Properties and Application of Indium Metal

Carol Gowans, Incubator Market Manager, Indium Corporation talks to AZoM about the properties and application of Indium metal.

Indium metal seems to play a part in so many cutting edge technologies. Why is this?

Although indium metal has been in commercial use for less than 100 years, many of today’s electronics now rely on its unique properties.

Indium-tin oxide is used to coat the glass of the displays on our smart phones, flat panel displays, tablets, and other electronics because it is electrically conductive and transparent.

Indium metal is also thermally conductive. With a thermal conductivity of 86W/mk, indium has become very popular for thermal management in many of the electronics devices that have become such an integral part of our lives: mobile phones, tablets, and especially gaming equipment. As these devices become smaller and more powerful, thermal management becomes critical to ensure smooth operations.

In addition, indium compounds, such as indium trichloride are used to make organic precursors that are used to build semiconductor layers for lasers, LEDs, and electronic circuits.

Electrically and thermally conductive? What else can it do?

Indium metal is found in many fusible alloys. These alloys are designed to melt at very specific temperatures. For example, fusible alloys are used in sprinkler applications. When a fire starts and reaches the melting temperature of the fusible alloy, the water is released, suppressing the fire.

Because indium metal remains malleable at cryogenic temperatures, it is used to manufacture equipment that will operate in harsh environments (such as outer space). It is also used for cryogenic seals, and, because it deforms to fill in voids, it makes a tight, hermetic seal.

Solder is also a very popular application of this versatile metal. The addition of indium to solder alloys can reduce the reflow temperature, improve thermal fatigue, minimize gold leaching, and improve wetting to a variety of surfaces. It also provides the basis for a variety of Pb-free alloys.

How do I know when to consider indium as a solution for bonding or soldering?

Indium-bearing alloys work very well in the following applications:

• Soldering two metals that expand at different coefficient of thermal expansion rates (CTE mismatch). With most solders, different expansion rates can result in a cracked solder joint. Indium accommodates the differing expansion rates, cushioning the joint.
• Assembling devices that see regular heating and cooling cycles when in service. Thermal cycling can compromise a standard solder joint. Indium reduces thermal fatigue-related joint failures, reducing field failures and assuring product quality.
• Multiple soldering steps or step soldering. Several indium-containing alloys reflow at temperatures below 183°C. This allows for a subsequent reflow step that does not disturb the initial solder joint.
• Bonding non-metallic surfaces like glass, ceramic, or quartz. Indium metal wets very well to these materials.
• Using components that cannot withstand the reflow temperatures needed for conventional soldering. Many indium-contained solders reflow at less than 175°C.

What are the main considerations when using indium as a solder?

Indium is a very exciting material to work with. Our Applications Engineers have seen a wide variety of designs and assemblies. Consulting with us early in your planning process will allow you to optimize your use of indium in your process.

Because pure indium is so soft, it is best used in:

• thicknesses equal to or greater than 0.002” (0.05mm) for solder preforms and solder ribbon;
• diameters equal to or greater than 0.010” (0.254mm) for solder wire.

However, adding tin, silver, or lead broadens these parameters while retaining many of the physical properties of indium. Optimum powder sizes for solder paste would be type 2, type 3, or type 4.

Other than that, indium and indium-containing alloys can be fabricated in a wide variety of forms. Even a small amount of indium added to an alloy can impart the physical properties of indium. For example, Indalloy #164 (92.5Pb/5.0In/2.5Ag) works in applications requiring improved thermal fatigue resistance and reduced gold leaching.

Is there any concern over the availability of indium? How would you address these concerns?

The US Geologic Survey (USGS) states that indium is more abundant than silver. Indium Corporation’s in-depth calculations regarding the world’s supply of indium reveals that indium-bearing raw materials exist abundantly - worldwide based on current consumption, the availability of virgin indium, and the recycle rate of existing supplies of indium - and there is enough indium to last for about 100 years.

For more information on this topic, I can refer to you to two articles. One is located on our website, The Availability of Indium and Gallium. The other is a recently published article in Compound Semiconductor, “Indium: Scarcity claim is scaremongering.”

What is being done to optimize the indium supply?

There are two identified areas that are improving the indium supply: improved extraction and enhanced reclaim.

Indium is a by-product of zinc mining. By improving the efficiency of the extraction, and adding capacity to current extraction operations at the base metal smelters, more indium is converted refined indium.

Reclaimed indium strongly augments the indium supply chain. Since so much indium is being converted into ITO targets for display coating applications, the unused portion of these targets is easily reclaimed and the indium reused. These processes have been improving in efficiency and speed so that now about 2/3 of the annual indium consumption consists of reclaimed material.

The indium supply chain is easily able to address all forecasted demand.

Is indium all there is at The Indium Corporation?

Although it was the basis for the company’s start-up back in 1934, we have branched out to other metals and materials. In fact, a large percentage of our solders contain no indium at all. We have the largest selection of Pb-free solder alloys, as well as products from alloys that contain bismuth, gold, tin, silver, copper, germanium, or gallium.

We manufacture inorganic compounds based on indium, gallium, and germanium, and we also produce polymers and nanomaterials. Our products are used in semiconductor assembly, thermal management, solar assembly, and electronics assembly.

We are definitely “more than indium!”

What is next for Indium Corporation?

Indium Corporation is continually helping our customers optimize their processes and improve end-product performance and reliability. One way we do this is to invest in research and development. We have a large staff of PhDs and metallurgists based around the world, working on new product and process development.

By staying close to our customers, we are able to anticipate their need. When we saw how customers were struggling with thermal management issues caused by inefficient materials like thermal grease, we created our successful Heat-Spring^® material, which does not experience the pump-out and bake-out issues that you get with thermal grease.

We also focus our efforts on the development of nanotechnology materials. Upstate New York, home to our global headquarters, is a hub for nanotechnology development, and it is where we manufacture NanoFoil^®.

An exciting advancement that has gained recent popularity is IGZO, which is comprised of indium-, gallium-, and zinc-oxide. Combined, these compounds have unique properties that allow for better pixel transistors or thin film transistors (TFT) on the inside glass surface of a display. Indium oxide is the biggest component in the IGZO compositions used today (about 40% of IGZO is indium).

IGZO is used in LCDs (liquid crystal displays) because of its electronic performance. IGZO has a higher mobility (which enables the electrons to move faster), and a higher on-off voltage (so it works better as an electronic switch).

Higher mobility means that TFTs can be made smaller – which is important as pixel densities are increasing in today’s more detailed and photo-realistic displays.

The switch-control property is significant because it means less current is needed to operate the display, which means mobile phone displays can use smaller batteries.

Simply put: cell-phones can now be much smaller (because we can use smaller batteries), and they will last much longer (because fewer electrons from the battery are needed to drive the more efficient device).

Indium Corporation continues to be at the forefront of the development of new technologies and new materials. That is a big reason for our success over the last 79 years, and for our continued growth. We clearly are an exciting company with a very bright future.

About Carol Gowans 

Carol Gowans is the Incubator Market Manager for Indium Corporation's solder products. Carol career background includes more than 25 years of experience in sales and product management to focus on emerging markets and technologies. This experience covers a variety of markets including medical, aerospace, and electronics manufacturing. Carol’s goal is to identify the requirements of each target market to match the right tools (including products, technical support, etc.) to meet those requirements.

Carol’s academic history includes a bachelor's degree in Public Relations from Utica College of Syracuse University. She has worked with Indium Corporation's Engineered Solder Materials and has authored papers on Solder Fortification^® and improving solder joint reliability with the use of solder preforms. She also authors a blog on Engineered Solders.