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Research Papers

Characterization of Chemical Cure Shrinkage of Epoxy Molding Compound With Application to Warpage Analysis

[+] Author and Article Information
Guojun Hu

 STMicroelectronics, 629 Lorong 4/6 Toa Payoh, Singapore 319521, Singaporeguojun.hu@st.com

Jing-En Luan

 STMicroelectronics, 629 Lorong 4/6 Toa Payoh, Singapore 319521, Singapore

Spencer Chew

 Cookson Semiconductor Packaging Materials, 12 Joo Koon Road, Singapore 628975, Singapore

J. Electron. Packag 131(1), 011010 (Feb 13, 2009) (6 pages) doi:10.1115/1.3068321 History: Received December 22, 2007; Revised September 26, 2008; Published February 13, 2009

After encapsulation, thermomechanical deformation builds up within the electronic packages due to the temperature coefficient of expansion mismatch between the respective materials within the package as it cools to room temperature. At the same time, the chemical cure shrinkage exerts important influence on the total deformation. Due to the complexity and time consuming of the calculation, it is almost impossible for an industry to carry out the numerical simulation using viscoelastic property, which is the most close to the real material property of polymer material. However, finite element analysis (FEA) using temperature-dependent elastic property, temperature-dependent thermal expansion coefficient, and accurate chemical cure shrinkage can help to improve the accuracy on the stress and warpage prediction. This study has developed an evaluation method for the chemical cure shrinkage based on the measurement of the warpage of bimaterial model. The results show that FEA simulations without chemical cure shrinkage fail to accurately predict the package warpage. On the other hand, FEA simulations with chemical cure shrinkage are outlined, which show fair agreement with experimental measurements of package warpage over a range of temperatures. Furthermore, this study has evaluated the effect of silica filler percentage on the chemical cure shrinkage and confirmed that the chemical cure shrinkage decreases with the increase in silica filler percentage.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Chemical cure shrinkage and thermal shrinkage during transfer molding

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Figure 2

Dimension of bimaterial specimen

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Figure 3

Young’s modulus of epoxy molding compound

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Figure 4

Thermal expansion coefficients of epoxy molding compound

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Figure 5

Comparison of warpage based on shadow moiré, bimetal theory, and FEA (without cure shrinkage)

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Figure 13

Effect of EMC on PBGA warpage

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Figure 12

Effect of chemical cure shrinkage on FEA simulation of PBGA warpage

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Figure 11

Example of PBGA warpage measurement using shadow moiré (25°C)

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Figure 10

Example of PBGA warpage based on FEA

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Figure 9

FEA meshes of one quarter of PBGA

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Figure 8

Effect of filler percentage on chemical cure shrinkage

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Figure 7

Comparison of warpage based on shadow moiré, bimetal theory, and FEA (εchemical cure=0.21%)

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Figure 6

Example of warpage measurement using shadow moiré (125°C)

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