Investigation on Chemical Etching Process of FPCB With 18 μm Line Pitch

Jiazheng Sheng,Ruijian Ming,Yinggang Tang,Daode Zhang,Shengnan Shen,Jian Wang,Bin Sun,Hui Li

doi:10.1109/access.2021.3069284

Jiazheng Sheng, Ruijian Ming + Show 6 more

Open Access

https://doi.org/10.1109/access.2021.3069284

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Abstract

Flexible printed circuit boards (FPCB) are widely used in smart devices with high wiring density and light weight. In this paper, the chemical etching process of FPCB with 18 $\mu \text{m}$ line pitch is investigated. A geometric model of the FPCB circuit with the shape of “T” is established and simulated by the finite element method. The time evolution of the etching cavity, concentration field and velocity field of CuCl2 solution are studied, as well as the effects of initial concentrations and inlet velocities on the etching cavity profile. Finally, the FPCB sample with 18 $\mu \text{m}$ line pitch is successfully fabricated by employing process parameters from the etching simulation. The results show that as the increase in the etching cavity, recirculating eddies form at the bottom of the photoresist in the corners of the etching cavity, resulting in more etching on the top sides of sidewalls over time. Higher initial concentration of the etching solution will result in a larger etching cavity profile, but the inlet velocity cannot affect the etching cavity profile significantly. Finally, the effectiveness of the simulation model is verified by comparing the etching cavity profiles with four experiments.

Highlights

With the high wiring density, light weight, thin thickness and good bendability, the flexible printed circuit board (FPCB) is widely used in full screen smartphone, smart TV with ultranarrow bezel, flexible wearable device [1] and flexible display screen
The huge market demand promotes the progress of FPCB manufacturing process, and puts forward higher requirements on the quality of the FPCB circuit
Breaking through the manufacturing process of 18 μm or finer line pitch is crucial for the further growth of the FPCB industry

Summary

INTRODUCTION

With the high wiring density, light weight, thin thickness and good bendability, the flexible printed circuit board (FPCB) is widely used in full screen smartphone, smart TV with ultranarrow bezel, flexible wearable device [1] and flexible display screen. J. Sheng et al.: Investigation on Chemical Etching Process of FPCB With 18 μm Line Pitch numerical simulation method is used to study the etching process, which reduces time and cost efficiently and can study the mechanism of the etching process. Shin and Economou [14] used a moving-grid approach to simulate convection-driven wet chemical etching, and showed that the shape evolution of etching cavities was affected by the etchant flow field, but which had not been applied to high rate anisotropic etching and verified by experiment. None of them studied the high-rate anisotropic of wet chemical etching, and the manufacturing process of FPCB with 18 μm line pitch or finer line pitch is still unknown. Where v is the velocity of the moving boundary, M is the molar mass and ρ is the density of the copper

SIMULATION MODEL

RESULTS AND DISCUSSIONS

CONCLUSION