I. First, understand: Why choose a thick copper PCB? (30-second introduction)
Thick copper PCBs, simply put, are circuit boards with a copper foil thickness ≥ 3oz (1oz ≈ 35μm). They are commonly found in "high-power, high-heat-dissipation" scenarios such as industrial power supplies, new energy vehicles, and medical equipment—for example, new energy vehicle charging piles need to withstand high current surges. Ordinary thin copper boards are prone to overheating and burning out. Thick copper acts like a "highway in the circuit," quickly dissipating current and heat, and also improving the mechanical strength of the circuit board (bending resistance, vibration resistance). However, thick copper is not "the thicker the better." Improper design can lead to problems such as "uneven heat dissipation, poor soldering, and soaring costs." This is the core issue we'll focus on today: how to meet performance requirements while also ensuring manufacturability (DFM)?
II. Key Considerations for Thick Copper PCB Design (First Step to Avoiding Pitfalls)
1. Copper Foil Thickness Selection: Don't blindly pursue "the thicker the better." Key principle: The current rating determines the copper thickness. A simplified formula is: Allowable current (A) ≈ Copper foil thickness (oz) × Trace width (mm) × 0.8 (Ambient temperature ≤40℃). Example: 3oz copper foil + 3mm wide trace can withstand approximately 7.2A of current, sufficient for most industrial power supply scenarios. Pitfall: Copper exceeding 10oz can cause PCB bending and drilling difficulties. Unless there are special requirements (such as aerospace equipment), prioritize the mainstream 3-6oz specification.
2. Trace Design: Avoid "narrow neck heating" and ensure smooth current flow. Trace width: Thick copper traces should not be too narrow! For 3oz copper foil, the minimum recommended trace width is ≥0.3mm (0.1mm is sufficient for ordinary thin copper). The width should increase proportionally with the current (e.g., for 6oz copper foil carrying 10A current, the recommended width is ≥5mm).
Trace transition: Avoid sudden narrowing/widening (e.g., dropping abruptly from 5mm to 1mm). Use a "gradual transition" (length ≥ 3 times the width difference), otherwise a "current bottleneck" will form, causing localized overheating and burnout. Heat dissipation optimization: Under high-power devices (such as MOSFETs), use "copper plating + thermal vias" (via diameter 0.8-1.2mm, spacing 2-3mm) to allow heat to be quickly conducted to the ground/power plane.
3. Via design: A "fatal flaw" of thick copper boards—pay close attention! Via Diameter: The copper layer on the via wall of a thick copper plate must match the thickness of the copper foil. A standard 0.4mm via diameter is insufficient for plating 3oz copper foil. A minimum via diameter of ≥0.8mm (with a copper wall thickness ≥20μm) is recommended.
Number of Vias: Do not use a single via on high-current paths! For example, if a 3oz copper foil carries 5A of current, it is recommended to use 2-3 vias in parallel (each via can withstand approximately 2-3A of current) to prevent the via from overheating and melting.
Solder Mask Opening: Sufficient solder mask openings (0.2-0.3mm larger than the via diameter) should be provided around the via to prevent solder from clogging the via during soldering, which would affect heat dissipation and conductivity.
III. DFM Design for Thick Copper PCBs: Enabling Factories to "Produce with Less Rework"
The core of DFM (Design for Manufacturability) is "design must adapt to manufacturing processes." DFM for thick copper PCBs focuses on solving the "process challenges brought by thick copper":
1. Copper Foil Etching: Avoiding Uneven Etching. Minimum linewidth/spacing: For 3oz copper foil, the minimum linewidth ≥ 0.3mm, and the minimum line spacing ≥ 0.3mm (0.1mm is sufficient for thin copper); for 6oz copper foil, a linewidth/spacing ≥ 0.4mm is recommended, otherwise, "inaccurate linewidth" and "short circuits" are likely to occur during etching.
2. Copper Laying with Openings: For large-area copper laying, use "grid copper laying" (grid spacing 2-3mm, line width 0.2-0.3mm) to avoid copper foil shrinkage during etching, which can cause PCB bending; if solid copper laying is required, "heat dissipation slots" (0.5mm width, 10-15mm spacing) should be reserved.
2. Lamination Process: To prevent "delamination and bubbling," the lamination sequence should be as follows: Thick copper foil should be placed on the "outer layer" or "near the outer layer" to avoid being sandwiched in the middle and preventing heat dissipation; the copper foil thickness of the multilayer board should be symmetrical (e.g., 3oz for the top layer and 3oz for the bottom layer), otherwise warping will occur after lamination. Substrate Selection: Prioritize high Tg substrates (Tg≥170℃), such as FR-4 Tg170 or PI substrates, to avoid substrate softening and delamination during high-temperature soldering (the soldering temperature of thick copper plates is usually 10-20℃ higher than that of thin copper).
3. Soldering Process: Selection of "high thermal conductivity" devices suitable for thick copper: Prioritize "high-power packages" (such as TO-220, D2PAK) to avoid soldering small packaged devices onto thick copper, where heat cannot dissipate and the solder will melt. Pad Design: Pads on thick copper should be 0.2-0.3mm larger than ordinary pads. For example, the pads for a 0805 resistor are typically 0.8×1.2mm, but for thick copper, 1.0×1.5mm is recommended to ensure a strong solder joint. Reflow Soldering Parameters: Thick copper absorbs more heat, so the reflow soldering temperature should be appropriately increased (5-10℃ higher than for thin copper), and the holding time extended by 10-15 seconds to avoid "cold solder joints."
4. Cost Control: The Hidden Value of DFM (Design for Manufacturing) - Avoiding Over-Design: For example, use 1-2oz copper foil in areas where high current is not required, and only use thick copper in critical paths to reduce material costs; Standardized Dimensions: Use factory-standard board thicknesses (e.g., 1.6mm, 2.0mm) as much as possible. Special board thicknesses (e.g., 3.0mm and above) will increase processing difficulty and cost; Early Communication: Confirm process capabilities with the PCB manufacturer before design (e.g., maximum copper thickness, minimum hole diameter, etching precision) to avoid designs that cannot be manufactured after completion.
IV. Summary:
Thick Copper PCB Design: "3 Core Elements"
Copper Thickness Matching Current: Avoid blindly increasing thickness; select mainstream specifications of 3-6oz according to current requirements; Risk Mitigation Through Details: Gradual trace transitions, parallel vias, and compliant trace width/spacing; DFM Priority: Consider etching, lamination, and soldering processes during design to reduce rework. Thick copper PCB design may seem complex, but by grasping the two core elements of "current conduction" and "process compatibility," most pitfalls can be avoided.
I. First, understand: Why choose a thick copper PCB? (30-second introduction)
Thick copper PCBs, simply put, are circuit boards with a copper foil thickness ≥ 3oz (1oz ≈ 35μm). They are commonly found in "high-power, high-heat-dissipation" scenarios such as industrial power supplies, new energy vehicles, and medical equipment—for example, new energy vehicle charging piles need to withstand high current surges. Ordinary thin copper boards are prone to overheating and burning out. Thick copper acts like a "highway in the circuit," quickly dissipating current and heat, and also improving the mechanical strength of the circuit board (bending resistance, vibration resistance). However, thick copper is not "the thicker the better." Improper design can lead to problems such as "uneven heat dissipation, poor soldering, and soaring costs." This is the core issue we'll focus on today: how to meet performance requirements while also ensuring manufacturability (DFM)?
II. Key Considerations for Thick Copper PCB Design (First Step to Avoiding Pitfalls)
1. Copper Foil Thickness Selection: Don't blindly pursue "the thicker the better." Key principle: The current rating determines the copper thickness. A simplified formula is: Allowable current (A) ≈ Copper foil thickness (oz) × Trace width (mm) × 0.8 (Ambient temperature ≤40℃). Example: 3oz copper foil + 3mm wide trace can withstand approximately 7.2A of current, sufficient for most industrial power supply scenarios. Pitfall: Copper exceeding 10oz can cause PCB bending and drilling difficulties. Unless there are special requirements (such as aerospace equipment), prioritize the mainstream 3-6oz specification.
2. Trace Design: Avoid "narrow neck heating" and ensure smooth current flow. Trace width: Thick copper traces should not be too narrow! For 3oz copper foil, the minimum recommended trace width is ≥0.3mm (0.1mm is sufficient for ordinary thin copper). The width should increase proportionally with the current (e.g., for 6oz copper foil carrying 10A current, the recommended width is ≥5mm).
Trace transition: Avoid sudden narrowing/widening (e.g., dropping abruptly from 5mm to 1mm). Use a "gradual transition" (length ≥ 3 times the width difference), otherwise a "current bottleneck" will form, causing localized overheating and burnout. Heat dissipation optimization: Under high-power devices (such as MOSFETs), use "copper plating + thermal vias" (via diameter 0.8-1.2mm, spacing 2-3mm) to allow heat to be quickly conducted to the ground/power plane.
3. Via design: A "fatal flaw" of thick copper boards—pay close attention! Via Diameter: The copper layer on the via wall of a thick copper plate must match the thickness of the copper foil. A standard 0.4mm via diameter is insufficient for plating 3oz copper foil. A minimum via diameter of ≥0.8mm (with a copper wall thickness ≥20μm) is recommended.
Number of Vias: Do not use a single via on high-current paths! For example, if a 3oz copper foil carries 5A of current, it is recommended to use 2-3 vias in parallel (each via can withstand approximately 2-3A of current) to prevent the via from overheating and melting.
Solder Mask Opening: Sufficient solder mask openings (0.2-0.3mm larger than the via diameter) should be provided around the via to prevent solder from clogging the via during soldering, which would affect heat dissipation and conductivity.
III. DFM Design for Thick Copper PCBs: Enabling Factories to "Produce with Less Rework"
The core of DFM (Design for Manufacturability) is "design must adapt to manufacturing processes." DFM for thick copper PCBs focuses on solving the "process challenges brought by thick copper":
1. Copper Foil Etching: Avoiding Uneven Etching. Minimum linewidth/spacing: For 3oz copper foil, the minimum linewidth ≥ 0.3mm, and the minimum line spacing ≥ 0.3mm (0.1mm is sufficient for thin copper); for 6oz copper foil, a linewidth/spacing ≥ 0.4mm is recommended, otherwise, "inaccurate linewidth" and "short circuits" are likely to occur during etching.
2. Copper Laying with Openings: For large-area copper laying, use "grid copper laying" (grid spacing 2-3mm, line width 0.2-0.3mm) to avoid copper foil shrinkage during etching, which can cause PCB bending; if solid copper laying is required, "heat dissipation slots" (0.5mm width, 10-15mm spacing) should be reserved.
2. Lamination Process: To prevent "delamination and bubbling," the lamination sequence should be as follows: Thick copper foil should be placed on the "outer layer" or "near the outer layer" to avoid being sandwiched in the middle and preventing heat dissipation; the copper foil thickness of the multilayer board should be symmetrical (e.g., 3oz for the top layer and 3oz for the bottom layer), otherwise warping will occur after lamination. Substrate Selection: Prioritize high Tg substrates (Tg≥170℃), such as FR-4 Tg170 or PI substrates, to avoid substrate softening and delamination during high-temperature soldering (the soldering temperature of thick copper plates is usually 10-20℃ higher than that of thin copper).
3. Soldering Process: Selection of "high thermal conductivity" devices suitable for thick copper: Prioritize "high-power packages" (such as TO-220, D2PAK) to avoid soldering small packaged devices onto thick copper, where heat cannot dissipate and the solder will melt. Pad Design: Pads on thick copper should be 0.2-0.3mm larger than ordinary pads. For example, the pads for a 0805 resistor are typically 0.8×1.2mm, but for thick copper, 1.0×1.5mm is recommended to ensure a strong solder joint. Reflow Soldering Parameters: Thick copper absorbs more heat, so the reflow soldering temperature should be appropriately increased (5-10℃ higher than for thin copper), and the holding time extended by 10-15 seconds to avoid "cold solder joints."
4. Cost Control: The Hidden Value of DFM (Design for Manufacturing) - Avoiding Over-Design: For example, use 1-2oz copper foil in areas where high current is not required, and only use thick copper in critical paths to reduce material costs; Standardized Dimensions: Use factory-standard board thicknesses (e.g., 1.6mm, 2.0mm) as much as possible. Special board thicknesses (e.g., 3.0mm and above) will increase processing difficulty and cost; Early Communication: Confirm process capabilities with the PCB manufacturer before design (e.g., maximum copper thickness, minimum hole diameter, etching precision) to avoid designs that cannot be manufactured after completion.
IV. Summary:
Thick Copper PCB Design: "3 Core Elements"
Copper Thickness Matching Current: Avoid blindly increasing thickness; select mainstream specifications of 3-6oz according to current requirements; Risk Mitigation Through Details: Gradual trace transitions, parallel vias, and compliant trace width/spacing; DFM Priority: Consider etching, lamination, and soldering processes during design to reduce rework. Thick copper PCB design may seem complex, but by grasping the two core elements of "current conduction" and "process compatibility," most pitfalls can be avoided.
