Influence of bias humidity testing and application on time-dependent,Arrhenius-law-based stability predictions for thin film resistors

The time dependence of the drift phenomena in thin film resistors has been shown in a previous paper, which described the conditions in a “dry heat” environment. However, the conditions when using electronic equipment in areas of the world or applications with high relative humidity are still a challenge for component reliability. Therefore, industry standard AEC-Q200 requirements include the biased humidity test 85 °C/85% RH for passive components as well. Qualified thin film resistors are designed with an appropriate stable R-layer and electro-isolation lacquer systems that are capable of passing the 85/85 test.The following questions arise:

• (1)What does passing the 1000 h biased 85/85 test mean for real world applications of thin film resistors?
• (2)Is it possible to predict the worst case drifts of resistors under load and environmental conditions over the time of use from the 85/85 or HAST data?

To answer these and other test-related questions, an experimental long-time comparison study was made at 40 °C/93% RH and 85 °C/85% RH; the usual standard tests. These were extended to 4000 h at approximately 0.5% and 10% of maximum specified operating power using our most sensitive thin film resistive layer systems. In addition to that, tests at 70 °C/90% RH, 90 °C/40% RH, and HAST130 were performed, enabling a check of the linearity of temperature, humidity, and voltage influence on drift.This paper will show the results of this comparison study, whose data points enabled us to give answers about acceleration factors of applied temperatures and voltages. The results will be compared with available prognosis models. These findings are the basis for the formulation of a new general model covering all aging conditions in the whole temperature–humidity–time expanse, system characterization, and components’ health prognosis.     

Rapid synthesis of ZnO dandelion-like nanostructures and their applications in humidity sensing and photocatalysis

In this study, ZnO dandelion-like nanostructures were rapidly synthesized on Si substrates using a two-step thermal oxidation approach. The ZnO nanostructures were grown at various thermal oxidation temperatures ranging from 400 °C to 700 °C. These nanostructures were then applied to humidity sensing and photocatalysis. The ratio of measured resistances in the humidity sensors for relative humidity (RH) levels of 11% and 95% at room temperature (RT) were found to rise from 10² to 10⁵ times for humidity sensors constructed with the nanostructures grown at temperatures from 400 °C to 700 °C, respectively, and sensor response time decreased from 15 s to 5 s. These results show that the proposed ZnO dandelion-like nanomaterial shows promise as a candidate for fabricating high-performance humidity sensors when the nanostructures are grown at 700 °C. In addition, the photocatalytic effect of the nanostructures was tested with a decomposition of methyl orange (MO) dye under UV illumination. Experimental results show that the ZnO dandelion-like nanomaterial grown at a thermal oxidation temperature of 700 °C exhibits an excellent photocatalytic effect, which degrades to almost 90% of the MO activity over 120 min.     

Studies on various chip-on-film (COF) packages using ultra fine pitch two-metal layer flexible printed circuits (two-metal layer FPCs)

Various fine pitch chip-on-film (COF) packages assembled by (1) anisotropic conductive film (ACF), (2) nonconductive film (NCF), and (3) AuSn metallurgical bonding methods using fine pitch flexible printed circuits (FPCs) with two-metal layers were investigated in terms of electrical characteristics, flip chip joint properties, peel adhesion strength, heat dissipation capability, and reliability. Two-metal layer FPCs and display driver IC (DDI) chips with 35 μm, 25 μm, and 20 μm pitch were prepared. All the COF packages using two-metal layer FPCs assembled by three bonding methods showed stable flip chip joint shapes, stable bump contact resistances below 5 mΩ, good adhesion strength of more than 600 gf/cm, and enhanced heat dissipation capability compared to a conventional COF package using one-metal layer FPCs. A high temperature/humidity test (85 °C/85% RH, 1000 h) and thermal cycling test (T/C test, ?40 °C to + 125 °C, 1000 cycles) were conducted to verify the reliability of the various COF packages using two-metal layer FPCs. All the COF packages showed excellent high temperature/humidity and T/C reliability, however, electrically shorted joints were observed during reliability tests only at the ACF joints with 20 μm pitch. Therefore, for less than 20 μm pitch COF packages, NCF adhesive bonding and AuSn metallurgical bonding methods are recommended, while all the ACF and NCF adhesives bonding and AuSn metallurgical bonding methods can be applied for over 25 μm pitch COF applications. Furthermore, we were also able to demonstrate double-side COF using two-metal layer FPCs.     

Development of chip-on-flex bonding using Sn-based bumps and non-conductive adhesive

We developed a reliable and low cost chip-on-flex (COF) bonding technique using Sn-based bumps and a non-conductive adhesive (NCA). Two types of bump materials were used for the bonding process: Sn bumps and Sn–Ag bumps. The bonding process was performed at 180 °C for 10 s using a thermo-compression bonder after dispensing the NCA. Sn-based bumps were easily deformed to contact Cu pads during the bonding process. A thin layer of Cu₆Sn₅ intermetallic compound was observed at the interface between Sn-based bumps and Cu pads. After bonding, electrical measurements showed that all COF joints had very low contact resistance, and there were no failed joints. To evaluate the reliability of COF joints, high temperature storage tests (150 °C, 1000 h), thermal cycling tests (−25 °C/+125 °C, 1000 cycles) and temperature and humidity tests (85 °C/85% RH, 1000 h) were performed. Although contact resistance was slightly increased after the reliability test, all COF joints passed failure criteria. Therefore, the metallurgical bond resulted in good contact and improved the reliability of the joints.     

Corrosion behavior of crystalline silicon solar cells

Corrosion behavior of crystalline silicon (C-Si) solar cells was investigated. For this purpose, three groups of cells were conducted with three kinds of aging test which cells setting in indoor environment (25 °C, 45% RH, 0– 2 months), cells immersing in moisture atmosphere (25 °C, 85% RH, 0– 240 h) and cells immersing in acetic acid atmosphere (25 °C, 85% RH, 0– 240 h). Subsequently the microstructure characteristic of the alumina paste layer (APL), rear electrode and soldered connection of cells and the corrosion production during aging test were analyzed and compared. The results show that the smooth oxide coating and looser structure were found in the APL of cell after aging test. In addition the discoloration and elements diffusion were found on the rear electrode. And the corrosion region expanded gradually from the edge to the center of soldered connection along the interface between Ag electrode and Sn₃₇Pb alloy. Thereafter, a model was put forward to try to explain the degradation mechanism of traditional photovoltaic (PV) modules during damp-heat (DH) test based on corrosion behavior of C-Si cells in this experiment.     

Low-temperature low-pressure die attach with hybrid silver particle paste

New types of die attach pastes comprising micron-sized Ag particles hybridized with submicron-sized Ag particles were considered as lead-free die attach materials for SiC power semiconductors. Micron-sized Ag particles in alcohol solvent were prepared by mixing the die attach paste with submicron-sized Ag particles. The alcohol vaporizes completely during sintering and no residue exists in the bonding layer. The Ag layer has a uniform porous structure. The electrical resistivity of the printed tracks decreases below 1 × 10^?5 Ω cm when sintered above 200 °C. When sintered at 200 °C for 30 min, the average resistivity reaches 5 × 10^?6 Ω cm, which is slightly higher than the value obtained by using Ag nanoparticle paste. A SiC die was successfully bonded to a direct bonded copper substrate and the die-shear strength gradually increases with the increase in bonding temperature up to 300 °C. The Ag die attach bond layer was stable against thermal cycles between ?40 °C and 300 °C.     

Distributed NGD active circuit for RF-microwave communication

This paper is aimed to the investigation on innovative distributed negative group delay (DNGD) circuits for RF communication. Thanks to the analogy between the lumped and distributed circuits, NGD circuit topologies were identified. By using the S-parameter theory, analysis and synthesis methods of these topologies are proposed. The DNGD circuits developed are mainly comprised of a transistor combined with a series resistance ended by a stub. Then, synthesis relations enabling to determine the NGD circuit parameters from the desired NGD and gain values are established. As application, an active phase shifter (PS) operating independently with the frequency based on the cascade of PGD and NGD devices was synthesized. First, an NGD PS with transmission phase of (135 ± 5)° around 2.56 GHz over the bandwidth of about 1.02 GHz was obtained. Then, a two-stage DNGD PS exhibiting 90° with ±10° flatness from 4.1 GHz to 6.8 GHz was designed. The DNGD circuit presented can be used in various telecommunication areas notably for correcting RF/numerical signal delays in the RF-microwave analogue-digital devices.     

Accelerated life test of high power white light emitting diodes based on package failure mechanisms

Accelerated life tests of high-power white light emitting diodes (LEDs) were conducted under an unbiased highly accelerated temperature and humidity test (HAST) and a normal aging test. The conditions in the unbiased HAST were 110 °C-85% RH, 130 °C-85% RH without bias. During the aging, the degradation mechanisms of optical power reduction and degradation of 455 mm blue wavelengths that were better than phosphors related yellow emission bands were observed. The microscopy analysis showed that this effect could be ascribed to the bubbling and discoloration of the silicone encapsulating material of the package. It is thought that these features are also responsible for the optical power reduction and thermal resistance increase.     

Flexible Chip-on-Flex (COF) and embedded Chip-in-Flex (CIF) packages by applying wafer level package (WLP) technology using anisotropic conductive films (ACFs)

Due to increasing demand for higher performance, greater flexibility, smaller size, and lighter weight in electronic devices, extensive studies on flexible electronic packages have been carried out. However, there has been little research on flexible packages by wafer level package (WLP) technology using anisotropic conductive films (ACFs) and flex substrates, an innovative packaging technology that requires fewer process steps and lower process temperature, and also provides flexible packages. This study demonstrated and evaluated the reliability of flexible packages that consisted of a flexible Chip-on-Flex (COF) assembly and embedded Chip-in-Flex (CIF) packages by applying a WLP process.The WLP process was successfully performed for the cases of void-free ACF lamination on a 50 μm thin wafer, wafer dicing without ACF delamination, and a flip-chip assembly which showed stable bump contact resistances. The fabricated COF assembly was more flexible than the conventional COF whose chip thickness is about 700 μm. To evaluate the flexibility of the COF assembly, a static bending test was performed under different bending radiuses: 35 mm, 30 mm, 25 mm, and 20 mm. Adopting optimized bonding processes of COF assembly and Flex-on-Flex (FOF) assembly, CIF packages were then successfully fabricated. The reliability of the CIF packages was evaluated via a high temperature/humidity test (85 °C/85% RH) and high temperature storage test (HTST). From the reliability test results, the CIF packages showed excellent 85 °C/85% RH reliability. Furthermore, guideline of ACF material property was suggested by Finite Element Analysis (FEA) for better HTST reliability.     

Dual stage modeling of moisture absorption and desorption in epoxy mold compounds

A dual stage diffusion model is developed in this paper for both absorption and desorption processes. Both stages in moisture absorption and desorption, i.e., Fickian and non-Fickian process, are described mathematically using a combination of Fickian terms. Absorption and desorption tests are also conducted on six distinct commercial epoxy mold compounds (EMCs) used in electronic packaging. For absorption, the samples are subjected to 85 °C/85% relative humidity and 60 °C/85% relative humidity soaking, respectively. Desorption conditions are above glass transition temperature at 140 °C and 160 °C. The dual stage models generate reasonable results for the diffusive properties and display outstanding experimental fits. All six compounds show strong non-Fickian diffusion behaviors, which are further verified by the experiments with different thicknesses. For absorption, while Fickian diffusion is dominant in the beginning of process, non-Fickian mechanism plays a large role with time increasing. Saturated moisture concentration associated with Fickian-stage diffusion appears to be independent of temperature under the tested conditions. For desorption, higher temperature leads to less percentage of the permanent residual moisture content in most compounds. At 160 °C, 90% of the initial moisture for all samples is diffused out within 24 h, following an approximate modified Fickian diffusion process. The dual stage model developed in this paper provides a mathematical formulation for modeling anomalous moisture diffusion behavior using commercial finite element analysis software.     

Fabrication of Ag nanoparticle/ZnO thin films using dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with photoreduction method and its application

We report a novel method to grow silver nanoparticle/zinc oxide (Ag NP/ZnO) thin films using a dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with a photoreduction method. The crystalline quality, optical properties, and electrical characteristics of Ag NP/ZnO thin films depend on the AgNO₃ concentration or Ag content and annealing temperature. Optimal Ag NP/ZnO thin films have been grown with a AgNO₃ concentration of 0.12 M or 2.54 at%- Ag content and 500 °C- rapid thermal annealing (RTA); these films show orientation peaks of hexagonal-wurtzite-structured ZnO (002) and face-center-cubic-crystalline Ag (111), respectively. The transmittance and resistivity for optimal Ag NP/ZnO thin films are 85% and 6.9×10⁻⁴ Ω cm. Some Ag NP/ZnO transparent conducting oxide (TCO) films were applied to InGaN/GaN LEDs as transparent conductive layers. The InGaN/GaN LEDs with optimal Ag NP/ZnO TCO films showed electric and optical performance levels similar to those of devices fabricated with indium tin oxide.     

Microstructure,electric flame-off (EFO) characteristics and tensile properties of silver–lanthanum alloy wire

Silver has potential for application in the electronic packaging industry because of its great electrical and thermal properties and lower price compared to that of gold. Silver oxidizes easily, so doping lanthanum to form Ag–La alloy improves its anti-oxidation capacity. In this study, the microstructure, tensile properties, electronic flame-off (EFO) characteristics, and fusing current of Ag–La alloy wire (φ = 20 μm) are studied. Samples annealed at three temperatures (325 °C, 375 °C, and 425 °C) are analyzed. According to the experimental results, after annealing at 425 °C, Ag–La alloy wire recrystallized, giving it a tensile strength similar to that of pure silver wire and a uniform structure. Doping lanthanum reduced the diameter of free air balls (FABs) in the EFO process. The fusing current of Ag–La wire was about 0.45 A, and the grains of Ag–La wire grew to the size of the wire diameter when a 0.4 A current (90% fusing current) was applied for a long time. Ag–La alloy wire can be used in the electronic packaging industry.     

Single-grain Si thin-film transistors SPICE model,analog and RF circuit applications

Single-grain thin-film transistors (SG-TFTs) fabricated inside location-controlled using μ-Czochralski process exhibit SOI-FETs like performance despite processing temperatures remaining below 350 °C. Thus, the SG-TFT is a potential technology for large-area highly-integrated electronic system and system-in-package, taking advantage of the system-on-flexible substrate and low manufacturing cost capabalities. The SG-TFT is modeled based on the BSIMSOI SPICE model where the mobility parameter is modified to fit the SG-TFT behavior. Therefore, analog and RF circuits can be designed and benchmarked. A two-stage telescopic cascode operational amplifier fabricated in a prototype 1.5 μm SG-TFT technology demonstrates DC gain of 55 dB and unity-gain bandwidth of 6.3 MHz. A prototype CMOS voltage reference demonstrates a power supply rejection ratio (PSRR) of 50 dB. With unity-gain frequency, f_T, in the GHz range, the SG-TFT can also enable RF circuits for wireless applications. A 12 dB gain RF cascode amplifier with integrated on-chip inductors operating in the 433 MHz ISM band is demonstrated.     

Experimental investigation of temperature and relative humidity effects on resonance frequency and quality factor of CMOS-MEMS paddle resonator

This paper reports an experimental approach to analyse the performance of an externally actuated CMOS-MEMS paddle resonator with proof mass. The surface morphology test of the device is performed with the help of field emission scanning electron microscopy (FESEM), before and after the reliability tests. The effects of temperature variation on the resonance frequency response of the fabricated CMOS-MEMS resonator is analysed under the variation of temperature from 25 °C to 80 °C inside a custom made environmental chamber at a constant relative humidity (32%RH). In the next step, the variation in the quality factor of the MEMS resonator is studied under the effect of varying temperature. Finally, the resonance frequency behavior is analysed under the variation of relative humidity from 32%RH to 90%RH at a constant temperature of 25 °C. The device is found to be eroded and there are some wastes of humidity on it. A total change of 6.9 Hz in resonance frequency is recorded from 25 °C to 80 °C. The drop in the resonance frequency of the MEMS device is found to be 137 MHz/°C with the rise in temperature. Under the temperature variation from 25 °C to 80 °C, the quality factor is found to be nonlinear. A total change of 1.3 Hz in the resonance frequency is observed from 32%RH to 90%RH. The resonance frequency is found to be − 21.8 MHz/RH% with an increasing humidity level.     

Effect of annealing on the microstructure and bonding interface properties of Ag–2Pd alloy wire

This study investigated the mechanical and electrical properties of Ag–2Pd wire after thermal annealing. The thermal stability of the tested wire was examined by separately imposing static annealing at 275 °C, 325 °C and 375 °C in a vacuum environment. It was found that annealing the Ag–2Pd wire at 275 °C promoted the formation of a fully annealed structure with equiaxed grains. Annealing Ag–2Pd wire had a shorter heat affect zone (HAZ) length than those of conventional wire, and offered outstanding mechanical properties. A long-term electrical test found Ag₃(Pd)Al and Ag₂(Pd)Al compounds between the Ag–Pd ball and Al pad. These results confirmed the high-reliability properties of annealed Ag–2Pd wires for the wire bonding process.     

In-situ investigation of EMC relaxation behavior using piezoresistive stress sensor

The relaxation behavior of an epoxy molding compound (EMC) subjected to a constant strain can cause new reliability challenges in automotive electronics. This problem will be exacerbated due to the ever-increasing demand in modern electronics systems for miniaturization with more functionality, yet it has not been studied extensively to mitigate its effect on reliability. In this study, a piezoresistive silicon-based stress sensor is used to understand the stress state in an electronic control unit (ECU), more specifically the relaxation behavior of EMC caused by the storage time of an ECU (i.e., duration between production and actual usage). Mechanical stresses are measured by the piezoresistive stress sensor that is encapsulated in a standard microelectronic 3 × 3 mm land grid array (LGA) package. The relaxation behavior is observed at three different temperatures for 1 week: 75 °C, 100 °C and 125 °C. The relaxation behavior is measured continuously for one more week after cooling the package to room temperature (at 25 °C). An additional test is conducted at 85 °C with 85% relative humidity to investigate the effect of moisture diffusion on the package. The experimental results clearly indicate that the proposed approach can be used for better understanding of the evolution of stresses in molded packages during their lifetime, especially during storage, which in turn can lead to more optimal designs in the future.     

High linearity,low power RF mixer design in 65 nm CMOS technology

A design of RF down-conversion Gilbert-Cell, with 65 nm CMOS technology, at a supply voltage of 1.8 V, with a new degenerating structure to improve linearity. This architecture opens the way to more integrated CMOS RF circuits and to achieve a good characteristics in terms of evaluating parameters of RF mixers with a very low power consumption (2.17 mW). At 1.9 GHz RF frequency; obtained results show a third order input intercept point (IIP3) equal to 11.6 dBm, Noise Figure (NF) is 4.12 dB, when conversion gain is 8.75 dB.     

Accurate operation of a CMOS integrated temperature sensor

A high-accuracy temperature sensor is designed by applying the temperature characteristics of substrate bipolar transistor in CMOS technology. Initial accuracy of the temperature sensor can be improved by chopper amplifiers and dynamic element matching. Using these two methods, the circuit realization of reference voltage is also described. Simulation results show that the inaccuracy is within×0.4 °C from ?40 to +100 °C. Experimental results, obtained from circuits fabricated in 0.5 μm CMOS process, indicate that the sensor is inaccurate within×0.7 °C from ?40 to +100 °C. The power dissipation is 0.35 mW and the chip area is 889 μm×620 μm. Compared with previously reported work, the temperature sensor in the paper has lower inaccuracy without calibration.     

Ag–Al alloy thin film on plastic substrate by screen printing for solar cell back contact application

Ag–Al alloy thin films with different thicknesses were screen printed onto polyethylene terephthalate plastic substrates at room temperature. Three different weights of pure Ag paste were mixed with Al paste to create alloy pastes with different viscosities. A uniform composition of Ag and Al was obtained with a 70:30 composition ratio. The variation in the viscosity of the mixed paste enabled production of different thicknesses of printed layers. The deposited films were annealed at 200 °C for 45 min. Structural characterization and elemental content analysis of the films were carried out using X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy. The surface morphology of the printed films was studied by scanning electron microscopy and atomic force microscopy. Their electrical properties were investigated by four-point probe measurements. The crystalline sizes and strain along the a and c axes were calculated from the XRD patterns. Both were found to increase with increased film thickness.     

Characteristics of InAIAs/InP and InAIP/GaAs native oxides

Characteristics of InAlAs/InP and InAlP/GaAs wet oxidation layers were measured for the first time. These oxidation layers can be a current blocking or an optical confining layer in laser diodes. These layers were well made at 500–575 °C. The oxidation rates at 525 °C are approximately 340 nm/h and 120 nm/h for InAlAs and InAlP oxides, respectively. The refractive index are 1.82–1.90 for InAlAs oxide and 1.565–1.595 for InAlP oxide between 0.6 μm and 1.65 μm wavelength. The characteristics are not much varied with processing temperatures except the oxidation rate. And a 200 nm thick InAlAs oxidation layer has a current–voltage characteristic that currents rapidly flow at about 10 V, which is much lower than that of SiO₂.