3 Oz Copper PCB , 105Micron ( 4.1339 Mil ) , When a design use 3 oz copper , We can call it heavy copper PCB . If base copper is 3oz , then completed copper will be 4 oz, for multi-layer , Inner 3 oz , the final will be 3oz, When do 3 oz PCB manufacturing, We need take care the solder mask , because the thick solder mask will flow .
Introduction
Printed circuit boards (PCBs) form the backbone of electronics, providing mechanical support and electrical connectivity for components. PCB copper thickness is a key design parameter that affects current capacity, electrical/thermal performance and manufacturability.
While 1 oz copper has been the traditional standard thickness, 3 oz copper boards are being increasingly adopted for high power and performance designs needing thicker conductors. In this article, we will look at what 3 oz copper PCB thickness means, how it compares to other copper weights, its applications and advantages, and the design considerations when working with 3 oz copper boards.
What Does 3 oz Copper Mean?
PCB copper thickness is specified by weight in terms of ounces per square foot (oz/ft2). This refers to the amount of copper foil weight present in one square foot of board area, excluding the fiberglass dielectric substrate weight.
Some common PCB copper weights are:
- 1/2 oz – 0.5 oz/ft2 (17 μm)
- 1 oz – 1 oz/ft2 (35 μm)
- 2 oz – 2 oz/ft2 (70 μm)
- 3 oz – 3 oz/ft2 (105 μm)
- 4 oz – 4 oz/ft2 (140 μm)
So a 3 oz copper PCB has around 3 ounces of copper foil per square foot on each metal layer. In terms of thickness, 3 oz copper equals approximately:
- 105 μm (micrometers)
- 4.2 mil (thousandths of an inch)
- 0.105 mm (millimeters)
This is over 3x thicker than standard 1 oz foil.
Why Use Thicker 3 oz Copper?
The trend towards 3 oz copper PCBs is being driven by several factors:
- Higher current capacity – The thicker copper can handle over 3 times the current compared to 1 oz material without overheating. This enables higher power PCBs.
- Lower losses – Increased copper mass reduces resistive losses and voltage drops across traces. This improves electrical efficiency.
- Thermal performance – The excellent thermal conductivity of copper spreads heat over larger board area, keeping components cooler.
- Finer lines and spaces – 3 oz copper allows very fine trace geometries and clearances for dense SMT boards.
- High frequency/high speed – Thicker traces reduce impedance mismatch and electromagnetic radiation for faster circuits.
- Reliability – Heavier copper is more resistant to thermal stress, electromigration and corrosion over product lifetime.
- High current components – New power devices often need PCBs exceeding 2 oz copper thickness.
For such reasons, 3 oz copper provides clear advantages over thinner foils in appropriate applications.
Applications Suited for 3 oz Copper PCBs
Some examples of products and systems that can benefit from upgrading to 3 oz copper thickness include:
- High power motor drives – Thick 3 oz layers handle large motor phase currents without overheating.
- Electric vehicle electronics – Low loss and current capacity aid powertrain and battery management systems.
- Power converters – Enhanced thermal dissipation rating and ampacity rating in AC-DC and DC-DC converters.
- Power amplifiers – RF power amps for communications systems need low loss boards to minimize distortion.
- Server/telecom hardware – High speed backplanes and data storage devices require thicker conductors.
- Medical equipment – Critical devices like MRI scanners and surgical systems demand maximum reliability under all conditions.
- Defense electronics – Mission-critical systems in extreme environments are designed with 3+ oz copper for ruggedness.
- Solar inverters – High currents handled with low losses and lower layer counts.
- LED lighting – Operating at elevated temperatures, thick copper PCBs keep LEDs cool and efficient.
For such demanding applications, 3 oz copper provides greater robustness, performance margin and long-term reliability versus standard 1-2 oz foils.
Key Benefits of 3 oz Copper PCBs
The advantages of increasing copper thickness from 1 oz to 3 oz include:
1. Lower Electrical Resistance
Copper’s resistivity is 1.72 x 10<sup>-6</sup> ohm-cm. Increasing cross-section area by using thicker copper lowers resistance proportionally. The 3 oz foil offers about 3 times lower trace resistance than 1 oz material:
| Trace Width | 1 oz Resistance | 3 oz Resistance | Resistance Drop |
|---|---|---|---|
| 10 mil | 19.8 mΩ/inch | 6.6 mΩ/inch | ~67% lower |
| 5 mil | 39.6 mΩ/inch | 13.2 mΩ/inch | ~67% lower |
| 3 mil | 66 mΩ/inch | 22 mΩ/inch | ~67% lower |
| 2 mil | 99 mΩ/inch | 33 mΩ/inch | ~67% lower |
| 1 mil | 198 mΩ/inch | 66 mΩ/inch | ~67% lower |
(Assuming standard 1.4 mil trace thickness. Table values approximate.)
Lower resistance minimizes undesirable power losses on the PCB due to I<sup>2</sup>R heating and IR voltage drops. This maximizes electrical efficiency.
2. Increased Current Carrying Capacity
For a given temperature rise, trace current handling capacity increases in proportion to the square root of the copper cross-sectional area.
Going from 1 oz to 3 oz thick copper almost triples the allowable current density. For example, a common 10 mil wide trace can handle:
- 1 oz: ~1.2 A
- 3 oz: ~3 A
This expanded ampacity matches the higher current loads of modern power electronics. A board’s power handling capability is increased without needing more layers.
3. Improved Electromagnetic Shielding
With trace signals becoming faster in high speed digital designs, containing electromagnetic interference (EMI) is critical.
A solid plane or enclosure of thick copper foil provides superior shielding and isolation against radiated EMI compared to thinner material. 3 oz copper is very effective at blocking interfering fields.
4. Enhanced Thermal Performance
Copper is the PCB conductor of choice due to its excellent thermal conductivity (385 W/m-K). This rapidly conducts heat away from hot spots to cooler areas.
Increasing copper thickness reduces the thermal resistance between components and board layers. This results in lower component temperatures for the same heat dissipation levels.
5. Finer Line Resolution and Spacing
The thicker 3 oz copper allows reliably etching very fine trace widths and clearances down to ~2 mils.
This high density interconnect capability supports complex routing in compact PCBs and integrating tiny chip components with fine lead pitches.
6. Lower Inductance Wiring
At higher frequencies, conductors exhibit self-inductance which opposes changes in current. Thicker traces reduce this inductance which otherwise can distort signals.
3 oz copper wiring has about 3x lower inductance than an equivalent 1 oz trace. This enhances high frequency AC performance.
7. Improved Signal Integrity
Electrical transmission line effects like reflections become significant at higher speeds and frequencies.
Thicker 3 oz traces better match characteristic impedances. Along with lower overall resistance and inductance, this reduces signal degradation in high speed channels.
8. Lower Layer Counts Possible
By carrying more current on outer layers, 3 oz copper may permit using fewer inner layers for power distribution on some designs. But enough should be retained for shielding.
9. Long-Term Reliability
Thicker copper is inherently more resistant to thermal stresses, electromigration, corrosion, and physical damage. This enhances PCB durability over product lifetime.
Reliability is especially critical for automotive, medical, military and aerospace applications where failure is not an option.
Comparison of 3 oz to Standard 1 oz Copper
Here is a summary comparison between typical 1 oz and 3 oz PCB material properties:
| Parameter | 1 oz Copper | 3 oz Copper |
|---|---|---|
| Copper Thickness | 1 oz/ft2 (35 μm) | 3 oz/ft2 (105 μm) |
| Trace Resistance | Higher | ~65% lower |
| Current Capacity | Lower | ~2.5x higher |
| Inductance | Higher | ~2x lower |
| Thermal Conduction | Moderate | Improved |
| EMI Shielding | Fair | Excellent attenuation |
| Fine Line Capability | 3-4 mil lines/spaces | 2-3 mil lines/spaces |
| Reliability | Moderate | Enhanced |
| Cost | Lower | Moderately higher |
So for high power, high frequency or mission-critical applications, 3 oz copper provides substantially improved performance over standard 1 oz foil.
Design Guidelines for 3 oz Copper
To fully utilize the benefits of 3 oz copper in a design, engineers should follow certain PCB layout practices:
- Employ minimum trace widths based on actual current needs rather than oversizing out of habit.
- Use space made available for tighter component placement and routing density. But observe spacing rules.
- Limit the length of low-amplitude high frequency traces as much as possible.
- Watch for acid traps and spacing violations from tighter lines and spaces.
- Increase the number of small vias used for connections instead of fewer larger holes.
- Ensure adequate thermal reliefs for leads, but remove for pads/vias if suitable.
- Add more copper fills for thermal and EMI shielding purposes if appropriate.
- In power planes, minimize cut-outs and splits which increase inductance.
- Account for possible manufacturer inspection issues with very fine geometries.
- Refine clearance grids, design rules and DFMs to match 3 oz capabilities.
- Watch for and correct acid traps, necking and over-etching of fine features.
With careful design practises tailored to the capabilities of 3 oz copper, PCB engineers can maximize the benefits of this thick copper technology for their specific application needs.
Frequently Asked Questions
Q1. Can 3 oz copper be used for multilayer boards?
Yes, 3 oz copper foils are commonly used on multilayer PCBs. The lamination process can accommodate the thickness.
Q2. Are there special drill requirements for 3 oz copper?
Laser drills are typically used for all multilayer boards regardless of copper thickness. Mechanical drills above 0.3mm are suitable.
Q3. Does solder mask adhesion change on 3 oz copper?
There is minimal effect on solder mask adhesion between different copper weights. The chemical bond to copper remains the same.
Q4. Does 3 oz copper withstand soldering heat?
Yes, soldering temperatures are well below the melting point of copper. The thicker 3 oz copper is more thermally stable against soldering exposure.
Q5. Is 3 oz copper readily available from manufacturers?
As 3 oz copper gains adoption, more PCB suppliers offer quick turnaround capability in 3 oz material at reasonable costs.
Conclusion
With its 3X thickness over standard 1 oz foils, 3 oz copper provides substantially increased current capacity, finer features, lower losses, improved thermal management, enhanced reliability and superior EMI control. These benefits make 3 oz copper the material of choice for leading edge high-performance and high-reliability electronics. To fully leverage 3 oz copper’s capabilities, engineers must follow disciplined layout and design practises tailored to the finer geometries and higher densities achievable. When designed properly, 3 oz copper PCB technology enables electronics to meet the demands of today as well as the future.
