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6803 |
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Thursday, September 17, 2020, Virtueller Raum 2 10:45 AM DVS CAMPUS - Prozessüberwachung |
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Reliability studies on power electronic modules silver sintered to non-DCB substrates |
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Nilavazhagan Subbiah* / University of Freiburg, IMTEK, Laboratory for Assembly and Packaging Technology, DE Juergen Wilde / IMTEK-Uni Freiburg, DE Anu Mathew/ Zentrum für Mikrotechnologien der TU Chemnitz, DE Rainer Dudek/ Fraunhofer ENAS, DE |
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Silver sintering technology has already been established as an alternative in the power electronics regime to replace soldering on DCB. New environmental regulations also stipulate this change in the electronic packaging industry. As the methods and processes for silver sintering are increasingly available, the need to diversify the substrate materials for silver sintering technique is also increasing. Most research works on silver sintering uses Direct Copper bonded substrates (DCB) due to its reliable thermal and electrical performance. Investigating silver sintering on some alternative substrates like high-temperature stable PCBs such as IS550H-PCB substrates, Insulated Metal Substrates (IMS) and Copper lead frames can diversify possible applications. Applying silver sintering to new substrates requires process optimization as each substrate has unique surface and thermomechanical properties. Typical operational and process environment of the modern power electronic modules involves high-temperature above 200 °C. The strength and reliability of the silver sintered joint is also greatly influenced by the CTE-mismatch of the materials. Alternative substrates and corresponding research works using silver sintering for applications at high-temperatures are limited. In this research, we investigate and establish the processes for each of these substrates (IS550H-PCB, IMS, Cu-lead frame) and compare it to conventional DCB substrates. Establishing silver sintering on these substrates can also enable sintering technology to be applied for wider range of applications where these non-DCB substrates are used. IS550H-PCB, IMS and Cu-lead frame are already widely used in power electronic applications with conventional techniques like solder and conductive adhesives. Each of the used substrates gives us a unique advantage as follows; IS550H-PCB substrates are based on benzoxazine material stable up to 200 °C. These high-temperature stable PCBs can enable high degree of miniaturization and integration of passive components in the power electronic circuits [1]. Insulated Metal Substrate has proven to be an efficient material in applications such as LED lighting, automotive applications, drives and power conversion [2]. IMS provides the functionality of a PCB with an added advantage of increased thermal performance. However, use of a dielectric layer in this substrate can be a limiting factor for high-temperature conditions. During the process development, the glass transition temperature of each layer in the IMS substrates has to be considered. Cu lead frames are a cheaper and widely used material in power electronics packaging. Hence, developing suitable processes for these materials with silver sintering will increase the scope of this technology. LTS 338-28 micro silver paste from Heraeus was used for all the assemblies. In this research work, process parameters for each substrate are established using Design of Experiment (DOE) by varying principle process parameters such as pressure (P), temperature (T) and time (t) [3]. The operational environment and process parameters also influence the lifetime of these modules. Lifetime of these sintered modules are also directly affected by their material properties (CTE, Youngs modulus), temperature and geometry of the chips and substrates. Influence of these parameters on the life time of the modules are analyzed using FEM simulations and compared to the experimental verification using active and passive temperature cycling tests. CTE mismatch in the assembly leads to thermomechanical stresses, it has a direct effect on the failure of these modules during operation. An optical Digital Image Correlation (DIC) technique is employed to study the out-of-plane warpage of these assemblies at different temperature. Measured warpage can be used to further extract the thermal stresses. Finite element analyses are carried out to study the thermo-mechanical behavior of different substrates with diode and IGBTs. The numerical analyses are done by using Abaqus software. Initially, warpage behaviors of the samples are studied to calculate the thermally induced stresses in the assemblies. Additionally, adjustment of the constitutive material properties can be made for simulation input. Warpage of the samples have been investigated by both simulation and experiment. The effects of porosity of 10% and 45% in the sintered layer is also studied during the simulation. It has been observed that, there is no significant difference in the warpage on the sample with 10% and 45% porosity in the sintered layer. The inference of warpage measurement from the simulation shows the thermal warpage is only slightly dependent on the porosity. A study on the behavior of Aluminum cladded copper wire based on nano-indentation is ongoing. Bond wires with different parameters like diameter of the wire bond, material concentration of Al and Cu (ratio 50:50, 40:60 etc) will be considered by simulation. This research aims at lifetime models of the assemblies on new substrate variants with sintered silver interconnect. The analysis of failure mechanism and failure modes, which occurs in the sintered silver, is also a main part of the research. Reference: [1] Alexander Schiffmacher, Lorenz Litzenberger, Juergen Wilde, and Till Huesgen, Silver Sintering on Organic Substrates for the Embedding of Power Semiconductor Devices, in Proc. IEEE Electronic Components and Technol. Conf. (ECTC), Las vegas, May 2019, DOI. 10.1109. [2] Dave Sommervold, Chris Parker, Steve Taylor, Garry Wexler, Optimizing the Insulated Metal Substrate Application with Proper Material Selection and Circuit Fabrication, Oiginally published in the IPC proceedings. [3]Cyril Buttay, Amandine Masson, Jianfeng Li, Mark Johnson, Mihai Lazar, et al.. Die Attach of PowerDevices Using Silver Sintering - Bonding Process Optimization and Characterization. HiTEN 2011,Jul 2011, Oxford, United Kingdom. pp.1-7. hal-00672619 |