Insulation resistance refers to the resistance value presented by applying voltage to the insulating part of the connector, so that current is generated on the surface or inside of the insulating part. The insulation resistance test determines whether the insulation performance of the connector meets the requirements of the circuit design or whether its insulation resistance meets the provisions of the relevant technical conditions when subjected to environmental stress such as high temperature and humidity, otherwise it will destroy the normal operation of the circuit.
1) Insulation material
It is very important to choose the insulation material when designing an electrical connector, which often affects whether the insulation resistance of the subsequent product can be stable and qualified. For example, a factory originally used materials such as acetic acid glass fiber plastic and reinforced nylon to make insulators. These materials contain polar genes and have high hygroscopicity. The insulation performance at room temperature can meet the product requirements, but the insulation performance is unqualified under high temperature and humidity. Later, special engineering plastic PES (polyphenylene ether sulfone) material was used. After the product was tested at 200℃ for 1000h and 240h, the insulation resistance changed little and was still above 105MQ, without abnormal changes.
2) Temperature
High temperature will damage the insulating material, causing the insulation resistance and voltage resistance to decrease. For metal shells, high temperature can make the contact parts lose elasticity, accelerate oxidation and plating deterioration. For example, for environmentally resistant quick-disconnect electrical connector series 2 products produced according to GJB598, the insulation resistance is specified to be no less than 5000MQ at 25℃, and at a high temperature of 200℃, it is reduced to no less than 500MQ.
3) Humidity
The humid environment causes the absorption and diffusion of water vapor on the surface of the insulator, which can easily reduce the insulation resistance to below the MD level. Long-term exposure to high temperature will cause the insulator to physically deform, decompose, and release products, resulting in breathing effects, electrolytic corrosion, and cracks. For example, for ribbon cable electrical connectors produced according to GJB2281, the insulation resistance value under standard atmospheric conditions should be no less than 5000 MQ, and the insulation resistance after a 96h warm test at a relative humidity of 90%~95% and a temperature of 40±2℃ is reduced to no less than 1000 MQ.
4) Contamination
The cleanliness of the inside and surface of the insulator has a great influence on the insulation resistance. Impurities are mixed in the powder used for injection molding of the insulator or the glue used to glue the upper and lower insulation mounting plates, or residual metal chips due to repeated plugging and unplugging and residual flux infiltrates the surface of the insulator during the terminal soldering, which will significantly reduce the insulation resistance. For example, during the finished product delivery test of a circular electrical connector produced by a factory, it was found that the insulation resistance of one product contact was very low, only 20MQ failed. After anatomical analysis, it was found that the reason was that the powder used for injection molding of the insulator was mixed with impurities, and the entire batch of products had to be scrapped.
