Technique bonds copper foil and PTFE for better 5G

September 06, 2021 // By Jean-Pierre Joosting
Technique bonds copper foil and PTFE for better 5G
Researchers have demonstrated a method to improve the adhesion of smooth copper foil to PTFE to make high-frequency PWBs for use in 5G and oter high frequency applications.

Researchers from Osaka University have demonstrated a method for strongly combining polytetrafluoroethylene (PTFE) and smooth copper foil. As communication systems become increasingly complex and and higher frequency bands come into use, the loss of transmission from the conduction component of the circuit becomes more critical. Consequently, materials must be continually improved to create future-ready printed wiring boards (PWBs).

Copper is the go-to wiring material for PWBs because it is highly conductive, and thus efficiently transports information to its destination. There is currently nothing superior to copper for this task, so the focus for improvement is to decrease transmission loss from the support material.

PTFE is ideal for this role because it has both low relative dielectric constant and low dielectric loss tangent. However, PTFE does not like to stick to things. An intermediate layer is often used between PTFE and copper to improve the adhesion, but using these layers is a tradeoff because they increase insertion losses.

In this study, the researchers have created an adhesive-free method of sticking commercially available PTFE to copper foil with high adhesion strength, thus dispensing with the need for a middle layer.

“Our technique involves what is known as heat-assisted plasma (HAP) treatment,” explains first author Misa Nishino. “We subjected the PTFE to a HAP to make the surface stickier, and then pressed the two layers together at a high temperature to ensure they were strongly bonded.”

Comparison of the developed printed circuit board and conventional alternatives. Credit: M. Nishino et al.

Picture: 
Left: Photograph of the extremely smooth Cu foil and its surface image. Right: Photograph of the Cu foil/PTFE assembly during the 90° peel test. Credit: M. Nishino et al.

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