Optimizing PCB Component Orientation

 In Uncategorized

With low-frequency circuits, PCB designers can place components on the board in almost any orientation they prefer. If while routing a part, a trace takes a long path around the board, it is not a big concern. They can handle thermal management easily, as component spacing is not an issue.

However, as circuit boards are now shrinking in size and their complexity increasing with different components crowding the board, designers do not have the luxury to orient components at their will. At Rush PCB, layout teams must fulfill the requirements of manufacturability and electrical performance before finalizing the orientation of components in their design.

PCB Library and Component Orientation

Proper orientation of components in a high-frequency circuit on a circuit board starts with the footprint construction. Unless the designer has built the footprint correctly, even with a proper orientation, the result will still be a non-functional board. For polarized parts like a diode, it is easy to swap pins, thereby misinterpreting its cathode and anode. Polarized parts with multiple pins can have their numbering sequences out of order, or their pin one can be in the wrong place,

Rush PCB guards against these problems by referring to the latest information on parts and data sheets when building PCB component footprints. The Latest design tools have utilities like part building wizards for the purpose. We also connect to online library services that allow downloading information of parts such as PCB footprints, schematic symbols, 3d step models, and more. Most of these services are available from component manufacturers, and help to save a good amount of time. They also guarantee the parts we use in the design will have the correct orientation.

While building the component footprint, we recommend placing markers for the polarity and pin one location. These help with placement of parts in the layout. Later, these markers come in handy for placing the component with its proper orientation. This is essential for the proper electrical functioning and performance of the board.

High-Speed Signals and Component Orientation

In high-speed circuits, a connection between components may not translate into a point-to-point straight copper trace. This is because in high-speed circuitry, a complete signal path may be the result of a conglomeration of multiple nets. For instance, a signal may start at the source, travel through some components, branch off at some point, and finally arrive at the load with a terminating resistor. The signal path here consists of two or more nets with components in the middle.

The designer must treat all the nets when considering signal integrity. They must also orient all components in the net for providing the signal path its most optimum performance.

Routing memory and data buses for high-speed performance requires providing adequate room for the multiple nets. Routing all the traces requires considering their escape vias as well. This means the designer must orient all components such that the traces take up the shortest path between them.

Similarly, for impedance-controlled nets, the orientation of components must be such that the traces connecting the two are the shortest and most direct. This is also true for components connected and routed with a differential pair of traces.

Power Supplies and Component Orientation

Printed circuit boards for power supplies also need component orientation for optimum configuration of connection. Traces carrying high currents often produce noise, and proper component orientation is necessary to reduce resistance and inductance to reduce noise coupling. Rush PCB recommends designers use short and direct routing of traces for power supplies.

With most high-capacity power supplies operating in switched-mode at high-frequencies to reduce component sizes, designers must not only place components tightly together, but also position them in unusual orientations. Most short and direct routing is only possible when designers position components on the same side of the board.

Designers of power supplies must satisfy the above power and signal integrity requirements with proper component placement. For this, they may have to orient some components at some intermediate angles rather than the usual 0- and 90-degree positions. This is necessary for achieving the best power and signal routing. However, designers must also discuss the orientation with their PCB manufacturer to know whether they can build the board.

Manufacturability and Component Orientation

Using DFM or Design for Manufacturability makes the process of PCB manufacturing error-free and more efficient. Apart from a reduction in errors, DFM also reduces manufacturing time, which, in turn, reduces costs. Some customers strictly demand the same orientation for all passive components. This helps to reduce the time taken by the pick-and-place machines for assembly, as the machine does not have to spend time rotating the part. Although this is not an issue for small runs of production, it adds up when producing several thousand boards.

For the reflow soldering process, orientation of small SMD components is an important issue. For instance, small two-pin components with unequal amounts of metal on their pins heat up differently when undergoing reflow. This can lift one side up, as the side with more metal melts faster, causing the component to stand up like a tombstone. Avoiding tombstoning requires the designer to reorient the component such that both pins receive equal amounts of heat, or there are equal amounts of metal on the two pins.

Testing and Component Orientation

During testing and rework, technicians will need to access components on the board. Unless the designer has oriented the components for easy access, this will add time and expense to the testing process.

Even for automated testing processes, specific clearance is necessary between components for easy access of test points. Moreover, adequate clearance is necessary between the edge of the board and the components for attachment of the test fixture. This may require rotation of some components to make more room.

CAD Tools and Component Orientation

Most CAD tools have inbuilt provisions for setting up component orientation. They also have provision for restricting the ability of further orientation of components that require a fixed orientation on the board. Designers must also set up design rules and constraints such that the CAD system will warn them when there is clearance violation. Viewing the board design in 3D also requires setting up additional clearances between components and other objects like connectors on the board.

Conclusion

Rush PCB recommends designers use modern CAD tools for obtaining proper component orientation on boards while designing them. This is an important issue related to efficient functioning when designing high-speed and high-frequency circuit boards, and must not be confused with the aesthetic placement designers often use.

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