Conformal Coating - Understanding environmental classifcations

The benefits of surface mount electronics (SMD) are now well known.  SMD provided major cost and size reductions in most electronic equipment.  This was largely due to the tiny electronic components being able to be placed on printed circuit board (PCBs) using automated machines with speed and accuracy production managers previously dreamed of.  Whilst SMD suited the domestic and consumer goods markets, major weaknesses were identified when these tiny components were exposed to industrial environments.  Poor reliability and premature product failure soon began to dog the industrial electronics manufacturing sector and manufacturers took steps to try to replicate the reliability of the earlier plated through-hole electronic PCB technology.  This saw insulating materials being applied by largely unscientific means to PCBs e.g. via paint brushes or spray guns, in an endeavour to improve the product’s field reliability – with varying degrees of success.  This process was loosely called “Conformal Coating”, but there was no consistency in materials being applied, or the manner of application.

Conformal standards began to evolve...

There are a number of standards relating to Conformal Coating. Some of these are;

EN 61086-1:2004: Definitions, classifications and general requirements.

EN 61086-3-1:2004: Property requirements for electrical insulating materials.

EN 60068-2-11: Compares resistance to deterioration from salt mist between specimens of similar construction. May be used to evaluate the quality and the uniformity of protective coatings.

EN ISO 6988:1984  Specifies a method for assessing the resistance of materials or products to condensed moisture containing sulphur dioxides.

However, the most widely quoted standard by equipment manufacturers is IEC 60721-3-3.  (With sub-classifications, 3C1, 3C2, 3C3)

There is a widely held belief that this this determines the level of conformal protection for a given piece of equipment.  This is incorrect. IEC 60721-3-3 classifies the environment that the equipment will be installed in.

General descriptions for these sub classifications are;

Class 3C1: Rural and urban areas with low industrial activities and moderate traffic.

Class 3C2: Locations with normal levels of contaminants, experienced in urban areas with industrial activities scattered over the whole area, or with heavy traffic.

Class 3C3: Locations in the immediate neighbourhood of industrial sources with chemical emissions.

The table below shows the severities of the various chemical elements in each of the three classifications;

Table shows the severities of the various chemical elements 3C1 3C2 3C3

As can be seen in the right-hand column of the above table, the difference in a 3C3 environment compared to a 3C2 environment is significant.

Clearly, a piece of equipment suitable for use in a 3C3 environment is going to be far more robust than one that claims suitability for a 3C1 environment.

If we refer back to the general descriptions for a Class 3C3 environment: Locations in the immediate neighbourhood of industrial sources with chemical emissions – this is what we see in many industrial environments e.g. Sewerage Treatment Plants, Sewerage Pumping Stations, Paper Mills, Metal Processing,Chemical Refining Processes, Galvanising Plants, Fertiliser Plants, Swimming Pool Complexes etc.   Also, New Zealand is unique because of the extremely high levels of H2S that can occur naturally in many parts of our country.  Rotorua is an obvious ‘hot spot”.

Where equipment manufacturers claim suitability for 3C1, 3C2, or 3C3 environments they must have the complete piece of equipment tested by an independent test laboratory. These tests are extremely aggressive and test the true capability of the device and it’s performance under extreme  exposure to a range of contaminants.  Be aware that if equipment suppliers say that their PCBs are conformally coated – this means very little. Coating the PCBs alone are only part of picture (and often the PCBs are coated on one side only). There are many other components that can be susceptible to aggressive ambient atmospheres, such as terminations, conductors, metalwork etc.


How does Power Electronics measure up? 

 All PCBs are coated (on both sides) using state of the art CNC equipment (pictured). This equipment uses a precise airless spray that applies the High Performance Acrylic (HPA) material to the components that need protection, whilst avoiding areas such as termination connectors and sockets etc. It should also be noted that only the connecting pins of Integrated Circuits and Microprocessors have the HPA material applied.  This is because the HPA material is also an insulator and coating ICs and microprocessors entirely, will result in them running at elevated temperatures. The HPA material has an additive which glows blue under UV light, making visual inspection that the coating has been correctly applied a quick and easy process.

state of the art CNC equipment

state of the art CNC equipment image close up

It’s not rocket science….. or is it?

Yes it is in Power Electronics’ case…. To achieve the highest possible performance the HPA material that power electronics applies to its products is formulated for the aerospace and military sectors and meets the following standards;

  • MIL Approval (MIL-1-46058C)
  • NATO Stock Number: 6850992608540 (HPA200H)


In conclusion…

If you are specifying or purchasing equipment for a given application you need to identify the environment classification and ensure that the equipment that you are selecting has the appropriate protection ratings for the application.

 Equipment installed in coastal locations (e.g. pumping stations) will be exposed to high levels of salt mist and widely ranging temperatures and humidity levels.  These are extreme conditions for electronic equipment and the highest level of protection should be selected.  3C1 classification makes no allowance for salt Mist, thus the classification for this location will be either 3C2, or 3C3.

It is safer to select a piece of equipment that is suitable for the most extreme cases.  Whilst under normal operating situations, a product may provide acceptable reliability.  However, in the case of a catastrophic event, such as an ammonia leak in a refrigeration plant the higher the environmental protection level of the equipment, the better.

Example certification to identify machinery class

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