In all the previous portions of our series on connectors, we focused a lot on usage in a PCB, signal and power handling, mechanical aspects, and grounding. There is one more important aspect of connector selection that is often overlooked: environmental factors. The environment where a connector is deployed can cause the connector to fail, or it can cause exposure within a device that leads to failure. This important aspect of engineering an assembly should be understood by anyone involved in connector selection.
The idea of “environmental factors” refers to more than just temperature. Previously, we had discussed vibration and ESD as some of the important environmental factors, but we also have issues with exposure to chemicals, moisture, solid debris, and the resulting ingress into the enclosure. This 6th part of our connectors series will examine these environmental factors, as well as connector assemblies are evaluated using a standardized system.
Connectors and Environmental Exposure
Connector bodies and contacts can degrade under environmental exposure, as well as exposure to certain substances within the target deployment environment. Some of these environmental factors include:
- Exposure to noxious chemicals that can corrode connector materials.
- Thermal cycling, may degrade insulator materials if cycling is extreme.
- Exposure to different levels of moisture, either in highly humid air or direct splash from liquids.
- Exposure to solid debris, such as dust or metal shavings, can interfere with connector mating or can infiltrate the enclosure/connector assembly.
Some system application areas like industrial systems and aerospace will have very strict requirements on these aspects of connector selection and enclosure design. These are enforced for purposes of reliability: any of these factors can slowly degrade the connector assembly, the PCB and other electronics in the enclosure, or all of these.
Connector Design Factors That Impact Reliability
Reliability is a system-level design consideration, and connectors are just one of many points of failure. Some of the design factors that impact environmental reliability are outlined in the table below.
The material used for insulating (such as a rubber seal on some connectors) can impact heat diffusion into/out of the connector body.
Connector body material
Some connector materials can corrode when placed into service. Certain materials can resist corrosion, as well as mechanical crushing forces and vibration.
Connector body seal
More likely to have high protection against solid debris ingress (see below for more details on ingress protection).
Although the connector material might resist corrosion and ingress, the enclosure may not. The result is failure at the board level, or possibly on connector contacts.
The contact material can limit the number of useful mating cycles. Mating can also slowly remove surface finishes, exposing metal to risk of corrosion.
The cable assembly should be designed to withstand the same environmental risks as the connector assembly.
In some cases, like with board-to-board connectors, the connector assembly in question might be totally enclosed. In this case, the enclosure becomes the point of failure, not the connector. When we start to look at these aspects of connector reliability, we need to understand the IP rating system. Connector IP ratings provide a useful guide for connector selection and enclosure design as they provide minimum performance requirements under certain environmental conditions.
Ingress Protection (IP) Ratings
If a device is at risk of exposure to moisture or solid debris, the connector and the enclosure together will need to be tested to determine the product’s IP rating. Some connectors are available that have a specific IP rating, but they must be matched with an enclosure that also has a matching IP rating. The lower of the two ratings (connector vs. enclosure) gives the overall IP rating of the product.
The IP rating system (or Ingress Protection Code as defined in IEC 60529) is written IPXY, where X and Y signify the solid ingress and liquid ingress resistance of the component, respectively. Connectors and enclosures that are designed and marketed as “water resistant” are generally at least IP-65 rated; they will have significant protection from solid debris, and varying levels of moisture protection.
Solid and liquid exposure protection
In all of the above entries, a solid debris ingress protection level of 5 (first digit) indicates near complete protection against dust with minor infiltration into the assembly. The highest solid ingress protection level (6, first digit) indicates total protection against infiltration by dust or other solids (including insects), requiring a vacuum be applied in the connector body with 8-hour test duration.
For the liquid protection rating, note that water is the baseline liquid used in determining IP ratings. If the risk of exposure is to some other liquid, then that liquid should be used for evaluation and testing of ingress protection resistance and used to assign an IP rating. For example, submersion in a higher density liquid, like glycol, will require tighter connector assembly specifications than a standard IP68-rated connector because the hydrostatic force experienced during submersion will be larger.
A Holistic Approach to Connector Selection
As we discussed in previous sections of this series, there are multiple factors that will drive connector selection, and this requires a holistic approach to systems design. Some of the functional requirements in off-the-shelf connectors may be in competition with the environmental factors listed above. For example, high bandwidth shielded connectors with corrosion-resistant materials could withstand vibration and crushing forces, but they may not be suitable in an environment where moisture ingress is a risk.
- Start with the greatest risk factor - this could be environmental or functional
- After finding connectors that address Point #1, look for connectors that come close to your electrical specifications
- If Point #2 is not possible, consider an alternative approach to the design, or possibly a custom connector
After you’ve determined the environmental risk factors that will impact electronic connector reliability, make sure you use the best set of system analysis tools to qualify your system at every level. The system analysis utilities from Cadence help you evaluate designs at all levels, from front-end schematic capture to back-end simulation and verification. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity.