Key benefits of choosing non-silicone gap filler material
As its name suggests, thermal interface materials (TIMs) are used to optimize thermal heat transfer between various interfaces. Generally, thermal gap fillers are made from a silicone polymer and add various auxiliary materials such as ceramic particles, silicone oil and thermally conductive powders to increase the polymer’s thermal conductivity.

However, the commonly used silicone oils or other TIMS constituents tend to dissipate with time, temperature or pressure, causing the liquid to creep along surfaces as an oily film or condense as a gas and contaminate surrounding areas such as electrical contact failure and reduced transmittance of optics. The various benefits of Shiu Li Technology’s non-silicone TIM, LiPOLY, allow this gap filler material to be used in a variety of applications.

Pitfalls of silicone-based TIMs
Silicone, also known as polysiloxane, is a synthetic polymer with alternating Si and O atoms in the backbone chain. These often contain volatile molecules, known as low molecular weight (LMW) siloxanes, which will evaporate through outgassing at both room and elevated temperatures before curing. When this outgassing occurs during the application and curing process in an enclosed electronic space with sensitive surround electronics, failures can occur, including:

• Electrical contact failure: Low molecular weight polysiloxanes will form silica and cause insulation if used in switch applications
• Lens fogging: If low molecular weight polysiloxanes are used in optical applications, they will form silica bonded glass lenses over time

Silicone migrating into surrounding electronics can lead to contact failures where, for example, contaminated connections become “uncontacted”, and an open circuit failure occurs. During the application and curing process, the gases can potentially adhere and solidify on the lens, causing the lens to go turn from clear and high performing to foggy and opaque. This is undesirable in optical products as it reduces light transmission of optically clear materials.

Another potential failure mode of non-curing silicone-based TIMs like pastes, putty and grease is pump-out, or the expansion and contraction of the interface surfaces with rapidly changing temperatures causes the pastes to be squeezed or “pumped out” of the gap. Silicone TIMs generally have a higher thermal expansion (that is also higher with increasing temperature). In an electric vehicle (EV) battery pack, for example, the high temperatures and pressures could cause pump out and dry out, which can lead to delamination, cracking and an increase in the contact resistance and overheating of the component.

Reliability of non-silicone based TIMs
For reliability reasons, silicone-free TIMs like LiPOLY are emerging as a strong candidate for applications that are particularly sensitive to these silicone-specific issues. LiPOLY will not volatilize siloxane, and only outgas a small amount to prevent the issues of lens fogging. Some silicone-sensitive use cases include optical devices and optoelectronics, high reliability medical equipment and sensors that require high integrity measurements without the potential for measurement inaccuracies due to contamination. Applications that house sensitive electronics in a small, enclosed space may suffer during the curing process. Both electronics and optical devices are found in smartphones, often requiring these components to include silicone-free TIMs where necessary.

The issue of lens fogging can impact automotive interfaces and modern displays in navigation systems that are facing increasing power densities in thinner enclosures. Non-silicone TIMs are important in modern vehicles where displays are pushed to constantly enhance the brightness, clarity and visibility. If the LiDAR system is covered by fog, it will affect the MCU warning and conformity.

Benefits of choosing LiPOLY gap filler
While silicone-based TIMs do have potential disadvantages to consider with specific applications, there are other aspects to consider when selecting a TIM. Generally, the silicone-free TIM should have a good thermal conductivity, high-temperature stability and low thickness after clamping. However, the different parameters are optimized depending upon the type of gap filler material used.

Advantages of each gap filler materials
The N-series LiPOLY thermal conductive pads have good compressive characteristics and achieve good contact without excessive PCB deflection. This is critical for thermal pads as the stress and strain to the PCB during application is a major consideration in optical precision equipment.

The thermal conductive, silicone-free N-putty is a non-curing material and therefore its vertical flow reliability, or its displacement under vertical suspension strain, is critical for functionality. Tests performed on the N-putty TIM showed excellent vertical flow reliability making it useful for EVs, laptops, telecom equipment, smartphones and more.

Another LiPOLY gap filler offering, the two-part thermal conductive adhesive allows for a conductive glued connection after curing. This material exhibits an excellent adherence where the bond between interfaces is exceptionally strong, making this material well-suited for automated dispensing for precision optical equipment and sensitive electronic components.

The LiPOLY non-silicone G3380Nx thermal grease has an extremely low thermal resistance and good thermal conductivity. The LiPOLY G3380Nx grease also allows for thin bond line thickness, which is a factor directly proportional to thermal resistance, making this ideal for high reliability electronics with CPUs, switching power supplies, and LEDs. This, for example, could be used between the baseplate and cooling. Thermally conductive sealing glues are used to allow hotspots to run hotter.Thermally conductive sealing glues are used to allow hotspots to run hotter.

Finally, the thermal conductive sealing glue can be poured onto an area to fill the gaps around the electronics and form a conductive coating that allows electronics and radiators to run at higher power This material has a high hardness, chemical mediator resistance and yellowing resistance. It is also waterproof and exhibits an extremely low shrinkage, ensuring that sensitive components within the circuit are not exposed.

Shiu Li Technology
Non-silicone TIMs bypass the potential migration and contamination issues of silicone-based materials with aging, high temperature conditions, humidity and pressure. All of these can wreak havoc in highly sensitive or environmentally strenuous systems. Shiu Li Technology’s LiPOLY TIMs not only mitigate the potentially negative impact of silicone-based TIMs, but have each been optimized to better perform their specific function. To learn more about Shiu Lu Technology and their materials, visit their website.

Shiu Li Technology Co., LTD 
Shiu Li Technology Co., LTD has established itself as a world-leading thermal management manufacturer, developing high-performance thermal solutions for product designers around the globe. Selling under its brand LiPOLY,  Shi Li Technology Co. LTD has heavily invested in the development of advanced thermal conductive products for high powered modules. In 2018, Shiu Li Technology LLC was established in the United States to better serve customers in North America and Europe.

Shiu Li Technology has served more than 2000 customers worldwide, delivering thermal solutions in computer manufacturing, data communication, consumer electronics, data centers, military equipment, automotive equipment, lighting, power conversion, and more.