Numerical Analysis of the Welding Behaviors in Micro-Copper Bumps

Yeong-Maw Hwang,Bo-Syun Chen,Sheng-Rui Jian,Cheng-Tang Pan

doi:10.3390/met11030460

Yeong-Maw Hwang, Bo-Syun Chen + Show 2 more

Open Access

https://doi.org/10.3390/met11030460

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Abstract

In this study, three-dimensional simulations of the ultrasonic vibration bonding process of micro-copper blocks were conducted using the finite element method. We analyzed the effects of ultrasonic vibration frequency on the stress field, strain field, and temperature field at the copper bump joint surface. The results showed that the bonding process is successfully simulated at room temperature. The stress curve of the bonding process could be divided into three stages: stress rising stage, stress falling stage, and stress stabilization stage. Moreover, it was found that the end of the curve exhibited characteristics of a solid solution phase at higher frequencies. It is hypothesized that the high-density dislocations formed at this stage may result in conveyance channels that facilitate the atomic diffusion at the contact surface. The simulation results indicated that copper micro-bump bonding occurs at an ultrasonic frequency of 50 kHz or higher.

Highlights

Modern science and technology are booming, and the development of semiconductors has progressed from two-dimensional integrated circuits (2D IC) to three-dimensional integrated circuits (3D IC)
To achieve the above-mentioned goals, semiconductor manufacturers have proposed some key technologies in recent years, which can be divided into two categories: through silicon via (TSV) and micro-bump bonding technologies
The key feature of the TSV technology is the formation of a vertical channel inside the silicon substrate, which is filled with a selected metal [5]

Summary

Introduction

Modern science and technology are booming, and the development of semiconductors has progressed from two-dimensional integrated circuits (2D IC) to three-dimensional integrated circuits (3D IC). To achieve the above-mentioned goals, semiconductor manufacturers have proposed some key technologies in recent years, which can be divided into two categories: through silicon via (TSV) and micro-bump bonding technologies It is noted, that despite the recent progresses driven by the increasing demands of converting from 2D to 3D IC, there are still plenty of challenges and opportunities requiring tremendous research and development in improving the reliability of vertical connections. Low temperature copper-to-copper bonding (LTCCB) technology requires a lower temperature (573 K) and Metals 2021, 11, 460 shorter bonding time (100 s) compared to those of the conventional method (CM) [19] This is a promising process because it can be performed at ambient temperature without requiring special environmental conditions. The effects of the ultrasonic vibration frequency applied on the stress field, the strain field, and the temperature field at the interface between the two copper blocks are addressed in detail

Methodology

Simulation Assumptions

Modeling and Setting of Finite Element Analysis

Geometry and Dimensions

Solid Solution Time Point Advances with Frequency

Conclusions