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A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line

Published online by Cambridge University Press:  18 March 2014

Kewei Xiao ,
Khai D.T. Ngo  and
Guo-Quan Lu
Kewei Xiao
Affiliation:
Center for Power Electronics Systems, Virginia Tech, Blacksburg, Virginia 24061; and Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061
Khai D.T. Ngo
Affiliation:
Center for Power Electronics Systems, Virginia Tech, Blacksburg, Virginia 24061; and The Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061
Guo-Quan Lu*
Affiliation:
Center for Power Electronics Systems, Virginia Tech, Blacksburg, Virginia 24061; Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061; and The Bradley Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061
*
a)Address all correspondence to this author. e-mail: [email protected]
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Abstract

The low-temperature joining technique (LTJT) by silver sintering is being implemented by major manufacturers of power electronic devices and modules for bonding power semiconductor chips. A common die-attach material used with LTJT is a silver paste consisting of silver powder (micrometer- or nanometer-sized particles) mixed in organic solvent and binder formulation. It is believed that the drying of the paste during the bonding process plays a critical role in determining the quality of the sintered bond-line. In this study, a model based on the diffusion of solvent molecules and viscous mechanics of the paste was introduced to determine the stress and strain states of the silver bond-line. A numerical simulation algorithm of the model was developed and coded in the C++ programming language. The numerical simulation allows determination of the time-dependent physical properties of the silver bond-line as the paste is being dried with a heating profile. The properties studied were solvent concentration, weight loss, shrinkage, stress, and strain. The stress is the cause of cracks in the bond-line and bond-line delamination. The simulated results were verified by experiments in which the formation of bond-line cracks and interface delamination was observed during the pressure-free drying of a die-attach nanosilver paste. The simulated results were consistent with our earlier experimental findings that the use of uniaxial pressure of a few mega-Pascals during the drying stage of a nanosilver paste was sufficient to produce high-quality sintered joints. The insight offered by this modeling study can be used to develop new paste formulations that enable pressure-free, low-temperature sintering of the die-attach material to significantly lower the cost of implementing the LTJT in manufacturing.

Keywords

bondingkineticssintering
Type
Articles
Information
Journal of Materials Research , Volume 29 , Issue 8 , 28 April 2014 , pp. 1006 - 1017
Copyright
Copyright © Materials Research Society 2014 

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