Measurement Capability of Laser Ultrasonic Inspection System for Evaluation of Ball-Grid Array Package Solder Balls

Laser ultrasonic inspection is a novel, noncontact, and nondestructive technique to evaluate the quality of solder interconnections in microelectronic packages. In this technique, identification of defects or failures in solder interconnections is performed by comparing the out-of-plane displacement signals, which are produced from the propagation of ultrasonic waves, from a known good reference sample and sample under test. The laboratory-scale dual-fiber array laser ultrasonic inspection system has successfully demonstrated identifying the defects and failures in the solder interconnections in advanced microelectronic packages such as chip-scale packages, plastic ball grid array packages, and flip-chip ball grid array packages. However, the success of any metrology system depends upon precise and accurate data to be useful in the microelectronic industry. This paper has demonstrated the measurement capability of the dual-fiber array laser ultrasonic inspection system using gage repeatability and reproducibility analysis. Industrial flip-chip ball grid array packages have been used for conducting experiments using the laser ultrasonic inspection system and the inspection data are used to perform repeatability and reproducibility analysis. Gage repeatability and reproducibility studies have also been used to choose a known good reference sample for comparing the samples under test.

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100°C to 175°C for up to 18,000 h. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

Designs for Reliability and Failure Mode Prevention of Electrical Feedthroughs in Integrated Downhole Logging Tools

To enable an electrical feedthrough integrated down-hole logging tool to maintain high reliability during its logging service in any hostile wellbores, it is critical to apply some guidelines for the electrical feedthrough designs. This paper introduces a safety factor-based design guideline to ensure an integrated electrical feedthrough has sufficient compression or thermomechanical stress amplitude in the stress well against potential logging failures. It is preferred to have a safety actor of 1.5–2.0 for an electrical feedthrough at lowest temperature, such as −60°C, and a safety actor of 2.5–5.0 at operating temperature range of 200–260°C. Moreover, the designed ambient pressure capability should be 1.5–2.0 times higher than the maximum downhole pressure, such as 25,000–30,000 PSI. To validate this thermomechanical stress model, several electrical feedthrough prototypes have been tested under simulated 200–260°C and 31,000–34,000 PSI downhole conditions. The observed testing data have demonstrated that there is a maximum allowable operating pressure for an electrical feedthrough operating at a specific downhole temperature. It is clearly demonstrated that an electrical feed-through may operate up to 60,000 PSI at ambient temperature in a real-life application, but it may actually operate up to 30,000–35,000 PSI at 200–260°C downhole temperatures.

Gallium-Nitride Field Effect Transistors in Extreme Temperature Conditions

Compact power electronic circuits and higher operating temperatures of switching devices call for an analysis and verification on the impact of the parasitic components in these devices. The found drift mechanisms in a gallium-nitride field effect transistors (GaN-FET) are studied by literature and related to measurement results. The measurements in extreme temperature conditions are far beyond the manufacturer-recommended operating range. Influences to parasitic elements in both static and dynamic operation of the GaN-FETs are investigated and related toward device losses in switch-mode power electronic circuits with the example of a half-bridge circuit. In this article, static operation investigation on the effect of temperature toward resistance, leakage currents, and reverse conduction is conducted. Dynamic operation between the two states of GaN-FET is also addressed and related to the potential impact in a switching circuit losses. A thermal chamber was built to precisely measure the effect of temperature toward parasitic elements in the devices using a curve tracer. It was found that the increment in RDSon, IDSS, IGSS, and VSD can be justified by the literature and verified by measurements. Incremental COSS and decreasing VGSth was found when exposing devices to extreme temperatures. These two parameters give real challenge over designing circuits at high temperature where timing is critical. Albeit temperature challenges, it is found that investigated GaN-FETs have potential to be used in extreme temperature-operating conditions.

State-of-the-Art and Outlooks of Chiplets Heterogeneous Integration and Hybrid Bonding

In this study, the recent advances and trends of chip-let design and heterogeneous integration packaging will be investigated. Emphasis is placed on the definition, kinds, advantages and disadvantages, lateral interconnects, and examples of chiplet design and heterogeneous integration packaging. Also, emphasis is placed on the fundamental and examples of hybrid bonding.

Shear Strength Degradation Modeling of Lead-Free Solder Joints at Different Isothermal Aging Conditions

SAC-based alloys are one of the most common solder materials that are utilized to provide mechanical support and electrical connection between electronic components and the printed circuit board. Enhancing the mechanical properties of solder joints can improve the life of the components. One of the mechanical properties that define the solder joint structure integrity is the shear strength. The main objective of this study is to assess the shear strength behavior of SAC305 solder joints under different aging conditions. Instron 5948 Micromechanical Tester with a customized fixture is used to perform accelerated shear tests on individual solder joints. The shear strength of SAC305 solder joints with organic solderability preservative (OSP) surface finish is investigated at constant strain rate under different aging times (2, 10, 100, and 1,000 h) and different aging temperatures (50, 100, and 150°C). The nonaged solder joints are examined as well for comparison purposes. Analysis of variance (ANOVA) is accomplished to identify the contribution of each parameter on the shear strength. A general empirical model is developed to estimate the shear strength as a function of aging conditions using the Arrhenius term. Microstructure analysis is performed at different aging conditions using scanning electron microscope (SEM). The results revealed a significant reduction in the shear strength when the aging level is increased. An increase in the precipitates coarsening and intermetallic compound (IMC) layer thickness are observed with increased aging time and temperature.

Mechanical Properties and Interface Microstructure of SAC305 Solder Joints Made to a Ag-Pd-Pt Thick Film Metallization: Part 2—Isothermal Aging Effects

The performance and reliability were documented for solder joints made between the 96.5Sn-3.0Ag-0.5Cu (wt.%, abbreviated SAC305) Pb-free solder and a Ag-Pd-Pt thick film conductor on an alumina substrate. The Sheppard’s hook pull test was used to assess the solder joint strength. The Part 1 study confirmed that the solder joint fabrication process had a wide process window. The current study determined that the SAC305 solder joints maintained that robustness after accelerated aging at temperatures of 70–205°C and time durations of 5–200 d. Short-term aging of 5–10 d caused a peak in the pull strength peak that resulted from precipitation hardening by Ag-Pd and (Pd, Pt)xSny intermetallic compound (IMC) particles. The pull strengths did not decrease significantly after longer aging times at 70°C and 100°C; those conditions were accelerations of typical service lifetimes. Longer aging times at temperatures of 135–205°C resulted in a gradual, albeit not catastrophic, strength decrease when the precipitation hardening mechanism was lost to dissolution of the particle phases and their reprecipitation at the solder/alumina interface. The failure modes were ductile fracture in the solder except for the most severe aging conditions. These findings confirmed that the SAC305 solder/Ag-Pd-Pt thick film interconnections have excellent long-term reliability for hybrid microcircuit and high-temperature electronics applications.

Thermal and Reliability Characterization of an Epoxy Resin-Based Double-Side Cooled Power Module

Wide-Band Gap (WBG) power devices have become a promising option for high-power applications due to the superior material properties over traditional Silicon. To not limit WBG devices’ mother nature, a rugged and high-performance power device packaging solution is necessary. This study proposes a Double-Side Cooled (DSC) 1.2 kV half-bridge power module having dual epoxy resin insulated metal substrate (eIMS) for solving convectional power module challenges and providing a cost-effective solution. The thermal performance outperforms traditional Alumina (Al2O3) Direct Bonded Copper (DBC) DSC power module due to moderate thermal conductivity (10 W/mK) and thin (120 mm) epoxy resin composite dielectric working as the IMS insulation layer. This novel organic dielectric can withstand high voltage (5 kVAC @ 120 μm) and has a Glass Transition Temperature (Tg) of 300°C, which is suitable for high-power applications. In the thermal-mechanical modeling, the organic DSC power module can pass the thermal cycling test over 1,000 cycles by optimizing the mechanical properties of the encapsulant material. In conclusion, this article not only proposes a competitive organic-based power module but also a methodology of evaluation for thermal and mechanical performance.

Mechanical Properties and Interface Microstructure of SAC305 Solder Joints Made to an Ag-Pd-Pt Thick Film Metallization: Part 1—Processing Effects

The processibility was document for interconnections made between the 96.5Sn-3.0Ag-0.5Cu (wt.%, abbreviated SAC305) Pb-free solder and an Ag-Pd-Pt thick film conductor on an alumina substrate. The Sheppard’s hook pull test was used to assess the solder joint strength. Microanalysis techniques documented the corresponding microstructures. Excellent solderability was observed across the process parameters defined by the soldering temperatures of 240–290°C and soldering times of 15–120 s. Molten SAC305 solder dissolved the Ag-Pd-Pt thick film, leading to the precipitation of Ag (trace of Pd) and (Pd, Pt)xSny intermetallic compound (IMC) particles upon solidification. The mechanical strengths of the solder joints were excellent (10–15 N) and remained largely insensitive to the processing conditions. The failure mode was ductile fracture in the solder. These findings confirmed that the SAC305 solder/Ag-Pd-Pt thick film interconnection system had the necessary process window for use in high reliability, hybrid microcircuit (HMC) applications.

A SiC Double-Sided Stacked Wire-Bondless Power Module for High-Frequency Power Electronic Applications

This article reports a double-sided stacked wire-bondless power module package for silicon carbide (SiC) power devices to achieve low parasitic inductance and improved thermal performance for high-frequency applications. The design, simulation, fabrication, and characterization of the power module are presented. A half-bridge module based on the SiC power MOSFETs is demonstrated with minimized parasitic inductance. Double-sided cooling paths are used to maximize heat dissipation. Besides conventional packaging materials used in the power module fabrication, a low-temperature cofired ceramic (LTCC) and nickel-plated copper balls are used in this module package. The LTCC acts as an interposer providing both electrical and thermal routings. The nickel-plated copper balls replace bond wires as the electrical interconnections for the SiC power devices. The electrical and thermo-mechanical simulations of the power module are performed, and its switching performance is evaluated experimentally.