronic devices and electrical connectors because of the benefits that such deposits provide...

AI Technical Summary

Benefits of technology

[0014] The invention relates to a number of methods for reducing tin whisker formation or growth in tin deposits on a substrate. Generally, at least one physical property or characteristic of a tin deposit is modified during deposition of the same on a substrate or immediately thereafter. Thus, the tin deposit is provided on the substrate with at least one physical property or characteristic that renders it less prone to tin whisker formation or growth so that tin whiskering is substantially reduced or is even prevented.

[0015] In one embodiment, the tin deposit can be provided on the substrate as a fine grain structure which minimizes tin whiskering, where the tin deposit preferably has an average grain size of about 0.05 to 5 and preferably less than about 2 to 3 microns.

[0016] In another embodiment, the tin deposit can be treated during deposition to render it less prone to tin whisker formation or growth. This can be done by rendering the tin deposit essentially free of surface oxides to minimize tin whiskering thereon. The prevention of surface oxide formation is conveniently achieved by providing the tin deposit from a solution containing a phosphorous compound, thereby incorporating trace or small amounts of phosphorous in the tin deposit. Preferably, the tin plating solution contains sufficient phosphorous compound to provide an amount of about 0.1 ppm to 30% by weight phosphorus in the tin deposit.

[0018] The invention also relates to an improvement in a tin plated electronic component that includes a copper surface upon which a fine grained tin deposit is present. The improvement comprises minimizing or preventing tin whisker formation or growth by providing the tin deposit with one or more of (a) a fine grained structure so that the tin deposit is less prone to tin whisker formation or growth compared to tin deposits having larger grain structures; (b) trace or small amounts of phosphorous so that the tin deposit is essentially free of surface oxidation and is less prone to tin whisker formation or growth compared to tin deposits having surface oxidation; or (c) a protective layer so that it is less prone to tin whisker formation or growth compared to tin deposits having no protective layer.

Problems solved by technology

When pure tin is used and is applied to a copper or copper alloy substrate, the resulting deposit suffers from interdiffusion of base material copper into the tin deposit and subsequent formation of copper-tin intermetallic compounds.

While these copper-tin compounds can be brittle and may impair the usefulness of the tin coated component, their presence also results in compressive stress formation in the tin deposit.

The presence of such whiskers is undesirable due to the very fine line definition required for modern circuitry, since these whiskers can form both electrical shorts and electrical bridges across insulation spaces between conductors.

The whiskers may create shorts or introduce failures into electronic circuitry.

However, this approach does not fully address or necessarily avoid the problem.

The formation of an intermetallic compound and diffusion of copper into the tin deposit have served this purpose but at prohibitive performance cost in the final product.

Unfortunately, lead and a number of other alloying elements are undesirable due to their toxicity and related environmental issues.

Thus, pure tin or very high tin content deposits are now used, and these are subject to whiskering under certain conditions.

This is particularly significant problem for small electronic parts that are provided with a tin deposit, as short circuits can result.

This problem is currently un-resolved in the industry today since most companies dealing in tin whisker growth phenomenon have not considered this newly discovered driving force for tin whisker growth or how to combat it.