The concept of dualism is probably one of the oldest or first truisms that we humans understood. We can see evidence of this in our interpretations of everything from abstract concepts; such as love and hate, to concrete observations; such as physical action and reaction. And at least as far as the physical world is concerned it is important to understand both the action and reaction to effectively utilize, apply or avoid either or their effects. An example is electrical power and the duality between voltage and current, which produce it.
Sign warning of possible industrial electrical arcing
One of the hazards that can exist in industrial environments is unwanted electrical power transfer in the form of an arc between two objects or locations at different charge levels. On circuit boards, the high voltage arc tracking rate (HVTR) is a standard measure of how well your PCB material will resist the effects of this situation. For a comprehensive understanding of arcing on circuit boards, we need to consider current, as well as voltage. Therefore, let’s explore the relationship between voltage, current, and arcs, which should enable us to establish means to avoid high current arc ignition that will result in physical damage to your board and likely delay or halt factory operations.
Voltage, Current and Arcs on PCBAs
Due to the power demands for industrial equipment, it is common for PCBAs to accept, process, and distribute high power. For many boards, this means that the high voltage considerations of production must be incorporated into the design and manufacturing processes. However, there are actually three industrial high power conditions, as listed in the table below, that can exist on your board and may impact your board development.
Industrial PCBA High Power Arcing Considerations
|Electrical Condition||Potential Hazard||Testing Metric(s)|
|High Voltage/Low Current||Surface Tracking||High Voltage Tracking Rate (HVTR)|
|High Voltage/High Current||Surface Tracking
|High Voltage Tracking Rate (HVTR)
High Current Arc Ignition
High-Current Arc Resistance to Ignition
|Low Voltage/High Current||Arc Ignition||High Current Arc Ignition
High-Current Arc Resistance to Ignition
|Low Voltage/Low Current||NA||NA|
As shown above, the primary contributor or cause of high power arcing on your board may be due to high current. Generally, this is not an issue provided board conditions do not exceed the limits of the appropriate performance level categories (PLCs), which provide an estimation of how your board’s material will respond for given electrical conditions. These categories are based upon standardized testing procedures that can be found in UL-746A and are organized for different arcing hazard types.
Hazards resulting from arcing that can impact industrial PCBAs are surface tracking, where an unwanted circuit path through the board material is formed along the surface, and arc ignition, where the board erupts into flames. Tracking can be a problem when an unanticipated high voltage appears on the board likely due to some contingency, such as input power line spiking. However, an eruption is typically associated with high current, which may occur for both low and high voltage conditions, and is more severe. A high current arc ignition not only can damage the PCBA on which it began, but nearby boards, other devices and may even threaten personnel in the area. Therefore, industrial PCBAs must be designed and built to avoid arcing ignition.
Preventing High Current Arc Ignition on Circuit Boards
High voltage PCB design for arc prevention is effective, provided that you incorporate the results of established standards testing, primarily from UL-746A. The same is true for preventing high current arc ignition episodes. The two tests that measure the effects of high current arcing are listed in the table below.
The results of these tests can be used to form a strategy to minimize the probability that a high current arc will cause ignition on your industrial PCBA as follows.
How to Avoid High Current Arc Ignition
- Compare HWI and HAI ratings for various materials.
These results should be acquired or tests performed for all board material considerations.
- Choose the board surface material using the ratings from A as a primary decision factor.
Select a material that will provide adequate time for the board to be isolated before ignition could spread other devices or threaten personnel.
- Institute a risk management plan based on the results of A and B to address high current arc events.
Develop and put into action a risk management plan to respond to arc events, including appropriate controls. For example, if your board is only exposed to a small number of events that last an average of a few seconds each, then board replacement may not be necessary. On the other hand, if exposed to one event for 100 seconds, the board is likely damaged enough that replacement is warranted.
|Tempo's Industry 4.0 Custom PCB Manufacturing Services
High power arcing, irrespective of the catalyst, can pose major problems on industrial circuit boards. If high current arcing is present, then interconnected PCBAs, other systems and equipment could be adversely impacted. At Tempo Automation, we have the expertise and capabilities, including material options, to meet your industrial PCBA requirements.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on avoiding high current arc ignition on your industrial boards, contact us.