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Numerical study of the integrated circuit package cylindrical copper bump atomic migration coupled field

Author: LiYan
Tutor: HuangHongZhong
School: University of Electronic Science and Technology
Course: Mechanical Design and Theory
Keywords: IC packaging Cu-Pillar bump atomic migration finite element method
CLC: TN405
Type: Master's thesis
Year: 2010
Downloads: 53
Quote: 0
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Abstract

With further miniaturization and harsh service loading, solder joint of integrated circuit (IC) will suffer the atomic migration. Cu-Pillar Bumps is a new, ultra-high-density flip-chip interconnect form, which will become the mainstream next-generation IC packaging technology. This paper aims to investigate electromigration, thermomigration and stressmigration of Cu-Pillar Bumps in coupled field via field theory, kinetic theory and viscoplastic thermal mechanical analysis. Through finite element method to analyze the specific model, extract the key parameters of atom migration, this work investigated the mechanism of atomic migration. At first, we would investigate electromigration, thermomigration stressmigration of Cu-Pillar Bumps individually. Then we conducted a comprehensive study of the three migration conditions in a multi-field coupling under different currents.The IC package solder joints is under current stressing at most time.We used the finite element method to simulate a specific model under of different currents. By which we got a clear picture of its current distribution, and draw the maximum current density and regional values to confirm the "suspicious" and the priority place in which electromigration will occure. It is shown that electromigration resistance of Cu-Pillar Bumps is improved because solder is far away from the current blocking area. We calculated the force from thermal gradient, then found that the force due to thermal gradient can greatly affecte electromigration. Thermomigration must be a hidden failure.IC package solder joints have to face a difference of temperature in its inner. This is due to the difference of the thermal properties and electrical resistivity among didifferent materials. In this paper, we simulated a specific model under temperature load. We obtained the temperature gradient and stress distribution in Cu-Pillar Bumps. The temperature is very important in the atomic migration. We set the the chip at 125℃, then found that thermal stress gradient can be significant to make the atomic migration occur. Also, the force is bigger than the force from temperature gradient. It indicates that under temperature load, stress migration can occur in the solder joints. Under current stressing, Cu-Pillar Bumps suffer the atomic migration in coupling fields. Can we get the right mechanism of the atomic migration only afer we give careful consideration on the force fome electromigration, thermal stress and temperature gradient.In this paper, we investigated the atoms migration (electromigration, thermomigration, stressmigration) of Cu-Pillar Bump in the multi-field (electric field, thermal field and force field) to analyze the failure mode and mechanism of atomic migration. It is expected that we would got a major breakthrough improvement in the atomic migration of IC package reliability.

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