Insulation Failure Analysis of Automotive Connectors

The insulation resistance refers to the resistance value presented by the surface or internal leakage current of the insulation part when a voltage is applied to the insulating part of the automotive connector. That is, insulation resistance (MΩ) = voltage applied to the insulation (V) / leakage current (μA). By inspecting the insulation resistance, it can be determined whether the insulation performance of the connector meets the requirements of the circuit design, or whether the insulation resistance meets the relevant technical conditions when subjected to environmental stresses such as high temperature and humidity.

The insulation resistance is a limiting factor for designing high-impedance circuits. Low insulation resistance means a large leakage current, which will disrupt the normal operation of the circuit. For example, the formation of a feedback loop, too much heat, and direct current electrolysis caused by a large leakage current will damage the insulation or deteriorate the electrical performance of the connector.

Insulation Material of the Automotive Connector
It is very important to choose the appropriate insulation material when designing electrical connectors. It often affects whether the insulation resistance of subsequent products can remain stable and qualified.

For example, a certain factory originally used insulation materials such as acetate fiberglass plastic and reinforced nylon, which contained polar genes and had high hygroscopicity. The insulation performance could meet the product requirements at room temperature but was not qualified in high temperature and humidity conditions.

Later, special engineering plastic PES (polyether sulfone) was used, and the insulation resistance of the product changed slightly after 200 ℃, 1000h, and 240h humid tests, still kept above 105MΩ without any abnormal changes.

Poor Sealing of Automotive Connectors
The electronic devices and wiring harnesses in the dry area are less affected by high temperature/high humidity, chemicals, and dust, while the wet area is just the opposite. If the sealing is poor, it may cause water ingress to electronic devices and wiring harnesses, causing internal circuit short-circuit/corrosion, and directly leading to malfunction, so the sealing of the connector joint of the wiring harness needs to be well protected.

Unreasonable Sealing Structure Design:

The compression of the sealing gasket is insufficient, and the sealing is no problem when the wiring harness is smoothly installed, but fails after bending.

Poor aging resistance and mechanical properties, long-term use will cause aging and cracking, resulting in sealing failure. It is recommended to choose a radial sealing structure during the sealing structure design.

Condensation: Due to the high air humidity inside the automotive connector during operation, water is condensed on the low-temperature surface due to temperature difference after stopping work, which leads to insulation failure, especially for connectors of heating components, such as drive motor connectors.

Siphon: The electronic components such as connectors mainly have two ways to get water. The first is that external liquid infiltrates into their interior by gravity, such as connectors without sealing rings. Or moisture enters from the internal connection points of wiring harnesses (such as unprotected welding points/pressure points/contact points). Here we emphasize the word "siphon", because generally electronic devices have a certain temperature during operation, and the internal air forms a certain pressure. When it stops working, the temperature drops and the internal pressure also decreases, which will form a pressure difference. If the sealing of the connector is poor, water vapor will enter the interior along the gap between the multiple copper wires, causing malfunction.