Thermal management of microelectronics, electronics and electric power equipment, exploring the development of the next generation thermal conductive adhesive

The increasing demand for mobile electronic devices has brought new design challenges, with increasing emphasis on mechanical strength and thermal management capabilities. As the substrate size shrinks and the operating environment becomes more robust, the integrated product design must overcome the challenge of heat dissipation while maintaining seismic resistance.

The application of thermal conductive adhesive is a practical and effective thermal management solution in electronic engineering, but it has not been fully applied at present.

Heat transfer after two components are bonded by thermal conductive adhesive

The adhesive can cover a large surface area to provide the necessary heat transfer and form a durable structural joint. In contrast, most other heat conducting materials (TIM), such as heat conducting grease, phase change materials or polymer pads, require mechanical fastening. Although welding can provide mechanical stability, its high welding temperature will damage precision components and equipment.

Traditional thermal conductive adhesives and potting applications include installing heat sinks in microelectronics, chip bonding, packaging, and sensor potting. In addition, the demand for non-traditional applications such as power electronics, electrical and power engineering, LED lights, solar energy equipment, heat exchangers and automotive components is growing. In addition to different mechanical properties, the products represented by this wide application also have unique requirements and processing parameters. In these devices, the application of thermal conductive adhesive can bridge the thermal mismatch between different components.

Thermal conductive adhesive is usually composed of one or two component epoxy resin and other materials. The advantages of epoxy resin are thermal stability, chemical stability and structural stability. The disadvantage is that the inherent thermal conductivity is very poor, 0.2-0.3 W/mK. However, when epoxy resin is filled with ceramic or metal powder (such as aluminum oxide, boron nitride, aluminum or copper), the heat transfer is significantly increased, and the overall thermal conductivity of these particles is between 30 and>300 W/mK.

Applying a simple mixing rule, one may conclude that the mixing of 50% epoxy resin and 50% hot filler will lead to the average thermal conductivity of the composite, but unfortunately, this is not the case. In addition, the thermal conductivity does not depend on the conductivity of the filler, but on the relative ratio of the filler to the epoxy resin. There have been a lot of studies on the composite thermal conductivity of filled polymers. A well-known model is the equation discovered by Lewis and Nielsen:

The data generated using this equation indicate that the volume fraction of filler should be 50% or more to achieve a thermal conductivity higher than 1 W/mK. More importantly, no matter whether the filler has 10, 100 or 1000 W/mK, a similar level of thermal conductivity will occur.

Considering these characteristics, a high proportion of filler content is required to maximize the thermal conductivity. However, a high proportion of filler particles will reduce the fluidity of the adhesive. In addition, when the filler replaces the epoxy resin, the mechanical strength may be affected. Therefore, the development team of thermal conductive adhesive must find a compromise between thermal conductivity and processing parameters.

In microelectronic components, thermal conductive adhesives are established methods for connecting and protecting components (such as chip connection, bottom filling, packaging and heat dissipation). Epoxy resin has high thermal stability. It is applied to temperature sensitive parts to make them withstand reflow soldering and improve operational stability.

Thermal management of LED chip

At present, a growing application trend is the thermal management of LED chips (bonding LED chips with heat sinks through thermal conductive adhesives). The power consumption of each LED module is>500 mW, and only 20% of the energy is converted into visible light. Most of the energy is converted into heat. The LED module temperature must be kept below 120 ° C. Under high temperature, the light output and service life of the lamp will be reduced. The service life of LED will be significantly shortened when the operating temperature increases by 1 ° C.

When the LED chip is installed to the heat sink through the thermal conductive adhesive, the heat is effectively dissipated.

After using the thermal conductive adhesive, the maximum temperature of the thermal image during the operation of the LED module is about 66 ° C

Sealing of temperature sensor

Another application of thermal conductive adhesive is the potting or sealing of temperature sensors in electronic products. The thermal conductive adhesive acts as an effective waterproof and moisture-proof sealant, and can achieve good heat transfer between the sensor and the environment.

Temperature sensor coated with thermal conductive sealant

Application in electric vehicle field

In recent years, the demand for innovative manufacturing concepts of batteries, motors and fuel cells for electric and hybrid vehicles has begun to increase. This demand can be solved by using thermal conductive adhesive, including connection and sealing of power battery, assembly of motor and coil sealing, installation of heating and cooling pipes, etc.