Formation and growth of tin whiskers on aluminum-tin alloys

Scopus : "In order to clarify the mechanism of formation and growth of nodules and whiskers on the leads used in aluminum electrolytic capacitors, aluminum-tin binary alloys were subjected to the investigation as the model alloys for the joints in the leads.

The concentration of tin in the binary alloys was 1, 5 or 10 at%. The alloy of 10 at% tin showed the largest number of nodules or whiskers on its polished surface after keeping under ambient conditions for 7.8Ms. Many whiskers whose length were more than several tens of micrometers were observed in the case of the alloy of 5 at% tin. The alloy of 1 at% tin showed few nodules or whiskers.

Growth of nodules and whiskers is caused by difusion of tin atoms from the strained or unstable areas into the stable ones or the root grains. Then, the extrusion toward the surface at the root grains develops nodules and whiskers. As a prevention measure of whiskers, selective etching of the aluminum phase using a solution of sodium hydroxide was confirmed to be successful. Thus the aluminum phase was thought to form a non-uniform distribution of strain in the tin phase. This acts as the driving force in difusion of tin atom"

Lead-Free Tin Alloy Electroplating Compositions and Methods

Factiva: "'Disclosed are electrolyte compositions for depositing a tin alloy on a substrate. The electrolyte compositions include tin ions, ions of one or more alloying metals, a flavone compound and a dihydroxy bis-sulfide. The electrolyte compositions are free of lead and cyanide. Also disclosed are methods of depositing a tin alloy on a substrate and methods of forming an interconnect bump on a semiconductor device"

Recent advances on Sn-Cu solders with alloying elements: Review

Scopus: "Nowadays, a major concern of Sn-Cu based solder alloy today is focused on continuously improving the comprehensive properties of the solder joints formed between the solders and substrates. The key issues and improvements about Sn-Cu-X (X = Ni, rare earths, Zn, Co, Ga, In, Bi, secondary particles etc.) solder are outlined and evaluated in this paper which compared to Sn-Cu solder. It can be summarized that by adding appropriate amounts of certain alloying elements X to Sn-Cu solder, and it is possible to tailor the properties of the solder, such as the melting and solidification behaviors, wettability, microstructure, interfacial reactions and mechanical properties of the solder. The reliability issues related to the implementation of Sn-Cu-X solder in advanced electronics system are also introduced, which indicates that further development on the Sn-Cu-X solders are to be underway"

Zeng, G., Xue, S., Zhang, L., Gao, L.

College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

Drivers for low temperature solders, high temperature solders

From visit to Alpha Cookson June 2011

There are a few driving forces behind it.

1. No silver (generally)

2. Lower processing costs due to lower temperatures

a. Lower energy consumption

b. Cheaper materials used for equipment as they tend to be less aggressive

c. Cheaper heating solutions

3. Allows use of cheaper components, laminates etc

4. Big expansion in use of substrates and components which cannot tolerate higher temperatures

a. OLEDs and other displays

b. Flexible electronics

c. ……..

5. Using a low temperature solder could solve some problems in finding a high temperature solder because you could shift everything down a level so don’t need to develop/use a HT lead-containing alternative