Humidity Stress Test Research Articles

Validation of IC Conducted Emission and Immunity Models Including Aging and Thermal Stress

Environmental factors, such as aging and thermal stress, can seriously impact the electromagnetic compatibility behavior of an integrated circuit (IC). The standardized IC emission model for conducted emission (ICEM-CE) and IC immunity model for conducted immunity (ICIM-CI) can be used in industry to predict electromagnetic behavior at the IC and the printed circuit board level. However, these do not take into account the effect of aging and extreme temperature variations. In this article, a custom IC designed in silicon-on-insulator technology, containing several independent analog blocks, is used to characterize the influence of aging and temperature on conducted emission and immunity through measurements and transistor-level simulations. The highly accelerated temperature and humidity stress test (HAST) was performed to evaluate aging and its influence on IC parameters. The results show that the passive distribution network is only influenced by thermal stress and not HAST aging. The latter mainly affects the active elements in the IC and reduces the conducted emission and immunity levels through intrinsic permanent degradation mechanisms. Furthermore, thermal stress mainly causes drifts in the transistor characteristics (such as threshold voltage and effective mobility), which affect the conducted emission and immunity levels and resulting in soft failures. All drifts/tolerances collected from measurements and simulations are characterized in a way that makes it possible to include them in potential future versions of the ICEM-CE and ICIM-CI standards.

Study on the interface mechanism of copper migration failure in solder mask-substrate package

Microelectronic packaging technology is developing towards a complex structure with finer routing layers, which will bring great challenges to the reliability of microelectronic packaging. The failure caused by the migration of trace on devices in high temperature and humidity environment is especially serious. Today, there is still a lack of detailed research on the effect of interface mechanism of stacked material on copper migration. In this paper, for more investigation of interface mechanism, two types of solder mask (SM) material with different characteristics, AUS 320 and AUS SR1, were used for comparative experiments. The interface mechanism of stacked material during copper migration was studied based on commercial Flip Chip-Chip Scale Package (FC-CSP) by Biased Highly Accelerated temperature and humidity Stress Test (B-HAST). The characteristics of interface bonding of the two types of solder mask-substrate bi-material samples were discussed in detail by analyzing the failure mode and characterizing migration sites. The study shows that material interface affects physical mechanism of failure, which shows different failure modes of migration of copper trace along the interface micro-cracks under bias. The research results can provide theoretical basis and experimental support for the study of reliability of packaging device.

Studies on Oxygen Permeation Resistance of SiCN Thin Film and RRAM Applications

In this study, a silicon carbon nitride (SiCN) thin film was grown with a thickness of 5~70 nm by the plasma-enhanced chemical vapor deposition (PECVD) method, and the oxygen permeation characteristics were analyzed according to the partial pressure ratio (PPR) of tetramethylsilane (4MS) to the total gas amount during the film deposition. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and X-ray reflectivity (XRR) were used to investigate the composition and bonding structures of the SiCN film. An atomic force microscope (AFM) was used to examine the surface morphology of the SiCN films to see the porosity. The analysis indicated that Si-N bonds were dominant in the SiCN films, and a higher carbon concentration made the film more porous. To evaluate the oxygen permeation, a highly accelerated temperature and humidity stress test (HAST) evaluation was performed. The films grown at a high 4MS PPR were more susceptible to oxygen penetration, which changed Si-N bonds to Si-N-O bonds during the HAST. These results indicate that increasing the 4MS PPR made the SiCN film more porous and containable for oxygen. As an application, for the first time, SiCN dielectric film is suggested to be applied to resistive random access memory (RRAM) as an oxygen reservoir to store oxygen and prevent a reaction between metal electrodes and oxygen. The endurance characteristics of RRAM are found to be enhanced by applying the SiCN.

Reliability Enhancement of 14 nm HPC ASIC Using Al2O3 Thin Film Coated with Room-Temperature Atomic Layer Deposition

In this research, a 14 nm high-performance computing application-specific integrated circuit was coated with a 5–20 nm Al2O3 thin film by atomic layer deposition in room-temperature conditions to study its performance in terms of reliability with different thicknesses. An open/short test, standby current measurement, interface input/output performance test, and phase-locked loops functional test were used to verify chip performance. Furthermore, an unbiased highly accelerated temperature and humidity stress test and a 72 h wear-out test were used to study the effects of the atomic layer deposition coating. The results showed that the coating thickness of 15 nm provided the best performance in the wear-out test, as well as the unbiased highly accelerated temperature humidity stress. This study demonstrates that room-temperature atomic layer deposition is a promising technique for enhancing the reliability of advanced node semiconductor chips.

Enhanced reliability of phosphor-converted white light-emitting diodes based on a laser-cured silicone encapsulant layer

The laser-induced heating method was implemented for the homogeneous curing process of silicone encapsulant layer in phosphor-converted white light-emitting diodes (pc-WLEDs). Using the curing process with infrared laser irradiation, we demonstrated that pc-WLEDs performed better in the highly accelerated temperature and humidity stress test (85 °C, 85 Rh%) and the sulfur exposure test than devices with convection oven curing. The results from FTIR spectra, dynamic mechanical analysis, and Brunauer-Emmett-Teller (BET) surface area analysis indicated that the enhanced reliability of the laser-cured device could be attributed to the lower permeation property of gas molecules inside the laser-cured encapsulant layer. In addition, the permeation mechanism in the encapsulant layer of pc-WLED was proposed based on the cross-linking density of a silicone polymer and the total pore volumes in the phosphor-mixed encapsulant layer.

Hydrogen infiltration into BaTiO3-based dielectrics for multi-layer ceramic capacitors under highly accelerated temperature and humidity stress test

To make electrical devices, such as smartphones and automotive devices, more functional, the mechanism of electrical reliability in multi-layer ceramic capacitors (MLCCs) under high temperature, high humidity, and electric field bias environments has been studied. Although it has been presumed that hydrogen influences this mechanism, it is difficult to analyze hydrogen itself. Therefore, we investigated BaTiO3-based dielectrics in which the leakage current increases by conducting highly accelerated temperature and humidity stress tests using heavy water (D2O) as a tracer instead of light water (H2O) and secondary ion mass spectrometry analysis. We report the detection of deuterium in the dielectrics between the inner electrodes where the leakage current increased, and deuterium was biased toward the internal electrode on the cathode side. These findings can help further improve the reliability of MLCCs.

Infiltration of water vapor into multi-layer ceramic capacitors under highly accelerated temperature and humidity stress tests

Although it has been suggested that infiltration of water vapor into multi-layer ceramic capacitors (MLCCs) can increase leakage current, few studies have reported how this increase is directly linked to the infiltration. In this work we performed accelerated temperature and humidity stress tests with heavy water as a tracer and investigated, using secondary ion mass spectrometry, whether traces of water vapor could be detected in MLCCs. In particular, deuterium was found in areas where an augmented leakage current was detected. It is clear that infiltration of water vapor into MLCCs increased the leakage current. This finding could lead to further improvements in MLCCs.

Influence of post-bonding heating process on the long-term reliability of Cu/Al contact

Copper (Cu) wire bonding had been increasingly used in the LST devices in the last decade, especially in the consumer product due to the cost advantage over gold (Au) wire. Recently, needs for replacing Au wire with Cu wire is increasing also automotive industry where electronic devices need to survive harsher environment for a much longer period of time as compared with consumer product. Accordingly, a research effort for understanding product failure mechanism and reliability testing for the Cu wire bond is more important than ever. In this study, post-bonding heating process was induced after Cu wire bonding as a new approach to understand its effect on bond reliability and further understanding of Cu bond failure mechanism. The results show that introducing the post-bonding heating process is effective to restrain the progress of corrosion at the CuAl IMC during the bHAST (Biased highly accelerated temperature and humidity stress test) and mechanical factors may be related to the progress of corrosion.

Evaluation of Emerging High Melting Point Lead-free Solder and Hybrid Sinter Paste as Attaching Material for Clip Bond Package

Abstract High melting point (HMP) lead-free solder, hybrid sinter and transient liquidus phase sinter (TLPS) are the emerging lead-free alternatives for the potential replacement of high-lead solder. Lead-free solder is perfectly compatible with existing high-lead soldering processes for clip bond packages. The benefit of hybrid sinter is that it has much higher thermal and electrical conductivity than lead-free or high-lead solder. In this study, ten materials (including lead-free solders, hybrid sinter paste and TLPS) were first evaluated via die shear test. With the initial material screening, two lead-free solders (solder 1 and 2), two hybrid Ag sinter pastes (sinter i and ii) and one TLPS proceeded to internal sample assembly. For the lead-free solders, a process optimization with the aid of vacuum reflow was made to reduce void rate. Due to the slow and unbalanced inter-diffusion of Ag-Cu sintering than Ag-Ag sintering, optimizations to enhance the hybrid Ag sintering include Ag finishing for the die metallization and Ag plating for the clip and bond area of the leadframe. In 0-hour package electrical test, solder 1 and sinter i passed and were sent for reliability testing while solder 2, sinter ii and TLPS failed due to intermetallic compound (IMC) cracking, material bleeding and die cracking, respectively. In the reliability testing, a basic scheme of thermal cycling (TC) 1000 cycles, intermittent operating life (IOL) 750 hrs and highly accelerated temperature and humidity stress test (HAST) 96 hrs was defined for the early feasibility study. 1 of 75 sinter i units failed by TC 1000 cycles due to separation between silver sinter structure and die bottom metallization. Solder 1 passed the basic scheme without defects, and next the material workability and clip bond strength need to be improved to the equivalent level of high-lead solders.

Robust ultrathin and transparent AZO/Ag-SnOx/AZO on polyimide substrate for flexible thin film heater with temperature over 400 °C

We developed flexible and transparent thin film heaters (TFHs) with a structure of AZO/Ag-SnOx/AZO/polyimide (PI) which exhibited superior stability under operational conditions. Ultrathin and robust doped silver (Ag) films were produced by introducing a small amount of SnOx during the sputtering process. The AZO/Ag-SnOx/AZO stacks showed the best figure of merit value of 139.9, which was higher than that of ITO counterpart (25.5) with the same thickness. In addition, it exhibited excellent durability, which showed unaffected optical and electrical properties under the heat treatment of 500 °C for 30 min in air, highly-accelerated temperature and humidity stress test (HAST) at 121 °C and 97%RH for 36 h, 10,000 times of scratching and 1500 times of inner and outer bending test. Furthermore, the TFHs based on AZO/Ag-SnOx/AZO/PI achieved a high temperature of 438.8 °C with response time in several seconds, which outperformed most previous studies. The robust high-temperature TFHs in this research hold promising commercial applications in flexible and high temperature occasions.

Result of Highly Accelerated Stress Test of Organic Substrate Made by Integrated Dry Process

We made the large experimental tool where Photodesmear could process an actual size of the print circuit board by static irradiation. And we proved that handling of such panel size was technically possible. The connection reliability of the contact via was evaluated after electric copper plating by quick via peel examination. We made a cross-section sample of the contact via holes and the smear removal properties of wet desmear processing and the Photodesmear processing were compared with the residual smear and the oxidation thin layer by observation of the connection interface. The interfacial surface state after desmear processing was analyzed in an X-ray photoelectron spectrum analyzer. We produced the test vehicle using Photodesmear technology and sputtering seed technology. We compared it with the same pattern sample produced by a conventional process. In this paper, we report the results of the highly accelerated temperature and humidity stress test.

Copper electrochemical migration growth in an air HAST

High performance electronics require printed circuit boards (PCBs) with an extremely narrow pitch between adjacent copper patterns. However, copper electrochemical migration in these fine-pitch PCBs is a major source of failure. This phenomenon is typically identified using a highly accelerated temperature and humidity stress test (HAST) in which the water vapor pressure inside a chamber is increased along with the temperature and humidity. However, a side effect of this is that little air remains in the chamber despite air being required when replicating actual environments. This can be overcome by using an air HAST system that includes air inputs in its chamber. In our experiments, we analyzed the copper electrochemical migration on coupon samples with a 125 μm pitch at temperatures above 120 °C under various air pressures. We then compared the results for the air HAST, HAST, and high temperature and high humidity (85 °C/85% R.H.) tests by plotting each lifetime in the form of a Weibull distribution. Upon inspection, the cross-sectional microstructures of the copper electrochemical migration were seen to vary between the HAST and air HAST methods due to differences in the growth mechanism of the copper electrochemical migration.

Effects of Pd addition on the interfacial reactions between Cu and Al during ultrasonic welding

The interfacial reactions between Cu and Al during ultrasonic welding were investigated, focusing on the effect of Pd in Pd-coated Cu and Pd-alloyed Cu (0.3 wt% and 2 wt% PdCu). For Pd-coated Cu–Al bonding, it is found that Pd layer would act as diffusion barrier layer at the interface, and intermetallic compounds (IMCs) formed at Pd-free location for as-welded condition. As annealing time increases, Cu atoms and Al atoms bypassed the fractured Pd layer to form IMCs at the interface. Combining experimental observations, a model of Pd diffusion barrier effect was first proposed at the Pd-coated Cu–Al interface. For Pd-alloyed Cu–Al bonding, Pd can promote the atomic diffusion of active elements and accelerate the formation of IMCs, and excessive 2 wt% Pd addition can lead to the appearance of voids and cracks at interface, which is destructive for reliable interconnection structure. The thickness of the interfacial IMCs for pure Cu and 0.3 wt% PdCu at different heat treatment conditions has a linear relationship with the square root of time, which means that the growth of IMCs is controlled by volume diffusion. The diffusion activation energy of IMCs for 0.3 wt% PdCu (46.08 kJ/mol, 52.88 kJ/mol, and 65.35 kJ/mol for Cu9Al4, CuAl and CuAl2 respectively) was smaller than that for pure Cu (60.24 kJ/mol, 58.12 kJ/mol, and 82.94 kJ/mol for Cu9Al4, CuAl and CuAl2 respectively). Furthermore, the percentage of Cu9Al4 in the whole IMC decreased for 0.3 wt% PdCu, which can reduce the halogen corrosion from epoxy molding compound (EMC) during the reliability test of highly accelerated temperature and humidity stress testing (HAST).

Effect of Air-HAST Conditions on Sn Whisker Growth

Sn whiskers are one of the major causes of failure in fine-pitch electronics because of the short distance between the leads in an electronic package. In various whisker mechanisms, it takes a long time to grow a whisker due to Sn corrosion because the temperature is limited to below 100°C in high humidity. In the highly accelerated temperature and humidity stress test (HAST), the corrosion phenomenon rarely occurred because of the little air inside the chamber. Therefore, air is needed in the whisker accelerating test to meet the same whisker mechanism under high temperature and humidity conditions. In this study, an Air-HAST with air inputs in the chamber with highly temperature and humidity was introduced. Whisker growth was accelerated with temperatures at 130°C and various air pressures using the thin quad flat package (TQFP) sample with Sn plating lead. The whisker growth in the Air-HAST, HAST, and high temperature and high humidity test (85°C, 85%R.H.) was compared by plotting each growth length and number of whiskers. The accelerated relationships of whisker growth under the various test conditions will help the electronic industry meet the short development cycles. Key words: Sn whisker, Air-HAST, 85°C/85%RH, HAST, TQFP

Preparation of humidity, abrasion, and dust resistant antireflection coatings for photovoltaic modules via dual precursor modification and hybridization of hollow silica nanospheres

Antireflection (AR) coatings on solar glass, used in photovoltaic (PV) modules, generally encounter harsh environments, which demands that AR coatings must hinder moisture penetration, scratch damage, and dust accumulation. Though chemical modification generally benefits the multi-functionalization of AR coatings, it is likely to bring about a degradation of optical and mechanical properties. We demonstrated that a well-controlled dual precursor modification/hybridization process of hollow silica nanospheres was the key to achieve the robust multifunctional AR coatings. The dual precursor-derived AR coatings exhibited an increase of 5.08% in average transmittance at wavelengths from 300 to 1200 nm and a small relative reduction below 0.6% after an ultra-long highly-accelerated humidity and temperature stress test duration of 120 h, equivalent to a 5000 h damp heat test at a temperature and a relative humidity of 85 °C and 85%, respectively, as well as the excellent abrasion and dust resistance. The effects of the dual precursor-derived AR coatings on PV devices were evaluated by the encapsulated crystalline silicon mini-modules, where the improvements of 2.45% and 3.20% in the short-circuit current and the power conversion efficiency (Jsc and PCE) on average, respectively, relative to the bare glass encapsulated mini-modules were observed; meanwhile, the dust resistance of the AR coatings brought about the less degradations of 1.01% and 1.15% in Jsc and PCE, respectively, after the dust settling and removal tests, while the mini-modules with bare glass were 3.45% and 4.40%. It was believed that the dual-precursor, potentially, multi-precursor protocols would pave the way towards developing mechanically robust AR coatings with various fascinating functionalities, such as anti-fingerprint, anti-soiling, anti-fogging, and anti-icing.

Estimation of strength degradation for engineering plastic (Under elevated temperature and humidity stress test)

A large quantity of engineering plastics are used in electric industrial products. It is necessary to estimate the life of the product made of engineering plastics because of its shorter life and lower strength than some of ceramics or metals. New test device was developed for accelerated stress test. It can make the unsaturated environment above 100 oC under atmospheric pressure using superheated water vapor. Then it becomes possible to set wide range condition of temperature and humidity. Polybutylene terephthalate (PBT) is one of the hydrolyzed engineering plastics. Test pieces of PBT were submitted to accelerated stress test under some conditions of elevated temperature and humidity. Then they were provided to three point bending test. The time required for strength degradation has a good relation with water vapor pressure at each temperature. Then it became clear that the time required for strength degradation on each water vapor pressure was accelerated with temperature using the Arrhenius type equation.

Insulation resistance degradation mechanisms of multilayer ceramic capacitors during highly accelerated temperature and humidity stress tests

The failure mechanisms of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes under high temperature and high voltage conditions have been investigated through highly accelerated life tests (HALTs) in recent years. Generally, insulation resistance degradation during HALTs is presumed to be because of the electromigration of oxygen vacancies. Reliability in high-temperature, high-humidity, and rated-voltage environments is important for MLCCs. However, only a few studies have investigated the causes of insulation resistance degradation in MLCCs in these environments. We investigated the failure mechanisms of MLCCs through a highly accelerated temperature and humidity stress test. On the basis of presence of a degraded area on the anode side, we presumed that hydrogen ions were produced by H2O electrolysis at the interface between the ceramics and internal electrodes on the anode side, and that these hydrogen ions caused insulation resistance degradation.

Result of high accelerated stress test of organic substrates made by integrated dry process

Abstract The uses of the semiconductor increase by the development of Internet of Things. Miniaturization of the semiconductor wiring to bring speedup, electric power saving advances, and various technologies are developed. The new technology that applied a semiconductor production technology is waited eagerly for the production of the printed circuit board and semiconductor packaging. We presented new dry process “Integrated dry process” using Photodesmear technology and sputter seed process in IMAPS2016 Pasadena. After the micro via formation with the laser, the smear is effective to remove a smear remaining behind in the via bottom by Photodesmear. Furthermore, we improved adhesion between copper metal and epoxy resin in a sputtering seed together. We made the large experimental tool that Photodesmear could process an actually size of the print circuit board by static irradiation. And we proved that handling of panel size was technically possible. The connection reliability of the contact via is evaluated after electric copper plating by quick via peel examination. A cross section of the vias was made and, the residual smear removal properties of wet desmear processing and the Photodesmear processing were compared with the residual smear and the thin oxidation layer by observation of the connection interface. The interfacial surface state after the desmear processing was analyzed in X-ray probe analyzer. We produced the test vehicle using Photodesmear technology and a sputtering seed technology. I compared it with the same pattern sample produced by a process conventionally. In this paper, we report the result of the high accelerated temperature and humidity stress test.

Degradation of adhesion between Cu and epoxy-based dielectric during exposure to hot humid environments

Degradation of adhesion between Cu and epoxy-based dielectric build-up film (EDF), which is used for fan-out wafer level packaging applications, was investigated by the reliability test. The samples were composed of four layers: epoxy molding compound substrate, laminated EDF, electroless Cu, and electrolytic Cu. Adhesion was evaluated by the 90° peel test before and after the temperature and humidity (T&H) test and the highly accelerated temperature and humidity stress test (HAST). The effects of the peel strip width and humidity exposure of the peeled edges on adhesion were determined. It was found that adhesion gradually decreased during the reliability tests. The adhesion reduction mechanism was explained by the combinatorial effect of the loss in chemical bonding and the degradation of mechanical interlocking due to moisture. A black strip was observed along the edges of the peeled Cu strips (herein referred to as the black band, BB). AES revealed the BB as the superficial oxidation of the Cu strip. HAST and the T&H test showed the effect of the BB in an additional adhesion loss. SEM revealed a local cohesive fracture of the polymer, which led to an additional loss due to an early failure of the degraded polymer. Furthermore, BB growth showed a linear correlation with the square root of time and was accompanied with adhesion reduction. Since the modern packages have micro-sized Cu lines, the formation of BB should be avoided for better reliability of devices.

Proposal of Ultrafine and High Reliable Trench Wiring Process for Organic Interposer

An organic interposer technology with ultrafine line and space is required to achieve high-density interconnection between chips. In this article, we propose a high reliability, ultrafine trench wiring process. Currently, trench wiring is made by laser ablation of dielectric, sputtering, copper plating, and then chemical mechanical polishing (CMP). However, it is challenging to achieve fine trench with smooth side wall using laser ablation, and CMP is also not suitable because of its high assembly cost. Reliability is another challenge because of the narrower and thinner insulator. We have developed a photosensitive insulation film (PIF) with fine resolution. The trench wiring of 2/2 μm line and space has been successfully assembled by photolithography, plating, and surface planer method as the alternative to CMP. The wiring layer of 2/2 μm line and space, which is covered with a thin barrier metal layer and PIF, has passed the biased highly accelerated temperature and humidity stress test (HAST) screening. A copper paste is applied as a seed layer instead of sputtering. The sintered copper filled with adhesive paste into the copper pores is compatible as the seed layer, and the wiring layer of 10/10 μm line and space has passed the reliability tests such as moisture sensitivity level 2 (MSL2), thermal cycling test, and biased HAST.