Curcit Formation on Glass Substrate Using a Titanium-Copper Oxide Catalytic Adhesion Layer for Copper Plating
Authors: Okabe Kyohei , Cordonier Christopher Ernest John , Noh Joohyong , Honma Hideo , Takai Osamu 
Published: February 2020

Introduction

 Glass has characteristics such as transparency, smooth surface, chemical and thermal stability, coefficient of thermal resistance similar to silicon, high dielectric constant, electrical insulation and physical strength, deaming it an attractive substrate material for electronic devices. Examples of application are 2.5D/3D electronic device and RF module packaging. Glass can be metallized electroless plating however, problems remain, the most predominant being inadequate adhesion between glass and plated films. Using a catalytic Ti-Cu oxide adhesive layer formed on the glass, adhesion strength of 0.5 kN/m has been obtained1
) In this study, circuit formation by semi-additive process that’s often used in the formation of fine circuit and the influence of the Ti-Cu oxide layer on post-treatment steps was investigated.

Experimental

　Schott Co., Ltd. Tempax 50 mm × 50mm × t 0.7 mm was used as the test substrate. Circuit formation by the semi-additive process is shown in figure 1. After the circuit formation, the removal of the Ti-Cu oxide layer was accomplished by immersion in an aqueous sodium hydroxide 100 g/dm3, trisodium citrate 5 g/dm3 solution at 80 ℃ for 10 min. Electroless NiP plating was performed as a post-process to evaluate the effectiveness of the Ti-Cu oxide layer removal method.

Results and Discussion

 Circuits of L / S = 50/50~200/200 µm and t=10 µm dimension were formed using the semi-additive process where adhesion after circuit formation was maintained. After the circuit formation, average roughness (Ra) was observed by atomic force microscopy (AFM) and elemental analysis was performed by X-ray photoelectron spectroscopy (XPS). The Ra was 6.4 nm and 14.9 %Ti was detacted prior to removal and when performing electroless NiP plating as the post-treatment, abnormal deposition occurs between the wiring patterns. On the other hand, after performing Ti-Cu oxide layer removal treatment, the Ra was 0.5 nm and 0.3%Ti detected. Abnormal deposition of electroless nickel does not occur, therefore it was possible to deposit the electroless plating selectively on the copper circuit.

Conclusions

　L / S = 50/50 ~ 200/200 um circuits formed on a smooth glass substrate was possible.The adhesion layer of Ti-Cu oxide can be removed by an alkaline solution. By performing the Ti-Cu oxide layer removal process, abnormal deposition of electroless nickel plating in a post-treatment step can be prevented.

 

Acknowledgments

 This work was funded in part by the “MEXT-supported Program for the Strategic Research Foundation at Private Universities” and the “Tokyo Ohka Foundation for the promotion of Science and Technology.”

 

References

 1)K. Okabe, T. Kagami, Y. Horiuchi, O. Takai, H. Honma, and C. E. J. Cordonier, “Copper Plating on

Glass Using a Solution Processed Copper-Titanium Oxide Catalytic Adhesion Layer”, Journal of The

Electrochemical Society, Vol.163, No.6, p. D201-D205, (2016)

Figure 1