5G COOLING DEMAND IS DOUBLED, HOW TO COOL THE SMART PHONE?

Smart phones are designed to be thinner and more portable, requiring better heat dissipation and reliability of internal components. The performance of electronic products is becoming more and more powerful, and the integration and assembly density are constantly increasing, resulting in a sharp increase in their power consumption and heat generation. According to statistics, the failure of materials due to heat concentration of electronic components accounts for 65% -80% of the total failure rate. Thermal management technology is a key factor for electronic products.

The penetration of OLED screen and the popularization of wireless charging technology also increase the demand and difficulty of heat dissipation. On the one hand, the fast charging power and wireless charging power of mobile phone are gradually improved, and the increase of power increases the demand of heat dissipation. On the other hand, the permeability of OLED screen increases gradually, and OLED materials are prone to decline due to high temperature, so the heat dissipation requirements are higher and higher. At the same time, the number of 5G smart phone antennas can reach 5-10 times of 4G mobile phones, and the innovation of wireless charging technology also improves the demand for heat dissipation.

There are two ways of mobile phone cooling: active and passive. The basic idea is to reduce the thermal resistance of mobile phone cooling (passive cooling) or the heat of mobile phone (active cooling). Active cooling is realized by reducing the power consumption and heat consumption of the chip, which is related to the development of electronic equipment. Passive heat dissipation is achieved by heat conducting materials and devices. The components that generate heat are CPU, battery, motherboard, RF front-end, etc. the heat generated by these components will be introduced into the interlayer with large heat capacity by the heat sink, and then it will be released through the phone shell and the heat sink.

There are three ways of heat transfer: heat conduction, convection and radiation. According to the heat transfer mode, the cooling system can be composed of fans, fins (such as graphite sheets, metal fins, etc.) and heat conduction interface devices. Taking the common CPU air-cooled radiator as an example, its working principle is that the CPU heat sink contacts the CPU surface through the heat conduction interface device, the heat on the CPU surface is transferred to the CPU heat sink, and the heat on the CPU heat sink surface is taken away by the air flow generated by the cooling fan. At present, the thermal conductive materials widely used in the market are thermal conductive adhesive, heat conductive mud, heat conducting gel, conductive graphite film, phase change thermal conductive interface material and so on.

Traditional heat conducting materials are mainly metal materials, such as copper, aluminum, silver, etc. However, due to the high density and high expansion coefficient of metal materials, the thermal conductivity of silver, copper and aluminum is 430W / m.k, 400W / m.k and 238 w / m.k, respectively. Heat conducting graphite sheet has a unique grain orientation, which can conduct heat uniformly in two directions; it can evenly dissipate heat by distributing the central temperature of the phone heating to a large area. At present, most of the heat dissipation schemes in smart phones use graphite fins. However, with the increase of the heat dissipation demand of electronic equipment, the heat conduction of single or double-layer graphite fins cannot meet the higher heat dissipation demand.

Comparison of mobile phone cooling solutions, heat pipe and temperature equalization board solutions stand out

With the continuous upgrade of mobile phone hardware, the tasks performed by it are more complicated, and chip components such as CPUs will face the attack of heat. However, the size of the mobile phone has certain limitations, and the performance of the processor system will be reduced due to the increase in temperature. Therefore, the heat dissipation problem of mobile phones is particularly important. 5G and wireless charging have higher requirements for signal transmission, and the defects of metal backplane shielding of signals will be amplified. It is expected that 5G mobile phones will no longer use metal backplane design, and the original graphite plus metal backplane heat dissipation technology faces major challenges. It is expected that smart phones will use more graphite + metal middle frame solutions. At present, the main heat dissipation solutions for mobile phones on the market are: thermally conductive gels, graphite sheets, graphene, temperature equalization boards, and heat pipes.