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Microelectronics Reliability, Volume 52, Issues 9–10, September–October 2012, Pages 2314-2320
L.A. Navarro, X. Perpinà, M. Vellvehi, V. Banu, X. Jordà
Institut de Microelectrònica de Barcelona, Centre Nacional de Microelectrònica IMB-CNM (CSIC), Campus UAB Bellaterra, 08193 Cerdanyola del Valles, Barcelona, Spain
Abstract
This work aims at the experimental thermo-mechanical evaluation of different die-attach materials using test vehicles representing the final packaging assemblies. The experiments are based on a harsh thermal cycling system and analysis tools for evaluating the final die-attach integrity. In this paper, we present a finite elements simulation analysis of the test vehicle, the design of the harsh thermal cycling system (−80 to 400 °C) and the first results obtained with AuGe and PbSnAg as die-attach alloys.
Additional Information
Nowadays, there is an increasing interest for high-temperature power electronics systems, mainly driven by the development of wide band-gap semiconductor devices. Space and harsh environment electronics are two of the main application areas. However, determining the appropriate technology and its testing procedures as a response to these application niches is open. Significant research efforts devoted to this field are currently addressed, where packaging of power devices have recently attracted much attention.
In high temperature packaging technology, one of the most critical elements is the semiconductor to substrate joint (die-attach). At this moment, several efforts are invested in determining which could be the best solution for high temperature die-attach: the thermo-mechanical properties of that material should be a trade-off between their surface adherence and plasticity behavior (stress absorption). There are several candidates that deal with these requirements: solder alloys (such as AuSn, PbSnAg, AuGe, AuSi), nano-particle (typically Ag) sintering and transient liquid phase bonding.
This work presents an experimental approach to perform the evaluation of high temperature die-attaches by means of a test vehicle submitted to thermal cycling tests. Thermal cycles are carried out with a specifically designed set-up. This set-up is based on a hot-cold plate located within a Nitrogen chamber that fixes the target temperature profiles (-80ºC – 400ºC) to test vehicles. The test vehicle used in this work has been a copper substrate, on which four Silicon dies have been soldered with the studied die-attach material. Moreover, the experimental procedure followed for its analysis has been based on acoustic microscopy and die shear tests.
As a case study, the first results corresponding to thermal cycling tests ranging from -65ºC to 275ºC for the evaluation of AuGe and PbSnAg die-attaches have been presented. PbSnAg is a well-known die-attach material and AuGe is one of the best solutions among all lead-free die-attach materials for high temperature applications. The obtained results have been compared between them using those from PbSnAg as a reference. Besides, their basic thermo-mechanical behaviour has been also discussed on the basis of simulation results, being in good agreement. As a main conclusion, PbSnAg die-attach presents a higher plastic behaviour which absorbs the stresses, delaying the apparition of delaminations in the die-attach.
In future works, we will extend this analysis to SiC and other die-attach materials. More accurate definition of the materials properties for thermo-mechanical simulation will be also carried out.
