Materials Science Changes the Electronics World: An Interview with Dr. Andy Mackie of Indium Corporation

Your company was founded in 1934. What were the major milestones of the Indium Corporation?

Mackie: It should come as no surprise that the early history of Indium Corporation is tightly linked with the element indium. Indium as an element was discovered in 1863, but Indium Corporation’s history really begins with the work of William S. Murray (Figure 1) and Daniel Gray, who independently began experimenting with indium as a coating to prevent silver from tarnishing. Indium Corporation was founded to explore other uses of indium. One of the first applications of indium was as a coating for ball bearings in airplanes: indium is a soft metal but forms very hard, and hard-wearing, intermetallics. In 1982, we expanded our manufacturing capabilities for our solder paste program in the fledgling surface mount technology (SMT) industry. In 1990, our first non-USA facility opened; we have since become a major global manufacturer and supplier of materials for the electronics and semiconductor assembly, thermal management, and thin-film markets.

 

Figure 1: Indium Corporation founder Dr. William S. Murray dedicated his life to investigating and developing the uses of indium metal

 

In general: What role does your company play in the worldwide electronics market?

Mackie: What are your challenges? We are a premier supplier of materials in a wide variety of different industries. Although we mostly serve the electronics and semiconductor assembly markets, we are also involved in medical devices and renewable energy, for example. The challenges are multifarious, and we have strong competitors. It is a daily challenge to develop and promote materials that differentiate us from our competition. We have a strong emphasis on collaboration:

• in consortia focused on growing markets and technology;
• with equipment partners (such as Mycronic), who provide deep process insights and opportunities for collaboration;
• with universities working on promising new technologies.

 

Your Solder Alloy Directory has over 220 alloys. Does that mean that the corresponding applications are very complex?

Mackie: Correct. complex and broad! Our complete solder and brazing alloy metallurgy directory has over 250 Indalloy entries, of which we annually ship around 150 in different forms: powder, paste, wire, microspheres, and a variety of shapes, sizes, thicknesses and even specialty surface treatments of engineered solders for specific applications, including those in power electronics.

 

Components and systems are getting smaller and smaller. How do you keep your soldering products and materials expertise ahead of this curve?

Mackie: In digital electronics, Moore’s law has been the force for transistor shrinkage, but the economies of scale down are no longer the main driver. The power semi world has also seen a revolution in shrinking die, alongside increasing current and power density. Not everything is getting smaller: for example in artificial intelligence (AI), we are seeing some die that are now as large as the wafer itself. This general “decrease” trend has resulted in not just smaller device feature sizes, but thinner die - a common theme across most semiconductors. In power devices, silicon is slowly being replaced by wide bandgap materials, and thinner die are reducing RDSON. However, thinner gate oxides are now impacting the longevity of SiC devices, so there are clearly some tradeoffs. Package shrink in mobile devices is growing the heterogeneous integration and assembly (HIA [SIP]) market, which now bridges the 3-way gap between contract electronics manufacturers (CEMs); outsourced assembly and test (OSATs); and major wafer fabs. The last are simply extending their post-back-end-of-line (BEOL) processes a little further, with the advantage of upstream supply chain control only dreamed of by the OSATs and CEMs.

Shrinkage impacts the pitch (I/O center-center distance), so Indium Corporation focuses on two aspects of materials: 1) The physical size of, for example, the printed or jetted solder paste deposit; and 2) Increasing quality expectations: for example, a material that works well for one specific application will exhibit increasing sensitivity to foreign matter as the package size shrinks to meet market needs. We have had to adopt a white room approach to manufacturing some of our more advanced materials as a result.

 

There is a clear move from water soluble to low residue no-clean fluxes in flip-chip for two different reasons:

• As flip-chip pitches shrink (60µm pitch and below for copper pillar applications), water soluble fluxes become very difficult to clean out, as clearances are very tight
• The proliferation of flip-chip on (increasingly delicate) leadframe (FCOL) is only feasible if you eliminate the damaging water wash process.

 

You fabricate and package materials with unique shapes and physical properties. What kind of market requirements are behind this?

Mackie: For solder preforms, we customize shapes to best meet customer needs, including extending into the z-axis. Each component or package has differing requirements for reliability, utility, and assembly process. For example, the small laser diodes used in an active optical cables assembly would need a die-attach to the submount of gold-tin (280°C melting point), while the submount attach to the PCB would be SAC305 (218°C MP), and final board attach would use a BiSnAg solder (238°C MP).

For SMT soldering, SAC305 (96.5Sn/3.0Ag/0.5Cu) can be used in many applications. Indium Corporation offers lead-free solder paste for a variety of melting points: Durafuse™ LT (235°C) for moderate MPs, and BiAgX® technology (>262°C) for higher MPs.

 

Figure 2: Indium Corporation has a long research and development history regarding the unique applications of indium metal.

 

Indium, Germanium, Gallium, and Tin Metals. Which properties make them unique for which applications?

Mackie: The importance of indium and its oxide can be seen in ubiquitous LED lighting, TVs, and displays. It is also used in cryogenic sealing and soldering applications in quantum computers. Indium’s softness and low melting point make it ideal for some soldering and other applications where its moderately high cost is countered by its unique properties. In electronics assembly, it can be found as a component in solder alloys and is also important in conductive thin-film indium-tin-oxide as well as in III/V CVD deposited layers in LEDs and VCSELs. We would be remiss not to mention the concerns about the availability of indium. We have written several papers (available for download from our website) that prove that indium metal will continue to be available for many years to come.

Germanium (Ge): Germanium has historically been used for transistors, but it has a very low bandgap (0.7eV), so it is much more heat-sensitive than silicon MOSFETs. There are emerging applications in spintronics and 3nm gate-all-around contact metals, such as SiGe. SiGe is also used in LIDAR and some low wattage power amplifiers.

Gallium (Ga): Its low melting point (29.8°C) and relatively low toxicity make gallium and its lower melting alloys an ideal replacement for mercury (Hg). In electronics, Gallium is most often used in III/V semiconductors, but can increasingly be found as GaAs and even GaN and InGaN in power RF amplifiers and LEDs. Gallium and its alloys have also been used as liquid metal thermal interface materials (TIMs) in new and emerging applications.

Tin (Sn): Tin is ubiquitous in solders as it reacts to form intermetallics (Cu and Ni are the metallizations of choice). It can also easily be recycled.

 

What is your expertise in Compound Semiconductors and what are the dominant applications?

Mackie: We manufacture many materials for CS. High-purity (6N and higher) indium ingots are used for making crystal substrates, such as InP, InAs, and so on. InP laser devices are crucial for data communications as the InP bandgap results in a photonic wavelength within the transmission window of optical fibers.

The epitaxial layers on compound semiconductor wafers are grown by metal oxide chemical vapor deposition (MOCVD). The organometallic CVD chemicals are made from indium trichloride and gallium trichloride; both of which are manufactured at our facilities in the USA. Because CVD chemical manufacturing is challenging, we concentrate on the high purity and physical aspects of these materials, such as density and pourability. For example, gallium trichloride at room temperature is a difficult-to-handle waxy, sticky material that will corrode stainless steel, so we developed a granulated form that makes it pourable and much easier to handle.

 

Indium Corporation is enabling the 5G Lifestyle". Can you explain your headline in more detail?

Mackie: 5G is a major driver of growth for the electronics industry, although we have recently seen signs that it may not be as reliable for automated driving as we had thought. Our products can be found at almost every place in the electronics supply chain: from no-clean solder pastes using high-reliability solder alloys, water-soluble flip-chip fluxes used in advanced logic and FPGA chips to gold-tin solder preforms for “coin” RF amplifier attachment.

 

What are 'Thermal Interface Materials' and in which applications do they have unique advantages?

Mackie: Thermal interface material (TIM) is a general term for a heat-conducting material placed between two adjacent surfaces. The TIM ensures a reliable path for heat energy to flow out of an object to facilitate cooling. An ideal TIM will be thin and highly thermally conductive, and will reliably ensure perfect thermal contact between the TIM and both the heat source and the underlying cooler/heatsink contact surface.

Solder as a TIM melts, but even under the best conditions voiding is seen. A soft non-melting laminar thermal interface material, such as a thin, flat piece of indium may appear to be an ideal TIM, but even under the best conditions, there is some non-planarity which leads to poor mechanical contact. So, we developed the Heat-Spring® TIM which is a soft, highly thermally-conductive metal that under pressure forms a strong interfacial bond that, unlike other TIMs, continues to improve over time.

Increased current density, such as in WBG, has also led to a focus on inconsistent bondline thickness. As you can imagine, low concentrations of widely distributed small voids will not lead to local increases in current, while a small difference in the bondline thickness, will cause an increase in the current flow at the die edge or die corner.

This has repeatedly been shown to create local stress that leads to die cracking. Maintaining absolute flatness of the bondline is therefore critical. Our InFORMS® preform technology uses a solid solderable metal framework embedded within solid solder to ensure that, after the solder melts, the bondline is consistent across the interface.

 

Is NanoFoil® your entrance into Nanotechnology?

Mackie: I believe so, from a product perspective. We also supply materials such as very high-purity indium to be used in vapor deposition processes, so nano is not new in applications! NanoFoil® was certainly the first Indium Corporation material to feature true 1D (one dimensional) nanotechnology. It is a unique product for many of our customers, as it can instantaneously bond solderable surfaces together without warpage, and withstands extremely high usage temperatures, as the end product is essentially an intermetallic.

More recent nanoparticle-containing materials include our small-die pressureless QuickSinter™ silver sintering materials to replace some high-lead (Pb) and gold alloy solder pastes in die-attach. Nanocopper pastes are also under development and scale-up.

 

You have a solid presence in Asia: Are your main markets there?

Mackie: Yes. More than 50 percent of our business is in Asia. That is why we have a major tech service and R&D focus there, as well as manufacturing capabilities. Our Asian customers range from mobile device manufacturers and subcontractors to wafer fabs for AI chips. We manufacture products in Suzhou, China, and we are further expanding capabilities in our main semiconductor and advanced materials hub in Singapore. Our recent addition of a new manufacturing facility in Chennai, India, is the start of a new wave of expansion.

 

What is your role in space?

Mackie: In 1989 we were honored to be part of NASA experiments in zero gravity alloy purification, led by our engineering team, so our technology has been in space a long time.

The military/aerospace (mil/aero) industry is notoriously conservative, and it is one of the last bastions of legacy eutectic tin-lead solder usage. Our long term association with the automotive electronics council (AEC) is also bearing fruit in mil/aero, as the latter increasingly look to the automotive industry to learn how low cost, high volume, and high reliability can exist together.

 

Figure 3: A 3D profilometric view of a jetting solder paste bump of Indium Corporation's PicoShot™ solder paste.

 

Our high-reliability assembly products developed for the automotive industry have already found their way into both federal and private space ventures.

Looking at the further future, we have been monitoring space mining to ensure the longevity of supply of non-indium rare elements. Asteroid or comet mining is fraught with difficulty. The ability to rapidly launch a vehicle capable of mining and retrieving minerals from a near-earth body is not there yet. Water can be split into H2 and O2, and is considered the “oil” of the solar system. As the race to mine water from the lunar polar ice caps heats up, we will be watching to see how we can supply materials to meet customer needs here.

 

What can our readers expect from your company in the near future?

Mackie: One constant with Indium Corporation is our ability to innovate to meet customer needs: both in the near term to meet more speculative needs further down the line.

In early 2020, we are commercializing a new jetting paste (PicoShot™, Figure 3), a lower melting high-reliability solder paste (Durafuse™ LT), and a new high-reliability automotive solder alloy (Indalloy®292). Additionally, we have a type 6/7 (SiPaste™) solder paste for system-in-package set for release later this year. For new TIMs, the recently developed m2TIM™ is a unique solid/liquid hybrid thermal interface material that combines liquid metal with a solid metal preform to provide reliable thermal conductivity while eliminating the need for die backside metallization.

Many thanks for the interesting questions!

 

About the Interviewee

Dr. Andy Mackie, Senior Product Manager, Semiconductor and Advanced Assembly Materials, Indium Corporation

 

Andy is an electronics industry expert in physical chemistry, surface chemistry, rheology, and semiconductor assembly materials and processes. He has more than 25 years of experience in new product and process development and materials marketing in aspects of electronics manufacturing from wafer fabrication to semiconductor packaging and electronics assembly. He is an award-winning industry leadership and technical contributor. He is also an IMAPS Fellow and Life Member, Chair of the Editorial Advisory Board for Chip Scale Review magazine, and Surface Mount Technology Association (SMTA) member and keynote speaker.

Andy has written papers and lectured internationally on subjects ranging from sub-ppb metals analysis in supercritical carbon dioxide to solder paste rheology. Additionally, he holds patents in novel polymers, gas analysis, and solder paste formulation. Andy earned his Ph.D. in Physical Chemistry from the University of Nottingham, UK, and a Master’s of Science (MSc) in Colloid and Interface Science from the University of Bristol, UK. He is an alumnus of the UC Berkeley Product Management program.