Multi-Circuit Board Design Rules and Considerations

Key Takeaways

• Each individual circuit board in a multi-circuit PCB should be designed precisely by taking into account the outer boundary, internal cutouts, mounting location, type of mounts, areas restricted for connectors, other mechanical parts, etc. 

• A good multi-circuit board takes into consideration the functional, mechanical, and electrical aspects of the board in the design phase.

• There needs to be a separation between high-voltage circuits and low-voltage circuits in multi-circuit boards.

By following multi-circuit board design rules, it is possible to enhance the reliability and compactness of the product

Power electronics is a sub-branch in electrical engineering that we use in numerous products. Most power electronics applications involve the conversion of power from one form to another – ac to dc, dc to ac, ac to ac, and dc-dc. In power electronic products, there can be multiple circuit boards such as sensor boards, power converter boards, controller boards, driver boards, filter circuits, etc. All these circuits are packed to form a multi-circuit board encompassed in an electronic cover. The multi-circuit board comprising the above circuits is mechanically held together, and interconnections are made using wires, cables, press-fit connectors, etc. By following multi-circuit board design rules, it is possible to enhance the reliability and compactness of the product.

Multi-Circuit Boards

Multi-circuit boards are common in the industry. In interdisciplinary projects, experts from electrical, mechanical, and other engineering departments (for example aerospace, marine, or instrumentation) participate to finalize the system design. As the printed circuit boards in the system need to interact with other designs, collaborative work is expected.

To develop multi-circuit boards for a system, information on the other panel items is needed to enhance the mechanical strength and pan out the design of the board. Each individual circuit board in a multi-circuit PCB should be designed precisely by taking into account the outer boundary, internal cutouts, mounting location, type of mounts, areas restricted for connectors, other mechanical parts, etc. 

An Example of Multi-Circuit Board Design  

If a sensor board is to sense the output voltage, the board should be designed to make an easy connection between the two. It would be good if the output voltage connections and the input voltage connections of the power circuit board and sensor board are routed toward the edges of the board to ensure smooth, obstacle-free interconnection. The type of connectors should be chosen properly to avoid loose connections or open circuits. However, there should be enough room left around the edges for drill holes and screw insertion. 

Multi-Circuit Board Design Rules

A good multi-circuit board design takes into consideration the functional, mechanical, and electrical aspects of the board in the design phase. There are several rules to be followed in multi-circuit board design to ensure compact, product-centric designs. 

Mechanical Considerations

In mechanical consideration, the mechanical stress on individual boards is of great concern. The general rule is to evenly load the circuit boards to avoid breaks, cracks, or any other fatigue. The need for spacing for mounting holes and other openings is also a major need in multi-circuit boards, and this consideration should be incorporated into the layout design.

Electrical Considerations

There needs to be a separation between the high-voltage circuits and low-voltage circuits in multi-circuit boards. Similarly, separation is much more important between the low-frequency and high-frequency circuits to eliminate the effects of noises, disturbances, interferences, etc. on the individual boards. Adequate clearance and creepage margins should be provided in multi-circuit boards. Grounding is an important electrical aspect to prevent ground loops, leakage, and antenna effects.

Functional Considerations

Keeping in mind the functional considerations is useful, especially when using automated placement machines for printed circuit board assembly. The areas where the components are to be mounted should be accessible to the pick-and-place machine as well as to the personnel troubleshooting. By following the functional rules, multi-circuit board assembly becomes a faster process. 

Multi-Circuit Board Design Steps

The multi-circuit board arrangement involves establishing firm and tight connectors between the individual PCBs. The multi-circuit PCB arrangement should progress in the following order to avoid design mistakes.

1. Use mechanical models to determine the design of individual boards and the complete arrangement of the multi-circuit board. 

2. Use the right connectors to support the multi-circuit board arrangement and to fix the board to the electronic cover or enclosure. 

3. Rearrange the circuit board depending on the functions to be performed by the board. In case the utility voltage is to be sensed before the conversion process commences, the arrangement should allow the order from the utility supply → sensor board → power circuit. The connectors for giving the utility supply to the sensor board and to the power circuit will be different, and the selection should be made properly based on the requirements. While choosing the connector, pay attention to the signal type, signal integrity, etc. 

Considering multi-circuit board design rules and following the key design steps will help you complete your system design within a limited time with fewer flaws. Cadence’s suite of PCB tools can assist you in accurately designing multi-circuit boards.

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