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Printed Circuit Board Copper Thickness Vs Current

Posted On 23 September 2022 BY

The right function of PCB depends on the copper thickness, trace width, and weight. Printed circuit boards have traces made of copper, and we also call them conductors. Copper traces have a specific thickness, width, length, and weight that affect the flow of current.

PCB has copper layers for the flow of electric current. The wrong copper thickness can affect the PCB assembly process. But, if you understand the relationship between copper thickness and signal transmission, as well as the cost of PCB fabrication, it would help you choose the right copper weight or thickness for PCB design.

So, you must know what is copper thickness or weight and why is it important. You should also know the heavy copper’s application, and PCB construction cost.

Sometimes you can’t change the trace width due to certain spacing requirements or PCB density. But, you can change the copper thickness to have maximum current flow. You have to consider signal integrity while designing a PCB. The signal integrity and current loss rely on the amount of impedance that happens on copper traces.

Printed circuit boards with heavy copper are used in high-power electronic devices which are vulnerable to tough environments. Thick traces ensure durability and can carry more current without increasing the trace width or length. However, lighter copper traces are also used to have a certain trace impedance without having a highly small trace width or length.

You must understand the relationship between the current flow and copper thickness while designing your PCB. So, you have to know the copper trace fabrication, in this case, and its effect on signal integrity.

PC Board Fabrication

PCB fabrication involves different steps, including etching which is done on the inner layers and the top surface of the board. You need a laminate sheet finished in copper. In etching, you have to remove additional copper from traces and several other parts of the PCB, like pads and angular rings. Fabricators use an ammonia-based liquid to complete the process of etching.

Generally, the copper sheet thickness is 1oz, like 0.5 oz. on each side of the sheet. You can etch it down to decrease the thickness or can increase the thickness by plating it up to have the desired sheet.

The sheets are done rough during fabrication to bond them to the dielectric material. However, the roughness can also affect the signal integrity in the case of high-frequency boards. The frequency above 100MHz can result in trace resistance that opposes the flow of current.

In the case of plated vias, you should add traces after drilling the holes and it often involves the process of electrodeposition. For example, the PC Board manufacturer places the circuit board in an electrolytic solution having copper ions. Then, he applies a direct current to create a potential around the hole, distributing the ions in the entire via, which is also known as filling. Such a distribution helps you to find the quality of the signal flow that occurs along traces. So, it is very useful to understand PCB fabrication to have a functional design.

Relationship Between Copper Thickness And Signal Flow

In general, fabricators buy copper sheets with specific weight and thickness as they want fixed numbers. But, engineers say that the copper parameters are changeable after having a set trace width and length to enhance the signal flow or integrity.

The current carrying capacity of a PCB is determined by a specific standard known as IPC-2152. It shows the trace parameters, including the thickness and weight of the copper, and trace length and width. These parameters are interconnected, depending on a material’s thermal and electrical properties.

Role of the PCB Copper Thickness to Enhance the Current

Engineers use some calculations and equations during PCB design as discussed below. These calculations are 99% correct in many PCB designs, so let’s understand them.

1-Finding the Signal Power, P (W) and Voltage, or V (Volts)
You must know these quantities from PCB operation design.
2- Finding Trace Impedance, R (Ω).
You have to set it and you can manage it during the fabrication of the PCB.
3-Finding The Maximum Flow Of Current For The Trace I (A).
You can find the current by using the below equations.
I = V2/R or I = P/V or I = √ (P/R)

4- Finding an Increased Temperature T (°C).

You must know the increased temperatures, or you can evaluate it from the PCB operation design.

5- Finding the Cross-Sectional Area of the Trace A (Mils2).

It involves constants of curve fitting, such as k, b, and c that approximate the
IPC-2152 curve. This curve links the area to its current carrying ability.

K for internal layers= = 0.024, b = 0.44, c = 0.725
K for external layers== 0.048, b = 0.44, c = 0.725

A = (I/ (k ×Tb)) 1/c

6- Finding Trace Width or W, Mils

You should also set the trace width as required.

7- Finding PCB Copper Thickness? (Mils).

= A / w

You can use the PCB design software to set the thickness of copper, or you can use values of the copper weight, as most contract manufacturers use it. Such parameters are proportional to each other. Here is how to find the copper weight.

Copper weight (oz.) = (copper thickness (mils) / 1.37
According to the thumb rule, the weight of one square foot of copper is one ounce. If you follow the right equations, you can create a well-designed PC Board even for the first time.
What Is Heavy Copper And Why Do You Need It?
If the copper weight is over 4oz, you can consider it heavy because a standard weight or thickness ranges from 1 to 3oz. You can use heavy copper to have

  • More current carrying capacity
  • High capacity to bear thermal stresses and have good thermal management.
  • Better heat dissipation
  • Great mechanical strength to have large through-hole components and heavy connectors.
  • Power converters and planar transformers

Sometimes the PCB fabricators use 1 oz. copper for internal layers and 4 oz. for external layers of a multi-layer PCB. Certain issues can be controlled by using the same copper thickness in stack-ups of opposing layers, as it can eliminate the PCB bending due to heat generated during its function.

Like, if you have a PCB with 8 layers, you can group the opposing layers as 1 & 8, 2 & 7, 3 & 6, 4 & 5. That means layers 1 and 8 should have a similar thickness or weight, and the same goes for layers 2 and 7 and other groups.

What Is Copper Thickness And Weight In Printed Circuit Boards?

Copper is used in a PCB having a thickness of 1 oz., however, some engineers measure it in ounces. The thickness of copper determines the copper weight. Like, when the weight of copper covers one square foot of sheet, it makes copper thickness. Hence, 1 oz. of copper covering 1 square foot will result in 1.37 mils or 0.0348 mm foil thickness.
Why You Have To Consider the Copper Weight In PCB?

You can determine the current carrying ability of a PCB with the help of the thickness of its copper traces or copper layer. For PCBs with well-controlled impedance, the trace width helps determine the essential copper thickness. Besides, some other factors are also essential, such as a circuit board’s weight, compatibility of PCB components, and the type of connectors on a PCB.

Does Copper Weight Affect The Cost Of PCB Construction?

A printed circuit board with heavy copper involves expensive manufacturing, besides, it needs more time to make it. In other words, thicker copper is always more costly than standard copper. The manufacturing time of heavy copper is also high that also increases the total cost of PCB manufacturing.

What Is Etching In PCB?

In etching, you have to remove additional copper from traces and several other parts of the PCB, like pads and angular rings. Fabricators use an ammonia-based liquid to complete the process of etching.

How To Determine The Current Capacity Of A Printed Circuit Board?

The current carrying capacity of a PCB is determined by a specific standard known as IPC-2152. It shows the trace parameters, including the thickness and weight of the copper, and trace length and width. These parameters are interconnected, depending on a material’s thermal and electrical properties.

Final Thoughts

PCB involves different materials, including copper that have certain parameters, including thickness and weight. The copper thickness has a direct link to the current flow and the signal integrity, so its knowledge is essential for PCB designers, engineers, and fabricators. PCBs with heavy copper help create more reliable devices with increased current flow and better performance.

However, many smart devices have thin copper layers, depending on their requirements. You can develop a flawless circuit board by considering copper weight, thickness, as well as trace width and length, and several other features as described above. Besides, you must hire a good fabricator in this case.

Would like to know more about PCB Copper thickness and current or PC Board assembly? Email us at sales@pnconline.com

Written by Sam Sangani

Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.

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