Efficient semiconductor thermal management
There is growing consensus in the semiconductor ecosystem that we are on
the cusp of significant changes in packaging technology. Evolving
semiconductor technologies are driven by new applications. These new
technologies call for semiconductor materials that are highly efficient,
smaller in size and highly reliable, with longer field life cycles and
the ability to operate across all climate conditions.
BY RAMESH KOTHANDAPANI, TECHNICAL DIRECTOR, MICROELECTRONIC PACKAGING, MATERION CORPORATION
Eletronics components have necessarily evolved since the late 1990s, yielding complex and compact designs with efficient performance for their intended applications. Companies are engaging in more research activities to develop new alloys and composite materials, ways to prolong the life of semiconductors, and suitable environments for semiconductor performance. Industry is capturing these developments in the technology roadmap.
Modern electronics pose several challenges during the design stage. One example is space constraints, which relate to the microelectronic packaging design process. The number of electrical connectors, the material selected, electrical resistances, weight and cost are just some of the factors that drive new technology.
Many devices within a microelectronic package may be operating simultaneously, which leads to thermal accumulation. This collected thermal energy or heat cause the semiconductor to perform inefficiently, or even to malfunction. Thermal energy is a constant threat to semiconductors, especially in critical applications. In past years, fins and cooling fans were often the first line of defense against high temperatures.
Today, advanced thermal interface materials with special features – such as wavy 3D surfaces, smaller heat sinks and unique enclosure designs – are playing a greater role in thermal management for advanced electronics.
Following is a partial list of sectors or industries in which advanced thermal management materials are required for reliable operation:
Telecommunications devices risk poor signal management and decreased efficiency without proper thermal management.
Space: Understandably, the space sector has no room for failure. The technology road map for space must support planetary exploration, space tourism, space mineral mining for new materials and probes and vehicles to travel vast distances. Semiconductor material used here must be able to tolerate harsh environmental challenges while performing critical operations.
Aerospace, low-altitude mobility: There can also be no failure with any type of flying vehicle. From passenger planes to war planes and even forthcoming low-altitude flying taxis, efficient electronics will be required for maximum performance. A future human-transporting drone must be equipped with sophisticated semiconductor chips. These chips must support uninterrupted communications, air current sensing and emergency landing. Thermal management is crucial to these semiconductors.
Uninterrupted communications: Smoother communication is always expected despite various types of noise and disturbances. The electronics and their respective packaging must enable the semiconductor to serve its designed function.
Radio wave-based telecommunications: Base station systems contain semiconductor devices operating within a multitude of different environmental conditions. They experience constant thermal management issues that can lead to interruption of communications. Inefficient electronics causes poor signal management and the need for frequent maintenance. The evolution of telecommunications has now reached its fifth generation, with ongoing changes in design and device size. Each generation demands incrementally better thermal management of electronic packaging. Microelectronics are especially challenging in this regard, as these semiconductors experience enormous loads that require efficient thermal management material. From military communication and airliners to consumer mobile devices and smart home and office systems, these applications all require the highest-quality communication.
Automobiles and autonomous travel: Increasingly, automobiles are combining telecommunication electronics with safety and optical sensing devices. Environmental concerns over the use of petroleum products have led to the development of temporary energy storage or battery products. Efficiently managing power adds a layer of design complexity, with additional electronic modules being integrated into a single semiconductor. As multiple applications operate simultaneously, loads on these semiconductor units generate high levels of thermal energy. These batteries also charge and discharge frequently, putting a strain on the electronics governing their operation. Electric vehicles contain an estimated four to six times more electronic components than conventional vehicles.
Human-wearable systems with efficient heat management materials: Human-wearable devices are challenging as a result of their small size, safety requirements and weight. Much like battery-operated devices, they are prone to heat generation that must be highly managed through material selection.
Designers must balance the thermal conductivity and weight of materials used in their systems.
Again, these are only a few examples illustrating emerging thermal management demands on semiconductor materials. To date, silicon-based materials have been most widely used because of their efficient operation and wide availability. Silicon’s cost, integration into established design and process flow, and favorable chemical and electronic properties also contribute to its popularity for semiconductor applications.
In new devices bundling multiple applications, however, the question arises whether existing semiconductor materials can deliver needed output. Newly developed and enhanced materials are rapidly coming onto the scene. These include gallium nitride, gallium arsenide and silicon carbide, each of which has its own pros and cons as designers continually balance cost, weight and other factors in their material selection.
These designers must consider several factors, including the reality that the lower thermal conductivity of new materials often increases cost while traditional materials, which do not tend to enhance semiconductor efficiency, offer undeniable cost benefits.
As mentioned earlier, the electronic module has shrunk considerably and now contains many more components than it did previously. During operation, it is natural for these devices to generate heat that gets transferred to other assemblies. Bonding materials used to assemble the semiconductors are constantly challenged by poor heat transfer. If heat is not transferred quickly, the semiconductor cannot perform its role efficiently, leading to device or system failures. In certain applications, high humidity combines with heat to create even more severe failures.
The effect of temperature on semiconductor efficiency is dependent on the materials being employed and their specific physical properties.
An efficiently designed semiconductor electronic system requires a good thermal management material to dissipate heat. Frequency switching, voltage handling capabilities and operating temperature are important considerations for future semiconductor materials. Gallium nitride (GaN) placed on silicon and silicon carbide are examples of materials gradually replacing silicon for this purpose.
Thermal overstress is an important point to consider during the design stage. A good electronic design team will consider the thermal transfer processes that add weight to the design and enlarge electronic architectures accordingly. Design teams should introduce longer-term reliability test simulations and good bonding materials that are able to tolerate high levels of heat.
Figure 4 clearly illustrates the effect of temperature on semiconductor efficiency. The standard GaN on Si measures 189 degrees Celsius with 1% of the active device on silicon. The undesired heat transfer will be passed onto semiconductor bonding materials – which could be any eutectic die bond material or solders – causing a catastrophic failure over time. GaN on SiC is significantly better, reducing heat by more than 50% to 77 degrees Celsius. The illustration of GaN on diamond refers to a diamond composite material that manages the heat transfer process extremely well. It yields a reduction of about 50% compared with GaN on SiC and four times lower than GaN on Si.