Reduction of Residual Stresses in Sapphire Cover Glass Induced by Mechanical Polishing and Laser Chamfering Through Etching

  • Shih-Jeh Wu Department of Mechanical and Automation Engineering, I-Shou University, Kaohsiung, Taiwan
  • Hsiang-Chen Hsu Department of Mechanical and Automation Engineering, I-Shou University, Kaohsiung, Taiwan
  • Wen-Fei Lin Department of Material Science and Engineering, I-Shou University, Kaohsiung, Taiwan
Keywords: picosecond laser, laser curvature method, residual stress, stress relief, wet etching, sapphire

Abstract

Sapphire is a hard and anti-scratch material commonly used as cover glass of mobile devices such as watches and mobile phones. A mechanical polishing using diamond slurry is usually necessary to create mirror surface. Additional chamfering at the edge is sometimes needed by mechanical grinding. These processes induce residual stresses and the mechanical strength of the sapphire work piece is impaired. In this study wet etching by phosphate acid process is applied to relief the induced stress in a 1” diameter sapphire cover glass. The sapphire is polished before the edge is chamfered by a picosecond laser. Residual stresses are measured by laser curvature method at different stages of machining. The results show that the wet etching process effectively relief the stress and the laser machining does not incur serious residual stress.

References

“Gorilla Glass Success, What is Sapphire glass?” http://www.corning.com/news_center/features/gorillaglasssuccess.aspx, Corning Incorporated.

“Everything You Wanted To Know About Sapphire Glass, But Were Afraid To Ask, ” http://www.cultofmac.com/267068/everything-wanted-know-sapphire-glass-afraid-ask-qa/

D. Wang, J. Lee, K. Holland, T. Bibby, S. Beaudoin, and T. Cale, “Von mises stress in chemical‐mechanical polishing processes,” J. Electrochem. Soc., vol. 144, no. 3, pp. 1121-1127, 1997.

G. Kermouche, J. Rech, H. Hamdi, and J. M. Bergheau, “On the residual stress field induced by a scratching round abrasive grain,” Wear, vol. 269, no. 1-2, pp. 86-92, May 2010.

C. Landesberger, C. Paschke, and K. Bock, “Influence of wafer grinding and etching techniques on the fracture strength of thin silicon substrates,” Advanced Materials Research, vol. 325, pp. 659-665, 2011.

K. Gurnett and T. Adams, “Ultra-thin semiconductor wafer applications and processes,” III-Vs Review, vol. 19, pp. 38–40, 2006.

Z. J. Pei, G. R. Fisher, and J. Liu, “Grinding of silicon wafers: a review from historical perspectives,” International Journal of Machine Tools and Manufacture, vol. 48, pp. 1297-1307, 2008.

J. Wang, P. Shrotriya, and K. S. Kim, “Surface residual stress measurement using curvature interferometry,” Experimental Mechanics, vol. 46, pp. 39-46, 2006.

Published
2016-10-01
How to Cite
[1]
S.-J. Wu, H.-C. Hsu, and W.-F. Lin, “Reduction of Residual Stresses in Sapphire Cover Glass Induced by Mechanical Polishing and Laser Chamfering Through Etching”, Adv. technol. innov., vol. 1, no. 2, pp. 29-32, Oct. 2016.
Section
Articles