Aptron - Fine-tuning The Component Placement In Pcb Circuit

By Author: Ravi ojha
Total Articles: 3
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The Component Placement
Components should be placed in the following order: connectors, power circuits, sensitive and precision circuits, critical circuit components, and then the rest. The schematic is built around each part on the PCB and completely interconnected. Routing priority for the circuit is chosen based on power levels, noise susceptibility, or generation and routing capability.
In general, trace widths of 10 to 20 mils are used for traces carrying 10 to 20 mA and 5 to 8 mils for traces carrying less current than 10 mA. High-frequency (greater than 3 MHz) and rapidly changing signals should be carefully considered when routed along with high-impedance nodes.
The lead engineer/designer should review the layout, and physical locations and routing paths should be adjusted iteratively until the circuit is optimized for all design constraints. The number of layers depends on power levels and complexity. Add layers in pairs since the copper cladding is produced that way. The routing of power signals and planes, the grounding scheme, and the board’s ability to be used as intended all influence operation.
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... Final inspections should involve verification that sensitive nodes and circuits are properly shielded from noise sources, solder mask exists between pins and vias, and the silkscreen is clear and concise. When determining layer stack-up, use the first inner layer below the component sides as ground and assign power planes to other layers. Stack-ups are created in a manner that balances the board relative to the midpoint of the Z axis.
Consider any concerns the PCB designer has during the reviews, and correct the PCB based on feedback generated by the reviews. Create and verify lists of changes during each review iteration until the board is finalized. During all stages of the layout, keep the design error free by using the design rule checker (DRC).
The DRC can only catch errors that it has been programmed to monitor, and DRC rule sets often change based on individual designs. At the minimum, the design rule checking should cover package-to-package spacing, unconnected nets (a unique name identifying each node of the circuit), shorted nets, air-gap violations, if vias are too close to solder pads, if vias are too close to each other, and vertical clearance violations.
Many other important DRC rules can be set to ensure a robust design, and they should be researched and understood. For example, keep clearances at or above 5 mils. Vias should not be located within surface-mount pads (unless back-filled). And, solder mask should be between all solder points.
Cost is often a driving influence behind PCB design, so it is good to understand the cost adders in PCB manufacturing. A typical board is two to four layers, with no drill holes less than 10 mils in diameter and 5-mil minimum air gaps and trace widths. It also should be 0.062 in.