Test Method for Moisture Resistance of Thermal Conductive Silica Gel Pad

1. 1. Significance

Thermal conductive silica gel pad is a kind of thermal conductive medium material, which is based on silica gel and added with metal oxide and other auxiliary materials. This material is filled into the gap between the heat source and the radiator to form a good heat dissipation path between them. Thermal conductive silica gel pad is widely used in LED industry, power industry, communication industry, automotive electronics industry, home appliance industry and other fields, such as the connection between the main board chip of notebook computer and the radiator for heat dissipation. Because the internal components of electronic products are sensitive to water vapor, preventing internal moisture is the prerequisite to ensure the service life and performance of the products. When the electronic chip and the radiator is sealed in a closed environment with thermal conductive silica gel pad, the water vapor barrier property of the thermal conductive silica gel pad used as a part of the sealing material directly affect the amount of water vapor that the electronic chip can be exposed to. Therefore, it is of great significance to choose the suitable thermal conductive silica gel pad to protect electronic products from moisture.

Figure 1 Thermal conductive silica gel pad

2、Standard

At present, the test methods of water vapor transmission of materials are mainly divided into four methods: cup method, electrolytic sensor method, infrared sensor method and humidity sensor method. In this paper, the electrolytic sensor method is used to test the water vapor transmission of heat-conducting silicon film. The test conforms to standard is ISO 15106-3:2003 Plastics — Film and sheeting — Determination of water vapour transmission rate — Part 3: Electrolytic detection sensor method.

3、Sample

The sample tested in this test is a brand of thermal conductive silica gel pad.

4、Test instrument

In this paper, W3 / 330 water vapor transmission rate test system is used as the test equipment, which is independently developed and produced by Jinan Labthink Instruments Co., Ltd.

图2  W3/330水蒸气透过率测试系统

4.1 Test principle

After the sample is mounted into the test chamber, the test chamber is separated into low humidity chamber and high humidity chamber. The dry nitrogen flows in the low humidity chamber, and the nitrogen with certain humidity flows in the high humidity chamber. The water vapor entering the low humidity chamber through the sample from the high humidity chamber is carried into the electrolytic cell by nitrogen. The structure of the cell is usually: there are two spiral metal electrodes inside, the electrodes are installed on the inner wall of the glass capillary, and the surface of the electrodes is coated with a thin layer of phosphorus pentoxide. The nitrogen passes through the glass capillary, and the water vapor carried by it is absorbed quantitatively by phosphorus pentoxide. By applying a certain DC voltage to the electrode, the water vapor is electrolyzed into hydrogen and oxygen. According to the value of electrolytic current, the amount of water vapor passing through the sample per unit area in unit time is calculated.

5、Test process

(1) Cut 3 specimens with special sampler.

(2) Mount 3 specimens on three test chambers of the instrument and clamp them to ensure good sealing and no air leakage.

(3) Set the parameters such as sample name, sample thickness, test temperature and test humidity, click the test option, and the test starts.

(4) Turn on the gas supply, adjust the nitrogen flow rate and nitrogen pressure to make the humidity and nitrogen flow rate of the test chamber reach the specified value.

(5) After the test, the instrument automatically calculates and displays the test results.

6、Test result

The water vapor transmission rate of the three specimens tested were 8.034 g/(m²·24h), 7.981 g/(m²·24h) and 8.116 g/(m²·24h), with an average of .044 g/(m²·24h).

7、Conclusion

The water vapor transmission rate of thermal conductive silica gel pad is one of the important factors that affect the service life and performance of electronic equipment. In this paper, the water vapor transmission rate of a brand of thermal conductive silica gel pad is tested by the electrolytic sensor method. The test operation is simple, the instrument is highly intelligent, and the test results show that the sample has good uniformity and high test accuracy.