Patrick McCluskey

Physics-of-Failure, Condition Monitoring, and Prognostics of Insulated Gate Bipolar Transistor Modules: A Review

Recent growth of the insulated gate bipolar transistor (IGBT) module market has been driven largely by the increasing demand for an efficient way to control and distribute power in the field of renewable energy, hybrid/electric vehicles, and industrial equipment. For safety-critical and mission-critical applications, the reliability of IGBT modules is still a concern. Understanding the physics-of-failure of IGBT modules has been critical to the development of effective condition monitoring (CM) techniques as well as reliable prognostic methods. This review paper attempts to summarize past developments and recent advances in the area of CM and prognostics for IGBT modules. The improvement in material, fabrication, and structure is described. The CM techniques and prognostic methods proposed in the literature are presented. This paper concludes with recommendations for future research topics in the CM and prognostics areas.

An Interactive Multistage ε-Inequality Constraint Method For Multiple Objectives Decision Making

Multiple objectives decision making (MODM) in engineering design refers to obtaining a preferred optimal solution in the context of conflicting design objectives. Problems with multiple objectives do not have a unique optimal solution but a set of Pareto optimal solutions. This paper presents a new interactive multistage MODM method which captures a decision maker’s preference structure in order to obtain a preferred Pareto solution even for non-convex problems. Representative subsets of an entire Pareto optimal set are generated and expanded based on the decision maker’s preference. The e-constraint method is used to constrain the multiple objectives problem based on the decision maker’s feedback. In addition, ideas from an interactive weighted Tchebycheff approach are applied to reduce the feasible region at each stage, ensuring that the process eventually converges to a preferred solution. The method is demonstrated with two examples: (i) a simple two-bar truss design, and (ii) a more complicated problem in power electronic module design.

Intermetallic growth on PWBs soldered with Sn3.8Ag0.7Cu

This paper describes the nature of the intermetallic phases observed at the interface and in the bulk of Sn3.8Ag0.7Cu solder immediately after reflow on PWBs coated with a variety of commercial plating systems. It also discusses the growth of these intermetallic phases after aging at homologous temperatures of 0.8Tm, 0.85Tm and 0.9Tm for 10, 100 and 1000 hours. The following board plating systems were investigated: organic solderability preservative (OSP) over bare copper, immersion tin, immersion silver, and immersion gold over electroless nickel. This study revealed that the composition, microstructure, and thickness of intermetallics at the interface were strongly dependent on the plating system. The effect of the bulk and interface microstructure on the shear strength of the joints was also investigated. For all plating systems, the shear strength of the solder joints did not degrade with aging, and the failure mechanism continued to be cohesive failure through the bulk of the solder.

Thermomechanical analysis of gold-based SiC die-attach assembly

The thermomechanical stresses due to mismatch of the coefficients of thermal expansion (CTE) of the base material (SiC) and the packaging has a significant impact on the stresses in MEMS pressure sensors used in high-temperature applications, to 600/spl deg/C. The pressure sensor studied essentially consists of a SiC die attached to an AlN substrate using a gold die attach. Characterization of the stress distribution within the die attach, die and substrate along with the fatigue resistance of the die attach at 600/spl deg/C is essential to estimating the reliability of the packaging structure. A parametric study has been performed using nonlinear finite element analysis to optimize the die-attach thermomechanical performance at high temperatures. This study includes the effects of varying porosity levels and varying reference temperatures (stress-free temperature). This study also provides information about the mechanical deformations of the pressure sensor due to the thermomechanical load, which must be compensated, for the effective performance of the pressure sensor. The outcome of the study provides guidelines to optimize the design of the pressure sensor.

Popcorning in PBGA Packages During IR Reflow Soldering

Plastic ball grid arrays (PBGAs) have been gaining increasing industry acceptance as potentially the lowest cost packages for high pin count applications. The main factors for their success include the inherent low cost of plastic packages, the high yields achievable with existing assembly equipment, the density advantages of an area array and, in many cases, superior electrical performance. The reliability of these packages with respect to solder joint fatigue has been extensively studied; however, little has been published on their reliability with respect to moisture‐related failure mechanisms during assembly, such as popcorning. In this study, two types of plastic ball grid array packages, a 225‐lead full matrix array and a 256‐lead perimeter array, which were preconditioned by baking at 125°C for 24 hours followed by exposure to 85°C and 30% relative humidity for 168 hours, were then subjected to three passes of simulated infra‐red reflow at 1°C/s and 0.67°C/s. Subsequent examination using scanning a...

Reliable use of commercial technology in high temperature environments

Abstract Over 97% of all integrated circuits produced today are available only in plastic encapsulated, surface mountable, commercial grade or industrial grade versions. This is especially true for the most advanced technologies, such as high-speed microprocessors. The cost, availability, and functionality advantages of these devices are causing many electronics manufacturers to consider using them in elevated temperature applications such as avionics and automotive under-hood electronic systems to ensure early affordable access to leading edge technology. However, manufacturers only guarantee the operation of commercial devices in the 0°C to 70°C temperature range, and industrial devices in the −40°C to 85°C temperature range. This paper describes the first study which addresses the reliability of plastic encapsulated microcircuits (PEMs) in the range from 125°C to 300°C, well outside the manufacturers suggested temperature limits. Previous work has indicated that PEMs sold for use in the commercial and industrial temperature ranges can often operate within the manufacturers suggested electrical parameter specifications at much higher temperatures. For example, in this study the Motorola MC68332 microcontroller, which is widely used in avionic systems, remained fully functional to 180°C. This is in accordance with previous work that indicated no fundamental constraints to the operation of silicon devices at temperatures up to 200°C. However, this study also revealed that industrial grade, plastic encapsulated MC68332 devices had less than half the lifespan at 180°C than similar MC68332 devices packaged in hermetic ceramic packages. In addition to the MC68332, the other nine types of plastic components studied had a shorter lifespan at 180°C than their ceramic packaged counterparts. Outgassing of flame-retardants with the associated catalysis of the growth of intermetallics was determined to be the principal cause of failure in the plastic components. Further studies conducted on 84-lead plastic quad flatpack (PQFP) leadframes encapsulated in two different molding compounds revealed that the plastic encapsulant itself begins to lose its ability to insulate leads at temperatures greater than 250°C and can actually combust at temperatures greater than 300°C. Both insulation resistance degradation and cracking were found to be more prevalent in novalac than biphenyl. In summary, these studies have shown that while plastic encapsulated microelectronics can operate at temperatures above 125°C, they have less than half the life of ceramic microcircuits at 180°C and they begin to show signs of insulation resistance degradation after 300 hours at 250°C.

Reliability of commercial plastic encapsulated microelectronics at temperatures from 125°C to 300°C

This paper describes the first study which addresses the reliability of plastic encapsulated microcircuits (PEMs) in the range from 125/spl deg/C to 300/spl deg/C, well outside the manufacturers suggested temperature limits. A Motorola MC68332 microcontroller, widely used in avionic systems, remained fully functional to 180/spl deg/C. However, industrial grade, plastic encapsulated MC68332 devices had less than half the lifespan at 180/spl deg/C of similar MC68332 devices packaged in hermetic ceramic packages. In addition, other types of plastic components studied had a shorter lifespan at 180/spl deg/C than their ceramic packaged counterparts. Outgassing of flame retardants with the associated catalysis of the growth of intermetallics was determined to be the principal cause of failure. Further studies on 84-lead PQFP lead frames encapsulated in two different molding compounds revealed that the plastic encapsulant itself begins to lose its ability to insulate leads at temperatures greater than 250/spl deg/C and can actually combust at temperatures greater than 300/spl deg/C. Both insulation resistance degradation and cracking were found to be more prevalent in novalac than biphenyl.

A comparison of the theory of moisture diffusion in plastic encapsulated microelectronics with moisture sensor chip and weight-gain measurements

In this paper, the issues pertaining to moisture diffusion in PEMs are explored and discussed. The existing models of moisture diffusion in plastic molding compounds and PEMS are reviewed. Results, modeling and analysis of moisture sorption experiments performed in this study are presented. The moisture sorption experiments were conducted on a set of PEM samples with a common type of encapsulant material to 1) characterize sorption behavior; 2) compare weight gain measurement to the measurement of moisture concentration using a moisture sensor device at the die surface; 3) assess the moisture sensor measurement method. In the case of PEM samples tested in this study, simple Fickian diffusion was shown to agree closely with the experimental results. In one case, a relatively small anomaly from Fickian diffusion was observed and was attributed to swelling and relaxation phenomena at later stages of moisture sorption in the molding compound. The calibration constants determined for the sensors in this study were found to be significantly different from those collected by the manufacturer prior to the encapsulation of the devices. This problem is believed to be degradation in sensitivity of the moisture sensor due to exposure to high temperatures and storage conditions.

Two-Phase Liquid Cooling for Thermal Management of IGBT Power Electronic Module

Recent trends including rapid increases in the power ratings and continued miniaturization of semiconductor devices have pushed the heat dissipation of power electronics well beyond the range of conventional thermal management solutions, making control of device temperature a critical issue in the thermal packaging of power electronics. Although evaporative cooling is capable of removing very high heat fluxes, two-phase cold plates have received little attention for cooling power electronics modules. In this work, device-level analytical modeling and system-level thermal simulation are used to examine and compare single-phase and two-phase cold plates for a specified inverter module, consisting of 12 pairs of silicon insulated gate bipolar transistor (IGBT) devices and diodes. For the conditions studied, an R134a-cooled, two-phase cold plate is found to substantially reduce the maximum IGBT temperature and spatial temperature variation, as well as reduce the pumping power and flow rate, in comparison to a conventional single-phase water-cooled cold plate. These results suggest that two-phase cold plates can be used to substantially improve the performance, reliability, and conversion efficiency of power electronics systems.

Popcorning in Fully Populated and Perimeter Plastic Ball Grid Array Packages

Two types of Plastic ball Grid array packages, a 225‐lead full matrix array and a 256‐lead perimeter array, were subjected to 168 hours of moisture preconditioning at 85°C and 30% relative humidity followed by simulated infra‐red reflow at temperature ramp rates of 1°C/s and 0.67°C/s. The packages were subsequently examined for delamination and cracking using scanning acoustic microscopy and environmental scanning electron microscopy. At the higher ramp rate, delamination and cracking were observed in both package types, originating in the die attach and propagating along the weakest interfaces. At the lower ramp rate, a small amount of delamination was observed. This suggests that there is a critical ramp rate below which popcorn cracking does not occur.