A simple, cost-effective way to increase the reliability and longevity of electronics components and systems.
by Conrad H. Blickenstorfer
While the wholesale migration from mechanical to mostly electronic solutions and components has virtually eliminated the wear and material fatigue inherent in exposed and moving parts, solid state technology has its own range of issues that can interfere with reliable operation.
One of them is moisture in electronics that can cause false alarms, faulty operation, and micro-corrosion that can lead to component and system failure. Another is accelerated aging due to air pockets and gaps as well as exposure to corrosive agents. Some of this can be addressed with suitable encapsulation of vulnerable components and systems in housings, but that increases cost and may add size and weight.
An alternate solution to mechanical encapsulation is "potting" of electronics. It's called potting because just like the vulnerable root system of a plant is stabilized and protected by placing the plant in a pot and the pot then filled with soil, electronic components can be "potted" in suitable enclosures and with suitable compounds that not only protect against shock and vibration, but also against formation of moisture and exposure to corrosive agents. The overall idea is to encapsulate vulnerable electronic parts so that they are kept from any kind of harm.
How does electronics potting work?
So let's take a closer look at electronics "potting." In essence, it's like creating a suitable "pot" to put electronics in, then filling that pot with special curable liquids (like epoxies, polyurethanes, silicones, etc.) that have whatever thermal, insulation, adhesive and structural properties as are required for a potting project. Note that a "pot" can also be a cast that's removed once the potting compound has hardened, or components may just be dipped in the compound to encapsulate them.
Among the many advantages of "potting" electronics is that it is a very flexible solution. Potting can be applied only to high-risk parts and components as well as to complete boards and assemblies. A large variety of potting materials are available, addressing issues such as conductivity, electrical and thermal isolation, and protection against various environmental conditions and threats.
The benefits of potting are considerable. Potting does not only protect against moisture and exposure but also against shock and vibration. It completely removes the harmful impact of air and moisture from the maintenance, reliability and longevity equation while still allowing the shielding of noisy parts and components sensitive to EMI.
What are some practical applications that benefit from potting?
As electronics are used in more and more areas of modern life and industry, putting is an important tool in keeping things up and running. Some examples are:
The automotive sector relies on numerous electronics parts and systems that may all be exposed to dirt, liquids, moisture, vibration and extreme temperatures. Potting of strategic parts and components can greatly improve reliability and guard against premature aging and failure.
Forklifts and other construction vehicles are routinely pressure-washed at the end of shifts, mandating suitable protection of electronic systems and conduits for ongoing reliable operation. Again, potting can protect vulnerable parts and keeps them from harm.
Infrastructure electronics such as traffic lights, switches, power supplies, sensors, etc., all depend on sealed enclosures for proper operation. Once those enclosures lose their effectiveness through aging, thermal and mechanical stress, UV exposure, etc., reliable operation is no longer guaranteed. Strategic component potting can greatly increase reliability and reduce repair and replacement costs.
Apart from these three examples, there are numerous other electronic applications and solutions where exposure to liquids and varying temperatures occurs. All are at risk because even minute breaches in enclosures will result in exposure to moisture and its corrosive effects. Here again, electronic potting can help.
How does potting compare to other protective solutions?
While potting is a mature and cost-effective way to protect electronics, there are other solutions that can get the job done. One is conformal coating where a thin protective coating is applied to an entire circuit board. Another is placing components and systems in fully sealed housings. Both methods are widely used and have many beneficial applications. But, depending on the application, they may be less cost-efficient than potting, and neither conformal coating nor full enclosures can address the issue of trapped hot air. As a result, strategically applied potting to at-risk components is often the best and most cost-efficient solution.
The electronics potting process
How is potting done? That depends on the type and use of the components to be potted.
On the chemical side, some materials or adhesives may have chemical reactions with certain potting materials, potentially resulting in non-cured areas. These must be identified so that the proper potting compounds will be used. On the electrical side, some parts or components may be inadequately sealed so that potting material may go where it is not supposed to go. Such components must be identified to avoid malfunction later on.
Different potting compounds require different processing. They may require special mixing, different temperatures, different ways to eliminate bubbles, and different curing to minimize shrinkage. Bubble elimination (or "degassing") may require vacuum chambers. For certain complicated potting projects, higher viscosity of the potting material is required and that's achieved via elevated temperatures.
To be successful, the electronic potting process requires highly specialized equipment. This includes machines for precise, uniform mixing of potting materials as well as de-gassing tanks that eliminate any air bubbles in the materials. Equipment must allow for precise adjustment of potting material ratios and flow speed. Electronic potting facilities also include vacuum and curing chambers with full temperature controls. Additional considerations here are the length and temperature of the curing process that have an impact on shrinking.
The pictures below show a potting machine setup complete with vacuum capability for degassing.
Quality and process inspections
Upon an initial potting run, technicians perform an inspection to determine potting flow patterns, proper filling, curing. To do that, sample units will be dismantled and/or sliced and then carefully examined. Findings are documented and inspectors will also compile notes and checklists for potting operators. If problems are found, the potting process and materials may be adjusted and inspections repeated until everything is as it should be. Potting samples may be kept for mixing ratio approvals.
Electronic potting: Road to success
The success of a potting project relies on four things.
- Pinpointing at-risk components with the highest return on investment from potting
- Determining the potting compound with the exact right mix of properties for the project
- A state-of-the-art electronics potting facility with all required equipment, and
- Using an experienced electronics potting operator.
Sources and references:
To be supplied