High-frequency printed circuit boards have gained immense traction in the electronics segment, and are extensively used in high-speed data transfers, telecommunications, and RF technology. These PCBs transmit electromagnetic waves in GHz with minimal losses. Designing high-frequency PCBs with specific characteristics is a tedious process as it demands balanced considerations of technical specifications. One of those considerations is a smooth copper layer in all possible designs. This is because the roughness of copper creates extra impedance, deviation, and losses. Now, you may think about how to overcome signal loss without selecting ultra-smooth copper for every PCB design? Copper foil is the answer. It is a negatively charged electrolytic material deposited on the base layer of the board to form a continuous metal foil. Different types of copper foil with varying roughness values can be used for high-frequency designs. Are you intrigued to know what they are?
Common Types of PCB Copper Foils for High-Frequency Design
The following list describes different types of PCB copper foils for high-frequency designs. Let’s take a look at them.
- Electro-deposited (ED) Copper: While fabricating ED copper, the copper foil is deposited on a titanium rotating drum connected to the DC power source. The anode is submerged in the copper electrolyte, while the cathode is attached to the drum. Copper is deposited in the drum when an electric field is applied. The overall speed of the drum determines the thickness of the copper foil. It means it takes more time to increase the copper thickness. The copper next to the rotating drum is smooth, and the other side has rough copper. Basically, electro-plated copper appears in red. Compared to other types, this type is mechanically more robust and has a higher tensile strength. This type of copper foil is ideal for applications where mechanical stress is highly a concern.
- Rolled-Annealed (RA) Copper: This type of copper is made using successive cold rolling operations, reducing the overall thickness of copper and extending its length. The smoothness of the surface mainly depends on the rolling mill condition. RA copper appears yellowish and smoother than ED copper. It is resistant to conductor cracking due to thermal stress where a thermal shock is concerned. RA copper is best suited for high-frequency applications.
- Reverse Treated ED Copper and LoPro Copper Foil: As the name suggests, reverse treated ED copper involves the treatment of electrodeposited copper. These layers are thin coatings, which improve the base foil adhesion to dielectrics as well as resistance to corrosion. This makes the shiny side of the copper rougher than it was before. The treated copper is laminated to the dielectric material while manufacturing printed circuit board panels. When it comes to LoPro copper foil, the reverse treated side of the copper foil is adhesive treated. The adhesive-treated side is bonded with the dielectric layer for better adhesion.
The optimum performance of the circuit board highly depends on the selection of appropriate materials. The type of copper foil used, its roughness, and its adherence to the dielectric material highly contributes to the optimal functionality of the PCB, mainly for high-frequency applications. Therefore, it is essential to check these aspects for high-frequency PCB designs. If there is any confusion or you don’t have enough experience of selecting copper foils for your application, it is always a good idea to consult an industry player with enough experience and knowledge. Rigiflex Technology is a prominent industry player, offering PCB manufacturing, assembly, and testing services for many industries. This ensures circuit boards are manufactured using the finest quality components and will meet the requirements of several challenging applications.