Power cycling test and failure analysis of molded Intelligent Power IGBT Module under different temperature swing durations

Molded IGBT modules are widely used in low power motor drive applications due to their advantage like compactness, low cost, and high reliability. Thermo-mechanical stress is generally the main cause of degradation of IGBT modules and thus much research has been performed to investigate the effect of temperature stresses on IGBT modules such as temperature swing and steady-state temperature. The temperature swing duration is also an important factor from a real application point of view, but there is a still lack of quantitative study. In this paper, the impact of temperature swing duration on the lifetime of 600 V, 30 A, 3-phase molded Intelligent Power Modules (IPM) and their failure mechanisms are investigated. The study is based on the accelerated power cycling test results of 36 samples under 6 different conditions and tests are performed under realistic electrical conditions by an advanced power cycling test setup. The results show that the temperature swing duration has a significant effect on the lifetime of IGBT modules. Longer temperature swing duration leads to the smaller number of cycles to failure. Further, it also shows that the bond-wire crack is the main failure mechanism of the tested IGBT modules.     

Reliability of AlN substrates and their solder joints in IGBT power modules

The reliability of IGBT modules was investigated with respect to the metallized ceramic (substrate) and the solder layer between the substrate and copper baseplate. Thermal cycles were performed between −55°C and +150°C on substrates based on different technologies and from various manufacturers. An incipient delamination of the metallization could be predicted from the mechanical resonance frequency. The warping of the substrates after cycling due to crack propagation and the adhesion of the metallization were determined. Thermal and active-power cycles were performed on 1200 A / 3.3 kV IGBT power modules to investigate the reliability of the solder joint between substrate and baseplate.     

Uneven temperature effect evaluation in high-power IGBT inverter legs and relative test platform design

This paper presents a high-power IGBT testing platform for uneven temperature conditions and its design criteria. Considering the influence of layout parasitic parameters on the measurement results, commutation rules and independent junction temperature control, a universal high-power switching characterization platform is built and operated. Importantly, it is capable of 3.6 kA current level test requirement, which can cover the largest current level for the state-of-the-art IGBT modules. To improve the test accuracy of double pulse test method, a compensation algorithm is proposed to eliminate the circuit power loss under high current test conditions. Moreover, in order to simulate the uneven junction temperature effects occurring in real life, the junction temperatures of inspected IGBT and freewheeling diode are controlled independently. Quantitative analyses of the switching characteristics for junction temperatures up to 125 °C are performed.     

Performance and reliability testing of modern IGBT devices under typical operating conditions of aeronautic applications

As for railway traction applications, aeronautical power electronics implies high power density handling. Moreover typical aeronautical applications impose a harsh thermal environment. SiC technology has recently emerged for high power and high temperature application, but is not yet mature enough. Consequently it is still important to push the silicon devices temperature limits in order to increase the amount of switched power. Device ageing is accelerated and there exists the risk of catastrophic failure by thermal runaway. In order to design correctly high temperature power systems, knowing the IGBT characteristics at extended temperature ranges becomes essential. This paper describes an experimental setup and test procedure conceived to experiment with different available IGBT technologies at temperatures beyond the limits rated by manufacturers (?55 °C, +175 °C). The aim is to characterize the devices for a better understanding and optimized safe application. This will ease prototyping for future development of IGBT modules in aircraft.     

Reliability and RF performance of BGA solder joints with plastic-core solder balls in LTCC/PWB assemblies

In this paper board-level reliability of low-temperature co-fired ceramic (LTCC) modules with thermo-mechanically enhanced ball-grid-array (BGA) solder joint structure mounted on a printed wiring board (PWB) was experimentally investigated by thermal cycling tests in the 0–100 °C and −40 to 125 °C temperature ranges. The enhanced joint structure comprised solder mask defined (SMD) AgPt pad metallization, eutectic solder and plastic-core solder balls (PCSB). Similar daisy-chained LTCC modules with non-collapsible 90Pb10Sn solder spheres were used for a reference test set. The reliability of the joint structures was analyzed by resistance measurements, X-ray microscopy, scanning acoustic microscopy (SAM) and SEM/EDS investigation. In addition, a full-wave electromagnetic analysis was performed to study effects of the plastic-core material on the RF performance of the LTCC/BGA package transition up to millimeter-wave frequencies. Thermal cycling results of the modules with PCSBs demonstrated excellent fatigue performance over that of the reference. In the harsher cycling test, Weibull’s shape factor β values of 7.9 and 4.8, and characteristic lifetime θ values of 1378 and 783 were attained for the modules with PCSBs and 90Pb10Sn solder spheres, respectively. The primary failure mode in all test assemblies was fatigue cracking in eutectic solder on the ceramic side.     

Accelerated active ageing test on SiC JFETs power module with silver joining technology for high temperature application

This paper presents the accelerated active power cycling test (APCT) results on SiC JFETs power module dedicated to operate at high temperature. This study partly focuses on the new chip joining technology (LTJT), which permit to use SiC JFETs transistors at higher temperatures. We present the different die attachments tested with high temperature lead solder and silver sintering joining technologies. Active power cycling results for high junction temperature T_jmax = 175 °C with ΔT_j = 80 K to perform an evaluation of main damages during active test are carried out and a comparison between lead and silver chip joining technologies is presented.     

Enhanced power cycling performance of IGBT modules with a reinforced emitter contact

A typical emitter contact of an IGBT consists of a front metallization and bond wires. In this study, the power cycling performance of a special emitter contact design is experimentally verified. The emitter contact includes a metal plate, which is Ag-sintered to the metallization and wire bonded on the top surface. Either Cu or Al bond wires were implemented. Power cycling tests were performed to investigate the performance of such IGBT modules. The results were very promising and a cycling lifetime was achieved, which is about 20 times higher than the lifetime of typical IGBT modules. For a better understanding of the experimental results, the electrical and thermal response of the IGBT modules were simulated by FEM. The results of this study, provide a key for high-reliability designs of the emitter contact of IGBT modules with superior power cycling capability.     

Fast power cycling protocols implemented in an automated test bench dedicated to IGBT module ageing

This paper presents fast test protocols for ageing IGBT modules in power cycling conditions, and a monitoring device that tracks the on-state voltage V_CE and junction temperature T_J of IGBTs during ageing test operations. This device is implemented in an ageing test bench described in previous papers, but which has since been modified to perform fast power cycling tests.The fast test protocols described here use the thermal variations imposed on IGBT modules by a test bench operating under Pulse Width Modulation conditions. This test bench reaches the maximal values of power cycling frequencies attainable with a given module packaging in order to optimize test duration.The measurement device monitors V_CE throughout the ageing test that is needed to detect possible degradations of wire bonds and/or emitter metallization. This requires identifying small V_CE variations (a few dozen mV). In addition, the thermal swing amplitude of power cycling must be adjusted to achieve a given ageing protocol. This requires measuring junction temperature evolution on a power cycle, which is carried out by means of V_CE measurement at a low current level (100 mA).Experimental results demonstrate the flexibility of this test bench with respect to various power cycling conditions, as well as the feasibility of the proposed on-line monitoring methods.     

Epitaxial growth of LaAlO3 on Si(0 0 1) using interface engineering

In this work, the potentiality of molecular beam epitaxy techniques to prepare epitaxial lanthanum aluminate (LaAlO₃) films on Si(0 0 1) is explored. We first demonstrate that the direct growth of LaAlO₃ on Si(0 0 1) is impossible : amorphous layers are obtained at temperatures below 600 °C whereas crystalline layers can be grown at higher temperatures but interfacial reactions leading to silicate formation occur. An interface engineering strategy is then developed to avoid these reactions. SrO and SrTiO₃ have been studied as buffer for the subsequent growth of LaAlO₃. Only partial LaAlO₃ epitaxy is obtained on SrO whereas high quality layers are achieved on SrTiO₃. However both SrO and SrTiO₃ appear to be unstable with respect of Si at the growth temperature of LaAlO₃ (700 °C). This leads to the formation of relatively thick amorphous interfacial layers. Despite their instability at high temperature, these processes could be used for the fabrication of twins-free LaAlO₃ templates on Si, and for the fabrication of complex oxide/Si heterostructures for various applications.     

Growth of epitaxial Pr2O3 layers on Si(1 1 1)

The growth of Pr₂O₃ layers on Si(1 1 1) has been studied by X-ray diffraction, Low-energy electron diffraction (LEED) and atomic force microscopy (AFM). Pr₂O₃ starts to grow as a 0.6-nm thick layer corresponding to one unit cell of the hexagonal phase (1 ML). The X-ray results indicate that layers thicker than 0.6 nm do not grow with the hexagonal phase. Growth takes place at a sample temperature of 500–550 °C. Annealing of the monolayer in UHV at a temperature above 700 °C leads to the formation of Pr₂O₃ and PrSi₂ islands. Silicide islands are found only at annealing in UHV and do not occur at annealing in oxygen atmosphere of 10⁻⁸ mbar. The LEED pattern after heating to 730 °C shows a (2×2) and (√3×√3) superstructure and after heating to 1000 °C a (1×5) superstructure occurs. The superstructures seen in the LEED pattern arise from silicide structures in the area between the islands. The silicide remains on the surface and cannot be removed with flashing to 1100 °C. Further deposition of Pr₂O₃ on the surface covered with silicide phases does not lead to growth of ordered layers.     

Low temperature electrical measurements of silicon bipolar monolithic microwave integrated circuit (MMIC) amplifiers

Outdoor telecommunications equipment can be exposed to ambient temperatures as low as −55 °C. However, microwave devices used in telecommunications infrastructure equipment are generally not rated to such low temperature. This paper assesses scattering parameters (S-parameters), the output power at 1 dB gain compression, and DC characteristics of a silicon bipolar monolithic microwave integrated circuit (MMIC) amplifier at low temperatures.     

The effect of electro-thermal parameters on IGBT junction temperature with the aging of module

This paper presents the effect of the change of electro-thermal parameters on IGBT junction temperature with module aging. Five IGBT modules are subjected to advance power thermal cycling, and IGBT I–V characterization, switching loss, and transient thermal impedance curve are measured every 1000 power thermal cycles. Then, electro-thermal models of IGBT module under power thermal cycles were built by change electro-thermal parameters, and the influence of various parameters of the electro-thermal model on the junction temperature was researched respectively. Experimental results demonstrate that IGBT collector-emitter voltage, switching loss and thermal resistance increase more quickly with the aging process of module. Simulation results indicate that the variations of electro-thermal parameters have crucial influences on the IGBT junction temperature. After 6000 power thermal cycles, the IGBT steady state junction temperature mean and variation are increased 1.97 K and 0.1656 K over its initial value, respectively. The relative temperature rise is 38.10% and relative temperature variation is 15.08% after 6000 power thermal cycles. The rise in switching loss increases both the steady state junction temperature mean and variation. The change of thermal impedance has great influence on the steady state junction temperature mean, but has little effect on steady state junction temperature variation.     

Influence of substrate temperature to prepare (1 0 3) oriented AlN films

(1 0 3) Oriented AlN films is an attractive piezoelectric material for the applications on surface acoustic wave (SAW) and film bulk acoustic wave (FBAR) devices. As regards the SAW properties of the (1 0 3) oriented AlN films, the electromechanical coupling constant (K²) is larger than the (0 0 2) oriented AlN films. As regards the bulk acoustic wave (BAW) properties of (1 0 3) oriented AlN films, it can excite a quasi-shear mode (velocity = 5957 m/s, K² = 3.8%) that can be used for FBAR liquid sensor. In this research, the (1 0 3) oriented AlN films were successfully prepared on the silicon substrate by rf magnetron sputtering. Different temperatures (100 °C, 200 °C, 300 °C, and 400 °C) were used in this experiment process. The crystalline structure of films was determined by X-ray diffraction (XRD) and the surface microstructure was investigated by the atomic force microscope (AFM). The result exhibited the optimal substrate temperature is 300 °C. The optimal (1 0 3) oriented AlN films have the strongest XRD intensity, the smallest full width at half maximum (FWHM) value (0.6°), the largest grain size (15.8 nm) and the smoothest surface (Ra = 3.259 nm).     

Assessment of temperature and voltage accelerating factors for 2.3–3.2 nm SiO2 thin oxides stressed to hard breakdown

The temperature and voltage acceleration for a large database of time dependent dielectric breakdown in 2.3 and 3.2 nm SiO₂ oxides is investigated. All results deal with the time to hard breakdown which is defined when a typical high current limit (1 mA) at operating voltage is reached rather than detecting the first current change as is conventionally done. Using an accurate experimental error evaluation, long range data are compared for consistency to the predictions of various state-of-the-art extrapolation models used to qualify these oxides, to point out which one describes the data best. The activation energies corresponding to the dominant degradation mechanisms are extracted over a temperature range from 50 °C to 125 °C for N type substrate stressed in accumulation regime. The voltage extrapolation models are compared for P and N type substrate with positive stress polarity on the gate. It is verified that a TDDB power voltage law is well predictive for both P substrate in inversion regime and N substrate in accumulation regime.     

Effects of current density and chip temperature distribution on lifetime of high power IGBT modules in traction working conditions

This paper deals with ageing parameters of high power IGBT modules in traction applications. Using the results of a great number of power cycling tests on 400A modules, it shows that, in addition to the junction temperature excursion, other parameters like the maximal chip temperature and the current density are involved in thermal fatigue failures. Besides, contact temperature measurements achieved on IGBT chip surface in cycling conditions to localise the maximal thermomechanical stress are presented and correlated with modules failure analysis. The role of the current density in the ageing process is finally shown by determining its influence on the temperature gradient on chip surface.     

Temperature compensation of piezoresistive micro-machined porous silicon pressure sensor by ANN

Porous silicon based micro-machined peizoresistive pressure sensors are fabricated and tested in the range of 0–1 bar and temperature range of 25–80 °C. The dependence of pressure sensitivity on the variation of ambient temperature is investigated. An intelligent online temperature compensation scheme using ANN technique has been described. The proposed scheme leads to an error reduction of approximately 98% from temperature uncompensated value. A hardware implementation of the proposed scheme using micro-controller is also described.     

Thermal fatigue endurance of collapsible 95.5Sn4Ag0.5Cu spheres in LTCC/PWB assemblies

The behavior of thermomechanically loaded collapsible 95.5Sn4Ag0.5Cu spheres in LTCC/PWB assemblies with high (LTCC/FR-4; ΔCTE 10 ppm/°C) and low (LTCC/Arlon; ΔCTE < 10 ppm/°C) global thermal mismatches was studied by exposing the assemblies into two thermal cycling tests. The characteristic lifetimes of the LTCC/FR-4 assemblies, tested over the temperature ranges of 0–100 °C and −40 to 125 °C, were 1475 and 524 cycles, respectively, whereas the corresponding values of the LTCC/Arlon assemblies were 5424 and 1575 cycles. According to the typical requirements for the industrial lifetime duration of solder joints, the former values are inadequate, whereas the latter are at an acceptable level in a few cases. Furthermore, the global thermal mismatch affected the thermal fatigue behavior of the 95.5Sn4Ag0.5Cu spheres in the temperature range of −40 to 125 °C.     

Optimisation of the number of IGBT devices in a series-parallel string

High-power semiconductor switches can be realised by connecting existing devices in series and parallel. The number of devices in series depends on the operating voltage of an application and the individual device voltage rating. For a given application, the use of higher voltage rated IGBTs leads to a fewer number of devices and vice versa. The total power loss of the series string equals to the sum of individual IGBT power losses and total loss increases with the increase in operating frequency. The level of increase in power loss depends on the device characteristics. For high current operation, the minimum number of devices depends on the current rating of individual device. In this paper, series IGBT string of six 1.2 kV, four 1.7 kV, two 3.3 kV and a single 6.5 kV IGBTs are simulated for a 4.5 kV/100 A application and power losses are analysed for different frequencies and duty cycles. This power loss analysis is extended for commercial IGBTs to compare the simulation results. The number of devices for minimum power loss depends on operating frequencies and power savings are significant both at low and high frequencies. In addition to the power losses, the other important issues in optimising the number of IGBTs are described in this paper. When IGBT modules are connected in parallel the principle of derating is applied to obtained reliable operation. This is explained with some examples.     

Effects of different bonding parameters on the electrical performance and peeling strengths of ACF interconnection

The effects of different bonding parameters, such as temperature, pressure, curing time, bonding temperature ramp and post-processing, on the electrical performance and the adhesive strengths of anisotropic conductive film (ACF) interconnection are investigated. The test results show that the contact resistances change slightly, but the adhesive strengths increase with the bonding temperature increased. The curing time has great influence on the adhesive strength of ACF joints. The contact resistance and adhesive strength both are improved with the bonding pressure increased, but the adhesive strengths decrease if the bonding pressure is over 0.25 MPa. The optimum temperature, pressure, and curing time ranges for ACF bonding are concluded to be at 180–200 °C, 0.15–0.2 MPa, and 18–25 s, respectively. The effects of different Teflon thickness and post-processing on the contact resistance and adhesive strength of anisotropic conductive film (ACF) joints are studied. It is shown that the contact resistance and the adhesive strength both become deteriorated with the Teflon thickness increased. The tests of different post-processing conditions show that the specimens kept in 120 °C chamber for 30 min present the best performance of the ACF joints. The thermal cycling (−40 to 125 °C) and the high temperature/humidity (85 °C, 85% RH) aging test are conducted to evaluate the reliability of the specimens with different bonding parameters. It is shown that the high temperature/humidity is the worst condition to the ACF interconnection.     

High temperature characterization of high-κ dielectrics on SiC

We have fabricated thin catalytic metal–insulator–silicon carbide based structure with palladium (Pd) gates using TiO₂ as the dielectric. The temperature stability of the capacitor is of critical importance for use in the fabrication of electronics for deployment in extreme environments. We have evaluated the response to temperatures in excess of 450 °C in air and observed that the characteristics are stable. Results of high temperature characterization are presented here with extraction of interface state density up to 650 °C. The results show that at temperatures below 400 °C the capacitors are stable, with a density of interface traps of approximately 6×10¹¹ cm² eV⁻¹. Above this temperature the C–V and G–V characteristics show the influence of a second set of traps, with a density around 1×10¹³ cm² eV⁻¹, which is close to that observed for slow states near the conduction band edge. The study of breakdown field as a function of temperature shows two distinct regions, below 300 °C where the breakdown voltage has a strong temperature dependence and above 300, where it is weaker. We hypothesize that the oxide layer dominates the breakdown voltage at low temperature and the TiO₂ layer above 300 °C. These results at high temperatures confirms the suitability of the Pd/TiO₂/SiO₂/SiC capacitor structure for stable operation in high temperature environments.