Welcome to visit Beijing Beihua New Rubber Special Material Technology Co., Ltd.官網網站！
The key issue in heat treatment is to effectively conduct the heat generated by the heat source to the heat sink.
Thermal interface materials TIMs=Thermal Interface Materials have been widely used to improve the efficiency of heat transfer. The heat generated by the device is conducted to the metal heat sink through its surface, and the heat is dissipated into the air through the heat sink. However, the surface of the component is usually made of plastic, ceramic or metal, and the surface is not completely flat (the surface of the radiator is also not completely flat). If the component is directly in contact with the radiator, a gap will inevitably remain in the middle, and air will remain in between. The contact surface will be reduced, and the heat will not be effectively conducted. The softness of the TIM material allows it to fill the gaps therebetween, helping to conduct heat transfer effectively.
Figure 1 Schematic diagram of using thermal interface materials to improve heat transfer efficiency
As shown in Figure 1, after the semiconductor is mounted on the circuit board, its thermal resistance at its junction (porous surface) will increase significantly. If the TIM material is filled in between, it can be seen that it effectively eliminates the contact thermal resistance of the semiconductor device mounted on the circuit board, forming a higher gradient temperature difference. Even if it is a polished surface, the two surfaces cannot be in full physical contact. To reduce thermal resistance, it is necessary to achieve complete physical contact, so as to form an efficient heat conduction path.
Thermal conductivity and testing
The rate of heat conduction through the material is proportional to the normal area of the heat flow and the temperature gradient along the heat flow path. For a one-dimensional, stable heat flow, the rate can be expressed by the Fourier equation:
K=thermal conductivity, W/m·K
Q=heat flow rate, W
d = heat flow distance
ΔT = temperature difference
Thermal conductivity is an inherent property of a material, and has nothing to do with the size, size, thickness, or direction of the material.
Beihua New Rubber adopts thermal conductivity tester DRL-III to measure the thermal conductivity of products in accordance with ASTM D5470 standard.
Figure 2 Thermal conductivity tester DRL-III test bench
The resistance encountered by the heat in the heat flow path, and the size of the reaction medium or the heat transfer capacity between the media.
The relationship between material thermal resistance and thermal conductivity is:
Thermal resistance is proportional to thickness
Since the actual surface cannot be truly flat or smooth, the contact surface between the surface and the material will also produce resistance to heat flow. This resistance is called contact thermal resistance.
The total thermal resistance in heat transfer is equal to the sum of the thermal resistance of the material and the contact thermal resistance between the contact surfaces.
(2) R total = R material + R contact
Surface smoothness, surface roughness, and clamping pressure have an important influence on contact thermal resistance.
For example, the relationship between thermal resistance and interface thickness of our company's high thermal conductivity gasket BH-T3160 is shown in Figure 3:
Figure 3 The relationship between thermal resistance and interface thickness of thermal pad BH-T3160
Determination of thermal conductivity
The thermal conductivity of the material is:
(4) K=d/R material
Substituting formula (4) in formula (3) will get:
(5) d=KR total-KR contact
Fitting is performed by measuring the thermal resistance (Rtotal) under different interface thicknesses (d). After removing the influence of the contact thermal resistance, the thermal conductivity of the material can be calculated. As shown in Figure 4, the thermal conductivity of BH-T3160 is 6.05W/m·K.
Figure 4 Fitting the thermal conductivity of thermal pad BH-T3160 by linear regression
Table 2 Product types and applicable interface thickness
T: Recommended typical applications
Use thin TIM thermal pad to obtain lower thermal resistance and improve thermal conductivity
Advantages of thick TIM thermal pad:
If there are multiple heating components, a thick TIM thermal pad can cover multiple heating components with one piece, even if the height of each component is different.
Thick TIM thermal pad has greater heat capacity. If the heat source generates a large amount of heat instantly, the thick TIM thermal pad can effectively absorb the large amount of accidental heat generated in this part, thereby protecting the components.
? TIM compression capability
The thermal interface material is usually placed between the heat source and the heat sink, supplemented by a certain pressure. Therefore, in the thermal design management, the compressibility of the TIM material will become an important consideration for our TIM material thickness tolerance design.
? Glass fiber and surface hardened non-stick treatment
For ease of use, you can choose a thermal pad with glass fiber cloth or with a surface hardness enhancement layer (non-stick) treatment.
? Product model description: