Indium Alloyed Tin Coatings Mitigate Whisker Growth
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Solution Overview
Problem
Tin whisker growth in electronic packages poses a significant risk of electrical shorts, particularly in long-term applications, as existing Pb-free solutions only slow down whisker growth rather than stopping it, and the industry seeks a reliable alternative to mitigate this issue without using lead.
Innovation Solution
Incorporating indium into tin coatings by electroplating and subsequent heat treatment to ensure indium is present throughout the entire thickness of the Sn film, effectively preventing whisker growth by reducing stress and diffusivity at grain boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pb is added to Sn-coating to mitigate whisker growth, then whisker growth is reduced, but Pb-free regulations cannot be complied with
Solution Approach 1:
The patent changes the chemical composition parameter by substituting Pb with In in the Sn-coating, achieving whisker growth mitigation while complying with Pb-free regulations. Specifically, adding 0.1-10 wt% In to the Sn-coating modifies the alloy composition to eliminate the harmful effects of Pb while maintaining or improving whisker resistance.
Solution Approach 2:
The patent creates a composite Sn-In alloy coating that combines the beneficial properties of Sn (solderability, corrosion resistance) with In (whisker growth inhibition). This composite material approach allows the coating to meet both reliability requirements and regulatory compliance simultaneously.
2Reliability
If polymeric conformal coating is applied on top of electroplated Sn to slow whisker emergence, then whisker growth is slowed, but whisker growth is not stopped and long-term applications remain problematic
Solution Approach 1:
The patent extracts the root cause of whisker growth (compressive stress and high diffusivity at grain boundaries) by alloying Sn with In, rather than merely covering the symptoms with a polymeric coating. This addresses the underlying mechanism to achieve long-term effectiveness.
Solution Approach 2:
The patent changes the physical and chemical parameters of the Sn-coating by adding In, which reduces both the compressive stress and the diffusivity at grain boundaries. This fundamental parameter change provides long-term protection without relying on external coatings that may degrade over time.
3Stress or pressure
If Sn is annealed or alloyed with bismuth to reduce stress, then compressive stress in Sn is reduced, but whisker growth is not actually reduced or stopped
Solution Approach 1:
The patent changes the composition parameter by adding In to the Sn-coating, which simultaneously reduces both compressive stress and diffusivity at grain boundaries. Unlike Bi alloying or annealing that only address stress, the In addition addresses both stress and diffusivity, providing complete whisker growth mitigation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The indium-containing Sn coatings completely mitigate whisker growth, with no whiskers of aspect ratio greater than 5 observed even after 6 months, making indium a direct substitute for lead in preventing tin whisker formation.
Implementation Method 1
incorporation of indium in tin coatings deposited by electroplating, that is a subject of this invention, has been shown to completely mitigate whisker growth... Indium, in the range of 1-20 weight percent, more particularly 1-15 weight percent, can be introduced into the Sn coating... provided that the entire Sn layer is alloyed with In
Implementation Method 2
methods for incorporating indium into an entire Sn film for preventing the growth of whiskers from the Sn film, wherein the Sn film is applied to a metallic substrate... Incorporating indium into tin coatings by electroplating
Implementation Method 3
Incorporating indium into tin coatings by electroplating and subsequent heat treatment to ensure indium is present throughout the entire thickness of the Sn film
Data Source
AI summary
A method comprising incorporating indium into an entire Sn film for preventing the growth of whiskers from the Sn film, wherein the Sn film is applied to a metallic substrate. The indium is present in the entire thickness of the Sn film.