SMTA International Conference Proceedings

Reliability Assessment of Die Attachment Materials for High Power Chip Package Design

Authors: Hanxue Liu and Fei Xie
Company: RelEng Technologies, Inc. and Engent, Inc.
Date Published: 9/17/2017   Conference: SMTA International

Abstract: High power chips are well seen in applications of such as lighting, communications, and microprocessors. With power density reaching the level of 8~9W/mm2, packaging of such chips faces increasing challenges in terms of reliability. An essential one is to maintain robust thermal dissipation as well as reliable electrical connection. Therefore, the assessment to figure out the required material properties for die attach must be developed.

In this paper, the performable assessment process for die attach materials is proposed and implemented. During the preliminary package scheme selection stage, finite element method (FEM) is available considering efficiency and cost. Also, the key factors which have influence on engineering credibility of assessment such as variations of material properties, zero thermal stress setup, thermal cycle and thermal shock test conditions, and crack in the substrate attachment layer are discussed in case study. Firstly, a mechanical 3D FEA model is created matching the real dimensions of the configuration in the stack up of die, die attachment material, substrate, substrate attachment material, and heat sink. The Anand model which describes plasticity and creep is applied to represent the constitutive behavior. Then, this paper details a physics of failure approach to calculate failure cycle numbers by fatigue model based on strain energy density which describes crack initiation and propagation. The results showed good agreement with previous study and indicated engineering credibility of assessment process. Moreover, the device under investigation is unlikely to pass a 500-cycle test given a 30% crack length as a failure criterion. Throughout the implementation, it is concluded that the simulation results are credible and the influential factors such as the temperature ramp rate and calculation approach are major contributors during assessment process.

Key Words: 

reliability assessment, die attach, high power chip, influential factors

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