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I. Key Considerations for Thick Copper PCB Board Design
1. Circuit Design
· Minimum Line Width/Spacing:
Avoid designing at the absolute limit of standard board manufacturing capabilities. Thick copper exhibits severe side etching during the etching process, causing “waist-thinning” of traces and simultaneous reduction in spacing.
As a rule of thumb, final line width/spacing should be at least 1.5 to 2 times larger than standard process limits, adhering to the principle of maximizing dimensions whenever possible.
Consequences: Insufficient spacing readily causes incomplete etching and bridging/short circuits.
· Copper Surface Uniformity:
Avoid isolated large copper pads or excessively fine traces surrounded by large pads. This creates uneven current density during plating, leading to overplating in thin areas (exceeding copper thickness limits) and underplating in thick areas (risking via breakage).
Optimization Method: Connect large copper pads using “grid patterns” or “cross-shaped heat dissipation pads” to balance current distribution.
2. Hole and Ring Width Design
· Minimum Ring Width:
Due to lamination misalignment and pattern transfer deviations, ring widths for thick copper boards must be increased.
Recommended: Outer layer ring width ≥ 8 mil, inner layer ring width ≥ 10 mil. For high-current through-holes, ring widths should be further increased to provide adequate pull-ring strength.
Consequences: Insufficient ring width risks copper foil peeling from the hole wall under thermal or mechanical stress.
3. Solder Mask and Surface Treatment
· Solder Mask Bridges:
Fine solder mask bridges are nearly impossible to preserve unless pad spacing is sufficiently large. On thick copper boards, solder mask ink may flow down the sides of traces. To prevent ink sagging between copper lines causing extremely thin or broken bridges, solder mask ink typically requires 2–3 printing passes.
Design Recommendations:
Trace spacing must be sufficiently large (e.g., >12 mil), and the manufacturer's solder mask process capability must be confirmed.
Consequences: Solder mask bridge failure may cause solder bridging during assembly.
· Solder Mask Thickness and Coverage:
Thick copper trace sidewalls and corners are vulnerable to inadequate solder mask coverage, potentially causing insufficient protection, chemical residue retention, and high-voltage breakdown.
Recommendation: Implement a “multiple printing” process at the board manufacturer to ensure thorough coverage of trace sidewalls.
· Surface Finishing:
HASL: The most common and reliable option, though it offers poor pad flatness. This finish is not recommended for thick copper boards. If absolutely necessary, select high-quality substrate with Tg ≥ 170°C.
Gold Plating/Electroless Gold: Offers good flatness, but requires sufficient nickel layer thickness (typically ≥150μm) to prevent failure due to “nickel migration” when high currents pass through thin nickel layers after gold layer damage. However, avoid designing electroplated gold on thick copper boards, as severe etching can cause neck breaks.
Electroless Tin/OSP: Generally not recommended for high-current thick copper boards due to relatively weak heat resistance and current-carrying capacity.
copper pcb board design
4. Laminating and Materials
· Dielectric Layer Thickness:
Using multiple PP sheets is one of the most critical principles. Thin dielectric layers cannot adequately fill the gaps between thick copper traces, leading to insufficient resin filling after lamination, vacuum bubbles causing board explosions, and board warpage.
Rule of thumb: Post-resin filling, the dielectric thickness should exceed the copper thickness of adjacent inner layers. For example, with 3oz inner layers, at least 3 PP sheets are recommended, subject to copper area ratio and manufacturer capability assessment.
Consequences of insufficient dielectric thickness:
· Insufficient resin filling
· Reduced insulation strength
· Inadequate voltage withstand
· Delamination and board failure
· Board Material Selection:
Prioritize high-Tg materials (e.g., Tg ≥ 170°C) to enhance thermal resistance and stability.
For scenarios with extreme thermal dissipation requirements, consider metal core substrates.
5. Thermal Management
· Heat Dissipation Vias:
Densely arrange heat dissipation vias beneath heat-generating components to conduct heat to inner layer copper or the backplane heat sink layer. For example, design heat dissipation vias on the IC's central ground plane.
Heat dissipation vias can undergo “via filling plating” to maximize thermal conductivity, though current copper paste via filling suppliers are limited.
· Copper Area:
Leverage thick copper as a heat dissipation medium by designing large copper planes connected to ground or power networks.
copper pcb board design
II. Design Optimization Recommendations
1. Early Communication is Critical
Communicate design intent and key parameters (e.g., target copper thickness, current density, voltage rating) to the PCB manufacturer before layout completion. Their engineers can propose laminate solutions and DFM rules best suited to their production capabilities.
2. Chamfering Treatment
At corners of thick copper traces, employ 45° bevels or rounded corners instead of 90° right angles. Right angles act as stress concentration points prone to cracking under thermal shock.
All corners of pads and copper pads should be chamfered.
3. Adopt “Stepwise” Copper Thickness Design
If only localized areas require high current, consider buried copper blocks or localized copper thickening processes.
Localized thick copper involves selectively thickening only high-current traces/areas on a standard copper thickness board (e.g., 1 oz). This reduces costs and manufacturing complexity but adds process steps and expenses. Note that some board manufacturers may not offer this service, requiring careful consideration.
4. Design for Manufacturing
Thick copper panels are inherently heavy, and V-CUTS pose challenges with high trace damage risk. We recommend using “stamp holes + bridging” for panelization to avoid V-CUT.
For warpage control, maintain symmetrical copper distribution across layers during design to prevent warping after lamination. Add balancing copper to large blank areas.
Copper pcb board design is a systematic engineering process that must incorporate manufacturing process capabilities as core design inputs.