1 Oz Copper Thickness: Is it Perfect For PCB Manufacturing?

What Is 1 Ounce Copper? 

Folded PCB with thin copper 

Copper, a preferred metal in PCB manufacturing, is typically spread over a surface when making the boards.

It is then measured for thickness based on how evenly it spreads on one square foot of the surface.

Therefore, 1 ounce of copper is a standard measurement of the thickness of copper spread over a square foot of a PCB’s surface. 

It is recorded in OZ since ounce is the common measurement unit for PCB copper thickness. 

Five Important Properties Of 1 Oz Copper  

Etchability

Copper lines in functional headphones

Etchability is the ability to cut designs and prints on a surface. In PCBs, copper is valued for its high etchability.

In addition to being highly etchable, it reacts well with ferric chloride acid, corrosive to most metals, which is essential in stripping away copper remnants from blank PCB boards. 

High Electrical Conductivity

As a non-precious metal, copper has a high electrical conductivity rating of 16.78 nΩ•m in resistivity at an average temperature of 20 °C.

That means it can conduct electricity well in various environments where you need electrical machinery. 

Excellent Solderability

Since PCBs are used in various applications, the copper board must have above-average solderability.

It exhibits good solder wetting and bonding capability for attaching vital components during production and repair. 

Thermal Relief

PCBs need the ability to expand and contract in different heat environments.

Copper has excellent expansion and contraction that allows it to maintain its structure without breaking or warping.

Additionally, thin copper is also ductile and malleable in its normal state. 

Excellent Laminate-to-Substrate Adhesion

Copper-clad laminate, common in consumer electronics needs to bond to copper substrates.

CCL and substrate in PCBs maintain excellent conductivity on both sides of the board. 

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.

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.

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.

Manufacturing With 1 Oz Copper

Etching

1 ounce copper has the right thickness for non-aggressive etching cycles. Also, materials such as cupric chloride can provide a usable product during the manufacturing process. 

Plating

Copper plating on hole walls requires enough thickness to cover 1 ounce copper. This thickness helps to apply standard chemistry during manufacturing. 

Soldermask

LPI(Liquid photo-imageable) materials come in a standard 25-75 μm thickness. They have the correct thickness for standard manufacturing with 1 ounce copper without adding any special machine or processes. 

Lamination

1 ounce yields good results when put under standard heat and lamination procedures. 

Photolithography

Unlike thicker copper foils, standard dry films and liquid photo resists can cover 1 ounce of copper. Increasing copper thickness would require upgrading to screen printing resists.

Measuring Copper Thickness In PCBs

Sure, there are tools that can help measure the thickness of copper in PCBs.

Tools such as Eddy Current thickness gauges and X-ray fluorescence analyzers measure copper layers in various ways, albeit non-destructively. 

Although microsectioning is a super-accurate method, it will destroy the copper. So, these practical ways can give you accurate readings for PCB copper thickness.

Using Micrometers and Calipers

Digital calipers and micrometers for precision copper measurement

You can use a micrometer or a caliper. However, quality assurance might require the use of both to guarantee a thinner margin of error.

These tools measure the thickness of the copper foil. 

Know the Measurement Units

Knowing the measurement units is a must. It helps with conversion. 

Manufacturers measure copper thickness in ounces per square foot. Therefore, if you measure 1 ounce per square foot, you can convert it to 34.79 micrometers or 1.37 mils. 

Extract the thickness using Weight Calculation.

1. Take a PCB sample without components. 
2. Weigh the copper.
3. Remove the copper from the substrate.
4. Weigh the substrate. 
5. Note the difference in the weight of the copper.
6. Use 1oz/ft² = 1.37 mils conversion. 

Why Would You Use Heavy Copper In A PCB?

There are several reasons to use heavy copper in PCBs. The most relevant reasons are to boost electrical current carriage, fortify their structural integrity and increase tolerance for high-temperature operations. 

Thicker copper handles more current better than thin 1-ounce copper in high-electric current environments and applications. 

Also, high-temperature applications need high heat dissipation. Using heavy copper is one way of increasing heat dissipation to maintain durability in high-power equipment. 

Since PCBs are subjected to environments with erratic temperature changes, heavy copper is great for maintaining mechanical structure against repetitive thermal strain and temperature changes. 

The Downsides Of Using Thinner Copper Foils

Copper thinner than 1 ounce is prone to limited solder mask thinness. And since solder mask thickness is typically about 0.8 mils, a thin copper foil and thin solder mask thinness can compromise PCB performance. 

Copper is preferred in PCBs because it is low-resistance. Thin copper foil has high resistance, which may increase losses and lower electrical performance. 

It goes without saying that thinner copper foils are also more vulnerable to fractures. 

How Does Copper Thickness Affect Current Carrying Capacity?

In applications where copper thickness must be above 1 ounce, it is usually to increase the carrying capacity. Wide and thick copper traces have low resistance and larger areas.

Therefore, they carry more capacity while also keeping the generated heat low.

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.