Failure patterns of solder joints identified through lifetime vibration tests

A method for non-destructively tracking the integrity of flip chip solder joints through life is investigated in this paper. An industry standard double-sided PCB was designed and manufactured with 14 flip chips to assess the failure patterns of each flip chip and each solder joint in lifetime vibration tests. Two configurations of PCB finish were tested, Electro Nickel Immersion Gold (ENIG) and Hot Air Surface Levelled lead (Pb HASL) using automotive industry manufacturing processes and quality standards. A random vibration test over a frequency range 10 Hz to 1000 Hz was specified by automotive engineers to replicate vibrations typically found on road vehicles. This vibration profile was applied to test circuit board assemblies (CBA) for 4-minute intervals until failure of all chips. At each interval test boards were extensively scanned by an acoustic micro-imaging (AMI) microscope to non-destructively measure parameters of solder joints. This enabled tracking of mechanical joint connection through-life. Methods were developed to process the large number of acoustic images of each solder joint and form metrics to evaluate solder joint integrity. Results from AMI show that the solder joints exhibit three distinct zones as they age: crack initiation, crack propagation and then failure

Comparative analysis of the effects of tantalum doping and annealing on atomic layer deposited (Ta2O5)(x)(Al2O3)(1-x) as potential gate dielectrics for GaN/AlxGa1-xN/GaN high electron mobility transistors

This paper describes a method to optimally combine wide band gap Al2O3 with high dielectric constant (high-κ) Ta2O5 for gate dielectric applications. (Ta2O5)x(Al2O3)1−x thin films deposited by thermal atomic layer deposition (ALD) on GaN-capped AlxGa1−xN/GaN high electron mobility transistor (HEMT) structures have been studied as a function of the Ta2O5 molar fraction. X-ray photoelectron spectroscopy shows that the bandgap of the oxide films linearly decreases from 6.5 eV for pure Al2O3 to 4.6 eV for pure Ta2O5. The dielectric constant calculated from capacitance-voltage measurements also increases linearly from 7.8 for Al2O3 up to 25.6 for Ta2O5. The effect of post-deposition annealing in N2 at 600 °C on the interfacial properties of undoped Al2O3 and Ta-doped (Ta2O5)0.12(Al2O3)0.88 films grown on GaN-HEMTs has been investigated. These conditions are analogous to the conditions used for source/drain contact formation in gate-first HEMT technology. A reduction of the Ga-O to Ga-N bond ratios at the oxide/HEMT interfaces is observed after annealing, which is attributed to a reduction of interstitial oxygen-related defects. As a result, the conduction band offsets (CBOs) of the Al2O3/GaN-HEMT and (Ta2O5)0.16(Al2O3)0.84/GaN-HEMT samples increased by ∼1.1 eV to 2.8 eV and 2.6 eV, respectively, which is advantageous for n-type HEMTs. The results demonstrate that ALD of Ta-doped Al2O3 can be used to control the properties of the gate dielectric, allowing the κ-value to be increased, while still maintaining a sufficient CBO to the GaN-HEMT structure for low leakage currents. VC 2016 AIP Publishing LL

Comparison of atomic layer deposited Al2O3 and (Ta2O5)0.12(Al2O3)0.88 gate dielectrics on the characteristics of GaN-capped AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors

The current research investigates the potential advantages of replacing Al2O3 with (Ta2O5)0.12(Al2O3)0.88 as a higher dielectric constant (κ) gate dielectric for GaN-based metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs). The electrical characteristics of GaN-capped AlGaN/GaN MOS-HEMT devices with (Ta2O5)0.12(Al2O3)0.88 as the gate dielectric are compared to devices with Al2O3 gate dielectric and devices without any gate dielectric (Schottky HEMTs). Compared to the Al2O3 MOS-HEMT, the (Ta2O5)0.12(Al2O3)0.88 MOS-HEMT achieves a larger capacitance and a smaller absolute threshold voltage, together with a higher two-dimensional electron gas carrier concentration. This results in a superior improvement of the output characteristics with respect to the Schottky HEMT, with higher maximum and saturation drain current values observed from DC current-voltage measurements. Gate transfer measurements also show a higher transconductance for the (Ta2O5)0.12(Al2O3)0.88 MOS-HEMT. Furthermore, from OFF-state measurements, the (Ta2O5)0.12(Al2O3)0.88 MOS-HEMT shows a larger reduction of the gate leakage current in comparison to the Al2O3 MOS-HEMT. These results demonstrate that the increase in κ of (Ta2O5)0.12(Al2O3)0.88 compared with Al2O3 leads to enhanced device performance when the ternary phase is used as a gate dielectric in the GaN-based MOS-HEMT

Band line-up investigation of atomic layer deposited TiAlO and GaAlO on GaN

A comprehensive study of the band alignments of TixAl1−xOy (with x = 9%, 16%, 25%, 36%, 100%) and GaxAl1−xOy (x = 5%, 20%, 80% and 95%) fabricated using atomic layer deposition on GaN has been presented using X-ray photoelectron spectroscopy and variable angle spectroscopic ellipsometry. The permittivity, k, has been found to be enhanced from ~10 for 9% Ti in TixAl1−xOy to 76 for TiO2, however TiO2 brings an unfavorable band alignment and a small conduction band offset (<0.1 eV) with GaN. The latter has been observed for all studied TixAl1−xOy films deposited on GaN. On the other hand, GaxAl1−xOy films show a substantial increase of the band gap from 4.5 eV for Ga2O3 to 5.5 eV for x = 20% Ga and 6.0 eV for x = 5% Ga. A strong suppression of leakage current in associated GaxAl1−xOy-based metal insulator semiconductor capacitors has also been observed, showing promise for device applications