無鉛覆晶構裝中薄膜與介金屬化合物機械性質之測定

Characterization of Mechanical Properties of Thin Film and Intermetallic Compound for Lead-Free Flip Chip Packages

蔡怡庭(I-Ting Tsai)

指導教授 ： 莊東漢

共同指導教授 ： 吳恩柏

國立臺灣大學/工學院/應用力學研究所/博士(2005年)

https://doi.org/10.6342/NTU.2005.02046

摘要

無資料

關鍵字

薄膜 ； 介金屬化合物 ； 熱膨脹係數

並列摘要

Technologies for flip chip bonding boomed to meet the requirement of smaller packages with higher performance that can sustain a substantially high temperature even under normal operating conditions. The coefficient of thermal expansion (CTE) mismatch between the chip and the carrier would make mechanical issues of the contact bumps even more severe for the reliability of flip chip packages during temperature changes. When employing the numerical simulation such as finite element methods to predict and optimize the reliability, only if the inputs of material properties are correct, can the outcome be referable. Under bump metallization (UBM) and intermetallic compounds (IMC), which usually have thickness of the thin-film order, are important parts in a contact bump. However, there are rare studies about the material properties of UBM and IMC, which are usually difficult to obtain because of the thickness of the thin-film order. The goal of this study is to develop a method to obtain the mechanical properties of materials with thickness of few micrometers. Copper films are employed due to the emergence as an important material in IC packages in the last few years, and IMC is set as another target because it might dominate the reliability of the interconnections owing to its characteristic material properties.
In this study, methods for determining elastic moduli and CTE of sputtered copper films and Cu3Sn IMC on silicon substrates are presented. The mechanical properties of silicon substrates were measured first. In addition, reflection moiré was developed to measure the slope change of the laminated composite structures subjected to thermal loading. As for analysis methods, the genetic search algorithm (GA) with FEM using ANSYS was then used to inversely obtain the elastic modulus and CTE of thin films with three different thickness and Cu3Sn, which was formed when tin reacted with copper. A large amount of data points such as 9600 points from whole-field slopes of two orthogonal directions make the algorithm more robust and immune to noise up to S/N ratio 10.
The optimally obtained elastic moduli are 105.8 Gpa, 97.5 GPa, and 92.5 GPa for copper films of 2.2 um, 3.7um, and 4.5um thick, respectively. Elastic moduli are less than that in bulk, but increase monotonically with decreasing thickness. The optimally obtained CTE values are 32.5 ppm/°C, 30.0 ppm/°C, and 29.9 ppm/°C for copper films of 2.2um, 3.7um and 4.5 um thick, respectively. CTEs are larger than that in bulk, and decrease monotonically with decreasing thickness. The results obtained are also discussed with further examination in this study.
This study also presents methods for obtaining elastic moduli and CTE of IMCs formed at the interface of lead-free solders and substrates. Up to tens micrometers of IMCs are formed on metal substrates. Such sufficient thickness of IMCs makes nanoindentor competent to obtain the elastic moduli of IMCs. The results of Cu6Sn5 and Cu3Sn agreed well with those in previous literatures with nanoindentation. The result of Ni3Sn4 is limited, and Cu33.5Zn66.5 from Sn-9Zn is new.
The conclusions of each topic are narrated respectively in the end. When materials are formed of thin-film order, it is not proper to neglect the discrepancy in material properties of thin films and bulks. In addition, as the elastic modulus and CTE for Cu3Sn are significantly different from those in Cu, the need to incorporate these material properties into stress analysis in solder bumps of a flip chip or wafer level packages might be essential.

並列關鍵字

Thin Film ； IMC ； CTE

參考文獻

2. Flip Chip Packaging Technology Solution. http://www.amkor.com

4. L. B. Freund and S. Suresh, Thin Film Materials: Stress, Defect Formation and Surface Evolution, Cambridge University Press, 2003.

5. D. T. Read, “Young’s Modulus of Thin Films by Speckle Interferometry,” Meas. Sci. Technol., Vol. 9, pp. 676-685, 1998.

6. Y. Xiang, X. Chen and J. J. Vlassak, “The Mechanical Properties of Electroplated Cu Thin Films Measured by Means of the Bulge Test Technique,” Mat. Res. Soc. Symp. Proc., Vol. 695, pp. L4.9.1-L4.9.6, 2002.

7. M. Chinmulgund, R. B. Inturi, and J. A. Barnard, “Effect of Ar Gas Pressure on Growth, Structure, and Mechanical Properties of Sputtered Ti, Al, TiAl, and Ti3Al Films,” Thin Solid Films, Vol. 270, pp. 260-263, 1995.