Electrochemical migration
"The process of electrochemical migration is the formation of an electrically conductive dendrite that can bridge conductors." This is how the new Annex A (informative) of the IEC 60664-1 Low Voltage Directive begins. It thus takes into account an increasing awareness of this failure phenomenon.
Manufacturers of equipment for solar arrays or wind turbines have been aware of the consequences of electrochemical migration for far longer than the automotive industry and its suppliers. This is because these two industries have been working in an environment that can favor electrochemical migration for two decades: Changing climatic influences, large temperature fluctuations, use in open fields.
In a dry, clean environment, electrochemical migration cannot normally occur - the mobile charge carriers, the ions, are simply missing. The situation is completely different if moisture occurs in a housing or component. This does not necessarily have to be condensation or even splash water. High humidity is sufficient, as some materials can absorb a lot of water (e.g. PA).
Factors
In addition to this most important condition for electrochemical migration, the presence of a carrier for ions, the following other factors are favorable:
- Amount of the voltage difference
- Conductivity of the substrate material
- The degree of soiling (environmental influences)
- Type of insulation material (susceptibility to electrochemical degradation)
- Type of conductor materials (e.g. wisker formation)
Minimize danger
For this reason, the annex, which has not yet been published as part of the standard, recommends several framework conditions that should be observed in order to minimize the risk of device failure due to electrochemical migration:
- Applying coatings to circuit boards (e.g. protective lacquers)
- Use of metal materials that are more resistant to electrochemical migration
- Use of insulation materials with high insulation resistance (electrochemical migration can occur at resistances below 10e8 Ohm even without the influence of moisture)
- Enclosure designs that prevent condensation (high protection class IP value) and installation location
- Where condensation cannot be prevented by other measures: anti-condensation heating or self-heating (electric heat)
- As with all other surface phenomena such as creep path formation: select larger distances as specified in the standard
- Avoidance of impurities on surfaces and in products (e.g. potting resins, printed circuit boards) that promote electrochemical migration
Electrochemical migration as a cause of faults
Electrochemical migration is the main cause of faults in direct current applications: The constant electric field favors the migration of metal ions from one conductor to another. Needle-like or tree-like metal structures form on the surface of an insulator, but also inside it (e.g. potting compounds), leading to a shortening of the insulation distance. They also encourage the formation of creepage distances, which in the worst case can lead to a short circuit.
It is also particularly problematic that this phenomenon is almost impossible to detect during an internal production quality check. The result is that only (sporadic) field failures reveal a weakness in the design.
Insulation products from CMC
As a developer, CMC Klebetechnik provides you with numerous high-quality insulation products. These can be products with a particularly high CTI value (up to >600V) or particularly high temperature-resistant films (up to >300°C) or those with particularly low water absorption. Tell us about your application and general conditions and we will find the right product for you from our portfolio.
Contact us
If you have any questions, please contact:
Electrochemical migration - Supplement to IEC 60664