Article : [ART188]

Info : REPONSE 1, le 06/05/2002.

Titre : W.D. ZHUANG, P.C. CHANG, F.Y. CHOU, R.K. SHIUE, Effect of solder creep on the reliability of large area die attachment, Microelectronics Reliability, Vol. 41, No 12, December 2001, pp. 2011-2021

Cité dans : [DIV334]  Recherche sur les mots clés power cycling of power device, mai 2002.
Cité dans :[REVUE280] Elsevier Science, Microelectronics Reliability, Volume 41, Issue 12, Pages 1915-2095, December 2001.

Adresse : Inst. of Mat. Sci. and Engineering National Dong Hwa University, Hualien 974, Taiwan
Source : Microelectronics Reliability v 41 n 12
Date : December 2001
Pages : 2011 - 2021
CODEN : MCRLAS
ISSN : 0026-2714
Année : 2001
Document_Type : Journal
Treatment_Code : Theoretical; Experimental
Language : English
Stockage :
Switches : power MOSFET
Lien : private/ZHUANG1.pdf - | Article | Journal Format-PDF (467 K)

Abstract :
High temperature solders have been widely used for power device die
attachment. One typical solder is Pb92.5In5Ag2.5, which is a ternary
eutectic alloy with a eutectic temperature of 310deg C. Such a Pb-based
solder has a low Young's modulus, a low yield strength, and a high strain
prior to failure. So it can be used to attach large size silicon die to
mismatched substrates. In this paper, stresses and strains have been
studied on a large size power MOSFET attachment using the Pb92.5In5Ag2.5
solders. A commercial finite element analysis software is employed as the
simulation tool. Three types of substrates, pure copper, copper-tungsten
composite, and pure molybdenum are used in the study, where molybdenum has
the closest coefficient of thermal expansion to silicon. In addition to
the plastic deformation simulation of the solder, a creep model of the
solder was incorporated due to the low melting temperature of the solder
alloy. Firstly, stresses and strains are calculated during the cooling
cycle after attachment. It is found that the creep strain is the dominant
plastic strain at low cooling rate ( Von Mises stress in the Si chip is decreased from 174 to 62.7 MPa after
adding creep strain. As expected, the maximum creep strain happens to the
die-to-copper substrate attach. Simulation on temperature cycling is done
from -55deg C to +150 deg C. The peak Von Mises stress occurs at the low
temperature extreme and holds steadily during the soaking period,
indicating insignificant contribution from creep. The Von Mises stress at
the high temperature extreme is much lower and decreases with holding
time. Significant plastic deformation of the solder layer is observed in
cooling cycles. For silicon to copper substrate attach, its plastic
deformation increases with each cycle. For all three substrates used,
considerable solder creep is observed at heating cycles. The creep strain
is much larger than the rate-independent plastic strain in the solder
alloy for all three types of substrates. It is concluded that solder creep
is the dominant factor affecting long term reliability of power
semiconductor die attachment.

Refrences : 34 Refs.

Accession_Number : 2001(56):660 COMPENDEX

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