High temperature induced failure in Ti/Al/Ni/Au Ohmic contacts on AlGaN/GaN heterostructure

Ti/Al/Ni/Au (200/1200/500/2000 Å) Ohmic contact on AlGaN/GaN was prepared and it was subjected to thermal aging experiments. Thermal processing at 400 and 500 °C did not change the contact resistance significantly, while high temperature storage at 600 °C resulted in a surge in the contact resistance. The Al–Au alloy in the contact metal is believed to re-melt because its lowest melting temperature is 525 °C. The liquid of Al–Au alloy is observed to diffuse to the AlGaN surface and consume some AlGaN layer. In addition, voids are found to be produced during thermal process, which can reduce the effective contact area and thus lead to higher contact resistance. The TEM and EDX results of Ohmic contact’s cross sectional images provide evidence for this proposed mechanism.     

Sn addition on the tensile properties of high temperature Zn–4Al–3Mg solder alloys

The Zn–4Al–3Mg based solder alloy is a promising candidate to replace the conventional Pb–5Sn alloy in high-temperature electronic packaging. In this study, the tensile properties of Zn–4Al–3Mg–xSn alloys (x = 0, 6.8 and 13.2 wt.%) at high temperatures (e.g., 100 °C, and 200 °C) were investigated. It was found that the uniaxial tensile strength (UTS) of Zn–4Al–3Mg–xSn solder alloys all decrease monotonously with the increment of temperature. The elongation ratio at 100 °C is superior to that at room temperature whereas follows a significant drop at 200 °C. The microstructure observations show that a typical brittle fracture of Zn–4Al–3Mg alloy occurs at room temperature and 200 °C under normal tension, whereas a ductile fracture is found at 100 °C. The 6.8 wt.% Sn addition in Zn–4Al–3Mg alloy causes a dramatic decrease of yield strength, and a slight deterioration of the ductility.     

Effects of acrylic adhesives property and optimized bonding parameters on Sn58Bi solder joint morphology for flex-on-board assembly

Acrylic resin with a fast curable property has been used in low temperature ACFs applications. However, its poor thermo-mechanical property was a concern for solder ACFs applications. In this study, a novel thermomechanical analysis (TMA) method was introduced to measure its polymer rebound amounts due to pressures removal after a thermo-compression (TC) bonding process. Polymer resin was laminated between two silicon chips (7 1 7 mm²), and then a compressive mode TMA measurement was done on the prepared samples. Constant compressive pressures were applied until the temperature was gradually increased to target temperature, and the forces were removed at the target temperatures. The polymer rebound was measured by monitoring the z-axis dimension change after the compressive forces was removed. In addition, the effects of bonding temperatures (from 150 to 250 °C) and the bonding pressures (1, 2 and 3 MPa) on the SnBi58 (139 °C melting point) solder joints morphologies and joint resistances were evaluated to investigate acrylic resin property and find out the optimized bonding conditions for low Tg acrylic-based solder ACFs applications.     

High-lead flip chip bump cracking on the thin organic substrate in a module package

Flip chip bump cracking was observed after Si die attach reflow on the organic substrate of a module package. High-lead bump and eutectic SnPb cladding were used on Si die and the substrate sides, respectively. The reflow peak temperature was 260 °C for compatibility with passive components attach using lead-free solder. Flip chip bump cracking occurred at high-lead solder close to the die side. The cracking was eliminated by lowering the reflow peak temperature down to 225 °C. Main cause of the cracking at 260 °C reflow was attributed to the extensive Sn diffusion into high lead bump. This decreased the melting point of the high-lead solder around the die side, which in turn worsened the adhesion between solder and die due to the coexistence of solid and liquid. Diffusion length estimation showed both of the liquid- and solid-state diffusions of Sn. Crack gap in the solder bump was consistent with thermal expansion mismatch between Si die and organic substrate. The bump cracking was mitigated by use of 225 °C reflow, limiting Sn diffusion and providing a good integrity of high lead bumps on die side.     

Design and implementation of micro-power temperature to duty cycle converter using differential temperature sensing

The CMOS based temperature detection circuit has been developed in a standard 180 nm CMOS technology. The proposed temperature sensor senses the temperature in terms of the duty cycle in the temperature range of −30 °C to +70 °C. The circuit is divided into three parts, the sensor core, the subtractor and the pulse width modulator. The sensor core consists of two individual circuits which generates voltages proportional (PTAT) and complementary (CTAT) to the absolute temperature. The mean temperature inaccuracy (°C) of PTAT generator is −0.15 °C to +0.35 °C. Similarly, CTAT generator has mean temperature accuracy of ±1 °C. To increase thermal responsivity, the CTAT voltage is subtracted from the PTAT voltage. The resultant voltage has the thermal responsivity of 6.18 mV/°C with the temperature inaccuracy of ±1.3 °C. A simple pulse width modulator (PWM) has been used to express the temperature in terms of the duty cycle. The measured temperature inaccuracy in the duty cycle is less than ±1.5 °C obtained after performing a single point calibration. The operating voltage of the proposed architecture is 1.80±10% V, with the maximum power consumption of 7.2 μW.     

High cycle fatigue behaviour and generalized fatigue model development of lead-free solder alloy based on local stress approach

This paper gives an insight into high cycle fatigue (HCF) behaviour of a Pb-free solder alloy in the region between 10⁴ up to 10⁹ fatigue cycles using fatigue specimen. By means of a local stress approach, the method can be translated into solder joint fatigue evaluation in an application. The effect of temperatures (35 °C, 80 °C, 125 °C) on the fatigue property of Pb-free solder alloy is considered in this work to understand the possible fracture mechanisms and micro structural changes in a solder alloy at elevated temperature. Experiments are performed for different interaction factors under mean stresses (R = 0, − 1, − 3), stress concentration (notched, un-notched) and surface roughness. SN (stress-life) diagrams presented in this work will compare the fatigue performance of Sn_3.8Ag_0.7Cu solder alloy for different conditions. Furthermore, mathematical fatigue model based on FKM guideline (in German “Fachkuratorium Maschinenbau) is extracted out of the experiments under all these external effects. The models can be exported later for lifetime evaluation purposes on applications. The paper thereby proposes the use of FKM guideline in the field of microelectronics.     

Investigation on thermal fatigue of SnAgCu,Sn100C,and SnPbAg solder joints in varying temperature environments

Thermal cycling tests have been performed for a range of electronic components intended for avionic applications, assembled with SAC305, SN100C and SnPbAg solder alloys. Two temperature profiles have been used, the first ranging between −20 °C and +80 °C (TC1), and the second between −55 °C and +125 °C (TC2). High level of detail is provided for the solder alloy composition and the component package dimensions, and statistical analysis, partially supported by FE modeling, is reported. The test results confirm the feasibility of SAC305 as a replacement for SnPbAg under relatively benign thermomechanical loads. Furthermore, the test results serve as a starting point for estimation of damage accumulation in a critical solder joint in field conditions, with increased accuracy by avoiding data reduction. A computationally efficient method that was earlier introduced by the authors and tested on relatively mild temperature environments has been significantly improved to become applicable on extended temperature range, and it has been applied to a PBGA256 component with SAC305 solder in TC1 conditions. The method, which utilizes interpolated response surfaces generated by finite element modeling, extends the range of techniques that can be employed in the design phase to predict thermal fatigue of solder joints under field temperature conditions.     

Effect of elevated temperature on PCB responses and solder interconnect reliability under vibration loading

In this paper, vibration tests are conducted to investigate the influence of temperature on PCB responses. A set of combined tests of temperature and vibration is designed to evaluate solder interconnect reliability at 25 °C, 65 °C and 105 °C. Results indicate that temperature significantly affects PCB responses, which leads to remarkable differences in vibration loading intensity. The PCB eigenfrequency shifts from 290 Hz to 276 Hz with an increase of test temperature from 25 °C to 105 °C, during which the peak strain amplitude is almost the same.Vibration reliability of solder interconnects is greatly improved with temperature rise from 25 °C to 105 °C. Mean time to failure (MTTF) of solder joint at 65 °C and 105 °C is increased by 70% and 174% respectively compared to that of solder joint at 25 °C. Temperature dominates crack propagation path of solder joint during vibration test. Crack propagation path is changed from the area between intermetallic compound (IMC) layer and Cu pad to the bulk solder with temperature increase.     

Study on the thermal stability of Ga-doped ZnO thin film: A transparent conductive layer for dye-sensitized TiO2 nanoparticles based solar cells

Generally, optoelectronic devices are fabricated at a high temperature. So the stability of properties for transparent conductive oxide (TCO) films at such a high temperature must be excellent. In the paper, we investigated the thermal stability of Ga-doped ZnO (GZO) transparent conductive films which were heated in air at a high temperature up to 500 °C for 30 min. After heating in air at 500 °C for 30 min, the lowest sheet resistance value for the GZO film grown at 300 °C increased from 5.5 Ω/sq to 8.3 Ω/sq, which is lower than 10 Ω/sq. The average transmittance in the visible light of all the GZO films is over 90%, and the highest transmittance is as high as 96%, which is not influenced by heating. However, the transmittance in the near-infrared (NIR) region for the GZO film grown at 350 °C increases significantly after heating. And the grain size of the GZO film grown at 350 °C after annealing at 500 °C for 30 min is the biggest. Then dye-sensitized TiO2 NPs based solar cells were fabricated on the GZO film grown at 350 °C (which exhibits the highest transmittance in NIR region after heating at 500 °C for 30 min) and 300 °C (which exhibits the lowest sheet resistance after heating at 500 °C for 30 min). The dye-sensitized solar cell (DSSC) fabricated on the GZO film grown at 350 °C exhibits superior conversion efficiency. Therefore, transparent conductive glass applying in DSSCs must have a low sheet resistance, a high transmittance in the ultraviolet–visible–infrared region and an excellent surface microstructure.     

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.     

Silicon melt density — problems of Archimedean technique

Si melt density has been found to have the maximum value around 2.54 g/cm³ at 24°C above the melting point, like H₂O. The anomalous variation near the melting point reported by Sasaki et al. [1] has been found to be due to the melt climbing to the bob when just touching the Si melt surface. It is needed to wait more than 2 h to get constant values. We used fresh bobs to measure one point temperature in order to eliminate the bob thickness variations. The density variations are discussed in terms of weight signal variations. Tentative density values are proposed.     

Thermal stability of back side metallization multilayer for power device application

Metallization multilayers on the back side of a power device were focused in this study. Si wafers coated with high melting point metals were exposed at 300 °C for 300 h to investigate diffusion condition of the metallization layer. We developed and examined the thermal stability of die bonding material (Au paste) including sub–micrometer–sized Au particles. Auger electron spectroscopy was applied to observe the atomic composition of the multilayers in depth direction after the high temperature aging. Surface morphology was observed using optical microscope and scanning electron microscope. While atomic composition on Ti/Au changed drastically after the high temperature aging, other multilayers maintained their metallization composition. However, the surface morphology was slightly changed on Ti/Ru/Au, W/Au, and Ta/Au. Bond strength on the Ti/Pt/Au kept over 40 MPa with unified bonding layer after exposing at 300 °C for 1000 h.     

High thermal annealing effect on structural and optical properties of ZnO–SiO2 nanocomposite

The effect of annealing temperature on photoluminescence (PL) of ZnO–SiO₂ nanocomposite was investigated. The ZnO–SiO₂ nanocomposite was annealed at different temperatures from 600 °C to 1000 °C with a step of 100 °C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO₂ matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 °C and dumbbell morphology above 800 °C. The absorption spectrum of ZnO–SiO₂ nanocomposite suffers a blue-shift from 369 nm to 365 nm with increase of temperature from 800 °C to 1000 °C. The PL spectrum of ZnO–SiO₂ nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 °C to 700 °C and then decreased for samples annealed at and above 800^°C. The XRD results showed that formation of willemite phase starts at 800 °C and pure willemite phase formed at 1000 °C. The decrease of the intensity of 396 nm emission peak at 900 °C and 1000 °C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO₂ at these temperatures. At 1000 °C, an emission peak at 388 nm is observed in addition to UV emission of ZnO at 396 nm and is believed to be originated from the willemite.     

Effect of annealing temperature on optical and electrical properties of lead sulfide thin films

Lead sulfide (PbS) thin films with 150 nm thickness were prepared onto ultra-clean quartz substrate by the RF-sputtering deposition method. Deposited thin films of PbS were annealed at different temperatures 100 °C, 150 °C, 200 °C, 250 °C and 300 °C. X-ray diffraction pattern of thin films revealed that thin films crystallized at 150 °C. Crystalline thin films had cubic phase and rock salt structure. The average crystallite size of crystalline thin films was 22 nm, 28 nm and 29 nm for 150 °C, 200 °C and 250 °C respectively. From 150 °C to 250 °C increase in annealing temperature leads to increase in crystallite arrangement. FESEM images of thin films revealed that crystallite arrangement improved by increasing annealing temperature up to 250 °C. Increase in DC electrical conductivity by increasing temperature confirmed the semiconductor nature of crystalline thin films. Increase in dark current by increasing annealing temperature showed the effect of crystallite arrangement on carrier transport. Photosensitivity decreased by increasing annealing temperature for crystalline thin films that it was explained at the base of thermal quenching of photoconductivity and adsorption of oxygen at the surface of thin films that leads to the formation of PbO at higher temperatures.     

Strain-insensitive and high temperature fiber sensor based on a Mach–Zehnder modal interferometer

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64 pm/°C from 200 °C to 1000 °C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675 °C/με. The reasons for realizing the high temperature sensitivity is also discussed.     

Effect of annealing on photoluminescence of passivated porous silicon

Photoluminescence (PL) of annealed porous silicon (PS) without and with nitrogen passivation has been investigated. The un-nitridated PS emits intense blue and green light, while that with passivation, emits only blue light and its intensity increases obviously. It is found that the PL intensity of the nitrified PS decreases with increasing temperature from 300 °C to 700 °C, but increases drastically after annealing at 800 °C and 900 °C, which might be due to the formation of Si–N bonds that passivates the non-radiative centers (Si dangling bonds) on the surface of PS samples. However, the intensity of the un-nitridated PS decreases continuously with increasing temperature from 300 °C to 900 °C, which might be due to desorption of hydrogen.     

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.     

Photoluminescence of phosphorous doped Ge on Si (100)

Photoluminescence (PL) of selectively grown phosphorus (P) doped germanium (Ge) is investigated. 350–600 nm thick P-doped Ge is grown on 100 nm thick P-doped Ge buffer layer, which is annealed at 800 °C before the main part of Ge deposition. In the case of Ge deposited at 325 °C, approximately two times higher PL intensity is observed by P doping of ~3.2×10¹⁹ cm⁻³. Further increase of PL intensity by a factor of 1.5 is observed by increasing the growth temperature from 325 °C to 400 °C due to improved crystal quality. Varying PH₃ partial pressure at 400 °C, red shift of the PL occurred with increasing P concentration due to higher bandgap narrowing. With increasing P concentration up to ~1.4×10¹⁹ cm⁻³ at 400 °C the PL peak intensity increases by filling electrons into the L valley and decreases due to enhanced point defect concentration and degraded crystallinity. By post-annealing at 500–800 °C, the PL intensity is further increased by a factor of 2.5 because of increased active P concentration and improved crystal quality. Reduced direct bandgap energy by introducing tensile strain is also observed.     

Failure and stress analysis of through-aluminum-nitride-via substrates during thermal reliability tests for high power LED applications

The objective of this study is to evaluate the reliability of through-aluminum-nitride-via (TAV) substrate by comparing those experimental results with the finite element simulation associated with measurements of aluminum nitride (AlN) strength and the thermal deformation of Cu/AlN bi-material plate. Two reliability tests for high-power LED (Light emitting diode) applications are used in this study: one is a thermal shock test from − 40 °C to 125 °C, the other is a pressure cook test. Also, the strength of AlN material is measured by using three-point bending test and point load test. The reliability results show that TAV substrates with thicker Cu films have delamination and cracks after the thermal shock test, but there are no failure being found after the pressure cook test. The determined strengths of AlN material are 350 MPa and 650 MPa from three-point bending test and point load test, respectively. The measurement of thermal deformation shows that the bi-material plate has residual-stress change after the solder reflow process, also indicating that a linear finite element model with the stress-free temperature at 80 °C can reasonably represent the stress state of the thermal shock test from − 40 °C to 125 °C without considering Cu nonlinear effect. The further results of the finite element simulation associated with strength data of AlN material have successfully described those of the reliability test.     

Design,development and reliability testing of a low power bridge-type micromachined hotplate

In this paper, the development and reliability of a platinum-based microheater with low power consumption are demonstrated. The microheater is fabricated on a thin SiO₂ bridge-type suspended membrane supported by four arms. The structure consists of a 0.6 μm-thick SiO₂ membrane of size 50 μm × 50 μm over which a platinum resistor is laid out. The simulation of the structure was carried out using MEMS-CAD Tool COVENTORWARE. The platinum resistor of 31.0 Ω is fabricated on SiO₂ membrane using lift-off technique. The bulk micromachining technique is used to create the suspended SiO₂ membrane. The temperature coefficient of resistance (TCR) of platinum used for temperature estimation of the hotplate is measured and found to be 2.2 × 10⁻³/°C. The test results indicate that the microhotplate consumes only 11.8 mW when heated up to 400 °C. For reliability testing, the hotplate is continuously operated at higher temperatures. It was found that at 404 °C, 508 °C and 595 °C, the microhotplate continuously operated up to 16.5 h, 4.3 h and 4 min respectively without degrading its performance. It can sustain at least 53 cycles pulse-mode of operation at 540 °C with ultra-low resistance and temperature drifts. The structure has maximum current capability of 19.06 mA and it can also sustain the ultrasonic vibration at least for 30 min without any damage.