How to solve the problem of silicone thermal pad becoming hard and brittle?
[ Date: 2021-01-20 16:17:12 Author: Popularity: ]
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Silicone rubber sheet is currently one of the most widely used products in the electronics industry. It is mainly used for sensing heat conduction and is one of the best materials specially selected for transferring heat through gaps. In the process of use, it can not only fill the gap and connect the channel between the heating part and the heat dissipation part, but also effectively improve the efficiency and stability of the heat transfer system. It can meet the needs of all kinds of small and medium-sized electronic equipment and has a good heat conduction system. It is a kind of traditional heat conduction filling material at present.


However, in the actual use process, the more common ones are the thermal sensor failure and the deterioration of the product aging life. Among these problems, the aging life is the main cause.


1. What does the "aging and hardening" of thermal pads mean?

In the process of using silicone thermal conductive pad, due to long-term exposure to high temperature, the hardness will increase, which will seriously affect the use effect and service life of the 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 is the harm of hardening of the thermal pad in the later stage?

1) After the pad becomes hard, it is not only inconvenient for construction, but also reduces the fit, severely increases the thermal resistance, and reduces the heat dissipation effect.

2) After construction, it becomes hard, the pad itself is easy to crack or even powder, the life of the gasket is shortened, and the heat dissipation effect is seriously reduced.

3) When it becomes hard in the later stage, the silicone pad and the protected components will be separated, causing the components to be directly exposed, which will easily cause short circuits, thermal oxidation, rust, etc., which will affect the life of the components.


3. What factors caused the later hardening?

Silicone thermally conductive pad is a composite material, which is prepared by mixing two parts of an addition-shaped silicone elastomer that provides high elasticity and thermally conductive filler that provides thermal conductivity. Therefore, the main influencing factors are as follows:

1). Too much cross-linking agent (this factor is the largest and the most likely to cause problems).


2). The volatile matter in hydrogen containing silicone oil is generally high, even about 12%. Some of these volatile matters are cyclosiloxane monomer (DMC), and some are hydrogen containing small molecular monomer (straight chain or ring). The characteristic of these hydrogen containing small molecules is that the activity is not high at medium and low temperature, and the reaction will be slow at high temperature, resulting in the phenomenon that the hardness becomes larger at later stage or 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 thermal pad to harden, but also reduce the thermal conductivity. After volatilization, the pad 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 pad also occupy one of them.


4 How to solve the problem?

Control the molar ratio of hydrogen to vinyl

Calculate the molar ratio of hydrogen to vinyl and control it at (1.2-1.8): 1. The amount of hydrogen-terminated silicone oil should not be too high, generally lower than 0.9 relative to vinyl. This will not only ensure the stability of the hardness, but also maintain the product resilience.