Printed Circuit Boards (PCBs) are an essential part of modern electronics. They are used in various applications, from consumer electronics to aerospace and military systems. The choice of materials for PCBs is critical for their performance, and copper is the most commonly used material. This blog post will explore PCB materials in detail, including the basic materials, why copper is chosen, and other alternative materials.
Basic PCB Materials
PCBs typically comprises four layers: substrate, copper foil, solder mask, and silkscreen. The substrate is the base layer, usually fiberglass, and supports the other layers. Copper foil is used for conductive traces and is the most critical material in PCBs. The solder mask protects the copper traces from oxidation and contamination, and the silkscreen is used for labeling and identifying the components on the board.
Why Choose Copper for PCBs?
Copper is the most commonly used material for the conductive traces in PCBs. Its use is primarily due to its high conductivity, low cost, and availability. Copper is an excellent conductor of electricity, which ensures that the signals transmitted through the board are not attenuated, leading to better signal integrity. Its high conductivity also means that less copper is required to achieve the same performance level, reducing the board’s overall cost.
Copper is also readily available, with many copper mines around the world. This abundance makes copper a cost-effective choice for PCB manufacturers.
Other Alternative Materials
While copper is the most commonly used material for PCBs, other materials can be used, depending on the application. Here are some alternative materials:
Aluminum: Aluminum is an alternative to copper for high-power applications, as it has better heat dissipation properties. However, it is not as conductive as copper, which limits its use in high-frequency applications.
Gold: Gold is an excellent conductor of electricity, and it is used in high-end PCBs, such as those used in aerospace and military applications. However, it is costly, which limits its use in consumer electronics.
Silver: Silver is another excellent conductor of electricity, but it is not as commonly used as copper or gold. It is mainly used in high-frequency applications like radio frequency (RF) circuits.
Conductive polymers: Conductive polymers are a relatively new material used in PCBs. They are flexible and can be molded into different shapes, making them ideal for flexible PCBs. However, their conductivity is not as high as copper, which limits their use in high-performance applications.
The role of copper in PCB
Copper has been the preferred material for Printed Circuit Boards (PCBs) for several decades. Copper is chosen for its excellent electrical conductivity, corrosion resistance, weldability, and ability to ensure high-performance circuits.
- Electrical Conductivity
Copper’s electrical conductivity makes it an ideal material for use in PCBs. Copper has a conductivity of approximately 59.6 MS/m, higher than other metals used in PCBs, such as aluminum, silver, or gold. High conductivity ensures that the electrical signals transmitted through the circuit board are not attenuated, which leads to better signal integrity. Copper’s high conductivity also reduces the amount of copper used in the circuit board, leading to cost savings.
- Corrosion Resistance
Copper is resistant to corrosion, making it an ideal choice for PCBs. PCBs can be exposed to different environmental factors, including humidity, heat, and chemicals, which can cause corrosion. Corrosion can lead to copper traces degradation, affecting the circuit board’s performance. Copper’s ability to resist corrosion ensures the durability and longevity of the circuit board, reducing maintenance costs and increasing its lifespan.
Copper is a highly weldable material, which makes it easy to use in PCBs. Welding is joining two metals together using heat, pressure, or both. The welding process is critical in PCBs, where the copper traces must be joined to the other components on the board. Copper’s high weldability ensures the traces are firmly joined to the other components, improving the circuit board’s performance and reliability.
- High-Performance Circuits
Using copper in PCBs ensures that the circuit board meets the high-performance requirements of modern electronics. Copper’s high conductivity allows for the efficient transmission of electrical signals, while its corrosion resistance and weldability ensure the circuit board’s durability and longevity. Copper is also a cost-effective material, reducing the overall cost of the circuit board. PCB manufacturers must consider the different properties of copper and carefully design the circuit board to ensure that it meets the required performance specifications.
copper thickness in PCB
PCB copper thickness is an essential factor to consider when designing a printed circuit board. The copper thickness determines the current carrying capacity, mechanical strength, and cost of the PCB.
- Importance of Copper Thickness
The thickness of the copper layer on a PCB is critical to the board’s performance. The copper layer’s thickness determines how much current can flow through the board without causing excessive heating or voltage drop. The thickness also affects the mechanical strength of the board, as a thicker copper layer provides better adhesion and resistance to wear and tear. The thickness of the copper layer can also affect the cost of the PCB, as thicker layers require more copper and manufacturing time.
- Measuring Copper Thickness
The thickness of the copper layer on a PCB can be measured using several techniques, including destructive and non-destructive methods. Destructive methods involve removing a small portion of the copper layer and measuring its thickness using a microscope or a micrometer. Non-destructive methods include eddy current measurement, X-ray fluorescence, and beta backscatter. These methods provide a more accurate measurement of the copper thickness without damaging the PCB.
- Standard Copper Thicknesses
PCB manufacturers offer several standard copper thicknesses, ranging from 0.5 oz to 10 oz. The thickness is expressed in ounces per square foot, with 1 oz equivalent to 1.4 mils or 35 µm. The standard copper thicknesses are shown in the table below.
|Copper Weight||Copper Thickness|
|0.5 oz||0.7 mils / 17 µm|
|1 oz||1.4 mils / 35 µm|
|2 oz||2.8 mils / 70 µm|
|3 oz||4.2 mils / 105 µm|
|4 oz||5.6 mils / 140 µm|
|5 oz||7.0 mils / 175 µm|
|6 oz||8.4 mils / 210 µm|
|10 oz||14.0 mils / 350 µm|
- Impact on Performance
The copper thickness on a PCB has a direct impact on the board’s performance. A thicker copper layer provides a lower resistance path for the current, leading to a higher current carrying capacity and reduced voltage drop. It also provides better mechanical strength and improved resistance to wear and tear. However, a thicker copper layer can also increase the manufacturing cost of the board and make it more challenging to solder components to the board. Additionally, thicker copper layers may require more current to etch, leading to longer etching times and higher manufacturing costs.
Copper in Heavy Copper PCB
Heavy copper PCBs are printed circuit boards that have copper traces and planes that are thicker than those found on regular PCBs. These boards are often used in high power applications, where they can handle higher currents and dissipate more heat than standard PCBs. The relationship between heavy copper PCBs and copper is evident in the board’s design and manufacturing process.
Heavy copper PCBs are designed to have thick copper traces and planes. The thickness of the copper layer can range from 2 oz to 20 oz or more, depending on the application’s requirements. The thickness of the copper layer directly affects the board’s performance, as thicker copper layers provide lower resistance paths for the current, reducing voltage drop and improving power dissipation. The copper layer’s thickness can also affect the board’s mechanical strength, making it more resistant to wear and tear.
To manufacture heavy copper PCBs, specialized equipment and techniques are required. The process involves starting with a copper-clad laminate, which is then coated with a layer of photoresist. The photoresist is then exposed to UV light through a photomask, which defines the circuit pattern. The exposed photoresist is then developed, leaving behind the circuit pattern on the copper layer. The unmasked copper is then etched away using an etchant solution, leaving behind the copper traces and planes.
The etching process for heavy copper PCBs can be more challenging than for standard PCBs due to the thicker copper layers. The etchant solution must be more aggressive, and the etching process may take longer to complete. The process can also be more expensive, as more copper is required to produce the board, and the manufacturing process may take longer.
Here is a table showing perfomance for copper in heavy copper PCBs:
|Copper weight (oz)||2-20 or more|
|Maximum current carrying capacity (A)||Up to 300|
|Thermal conductivity (W/mK)||400|
|Coefficient of thermal expansion (ppm/°C)||16-18|
|Surface finish||Immersion gold, ENIG, OSP, HASL|