Silicone rubber sheet is one of the most widely used products in the electronics industry. It is mainly used for sensing heat conduction. It is one of the best materials specially selected to transfer heat through the gap. It can not only be obtained during use. Filling the gaps and penetrating the passages between the heating and heat-dissipating parts can also effectively improve the efficiency and stability of the heat transfer system, and use silicone materials to obtain certain insulation, shock absorption, sealing, and protection functions, which can meet various Small and medium-sized electronic equipment has a good thermal conduction system, which is a relatively traditional type of thermal conduction filler.
However, in the actual use process, different product quality problems also appear. Among them, the most common are thermal sensor failure and aging life product degradation problems. Among these problems, the aging life problem occupies the main factor. What phenomena do materials have that affect service life?
I. What does “aging and hardening” of thermal pad mean?
In the process of using silicone thermal pads, the hardness will increase due to long-term exposure to high temperatures. This will seriously affect the use effect and service life of the pads, and will also cause damage to electronic and electrical equipment.
Therefore, users will do an aging test on the product. Different manufacturers and different applications will have different standards. It is common to bake at 150 ° C for 72 hours to compare the hardness before and after baking.
II. What are the hazards of later hardening of the thermal pad?
Because such thermally conductive materials are mostly used in sophisticated electronic and electrical products, once such problems occur, the common hazards are as follows:
1. After the gasket becomes hard, it will not only be inconvenient for construction, but will also reduce the fit, seriously increase the thermal resistance, and reduce the heat dissipation effect.
2, it becomes hard after construction, the gasket itself is easy to crack or even powder, the life of the gasket is shortened, and the heat dissipation effect is severely reduced.
3. In the later period of hardening, separation of the gasket and the protected component will occur, which will cause the component to be exposed directly. This will easily cause short circuit or thermal oxidation and rust, which will affect the component life.
III. What causes the later hardening?
Organic silicone thermal pad is a composite material, which is prepared by mixing two parts: a highly elastic addition silicone elastomer and a thermally conductive filler that provides thermal conductivity. Therefore, the main factors are as follows:
1. Too much cross-linking agent (this factor is the largest, and it is also the most prone to problems)
Generally speaking, when adding hydrogen-containing silicone oil, the molar ratio of hydrogen-containing to vinyl needs to be controlled at (1.2-1.8): 1. Here, the hydrogen-containing silicone oil includes side hydrogen and hydrogen-terminated silicone oil. Many people mistakenly believe that adding a little more hydrogen to the terminal will increase the strength and lower the hardness, so excessively adding hydrogen-terminated silicone oil will result in a decrease in colloidal resilience, a decrease in surface viscosity, and a rapid increase in hardness after aging.
2. The volatile content in hydrogen-containing silicone oil is generally relatively high, even as high as 12%. Some of these volatiles are cyclosiloxane monomers (DMC), and some are hydrogen-containing small molecular monomers (straight). Chain or cyclic), these hydrogen-containing small molecules are characterized by low activity at low and medium temperatures, and slow reactions at high temperatures, resulting in a phenomenon that the hardness becomes larger in the later stage or after aging.
3. When the volatile content in vinyl silicone oil and hydrogen-containing silicone oil is too high, these small molecules will run out during the aging process, which is equivalent to reducing the amount of system oil. This will not only cause the gasket to harden, but also cause thermal conductivity. decline. After volatilization, the contact interface of the gasket will dry out and the surface viscosity will decrease.
4. Powder factors, the chemical additives added to the raw materials are different, and the quality of each powder is different from the standard method of refining, so the factors that cause the quality problems of silicone rubber gaskets also occupy one of them.
IV. How to solve this problem?
1, control the molar ratio of hydrogen and vinyl
Calculate the molar ratio of hydrogen to vinyl and control it to (1.2-1.8): 1. The amount of hydrogen-terminated silicone oil should not be too high, generally less than 0.9 relative to vinyl. This can not only ensure the hardness is stable, but also maintain the product resilience.