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High voltage circuit boards power advanced technologies including industrial machinery, electric vehicles and many other renewable energy systems. There are additional design factors and parameters that you need to consider while designing HV PCB.
What is a High Voltage Circuit Board?
How do you think that fast electric cars, big telescopes, and industrial washing machines work? Beacuse they have high-voltage PCBs. High voltage PCBs are boards that can handle voltage above 100V. The difference between an LV PCB and an HV PCB is the design considerations. High voltage PCBs are designed using strict standards, larger clearance and creepage, and materials having higher dielectric strength.
All in all, high voltage PCB is designed to support high voltage maintaining safety and reliability under any harsh environmental conditions.
Materials in High Voltage PCB
When you want to select the right material for your high voltage PCB, a selection criteria called CTI (Comparative Tracking Index) is used. CTI define the maximum voltage a PCB can withstand before breaking down and creating more conduciveness. According to the IEC-60950 standard, there are specific values of CTIs that represent the right type of material used for high-voltage PCB.
The common materials that are widely used in the production of high-voltage PCBs includes.
- HVPF (High Voltage Teflon)
- BT epoxy
- Phenolic-cured rigid laminates
- Isola Laminate
While selecting the material best suited for your voltage needs, you can consider some of the following factors.
- Hardness
- Tensile strength
- Resistance against chemicals
- Thermal expansion
- Dielectric strength
Creepage and Clearance Parameters
in HV PCB Design
An effective HV PCB should be met with the UL and IEC standards. There is a minimum distance that should be incorporated between the components to avoid damage. That is where creepage and clearance distance come in.
Clearance is the minimum distance that is measured between two conductors in air. The creepage is also the mininum distance between two conductors. The distance is measured along the surface of the insulation that separates the conductors. If the clearance and creepage voltage is small, it can cause arching between the conductors due to the presence of air or dust particles.
In order to avoid such faults happening, consider the following.
- Peak voltage
- Laminating material
- Operating environment
- Coated or bare traces
- Location of circuit
- Traces on the outer or inner layer
When Can You Work on Live High Voltage?
Standard UL-60950-1 “table 2K-2N” states the minimum distance values for clearance and creepage in respect to coating and insulation. The standard covers the details of insulation type to prevent the arcs. If there is any low voltage operating circuit near the HV circuit, the standard specifies the different types of insulation options.
So, let’s take a look at the various safety standards for high voltage circuit boards.
Safety Standards of High Voltage PCB
In the case of high voltage PCB, safety is ultimately paramount. To prevent any mishaps and damages, there are specific safety standards that are defined by different governing bodies.
- For instance, IPC-9259 states the requirements of distance spacing for power components that operate on voltage higher than 100V.
- Similarly, another standard, UL-61010-1, specifies the requirements highlighting the safety to consider when designing testing/laboratory equipment, including industrial machines.
- Lastly, there is UL-60950-1 which refers to low-voltage and high voltage applications covering a wide range of electronics.
Tips for HV PCB Design
High voltage PCB should be designed in such a way that they can handle voltage reaching up to KVs. When creating such boards, there are certain guidelines which are important to follow.
- There should be no edges and sharp turns in the PCBs because that can lead to fatal damage. Sharp turns can cause leakage current and arcs, further damaging the board and surrounding components.
- Ensure that the board does not contain any burrs once the routing is completed.
- The board should contain a smooth finish to prevent arcs and flashes.
- When selecting the copper weight, ensure that the weight is able to carry high voltage and high current.
- Material selection should be done using the Comparative Tracking Index (CTI) scale, and ensure that the board lies in the category defined by Performance Level Category (PLC).
Understand High Voltage Arc Flash
In the use of HV PCBs, there is a special phenomenon called “High Voltage Arc Flash“. In a high-voltage environment, when the voltage reaches a certain threshold, the insulating medium such as air will be broken through, thus generating an electric arc.
- Line spacing on the board, insulation materials, and other factors directly affect whether an arc flash would occur or not for HV PCBs. For example, the smaller the line spacing, the more likely it is to form a strong electric field at high voltages, thus having electrons jump to the other conductor and trigger an arc.
- Besides, in the HV PCB, the stability of the power supply is the most important thing. If the fluctuation of the power supply is large, the instantaneous high voltage may be higher than the limit that the PCB line and components can withstand, thus triggering an arc flash.
High Voltage Arc Flash Damage
- Arc flash in HV generates very high temperatures, bright lights, and powerful electromagnetic radiation, which are very dangerous to personnel. If arc flash occurs in HV PCBs during maintenance or testing, operators may suffer burns in their bodies and eyes, damage to bodily functions due to electromagnetic radiation.
- Also, the enormous energy thrown out by an arc flash can cause irreparable damage to precision components on HV PCBs.
High Voltage DC
Circuit Breaker
- High-voltage DC circuit breakers shall play an important role in the high voltage DC system where the location of HV PCBs is involved. The DC circuit breakers can cut the circuit quickly when detecting abnormal conditions which may trigger an arc flash, such as the short circuit or voltage surge in the PCB circuit, and inhibit the generation of arc flash.
- Thus, the DC circuit breaker can prevent the chain reaction caused by the arc flash by cutting the circuit in time and thereby stabilize the whole high-voltage system.
- However, it is worth noting that the rated voltage and rated current of the circuit breaker should also meet the operating parameters of the HV PCB. If the rated voltage is too low and the fault current is high, it cannot work properly, and it will also fail to protect the HV PCB from arc flash hazards.
Arc Flash Categories By Voltage Chart
- The arc flash voltage chart is divided into different arc flash categories, depending on the voltage level; each category corresponds to different characteristics of an arc flash, like the range of energy release, probability of flash, and so on. It can be used as an important basis to evaluate the arc flash risk of HV PCBs under different voltages.
- As we can see from the above descriptions, arc voltage charts may help a lot and might have an important referring role in HV PCB design and maintaining selection equipment. According to the different voltage charts in arc flash categories, one will be able to choose the required protection equipment. Taking as examples fuse, surge protectors, among others.
- Arc flash voltage graphs for HV upgrades to PCB: The engineer should use them to decide on whether the newly operating voltage shall replace the existing protective equipment or the change in PCB design parameters should be developed to ensure effective prevention of arc flash for different voltage conditions.
Highlights & Technical Barriers
in High Voltage Circuit Board
Optimizing Power Transistors
Fast-switching HV GaN transistors challenge the PCB layout with regard to the understanding and management of parasitic impedance for proper operation of the circuit and avoidance of EMI.
The parasitic impedance, which ensures circuit operation and avoids EMI, optimization strategies to understand and manage, include:
- Considering parasitic components with current paths and return paths,
- Optimization of layout inductance by making use of thin dielectric layers,
- Selection of top-cooled packages, performing optimization in gate drive layout,
- Planar return paths avoid capacitive current disturbances,
- Keeping the switching nodes compact to reduce capacitance and radiation.
AC-DC controller PCB layout
Layout consideration: The noise and stability problems in power converters require consideration of the PCB layout and wiring. For example, with the integrated controller NCP1937, since different parts of the gate driver can be turned on/off arbitrarily, particular attention must be given to the current path and grounding points to avoid noise interaction.
Pulse Copper Plating Technology for High Aspect Ratio
Technical advantages: High-end multilayer board manufacturing, when the board thickness and aperture ratio of 20:1 or more, high aspect ratio pulse copper plating technology deep plating capability, uniform plating, high production efficiency, is the best process.
International Circuit Board Standard
Importance and ways of implementation: International standards play an important role in ensuring quality and reliability regarding PCBs, not only in materials, design, and process but also in a wide range of applications. You can ensure compliance by studying standard documents such as IPC-2221, IPC-A-600, referring to specifications such as IPC-6012.
Conclusion
High voltage PCBs are getting in demand due to the applications they can cater to. The operation of a high voltage PCB should be optimized in such a way that it runs exactly as designed and follows the safety standards to prevent any mishaps.
FAQs
A1: It depends. First of all, the low resistance of the circuit board chassis is mainly designed for efficient heat dissipation or low impedance circuits.
It is mainly used in high frequency circuits and high current applications. In the former case, a low-resistance circuit base can reduce signal attenuation and improve the quality and speed of signal transmission; while in circuits that need to carry high currents, a low-resistance circuit board base can reduce energy loss and thus improve efficiency.
In short, if heat dissipation is met or in high current situations, it may have low resistance.
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