When starting a new hardware design, many teams devote most of their time to circuit design and component selection. By the time PCB layout begins, gaps in experience and insufficient planning can lead to problems when the design transitions from schematic to physical reality. Those issues often surface during manufacturing or, worse, as functional defects after assembly.
What, then, ensures that a board is both robust on paper and reliable as hardware? The following six guidelines concentrate on manufacturability and functional reliability, offering practical direction from component placement through verification.
1. Fine-Tune Component Placement
Component placement is both science and art. Strategic placement of major devices frames the overall layout, affects how easily the board can be manufactured, and determines how well the design meets its original performance targets.
While a conventional placement sequence—connectors, mechanical keep-ins/outs, power circuits, precision circuits, and other critical circuitry—works well, several specific practices consistently improve outcomes:
- Orientation – Align similar components in the same orientation. Consistent orientation simplifies assembly and reduces soldering errors.
- Arrangement – Avoid hiding small parts behind large components, where thermal mass and shadowing can disrupt reflow profiles or wave soldering and complicate inspection or rework.
- Organization – Place all SMT components on one side of the PCB whenever possible and put through-hole parts on the top side. This reduces assembly steps, process changes, and handling. Mixed technology (TH + SMT) often requires additional processes and can increase manufacturing cost.
2. Place Power, Ground, and Signal Routing Appropriately
Once the major components are placed, plan power, ground, and signal routing to provide clean, low-impedance paths and predictable return currents.
2.1 Position Power and Ground Planes
It is generally recommended to place power and ground planes on internal layers, kept central and symmetric in the stackup. Symmetry helps minimize board warp and bow, which affects component coplanarity and solder joint quality.
For distributing power to ICs, use a common trunk or plane per rail with stout trace widths rather than daisy-chaining power from component to component. This approach reduces voltage drop and avoids uneven current distribution.
2.2 Signal Routing Practices
Route signals according to the schematic, favoring the shortest practical and most direct paths between components. Near component pads, begin routes parallel to the component's orientation (for example, horizontally from a pad when components are aligned horizontally), then turn vertically or change direction further away. This practice can help maintain component alignment during soldering, as solder wetting forces will tend to keep the component stable instead of rotating or skewing.
2.3 Define Trace Widths
Different nets carry different currents, which set minimum trace width requirements. As a general starting point, 0.010 in (10 mil) is suitable for low-current analog and digital signals. For traces carrying more than 0.3 A, increase the width to control temperature rise and voltage drop. Use a trace width calculator that considers copper thickness, allowable temperature rise, and current to size power traces and planes appropriately.
3. Isolate Effectively
High-voltage swings and current spikes in power stages can couple into low-level control circuits and degrade performance. Thoughtful isolation and return-path control reduce these risks:
- Separate returns – Maintain separate power ground and control ground for each power rail. If they must be joined on the PCB, connect them at a single point as close as possible to the end of the power path (a star or single-point connection) to limit circulating currents and noise injection.
- Low-impedance return paths – If you have an internal ground plane, ensure low-impedance return paths under critical signals. This lowers the risk of interference and protects sensitive control signals. Apply the same principle to keep digital and analog sections separated, with clearly defined return paths.
- Controlled coupling – Large ground planes can introduce capacitive coupling to traces running above or below. Where analog and digital grounds are partitioned, only cross the analog ground at designated analog signal paths to control coupling and maintain a clean reference for precision circuitry.
4. Manage Heat
Excess heat can degrade performance or even damage the board. Proactive thermal design mitigates these risks:
4.1 Identify Hot Components
Begin by identifying components that dissipate the most heat. Datasheets typically provide thermal resistance metrics (for example, junction-to-ambient). Apply recommended heat-spreading and cooling methods: heatsinks, thermal vias under pads where appropriate, airflow, and adequate copper area. Keep thermally sensitive components away from hot spots and confine heat-generating devices to areas where heat can be managed.
4.2 Use Thermal Reliefs
Thermal reliefs are essential for manufacturable PCBs, especially for wave soldering and on multilayer boards with high copper content. Through-hole pins connected directly to large planes sink heat rapidly, making it difficult to reach and maintain soldering temperature. Thermal relief connections (spoked connections from pad to plane) reduce heat flow during soldering, improving wetting and solder joint quality. As a general rule, use thermal reliefs for any through-hole pin or via that ties into a ground or power plane.
In addition to thermal reliefs, consider adding teardrops at pad-to-trace junctions. Teardrops provide extra copper support, improving mechanical robustness and reducing stress concentration from thermal cycling.
5. Thermal Reliefs Explained
Assembly and SMT process engineers frequently encounter solder defects such as non-wetting, dewetting, cold solder joints, and partial soldering. Sometimes, no matter how the reflow profile is tuned, a certain percentage of joints refuse to wet properly. Beyond oxidation or contamination, a common root cause is layout: pad connections tied directly into large copper pours.
Large copper areas used for power and ground (VCC, VDD, VSS, GND) often connect directly to IC and component pins. Heating these planes to soldering temperature requires more time than isolated pads, and they cool faster due to their thermal mass. If one terminal of a small resistor or capacitor connects to a plane while the other terminal does not, the two pads reach liquidus at different times. The mismatch in heating and cooling creates soldering issues and poor wetting.
If the reflow profile lacks adequate preheat or soak, pads tied to large planes may never reach proper solder temperature, resulting in voids or open joints. During hand soldering, the rapid heat sinking of large planes can prevent the joint from reaching temperature within the allowed dwell, yielding cold joints or damaging the component due to prolonged heating.
Typical visual symptoms include encapsulated solder, solder balls, or joints where solder wets the lead but not the pad, creating a spherical or incomplete bond. Increasing iron temperature or extending dwell can overheat or damage sensitive parts.
The practical fix is to use thermal reliefs. With thermal reliefs, a pad connects to the plane through narrow copper spokes. This significantly reduces thermal mass at the pad, limits heat loss during soldering, and improves wetting. The comparison below shows a direct plane tie (left) versus a thermal relief (right): the relief limits contact area and reduces heat flow, enabling consistent soldering results.
6. Verify Your Work
As you push toward release, it's easy to miss details that later become costly failures. Rigorous checks before manufacturing can make the difference between success and rework.
Start with an Electrical Rule Check (ERC) and a Design Rule Check (DRC) to confirm the design meets all constraints: clearances, trace widths, manufacturing limits, and any high-speed requirements. When ERC/DRC are clean, review routing net by net. Cross-probe from the schematic to the PCB to ensure every connection is present and correct. Use the design tool's probe and filtering features to confirm that the physical layout matches the intended schematic connectivity and constraints.
Conclusion
By applying these guidelines—disciplined placement, solid power and ground planning, practical signal routing, isolation discipline, thermal relief usage, and thorough verification—you can produce boards that assemble cleanly and perform reliably. Good PCB design practice underpins consistent project success and provides a foundation for continuous improvement across designs and teams.
