About 1 oz copper thickness, PCB stack-up is probably the last thing you’d consider as an electronics designer or beginner in engineering.
While it’s easy to jump into new designs with blazing enthusiasm, you may forget a crucial aspect of PCB setup.
For instance, you may fail to choose 1 oz copper thickness or something higher/lower.
Copper thickness is critical as it adds to your design’s overall outer layer thickness. So, should you stick with 1 oz copper thickness?
Or opt for something thicker than the standard fabricator value?
This article will explore guidelines and situations to help you choose the right copper thickness for your designs.
How to Choose PCB Copper Thickness
Gray PCB
Although essential, not all applications require you to specify copper thickness except for a standard value. Usually, copper-clad laminates come with a 0.5 oz or 1.0 oz/sq ft thickness, but fabricators can also apply heavier copper when needed.
Interestingly, manufacturers may add plates to exposed copper, buffing it up your desired thickness. However, these extra steps or materials for copper thickening will cost more time and money.
Nevertheless, thickness in this context refers to the weight of copper you can use in your PCB designs. So, how heavy is 1 oz of copper? Keep reading to find out.
How Thick is 1 Oz Copper?
A hand holding a finished PCB
Ounces (oz) are the most common way to express copper thickness in the PCB industry. But why is this unit of weight popular for specifying thickness? Let’s say you flatten 1 oz (approx. 28.35 grams) of copper to envelop a surface area of 1 square foot evenly. You’ll get a 1.37 mils (0.034mm) copper thickness.
Hence, we determine the copper’s weight before knowing how thick it will be. Here’s a conversion table for better understanding.
| Oz | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1.5 | 1 |
| mils | 12.33 | 10.96 | 9.59 | 8.22 | 6.85 | 5.48 | 4.11 | 2.74 | 2.06 | 1.37 |
| inch | 0.01233 | 0.01096 | 0.00959 | 0.00822 | 0.00685 | 0.00548 | 0.00411 | 0.00274 | 0.00206 | 0.00137 |
| mm | 0.3132 | 0.2784 | 0.2436 | 0.2088 | 0.1740 | 0.1392 | 0.1044 | 0.0696 | 0.0522 | 0.0348 |
| µm | 313.18 | 278.38 | 243.59 | 208.79 | 173.99 | 139.19 | 10439 | 69.60 | 52.20 | 34.80 |
How much Copper do You Need?
Interestingly, most manufacturers make PCBs with a default 1 0z copper thickness on each layer. If you don’t include fab print or other specifications in your Gerber files, they assume you want 1 oz on all your copper layers.
As a result, it’s imperative always to lay out your specifications, especially if your design needs higher resistance, impedance, or voltages. You can use various online tools to determine your trace’s length, width, and thickness for the best results.
In addition, manufacturers often assume that all copper layers have the same finished weight unless you specify otherwise in the fabrication notes. For instance, if you have a 4-layer board with a set 1 oz weight, they’ll work with finishing all copper layers with 1.37 mils thickness or more.
What are the Minimum Spacing Rules for Copper Weight?
Generally, the more copper thickness your design needs, the more spacing you’ll need between your PCB’s copper features. Look at the table below for the minimum recommended spacing according to weight.
| Copper weight | Min. recommended space and min. trace width |
| 4 oz | 14 mils (0.355mm) |
| 3 oz | 10 mils (0.254mm) |
| 2 oz | 8 mils (0.203mm) |
| 1 oz | 3.5 mils (0.089mm) |
Regardless, the spacing we recommend in this table is only a general guide.
Typically, different manufacturers present various capabilities, but this chart will provide an idea of the minimum trace and spacing your designs should have.
Further, the more spacing between your copper features, the better your designs will be.
Tips for Applying the Proper Copper Thickness
Distribute your Copper as Even as Possible
Always endeavor to spread your copper as evenly as possible. Think beyond copper thickness to how you distribute them on each layer. Although some applications make it impossible, consider it when designing your layout.
Why did we say some applications make it impossible? The plating and etching processes are entirely organic, meaning you’ll submerge a copper-clad laminate into some chemicals.
For this reason, you won’t have precise control over where the process removes or plates copper.
While etching, you’ll have to mask off the desired image to secure it from the process.
However, the chemicals will still dissolve the copper at vaguely different rates.
But it depends on a few factors, like where you place the features on the panel, its placement inside the tank, and how densely you distribute the copper.
Additionally, fabricators agitate and circulate the chemical solutions in etching and plating tanks to water down these issues.
But panels with vastly different copper densities will make things tricky. So, we recommend trying as much as possible to distribute copper evenly across your entire board–during the design phase.
Can One Layer have more Copper than the Other?
You can use more copper thickness on one layer than others on your PCB design. For instance, you can set 3 oz on your outer layers and 1 oz copper on the inner ones—or vice versa.
Nevertheless, the best practices demand that you use the same copper weight across all layers on your stack-up.
Let’s use a 4-layer board as an example. On such setups, layers 4 and 1 can have 2 oz, while layers 2 and 3 will stick to 1 oz.
Interestingly, this stack-up example provides a balanced structure, reducing the chances of bowing or twisting under high operating temperatures or extreme heat during assembly.
Use the Same Copper Weight on your Outer Layers
Your outer layers must always have similar copper weights for the perfect balance. For instance, if your top copper layer’s final weight is 2 oz, your bottom layer should use the same.
So what happens if your outer layers have different copper weight specifications? The etching process will have different durations for the top and bottom layers. As a result, you may end up over-etching the bottom layer.
Also, manufacturers would have to handle each outer layer independently, making the process more complex and time-consuming. In addition to being more expensive, many manufacturers may reject your designs. Also, your board will have increased chances to twist or bow under extreme temperatures.
Final Words
1 oz copper thickness is a universal or default value for most fabricators. Interestingly, manufacturers will often build designs without specifications with 1 oz. However, if necessary, you can increase the copper weight to meet your application’s demands.
But remember that thicker copper attracts higher costs. Why? Because extra copper thickness requires additional raw materials and processing time. Plus, pulling it off is trickier than the standard 1 oz thickness.
Do you have more questions? You can reach us anytime, and we’ll be happy to help.