Surface Modification of Fluoropolymer Using Open-Air Plasma Treatment at Atmospheric Pressure with Ar, Ar＋O₂, and Ar＋H₂ for Application in HighAdhesion Metal Wiring Patterns

Abstract

We performed open-air plasma treatment of polytetrafluoroethylene (PTFE) at atmospheric pressure to increase the adhesion strength between PTFE and an Ag metal film formed from Ag ink. Coloration of the PTFE surface occurred during 600 s treatment with Ar plasma. The Ag/PTFE adhesion strength was 0.06 N/mm. To resolve the problem of coloration and to improve the adhesion strength, O2 or H2 gas was added. During treatment with Ar + O2 plasma with O2 content of 0.33% for 600 s, no coloration occurred but the adhesion strength decreased to zero. During treatment with Ar + H2 plasma for 600 s, coloration did not occur. Moreover, the adhesion strength increased to 0.25-0.55 N/mm. These results showed that H2 addition was effective for preventing coloration and improving adhesion strength during long-period plasma treatment. Furthermore, the uniformity of surface treatment with Ar + H2 plasma was higher than that for Ar plasma.

Open-air-type Ar + H2O plasma treatment of polytetrafluoroethylene for improving Ag/PTFE adhesion strength: application to highly adhesive Ag direct wiring patterns

“…We previously observed that the coloration occurred because the plasma-treated PTFE surface was covered with a reddish-yellow deposition layer of C x F y monomers and/or polymers. 28) This deposition layer was readily peeled from the PTFE sheet, i.e. this deposition layer decreased the Ag/PTFE adhesion strength.…”

“…Although the surface roughness remained almost unchanged, the adhesion strength between PTFE and an Ag film, which was prepared by sintering a Ag salt ink, was 0.64 N mm −1 . 28) This value is insufficient for use in practical industrial applications because the Ag/PTFE adhesion strength was less than the target value of 0.70 N mm −1 , which is the Japan Electronics Packaging and Circuits Association (JPCA) standard value. 29) In some cases, 0.8 or 0.9 or 1.0 N mm −1 is set up as the target value of PCBs by some companies.…”

“…When O 2 gas was added to the Ar gas, the adhesion strength decreased to 0.00 N mm −1 with increasing oxygen concentration. 28) Oxygen molecules in the Ar plasma are transformed to oxygen atoms, which demonstrate high etching performance for PTFE. Thus, the surface of the PTFE excessively etched with oxygen atoms in plasma looking similar to an untreated PTFE surface, exhibiting poor adhesion properties.…”

“…When H 2 gas was added to the Ar gas, the adhesion strength increased from 0.06 to 0.55 N mm −1 . 28) Hydrogen molecules in Ar plasma are transformed to atomic H. The H atoms reacted with carbon radicals, resulting in the formation of C-H bonds. Although C-F bonds on the PTFE surface were converted to C-H bonds, the adhesion strength was still poor.…”