Copper Weight vs. Thickness: A PCB Designer's Guide
Decoding 'ounces' and choosing the right copper for your application.
In the PCB industry, copper thickness is weirdly measured in 'ounces.' This doesn't refer to the weight of the board, but the weight of copper if you rolled it out to cover exactly one square foot. For designers, converting these ounces into physical thickness (microns or mils) is a daily necessity for trace width and thermal calculations.
The Ounce-to-Micron Conversion
Standard 1 oz copper equates to approximately 35 micrometers (µm) or 1.4 mils. 0.5 oz is 17.5 µm, and 2 oz is 70 µm. This is the starting point for every trace capacity calculation. Our converter makes these shifts instant, ensuring you don't use the wrong thickness in your heat rise models.
When to Choose 0.5 oz (Half-Ounce) Copper
Half-ounce copper is ideal for high-density interconnect (HDI) boards with very fine traces and spaces (under 4 mils). Because the copper is thinner, it is easier to etch precisely without 'under-etching,' allowing for tighter tolerances in complex smartphone or wearable electronics.
The Power of 2 oz and 3 oz Copper
Heavier copper (2 oz and above) is essential for power distribution, motor controllers, and heat dissipation. It reduces the resistance of the traces, leading to less voltage drop and lower operating temperatures. However, heavier copper requires wider minimum spacing between traces due to the etching process, which designers must account for in their layout.
Finished Thickness vs. Base Copper
One common trap is the difference between 'base' and 'finished' copper. During manufacturing, plating is added to the surface. A board ordered with 1 oz base copper may end up with 1.5 oz finished thickness on the surface layers. Internal layers do not get this extra plating, so their thickness remains the base value.
FAQ
What is the most common copper weight?
1 oz (35µm) is the standard for the vast majority of consumer and industrial electronics. It provides a good balance between current capacity, cost, and ease of manufacturing.
Is copper weight the same for all layers?
No. You can specify different weights for different layers. For example, a 4-layer board might have 1 oz on the external layers but 0.5 oz on the internal signal layers to save cost or allow for finer routing.
Why does heavier copper require more spacing?
The chemical etching process is isotropic, meaning it etches sideways as well as downwards. Thicker copper takes longer to etch, so the sideways etching (undercutting) is more pronounced, requiring a wider gap between traces to prevent shorts.