14 high-power PCB design techniques, pictures and examples, understand in seconds

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14 high-power PCB design techniques, pictures and examples, understand in seconds [Copy link]

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What I will share with you today is high-power PCB design and high-power PCB design techniques.

1. What is a high-power PCB?

High-power PCB is a printed circuit board made of heavy copper. Compared with other circuit boards, high-power PCB is able to handle higher current rates, it can resist high temperatures for a long time, and provides strong connection points.

High Power PCB

High Power PCB Characteristics

Manufacturing high-power PCB designs for specific devices requires higher amounts of current and is often subject to varying temperatures.

In order for them to perform effectively, high-power PCB designs include the following features: Compared to copper layers in other PCBs, the copper layers in high-power PCB designs are thicker and heavier, capable of conducting higher currents.

Heat Transfer in PCB

This ability to conduct higher currents is combined with the ability to dissipate heat, which helps ensure that short circuits do not occur during the operation of a device made from the circuit board. For these reasons, high-power PCBs are able to resist and adapt to the fluctuating temperatures in which the device is used.

2. Types of High-Power PCB Design

There are many high-power PCBs available on the market. Here are three common classification standards:

1. Double-sided high-power PCB

These are high power printed circuit boards that allow for components to be mounted on both sides. This is an entry level product made using high power PCBs.

Using vias, routing is alternated between the top and bottom layers, making them more efficient and reliable than single-sided high-power printed circuits.

Double-Sided PCB

2. Rigid-flexible high-power PCB design

High power printed circuits consist of rigid and flexible circuit substrates.

Typically, rigid-flex high-power boards consist of multiple layers of flexible substrates that are then attached to one or more rigid boards.

Rigid-Flex PCB Design

Whether this attachment is done internally or externally, the intended application of the high-power rigid-flex board is critical in determining how the connection is accomplished.

Additionally, flexible components are designed to be flexible at all times. This flexibility is helpful in corners and areas where extra space is needed. Rigid substrates are helpful in areas where additional support is needed.

With these features, it is ensured that these high-power rigid-flex boards can bend during manufacturing and installation. Rigid-flex technology enables high-power PCBs to fit into smaller applications, which leads to enhanced performance and convenience.

3. Multi-layer high-power PCB design

Multilayer high-power circuit boards have at least three conductive layers. Intersecting circuit board plated through holes is the most common electrical connection strategy in these boards.

Depending on the purpose of the board, there can be as many as twelve conductive layers. However, some companies are now manufacturing PCBs with as many as 100 layers, providing room for some of the most complex and high-power PCB applications.

Multilayer PCB

3. Advantages of High-Power PCB Design

High Power PCB Design

1. Increase tolerance to thermal strain

The thick copper of high-power PCB enables it to withstand the thermal stress it is subjected to. Therefore, devices made of high-power PCB are able to resist thermal fluctuations, making them reliable, so they are generally used in manufacturing military applications.

2. Increase current carrying capacity

Heavy copper also enables high-power PCBs to conduct high currents without too much stress, high currents on PCBs with lighter copper are prone to malfunctions and failures.

Devices such as power transformers are exposed to very high currents, and without a high-power PCB, they are likely to fail or cause some circuit disaster.

3. Increase the mechanical strength of the connector and PTH hole

The heavy copper used to make high-power PCBs gives it mechanical strength, which is very important for supporting the components mounted on the board. The connector area is reinforced in high-power PCBs. This extends to the through-holes, which are also made of copper.

4. Reduce product size

High-power PCB design also helps in reducing product size. This is achieved by combining multiple copper weights onto the same layer of the circuit, explaining its preference in military applications as most products have to be portable.

5. Heat transfer to external radiator

Using heavy copper plated through-holes, high current transfer through the board is possible. This helps transfer heat to an external heat sink, making high power PCBs the most effective boards for applications that require high currents to operate efficiently.

The heat sink in high-power PCB design can also be plated directly on the board, which explains why high-power PCB design is often used in industry.

4. Example High Power PCB Design Schematic

Here is an example of a high-power PCB design based on the Atmega328 microcontroller. The board controls two DC motors with an integrated H-bridge driver. Since the H-bridge can also drive almost any inductive/resistive load, it can also drive a high-current LED panel, specifying each output to drive a 15A load, for a total of 30A.

High Power PCB Design

The schematic above uses two VNH5019A integrated H-bridge drivers, each of which can continuously drive 30A of current. The Atmega328 will control the logic of the drivers, and a single 12VDC supply will power the board.

The switching regulator drops down to provide 5VDC power to the ATmega. VNH has all the logic pulled high, except for the Ina/b lines that provide the direction of rotation for the motor. If more control is needed, you can control the ENa/b pins from the ATmega.

The VNH is able to handle most of the flyback protection and only requires a 1000uF electrolytic capacitor. A 74651195R 85A screw terminal is used here as the main 12VDC power input, and two 1792229 30A snap-on terminal blocks are used as the motor outputs.

Each VNH driver has a 30A input fuse and a 15A fuse. The driver's fuse is before the driver, and since the driver can provide 30A, the fuse should blow before the driver is overloaded.

This ensures that both sides are cut off if the fuse blows, since there is no power to the driver at all. Another option is to fuse the two outputs of the H-bridge driver, but this may leave one side still hot after the short circuit.

5. High-power PCB design skills

1. Consider safety

As with any circuit, the main concern with a high current circuit is ensuring it operates safely. There are some unique potential issues with boards driving such high power loads, the main thing to watch out for is heat. No matter how you design and lay out the board, it will generate more heat than a standard board.

This must always be taken into account when building the enclosure and external vents/fans should be used. What I do on all designs driving more than a few A is to install a dedicated temperature sensor on the PCB. This is a great firmware-based failsafe. With the ability to monitor temperature you should always be able to react to any overheating conditions. To reduce the heat generated by the board itself it is best to choose components with low resistance.

The next potential safety hazard concerns short circuits. Since this board is designed to drive high power devices, it will be able to source considerable current when shorted. It is vital to consider this possibility during the design phase. The simplest way to handle a short circuit is to install a fuse on all outputs leaving the board, as well as an input fuse. Fuses should always be rated for less than the current the wires being used can handle. They should also be rated for less than/equal to the amount of current the board traces/pourings are designed for. It is also a good idea to use drivers with built in short circuit prevention features.

2. PCB power design

The establishment of the power path is the most important rule for high-power PCB circuits, which is crucial to determining the location and amount of power that should flow through the circuit, as well as the location of the IC and the amount of heat dissipation required by the circuit board.

There are many factors that influence the layout of a given design:

• The first thing to consider is the amount of electricity flowing through the circuit.

• Also important is the ambient temperature of the device and board design

• Also consider the expected airflow around the device and even the board.

• Another consideration is the circuit board material that will be used.

• A final and equally important factor is the IC density of the board you intend to use.

3. PCB design layout

Board layout should be considered from the early stages of PCB development, and an important rule that applies to any high-power PCB is to determine the path that the power follows. The location and amount of power flowing through the circuit are important factors in evaluating the amount of heat that the PCB needs to dissipate. The main factors that affect printed circuit board layout include:

• the power level flowing through the circuit;

• The ambient temperature of the circuit board;

• Affects the airflow of the circuit board;

• Materials used to make PCBs;

• The density of components that populate a circuit board.

But usually like to split a board like this into low power and high power sections. This ensures that all high power traces are as close to the power supplies and outputs as possible. The board will be 2 layers with 2 oz copper.

Something I learned when doing high current PCBs is to do a rough initial layout with 8 mil traces on everything to ensure that the components are placed in an optimized manner. This helped a lot with this example because it showed exactly where the high current paths were and how to best position the H-bridge drivers.

Rough board layout with 8 mil traces

The image above shows the initial layout of all the components, along with the 8 mil traces used to specify the path for all the final traces. Power will enter from the bottom terminals, go to the input fuse, branch out to the H-bridge driver, and the low current power will go up through the center of the board to the 5V regulator.

For the H-bridge drivers, power will go to them through large electrolytic capacitors on the bottom layer, connected to the top layer and pads by many stitching vias.

PCB high power design

4. Component selection

High current designs and power systems often get most of their reliability from their components. As obvious as it sounds, make sure you factor in component safety margins during the selection process. Generally speaking, it’s best to start by looking at two specifications:

• Current rating, especially for MOSFET and inductor components

• Thermal resistance

You can use the estimated or designed operating current (if available) to determine the power dissipation, or use the first specification above to get a worst-case value. Both will help with thermal management, which requires using thermal resistance values to estimate temperatures. For some components, you can determine if a heat sink is needed to ensure reliability.

Other components that are important to high current circuit boards, such as connectors, may have very high ratings and are useful in power systems. Shown below are two examples of machine screw terminal connectors that can handle very high currents.

Connector

5. Appropriate copper weight

The copper resistance used in the traces will generate some DC power losses which will be dissipated as heat. For designs with very high currents this becomes very significant, especially at high component densities.

The only way to prevent DC losses in high current PCBs is to use copper with a larger cross-sectional area. This means that either heavier copper is needed or wider traces are needed to keep Joule heating and power losses low enough.

Use the PCB Trace Width vs. Current table to determine the copper weight and/or trace width required to prevent excessive temperature rise.

6. Grounding

PCB high power systems can require the same fail-safe measures. A certain degree of safety and EMI can be achieved through proper grounding strategies. Generally, grounding should not be separated, but power systems involving high currents and/or high voltages are an exception. Grounding needs to be separated between the input AC, unregulated DC, and regulated DC sections.

A good place to start is with the grounding strategies you would find in an AC system or isolated power supply. Typically for high current power systems you would have a 3 wire DC arrangement (PWR, COM, GND) where the GND connection is actually a ground connection. Your board may use an isolation strategy where the output side is disconnected from GND and the input side is grounded for safety in the event of a fault.

7. Component placement

It is critical to first determine the location on the PCB of high-power components, such as voltage converters or power transistors, which are responsible for generating a lot of heat.

High-power components should not be mounted near the edge of the board, as this can cause heat buildup and significant temperature increases. Highly integrated digital components, such as microcontrollers, processors, and FPGAs, should be located in the center of the PCB to achieve uniform heat spreading across the board, thereby reducing temperatures. In any case, power components must never be concentrated in the same area to avoid the formation of hot spots; instead, a linear arrangement is preferred. The figure below shows a thermal analysis of an electronic circuit, with the areas of highest heat concentration highlighted in red.

Thermal Analysis of PCB High Power Design

The layout should start with the power devices, whose traces should be as short as possible and wide enough to eliminate noise generation and unnecessary ground loops. In general, the following rules apply:

PCB component placement

• Identify and reduce current loops, especially high current paths.

• Minimize resistive voltage drops and other parasitics between components.

• Keep high-power circuits away from sensitive circuits.

• Take good grounding measures.

In addition to the above layout considerations, it is also important to avoid mixing the different power components on the board. To achieve thermal balance on the board, ensure that these thermal elements are evenly distributed across the board.

This will also effectively protect the board from warping. Therefore, you can ensure that the heat on the board is reduced and the sensitive circuits are protected. The signals will also be equally protected during operation.

8. IC and component installation

Whenever there is power flow in a circuit, it is obvious that all components will generate heat. When passive components and ICs generate heat, the heat is likely to be dissipated. This heat is dissipated into the cooler ambient air surrounding the device.

IC component mounting

This dissipation is either achieved through the lead frame of the device or through the package. Therefore, most IC packages are designed without leaving much room for an external heat sink.

Additionally, this requires a method by which heat can be extracted from the device. An exposed pad is one such method. For optimal thermal performance, use a bare die within a package.

This die should have an EP directly connected to it. These ICs can then be properly mounted on the board. This way, the heat transfer from the package to the board will be optimized.

9. Heat sink

The purpose of using heat is to prevent heat wicking into the surrounding copper pour while soldering. For a lot of high power PCB designs, this is hand soldered internally with a high power iron. It can make quick work of solid pads even on 2Oz copper. I tend to use heatsinks on all non-power nets and use solid connections on the power nets.

Fill plane showing heat relief

The image above shows where the heat sink is placed. The main input power, fuses and outputs do not use heat, all other nets do. This technique has worked very well on multiple designs, with hundreds of boards produced, and I have rarely encountered issues with soldered components coming loose or any other issues related to cold solder joints.

10. Trace thickness and width

When designing any circuit board, you need to be aware of the minimum trace width. This becomes critical when dealing with high-power PCBs.

In principle, the longer the track, the greater its resistance and the greater the heat dissipation. Since the goal is to minimize power losses, in order to ensure high reliability and durability of the circuit, it is recommended to keep the traces that conduct high currents as short as possible. To correctly calculate the width of the track, knowing the maximum current that can pass through it, the designer can rely on the formulas contained in the IPC-2221 standard, or use an online calculator.

As for trace thickness, typical values for standard PCBs are around 17.5 m (1/2 oz/ft 2 ) for inner layers and around 35 m (1 oz/ft 2 ) for outer layers and ground planes. High-power PCBs often use thicker copper to reduce the trace width for the same current. This reduces the space that the trace takes up on the PCB.

Thicker copper, ranging in thickness from 35 to 105 m (1 to 3 oz/ft 2), is typically used for currents greater than 10 A. Thicker copper inevitably incurs additional cost, but helps save space on the card because the viscosity is higher and the required track width is much smaller.

Trace thickness and width

11. Solder mask

Another technique that allows traces to carry large amounts of current is to remove the solder mask from the PCB. This exposes the copper material underneath, which can then be supplemented with additional solder to increase the copper thickness and reduce the overall resistance of the PCB current-carrying components. While it may be considered a workaround rather than a design rule, this technique allows PCB traces to carry more power without increasing the trace width.

12. Decoupling capacitor

When a power rail is distributed and shared among multiple board components, active components can develop dangerous phenomena such as ground bounce and ringing. This can cause voltage drops close to the component power pins.

To overcome this problem, decoupling capacitors are used: One terminal of the capacitor must be as close as possible to the pin of the component receiving the power supply, while the other terminal must be directly connected to a low-impedance ground plane. The goal is to reduce the impedance between the power rail and ground. The decoupling capacitor acts as an auxiliary power supply, providing the required current to the component during each transient (voltage ripple or noise).

There are several aspects to consider when selecting a decoupling capacitor. These factors include choosing the correct capacitance value, dielectric material, geometry, and placement of the capacitor relative to the electronic component. A typical value for a decoupling capacitor is a 0.1μF ceramic capacitor.

13. Double the layers

One technique that is used in a lot of high power circuits that is not used often is to double the copper pours and stitch them together with vias, this double layer allows twice the amount of copper to be in the same area. For this board, the copper on the main power input was doubled from the terminal to the input fuse. The picture below shows this.

When you use this technique, the chances of creating a current loop increase because there is a section where no return current can flow. I do not believe in using two layers on the net from the input fuse to F3/F4 because this is where a lot of the return current flows.

Double layer close-up of main power input

The minimum width for this pour is 460 mils, but because it is on both the top and bottom layers, it is actually twice as wide, resulting in a much smaller voltage drop across the net. The smaller the voltage drop, the less heat is generated.

14. Copper coating

Regardless of what type of board you are designing, you will generally try to use a copper pour for all of your power nets. When dealing with dedicated, high-current designs, all nets that carry high power should have a single pour. Copper pours can significantly increase the width of copper that can be mounted on the board.

Layout using copper pours on all high current nets

The image above shows a high current section of the board with copper pours used on all the high current nets. By using pours instead of traces, the amount of copper can be increased significantly. A trick used to help the design go a little faster is to use a 20mil grid and use that to make sure all the pours are symmetrical at 45 degree angles.

6. High-power PCB design steps

1. Prepare the substrate

Before the manufacturing process begins, the laminate must be thoroughly cleaned. This pre-cleaning is essential as the copper coils used in high-power PCB designs often have rust-resistant properties, and these are often completed by suppliers to provide anti-oxidation protection.

2. Generation of circuit patterns

When designing a high power PCB, two main techniques are used to achieve this goal. These techniques include:

• Screen Printing – This is the most preferred method as it is able to produce the desired circuit pattern. This can be attributed to its ability to accurately deposit on the surface of the laminate.

• Photo Imaging – This is the oldest technique used in designing high-power PCBs. However, it is still a common method for delineating circuit traces on laminate boards.

This technique helps ensure that a dry photoresist film consisting of the intended circuit is placed on the laminate. The resulting material is exposed to ultraviolet light. Thus, the pattern on the photomask is transferred to the laminate. The film is chemically removed from the laminate. This leaves the laminate with the intended circuit pattern.

3. Etching circuit pattern

When designing high-power PCBs, this is usually achieved by immersing the laminates in an etching tank. Alternatively, they can be sprayed with an appropriate etchant solution. To achieve the desired result, both sides are etched simultaneously.

4. Drilling process

After etching, the next step is drilling. In this step, holes, pads, and vias are drilled. To drill precise holes, you have to make sure that the drilling tool is high speed and use laser drilling methods when creating ultra-small holes.

5. Through-hole plating

This is a step that must be handled with great care and precision when designing high-power PCBs. After the required holes are drilled, copper is deposited in them.

Unlike other circuit boards, this is done in bulk and made thicker. They are then chemically plated. The result is electrical interconnections across the layers.

6. Application of covering layer or covering coating

Protecting both sides of the board is essential in high power designs. This can be achieved by applying a coverlay.

The importance of this is to provide protection from harsh environments. This is critical for high-power PCBs as they are subject to temperature fluctuations. This cover also provides protection from harsh chemicals and solvents.

Polyimide film supported by an adhesive is the most commonly used cover layer material, and the cover layer can be pressed onto the surface by screen printing.

Using UV radiation, curing is achieved. Controlled heat and pressure are applied during the lamination process of the coverlay. There is a significant difference between coverlay materials and overlays. Coverlay is a laminating film whereas overlay refers to the material that can be applied directly to the surface of the substrate.

There are many factors that determine the type of covering. They include the methods used in the manufacturing process, the materials used, and the application area. Both types of coatings are essential to enhance the electrical integrity of the entire assembly.

7. Electrical testing and verification

The boards go through a battery of electrical tests that scrutinize factors like performance. You also need to use the design specs as a threshold to assess quality.

7. High-power PCB processing

These are the basic steps:

• Print inner layer

• Align Layers

• drilling

• Copper plating

• Outer layer imaging

• Copper and tin plating

• Final Etching

• Applying Solder Mask

• Applying Surface Finish

• Application Silk Screen

• Cutting Board

1. Heavy copper circuit structure

In high-power PCB design, thick copper circuits are used. This usually requires special etching techniques.

One-stop high-power PCB design

The technology used for the weaving here is also completely different from that used for other PCBs, using high-speed plating and differential etching.

When plating thick copper circuits, you can continue to increase the thickness of the board. You can also mix thick copper with standard features on a single board. This is also called power link. This will translate into many advantages, including a reduced number of layers. Power will also be distributed efficiently.

This will also allow the incorporation of high current circuits and control circuits on the board. It also provides a simple board construction.

2. Current carrying capacity and temperature rise

Estimate the maximum current the trace can comfortably carry. This can be determined by figuring out a method that can estimate the heat rise. This is related to the current of your application.

The ideal situation is to reach a stable operating temperature, in which case the heating rate equals the cooling rate. When your circuit can withstand temperatures up to 100°C, you are ready to go.

3. Circuit board strength and survivability

You can choose from a variety of dielectric materials. These include FR4, which operates at temperatures up to 130°C. Another dielectric material is high-temperature polyimide, which can operate at temperatures up to 250°C.

Higher temperatures require the use of special materials so that they can survive extreme conditions. There are several methods that can be used to test and determine the thermal integrity of a finished product. One of these methods is to use a thermal cycle test. It helps to check the resistance of a circuit while doing an air-to-air thermal cycle. This cycle is checked from 25°C to 260°C.

The increased resistance can lead to a breakdown in electrical integrity through cracks in the copper circuit. For this test, make sure to use a chain of 32 plated through holes. This is because they are considered the weakest point in the circuit, especially when they are subjected to thermal stress.

Thick copper circuits often reduce or eliminate the failures inherent in these boards. This is because the copper circuits become impermeable during the mechanical stress phases caused by thermal cycling.

4. Thermal management

Heat is typically generated during the operation of electronic devices and must be dissipated from the source and radiated to the external environment. If this is not done, components may overheat, resulting in failure.

Heavy copper helps in reducing heat. It conducts the heat away from the component, thus greatly reducing the failure rate. Use a heat sink to achieve proper heat dissipation of the heat source. The heat sink will likewise dissipate the heat away from the source where the heat is generated. This is done by conduction and dissipation of the heat to the environment.

The connection is made with copper vias to the bare copper area on one side of the board. Classic heat sinks can be bonded to the copper base surface. This is achieved with thermally conductive adhesives. In other cases, they are riveted or bolted.

These heat sinks are usually made of copper or aluminum and when manufacturing high power PCBs a built-in heat sink is created. This requires no additional assembly. Copper Circuit Technology allows for the addition of a thick copper heat sink to any part of the board surface.

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