Silicone rubber sheet is one of the most widely used products in the electronic industry. It is mainly used for sensing and heat conduction. It is one of the best materials specially selected for the use of gap to transfer heat. In the process of use, it can not only fill the gap and connect the heating part with the cooling part, but also effectively improve the efficiency and stability of the heat transfer system, And the use of silica gel material to get a certain degree of insulation, shock absorption, sealing and protection, etc., can meet the needs of a variety of small and medium-sized electronic equipment has a good heat conduction system, is a relatively traditional heat conduction filling material.

However, in the actual use process, there are also different product quality problems, among which the more common ones are thermal conductivity sensor failure and aging life decline of products. Among these problems, aging life is the main factor, so what are the phenomena that affect the service life of thermal conductivity silicone sheet?

1、 What does "aging and hardening" of thermal conductive gasket mean?

During the use of silicone thermal conductive gasket, due to long-term high temperature environment, the hardness will increase, which will seriously affect the use effect and service life of gasket, and also cause damage to electronic and electrical equipment.

Therefore, the user will do an aging test on the product. Different manufacturers and different applications will have different standards. The common method is baking at 150 ℃ for 72 hours to compare the hardness before and after baking.

2、 What's the harm of heat conduction gasket hardening later?
Because this kind of thermal conductive material is mostly used in precision and complex electronic and electrical products, once such problems occur, the common hazards are as follows:

1. After the gasket is hardened, it is not only inconvenient for construction, but also reduces the adhesion, seriously increases the thermal resistance and reduces the heat dissipation effect.

2. The gasket is easy to crack or even pulverize after construction, which shortens the service life of the gasket and seriously reduces the heat dissipation effect.

3. In the later period of hardening, the gasket and the protected components will be separated, resulting in the direct exposure of the components, which is easy to cause short circuit, thermal oxidation, rust, etc., and affect the service life of the components.

3、 What causes late hardening?
Silicone thermal conductive gasket is a composite material, which is made of two parts: an addition silicone elastomer providing high elasticity and a thermal conductive filler providing thermal conductivity. Therefore, the main influencing factors are as follows

1. Too much crosslinking agent (this factor is the largest and most likely to cause problems)
Generally speaking, when adding hydrogen containing silicone oil, the molar ratio of hydrogen to vinyl should be controlled at (1.2-1.8): 1, where hydrogen containing silicone oil includes side hydrogen and end hydrogen. Many people mistakenly believe that if more hydrogen is added to the end, the strength will be higher and the hardness will be lower. Therefore, excessive hydrogen terminated silicone oil will be added. As a result, the resilience of the colloid will be reduced, the surface viscosity will be reduced, and the hardness will rise rapidly after aging.
2. The volatile matter in hydrogen containing silicone oil is generally high, even up to about 12%. Some of these volatile matter are cyclosiloxane monomer (DMC), and some are hydrogen containing small molecular monomer (straight chain or ring). The characteristics of these hydrogen containing small molecules are low activity at medium and low temperature and slow reaction at high temperature, The resulting phenomenon is that the hardness increases after aging.
3. When the volatile content of vinyl silicone oil and hydrogen silicone oil is high, these small molecules will run out during the aging process, which is equivalent to the decrease of the amount of system oil. This will not only cause the gasket to harden, but also reduce the thermal conductivity. After volatilization, the gasket contact interface will become dry and the surface viscosity will decrease.
4. Powder factors, different additives added in raw materials, the quality of each kind of powder and refining standard method are different, so the factors leading to quality problems of silicone rubber gasket also occupy one of them.