Introduction
Printed circuit boards (PCBs) form the core of electronic products, providing the mechanical support and electrical connectivity for components. An important characteristic of PCBs is the weight or thickness of the copper foil used – typically specified in ounces per square foot (oz/ft2). While 1oz copper has been the traditional standard, 2oz copper PCBs are being increasingly adopted in modern high performance designs.
In this article, we will look at what 2oz copper PCB thickness means, why 2oz copper is preferred today, how it compares to 1oz, the key benefits 2oz copper provides, and the design guidelines to follow to best utilize the advantages of this thicker copper PCB technology.
What is 2oz Copper PCB?
The copper thickness or weight on a PCB is specified in ounces per square foot (oz/ft2). This refers to the weight of copper foil in a square foot area, not counting the weight of the insulating fiberglass substrate. Some typical copper weights are:
- 1/2oz – 0.5 oz/ft2 (17 μm)
- 1oz – 1 oz/ft2 (35 μm)
- 2oz – 2 oz/ft2 (70 μm)
- 3oz – 3 oz/ft2 (105 μm)
So a 2oz copper PCB uses 2 ounce of copper foil per square foot on each metal layer. This equals a copper thickness of about 70 μm (micrometers) or 2.8 mils. The key benefits of 2oz over standard 1oz copper are:
- Lower electrical resistance and losses
- Ability to handle higher currents
- Improved heat dissipation
- Better electromagnetic and EMI shielding
- Higher reliability under temperature swings and current stresses
Why Use 2oz Copper instead of 1oz?
While 1oz copper PCBs have been widely used in the past, 2oz copper offers a number of advantages driving its increasing adoption:
Higher Currents – Electronic devices are handling ever increasing power levels. The thicker 2oz copper can carry over twice the current of 1oz copper without overheating. This reduces the number of layers needed.
Lower Loss – The 2x lower resistivity cuts resistive losses in half compared to 1oz copper. This improves power efficiency and signal quality.
Finer Lines/Spaces – The thicker copper allows narrower trace widths and spacing which helps increase PCB component density.
EMI Shielding – With increasing circuit speeds, electromagnetic interference (EMI) is a growing concern. The thicker 2oz copper provides superior shielding against EMI.
Thermal Dissipation – The excellent thermal conductivity of copper helps spread heat better and improves thermal management with 2oz copper boards.
Reliability – Under temperature swings and current stresses, 2oz copper suffers less electrical migration issues and dendrite growth over long-term use.
High Speed – Lower resistance and inductance of 2oz copper traces enhances high speed signal quality in today’s high frequency digital circuits.
Component Miniaturization – Finer 2oz copper features allow matching PCBs to smaller, closely spaced component packages.
Cost – Although 2oz copper is costlier than 1oz materially, this is offset by lower layer count, improved yield and better reliability.
Key Benefits of 2oz Copper
Let’s examine some of the technical advantages of 2oz copper PCBs in more detail:
1. Lower Electrical Resistance
Copper is the standard PCB conductor due to its high electrical conductivity. Its volume resistivity is 1.72 x 10<sup>-6</sup> ohm-cm. For a given cross-section area, increasing copper thickness decreases resistance proportionally.
The table below shows resistivity comparisons for common PCB trace widths:
| Trace Size | 1oz Resistance | 2oz Resistance | % Resistance Drop |
|---|---|---|---|
| 10 mils | 19.8 mΩ/inch | 9.9 mΩ/inch | ~50% |
| 5 mils | 39.6 mΩ/inch | 19.8 mΩ/inch | ~50% |
| 3 mils | 66 mΩ/inch | 33 mΩ/inch | ~50% |
| 2 mils | 99 mΩ/inch | 49.5 mΩ/inch | ~50% |
| 1 mil | 198 mΩ/inch | 99 mΩ/inch | ~50% |
(Table data assumes standard 1.4mil trace height and bulk copper resistivity)
We can see the 2oz copper thickness cuts conductor resistivity in half versus 1oz material. This lowers losses like I2R heating, improves power efficiency, reduces voltage drops, and minimizes cross talk.
2. Increased Current Carrying Capacity
The maximum current a PCB trace can safely carry without overheating is proportional to the copper cross-sectional area. By doubling thickness from 1oz to 2oz, the cross-section and current capacity approximately doubles.
For example, a common 10 mil wide trace can handle:
- 1.2A max on 1oz copper
- 2.4A max on 2oz copper
This helps reduce the layer count for heavily loaded boards by carrying more current per layer with 2oz copper.
3. Finer Trace Resolution
The thicker 2oz copper can be etched to finer trace widths and spacing compared to 1oz material. Width and space down to 2-3 mils is achievable with 2oz boards.
This denser trace resolution enables complex, high component density PCBs with fine geometry to route traces between closely placed small components.
4. Lower Inductance Wiring
For high frequency AC signals, the magnetic flux penetrating the loop area of a wire produces self-inductance which increases with current frequency. This self-inductance can distort signals.
2oz copper traces have less inductance than thinner 1oz traces. Because inductance reduces with increasing conductor thickness while keeping loop area constant. This improves high frequency AC performance.
5. Better Electromagnetic Shielding
With fast switching digital circuits, controlling stray electromagnetic interference (EMI) is critical. A solid copper plane or enclosure provides effective EMI shielding.
The thicker 2oz copper offers superior shielding compared to 1oz material by reducing penetration of magnetic fields. It also has higher reflection attenuation for radiated fields.
6. Improved Thermal Management
The excellent thermal conductivity of copper (385 W/m-K) allows it to rapidly conduct heat away from hot spots and spreading it over the PCB area. Thereby lowering peak temperatures.
With 2oz copper, the higher copper mass reduces thermal resistance in the planes. This keeps the board and components cooler during operation.
7. Lower Impedance Ground/Power Planes
Continuous ground and power planes are commonly used in multilayer PCBs. At high frequencies, these planes have non-zero impedance which causes noise if large currents flow.
2oz copper planes reduce this impedance due to larger thickness. Resulting in cleaner power distribution and lower ground noise.
8. Better Power Handling and Reliability
The combination of lower operating temperature, reduced current density, lower electromigration and thicker copper gives 2oz boards greater long-term reliability under electrical and thermal stresses.
This enhances product life span and reduces field failures – critical factors for applications like automotive, aerospace and medical electronics.
9. Improved Manufacturing Yield
The thicker 2oz copper is inherently more resistant to defects like nicks, scratches and denting during PCB fabrication handling. This leads to higher manufacturing yields and lower costs.
Also, improved etch control results in fewer open or partially open traces reducing scrap and rework. The higher yield offsets the marginally higher 2oz material cost.
Applications that Benefit from 2oz Copper
Some types of PCB designs and applications that can take particular advantage of the superior performance of 2oz copper are:
High Power Electronics – Power devices for HVAC, motor drives, battery charging, power supplies etc. need heavy duty PCBs to handle large currents without overheating.
Automotive Electronics – Under-hood circuits for engines, drivetrains and auxiliary systems require high reliability PCBs with 2oz copper for the thermal and vibration extremes.
LED Lighting – High brightness LED systems often operate at elevated temperatures. 2oz boards keep the LEDs and drivers cooler for efficient light output.
Power Amplifiers – Audio amplifiers and transmitters deal with large RF signals. Low loss 2oz material ensures clean signal amplification.
Computer Servers – High density computing clusters require dense 2oz PCBs to interconnect many processors operating at high power levels.
Wireless Base Stations – Handling many simultaneous cellular signals generates substantial heat. 2oz boards dissipate heat efficiently in the crowded enclosure.
Defense/Avionics – Mission-critical aerospace systems demand maximum reliability. 2oz copper provides this under demanding operating conditions.
Medical – For implanted devices like pacemakers and monitors, 2oz PCBs ensure robust operation under body thermal stresses and currents.
For such applications, 2oz copper is preferred over 1oz to leverage its advantages while accepting the moderately higher cost.
Design Guidelines for 2oz Copper Boards
To fully optimize a design using 2oz copper thickness, engineers should follow certain PCB layout guidelines:
Utilize Available Space – With 2oz copper allowing narrower traces and spacing, component placement can be more dense. Spread components out to utilize the extra space.
Minimize Trace Lengths – The low resistivity of 2oz copper means less need for fat traces. Use the space for routing shorter, more direct connections.
Reduce Layer Count – Lower current density enables removing layers if layout permits. But maintain adequate ground/power planes.
Use Smaller Vias – Taking advantage of the finer 2oz resolution, vias can be shrunk maintaining routing density.
Increase Component Density – Smaller package components packed closer together are now easier to interconnect with thinner 2oz traces.
Watch AC Impedance – For sensitive high frequency signals, keep narrow 2oz traces short and avoid thin/long traces.
Remove Thermal Reliefs – If suitable for components/leads, thermal reliefs can be eliminated to reduce thermal resistance.
Increase Copper Fills – Use more copper pours for thermal and EMI shielding. Maintain isolation from traces.
Reduce Plane Splits – Minimize splits in ground and power planes. Use more vias for connections through splits.
Watch Spacing at Edges – Higher etch resolution can result in insufficiently spaced traces along board edges.
Refine Grids/DRC Rules – Tighten clearance grids and design rule checks to match 2oz capabilities.
Account via-in-pad – Ensure designers consider via-in-pad rules for densely placed vias.
With careful 2oz PCB layout practises, board sizes can be shrunk, performance maximized and overall assembly costs potentially reduced.
Comparison Summary – 1oz vs 2oz Copper
Here is a summary comparison of key differences between standard 1oz and 2oz copper PCBs:
| Parameter | 1oz Copper | 2oz Copper |
|---|---|---|
| Copper Thickness | 1 oz/ft2 (35 μm) | 2 oz/ft2 (70 μm) |
| Trace Resistance | Higher | Lower by ~50% |
| Current Capacity | Lower | Nearly 2x higher |
| Inductance | Higher | Lower |
| Thermal Conduction | Moderate | Improved heat spreading |
| EMI Shielding | Moderate | Better attenuation |
| Fine Line Resolution | 3-4 mil lines/spaces | 2-3 mil lines/spaces |
| Layer Count | Typically higher | Can potentially be lower |
| Cost | Lower | Marginally higher |
| Reliability | Moderate | Enhanced under stresses |
So for high current, fine pitch and demanding applications, 2oz copper is preferable over 1oz to leverage its advantages.
Frequently Asked Questions
Q1. Is 2oz copper suitable for multi-layer PCBs?
Yes, 2oz copper material can be used on all layers of multilayer boards equally well. The higher thickness still allows tight registration and lamination.
Q2. Does solder mask adhesion differ between 1oz and 2oz copper?
There is negligible difference in solder mask adhesion between the two copper thicknesses. The chemical bond to copper remains similar.
Q3. Can 2oz copper withstand soldering heat exposure?
Yes, the soldering temperatures typically used for PCB assembly are well below the melting point of copper. So 2oz copper remains stable against soldering heat.
Q4. How are vias drilled on 2oz copper boards?
Vias are typically made using laser drilling, which can easily drill through the 2oz copper layer. Mechanical drilling is slower but possible too.
Q5. Is 2oz readily available from PCB manufacturers?
Nowadays most PCB fabricators offer 2oz copper as a standard option at reasonable costs due to its widespread adoption. Quantity minimums may be higher.
Conclusion
With the increasing performance demands of modern electronics, 2oz copper PCBs are becoming the preferred choice over traditional 1oz material in many applications due to their many electrical, thermal, reliability and fabrication advantages.
To fully leverage the lower losses, higher currents, improved resolution and shielding possible with 2oz copper, designers must follow disciplined layout practices specialized for the capabilities of thicker copper boards.
By combining robust 2oz PCB technology with optimized design techniques, engineers can build electronics products with maximized efficiency, density and reliability to meet the needs of the future.
