Electronic devices using semiconductors such as insulated-gate bipolar transistors, metal–oxide–semiconductor field-effect transistors, and diodes are extensively used in electrical traction applications such as locomotive, elevators, subways, and cars. The long-term reliability of such power modules is then highly demanded, and their main reliability criterion is their power cycling capability. Thus, a power cycling test is the most important reliability test for power modules. This test consists in periodically applying a current to a device mounted onto a heat sink. This leads to power loss in the entire module and results in a rise in the semiconductor temperature. In this paper, the different kinds of semiconductors and power modules used for traction applications are described. Experimental and simulation methods employed for power cycling tests are presented. Modules' weak points and fatigue processes are pointed out. Then, a detailed statistical review of publications from 1994 to 2015 dealing with power cycling is presented. This review gives a clear overview of all studies dealing with power cycling that were carried out until now. It reveals the principal trends in power electronic devices and highlights the main reliability issues for which an important lack of knowledge remains.

Power Cycling Reliability of Power Module: A Survey

The evaluation of power cycling results needs correct measurement of the course of thermal resistance. Hence an accurate online measurement of the junction temperature is necessary. Different measurement and power cycling methods were evaluated. The method of measuring the voltage drop of the SiC MOSFET body diode pn-junction at low measurement current with sufficient negative gate-voltage was found most suitable one. In addition power losses during power cycling test should be generated in forward MOSFET-mode at high positive gate-voltage. Otherwise test results will not be application conform.

Power cycling methods for SiC MOSFETs

This paper explores the possibility of using Ag paste containing silicon carbide particles (SiC-p) as a novel high-temperature die-attachment solution for the design of power devices. The bonding structure used in this research was composed of silicon dies and a direct bonded copper (DBC) substrate. A SiC-p/microporous Ag composite structure was prepared by sintering a Ag microflake paste containing 2 wt% sub-micron SiC-p under mild conditions (250 °C and 0.4 MPa for 30 min). In addition to the Ag paste, the surface metallization of the DBC substrate was also evaluated in this research. Ag metallization layers deposited by electroplating and sputtering were compared, along with samples also containing a titanium (Ti) diffusion barrier layer between Cu and Ag. The results indicated that the SiC-p-containing Ag sinter paste showed better stability in storage tests than the paste without SiC-p at the temperatures such as 150, 250 and 350 °C. Additionally, the Ti diffusion barrier layer played an active role in preventing the oxidation of Cu and inter-diffusion between Cu and Ag during use at high temperatures exceeding 250 °C. The joint bonded by SiC-p-containing Ag paste on DBC substrate with Ti barrier layer exhibited excellent stability up to 1000 h at 150 and 250 °C.

Thermostable Ag die-attach structure for high-temperature power devices

The microstructure, thickness, porosity, and shear performance of the silver (Ag) sintering layers under different sintering pressures were investigated. Experimental results demonstrated that the thickness and the porosity of the sintering layer decreased when the sintering pressure varied from 5 MPa to 30 MPa. This densification phenomenon facilitated the enhancement of the Ag sintering layers. The shear strength was improved significantly from 44.19 MPa to 69.41 MPa when the sintering pressure increased from 5 MPa to 10 MPa. When the sintering pressure ranged from 10 MPa to 30 MPa, the shear strength presented a slow increase from 69.41 MPa to 73.38 MPa. According to the results of the failure analysis, fracture mode transformation was considered as the basic reason for this phenomenon. The increasing sintering pressure promoted the bonding of the nano-Ag particles during the sintering process. Consequently, the fracture of the sintered-Ag layer transformed from brittle fracture to ductile fracture because of the increasing sintering pressure. The delamination area between Cu and Ni layers coated on the bottom Mo plate was clearly enlarged with the increasing sintering pressure. The delamination between Cu and Ni layers coated on the bottom Mo plate turned to be the main failure mode when the sintering pressure was higher than 10 MPa.

/pdf/effect-of-sintering-pressure-on-the-porosity-and-the-shear-3bccn9o0r6.pdf

Effect of Sintering Pressure on the Porosity and the Shear Strength of the Pressure-Assisted Silver Sintering Bonding

Reliability experiments of sintered silver based interconnections by accelerated isothermal bending tests

Increasing the temperature in power electronic applications usually causes a decreasing lifetime and reliability. This study shows that packaging materials and technologies like silver sintering or gold germanium solders can easily deal with temperatures above 150°C. Furthermore the power cycling capability at increased temperatures can be much better than at room temperature. Active power cycling tests with 240 devices offered more cycles to failure at 120°C cooling temperature than at 40°C. The three tested sample groups consisted of silicon carbide diodes which were soldered (gold germanium/ tin lead) or silver sinter to copper-ceramic-substrates (DBCs). The reason behind this effect is the decreasing of Young's modulus, yield strength and ultimate strain over temperature. The materials are getting much more ductile and robust against load cycling at higher temperatures. The three mentioned material properties were measured by nano-indentation and tensile tests up to 200°C. In summary, packaging materials and their properties should be adopted to the intended application and its requirements, starting with a temperature-dependent analysis.

Increasing the lifetime of electronic packaging by higher temperatures: Solders vs. silver sintering

Extending the lifetime of power electronic assemblies by increased cooling temperatures

Increasing the temperature in power electronic applications usually causes a decreasing lifetime and reliability This study shows that packaging materials and technologies, such as silver-sintering or gold germanium solders combined with silicon-carbide devices, can easily deal with temperatures above 200 °C/392 °F Furthermore, lifetime tests (active power cycling) with 300 devices offered more cycles to failure at 120 °C/248 °F heat sink temperature than at 40 °C/104 °F (same ΔT) for silver-sintered samples and gold-germanium solders SAC305 and tin-lead solders were also tested for comparison but could not withstand the harsh conditions The samples were silicon carbide diodes attached to copper-ceramic-substrates (DBCs) For testing, the devices were heated up by current to achieve a 130 K temperature swing at different coolant temperatures (250 °C/482 °F maximum temperature) The reason behind the higher lifetime at elevated temperatures is the increasing ductility over temperature The materials capability against thermo-mechanical stress is better at higher temperatures, while creep effects are not dominating This effect can be used especially for high temperature application with extraordinary requirements on lifetime and reliability Analytical models based on stress strain calculations can explain this material behavior Together with an in-situ measurement of the thermal impedance the models can predict the lifetime consumption of the application and thereby upcoming maintenance

High temperature die-attach materials for aerospace power electronics: Lifetime tests and modeling

Increas ing the temperature in power electronic applications usually causes a decreasing lifetime and reliability. This study shows that packaging materials and technologies, such as silver-sintering or gold germanium solders combined with silicon-carbide devices, can easily deal with temperatures above 200 °C/392 of. Furthermore, lifetime tests (active power cycling) with 300 devices offered more cycles to failure at 120 °C/248 of heat sink temperature than at 40 °C/104 of (sameT) for silver-sintered samples and gold­ germanium solders. SAC305 and tin-lead solders were also tested for comparison but could not withstand the harsh conditions. The samples were silicon carbide diodes attached to copper-ceramic-s ubstrates (DBCs). For testing, the devices were heated up by current to achieve a 130 K temperature swing at different coolant temperatures (250 °C/482 of maximum temperature). The reason behind the higher lifetime at elevated temperatures is the increasing ductility over temperature. The materials capability against thermo­ mechanical stress is better at higher temperatures, while creep effects are not dominating. This effect can be used especially for high temperature application with extraordinary requirements on lifetime and reliability. Analytical models based on stress strain calculations can explain this material behavior. Together with an measurement of the thermal impedance the models can predict the lifetime consumption of the application and thereby upcoming maintenance.

Adam Tokarski

Papers

Increasing the lifetime of electronic packaging by higher temperatures: Solders vs. silver sintering

Extending the lifetime of power electronic assemblies by increased cooling temperatures

High temperature die-attach materials for aerospace power electronics: Lifetime tests and modeling

Power Electronics: Lifetime Tests and Modeling