Thermal deformation measurement of the solder joints in electronic packages using electron moiré method

In this paper, electron moiré method is used to measure the thermal deformation of electronic packages. In order to observe the electron moiré fringe, a holographic grid was replicated on the cross section of the BGA type package at 150°C. This grid was fabricated on a glass plate using a moving point holographic system, and was replicated to measured area at high temperature. Under SEM, the holographic grid(specimen grid) and a programmed electron beam scan(master grid) interfere and form electron moiré patterns. The shear strain measurement technique using electron moiré method is described. Using the electron moiré method, the shear strains in the different solder joints were measured and analysed. Some useful results were obtained.     

Development of temperature compensated high elongation resistance strain gauges for use up to 250°C

The paper describes the development and evaluation of temperature compensated high elongation resistance strain gauges for use from room temperature to 250°C. These gauges could be temperature-compensated on steels with coefficient of thermal expansion α = 11 ppm/°C. Thermal output within 250°C was about 1 μm/m/°C and maximum standard deviation of 5 gauges was 34 μm/m. Strain limit was > 4% at room temperature and at 250°C. Gauge factors of different strain ranges at R.T. and at 250°C are tabulated. Some applications are stated.     

A PRELIMINARY STUDY ON CRACK HEALING BEHAVIOUR OF Si3 N4 /SiC COMPOSITE CERAMICS

Ceramic (Si3 N4 /SiC) composites have been produced by sintering. From the sintered block, three point bend specimens were cut out. A semi-circular crack was made on the centre of the tension surface of the test specimen with the aid of a Vicker's indenter. The diameter of the semi-circular crack was about 60–70  μm. The specimens were subsequently heat treated at 1300°C for 1  h in vacuum, nitrogen or air. The bending strength was measured at room temperature, 800 and 1000°C. The specimens heat treated in air recovered considerably their bending strength at 1000°C, several specimens failed at a location different from the healed crack and their average strength showed the same value of that for smooth specimens. From these results, it is concluded that the recovery in bending strength of a cracked specimen was caused by crack healing.     

大量程光栅位移测量累积误差的修正

提出了一种自动测量光栅栅距修正累积误差的方法。栅距测量是基于高阶累积量估计光栅传感器输出的两路莫尔条纹信号的时间延迟而得到的,该方法能够实现每个栅距的测量,通过对每个光栅栅距的误差进行修正来减少累积误差,为大量程高精度测量奠定了基础。实验采用长为500 mm的50线/mm的光栅传感器,该传感器包含栅线25 000条,实现栅距测量分辨力为3 nm,达到了纳米级测量。该方法抗干扰能力强,适合在生产现场应用。     

A high accuracy, low power, reproducible temperature telemetrysystem

A low-power temperature telemetry system incorporating a miniature micropower temperature sensor/modulator and hand-held decoder with direct digital readout is described. The system is designed to avoid the need to calibrate and characterize individual units while guaranteeing an accuracy of ±0.25°C and a resolution of 0.1°C. The combined sensor and transmitter is constructed using thick-film technology and weighs less than 2.5 g without batteries. Developed principally for wild life tracking and monitoring, the system also has other applications where remote environmental monitoring is required     

The NPL InSb-based Radiation Thermometer for the Medium Temperature Range ( < 962°C)

Over the temperature range from 156 to 962°C, the NPL maintains a series of heatpipe blackbody sources for the calibration of customer sources, radiation thermometers, and thermal imagers. The temperature of each of the sources is determined using a calibrated platinum resistance thermometer or gold-platinum thermocouple placed close to the radiating surface at the back of the cavity. The integrity of such a blackbody source relies on it having good temperature uniformity, a high and well-known effective emissivity, and having the sensor in good thermal contact with the cavity. To verify the performance of the blackbody sources, it is necessary to use an infrared thermometer that has been independently calibrated to compare the radiance temperature of the source with the temperature measured by the contact sensor. Such verification of the NPL blackbodies has been carried out at short wavelengths: from 500 to 1,000°C using the NPL LP2 calibrated using the NPL gold point, and at 1.6 μm using an InGaAs-based radiation thermometer calibrated at a series of fixed-points from indium (156°C) to silver (962°C). Thermal imaging systems traditionally operate over the 3–5 μm waveband and are calibrated using NPL sources. Up until now, it has not been possible to verify the performance of the sources in this waveband except indirectly by cross-comparison of the sources where they overlap in temperature. A mid-infrared (nominally 3–5 μm) radiation thermometer has, therefore, been designed, constructed, and validated at NPL. The instrument was validated and calibrated using the fixed-point blackbody sources and then used to validate the heatpipe blackbodies over their temperature range of operation. The results of the instrument validation and blackbody measurements are given.     

Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC

An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.     

Design and development of long-period grating sensors for temperature monitoring

Long Period Gratings (LPGs) have been developed using carbon dioxide laser in a standard optical fibre. LPGs with a periodicity of 600 μm and grating length of 24 mm have been inscribed on standard single mode fibre. Such gratings have been used in designing temperature sensors and temperature is monitored up to 80°C. The sensitivity of such type of sensor is 0·06 nm/°C where as for standard Fibre Bragg Grating (FBG) it is 0·011 nm/°C. The LPG performance is also evaluated after γ-ray irradiation for total dose of 5 KGy and has not shown any effect on transmission spectrum.     

Development of a Multiband near-to-far Infrared Radiance COmparator (MIRCO)

In recent years, there has been a growing demand to calibrate industrial blackbodies both at short wavelengths for lower temperatures and at long wavelengths for higher temperatures. User requests cover a very wide temperature range, from  −20°C to 1,500°C in the infrared bands used by thermal cameras or as defined by specific applications (especially the 1–3 μm, 3–5 μm, and 8–12 μm bands). Therefore, LNE (Laboratoire National de Métrologie et d’Essais) has developed a radiance comparator with a mirror-based optical system, an associated set of interference filter wheels, a modular holder for several infrared detectors, and a lock-in amplifier. This setup is designed to be very versatile in terms of wavelength and temperature. Targeted performances have a thermal resolution better than 0.05°C, and a known and controlled size-of-source effect (SSE). A silicon detector and a visible-to-near infrared integrating sphere were used to assess the stray light inside the housing, and supplementary baffles and stops were used to reduce it to an acceptable level. The investigation included measurement of the SSE for this comparator layout. Then, the performance in the 3–5 μm and 8–12 μm bands, using, respectively, indium antimonide (InSb) and mercury cadmium telluride (MCT) detectors, was evaluated using a water heat-pipe blackbody. This paper describes the modeling and the technical solutions implemented to optimize the optical system. Preliminary results are presented for the short-term stability, the thermal resolution between  −20°C and 960°C, and also the SSE up to 60 mm in these bands.     

基于微型镓基共晶固定点的温度传感器在轨校准方法研究

介绍了微型镓基共晶固定点的灌注工艺和准绝热相变特性测量系统;结合空腔黑体和非近位安装的温度传感器,研究了Ga-Sn和Ga-Zn共晶固定点的相变温坪重复性和Ga固定点的相变温坪长期稳定性;通过特定的热环境下镓及2个镓基共晶固定点三者熔化过程中温度传感器测量到的相变温坪值,对嵌入空腔黑体底部的温度传感器进行校准,其校准结果与实验室常规校准方法得到的结果差异均小于2mK。实验结果表明:在热环境保持不变的条件下,随着相变时间的增加,相变温坪值就越靠近理论上相变物质的熔化温度,即固定点与温度传感器测孔之间的异位温差越小;对于Ga-Sn和Ga-Zn共晶固定点,温度传感器测量到的相变温坪值与加热功率呈线性关系,零功率下的单点校准温度分别为20.352℃和25.187℃。     

Fatigue strength of crack-healed Si3N4/SiC composite ceramics

Si₃ N₄ /SiC composite ceramics were sintered and subjected to three-point bending on specimens made according to the appropriate JIS standard. A semi-circular surface crack of 110 μm in diameter was made on each specimen. By using three kinds of specimen (smooth, cracked and crack healed), crack-healing behaviour, cyclic and static fatigue strengths were determined systematically at room temperature and 1000 °C. The main conclusions are as follows: (i) Si₃ N₄ /SiC composite ceramics have the ability to heal after cracking; (ii) crack-healed specimens showed similar cyclic and static fatigue strengths as smooth specimens, this being caused by crack healing; (iii) crack-healed zones had a sufficient fatigue strength and most fractures occurred outside the pre-cracked zone in those crack-healed specimens.     

Hot embossing of grating-based optically variable images in thermoplastic acrylic lacquer

We report the novel use of thermoplastic acrylic lacquer (automotive paint) in the hot embossing of nanoscale structures. Replicas of grating arrays have been produced in coatings of acrylic lacquer using a standard embossing process. The master dies for the experiments comprised grating arrays fabricated by electron beam lithography. Grating patterns with a pitch of 0.7–1.3 μm were configured to produce diffractive images over an area of ∼25 × 25 mm. The embossing experiments used a replicated Ni shim as a die and were performed at 100–150 °C and 80 kN force. A temperature above the glass transition temperature for the lacquer, T = 120–150 °C, was required in order to achieve a uniform impression across the embossed area of ∼80 × 80 mm. The diffractive grating patterns which were embossed into acrylic lacquer have shown optical effects suitable as a security feature including image switching and color movement.     

Enhancing electron field emission of carbon nanoflakes by hydrogen post-annealing process

In this study, the carbon nanoflakes (CNFs) fabricated by sputtering were chosen as the field emission emitters because of their very sharp and thin edges which are potentially good electron field emission sites. The as-deposited CNFs were annealed in the furnace under hydrogen atmosphere. The results showed that the optimum field emission properties with smaller turn-on field and larger current density were obtained at annealing temperature of 600 °C for 10 min. The hydrogen thermal annealing has chemical etching on the surface of the CNFs and produces appropriate emission site density to increase the emission current density. The turn-on field was reduced from 6.7 to 5.8 V/μm and electric current density was increased from 22 to 187 μA/cm² under 8 V/μm after hydrogen thermal annealing.     

Propagation of short fatigue cracks from notches in a Ni base superalloy: experiments and modelling

A notched specimen containing a semicircular slot (0.1 mm deep) was designed to simulate the growth of three-dimensional short cracks under a stress concentration. Fatigue tests were performed on N18 superalloy at 650 °C with trapezoidal loading cycles. A high-resolution optical measurement technique proved to be capable of detecting half-surface crack increments as small as 10 μm, and the potential drop method was found to be inappropriate for very small crack lengths. The stress intensity factor, Δ K , was calculated using a weight functions method. Non-uniform stress fields were determined by FEM modelling using elasto-viscoplastic constitutive equations. The plasticity-induced crack closure effect was calculated within the specimen using viscoplastic FEM modelling. The prediction of crack aspect ratio was used to investigate differences of closure along the crack front. The role of notch plasticity on these differences is discussed. Using these calculations, it is shown that the apparent differences between the growth behaviour of short and long cracks can be largely accounted for.     

A new ultra long-period fiber grating for measuring torsional characteristics

In this paper, we proposed a novel kind of periodic helical ultra-long period fiber grating (U-LPFG) for measuring the torsion rate and distinguishing the torsion direction. The sensor was fabricated by spirally deforming a common fiber by local heating for 4 periods. This method of fabrication was not only easy to implement, but also further increased the sensitivity of the grating to the torsion because of the spiral structure. This paper introduced the torsional characteristics of this sensor in detail and drew some relevant conclusions. Experimental results showed that the twist sensitivity of 0.085?nm/(rad/m). Meanwhile, the temperature sensing characteristic of the proposed U-LPFG was also tested as 68?pm/°C within the range of 30?°C ～210?°C. Therefore, this proposed sensor could achieve good results in simultaneously measuring the torsion rate and distinguishing the torsion direction, and it may have great potential in some practical applications.     

FATIGUE CRACK GROWTH IN TWO ADVANCED TITANIUM ALLOYS UNDER CONSTANT AND VARIABLE AMPLITUDE LOADING AT 25 AND 175 °C

Fatigue crack growth of β-21S and Ti-62222 in sheet form was investigated under constant and miniTWIST flight spectra loading conditions at 25 and 175 °C. Variable amplitude results were compared with life calculations performed using NASA/FLAGRO software and constant amplitude fatigue crack growth results. Single tensile overloads under constant Δ K were performed to evaluate load interaction effects. Constant amplitude results showed that fatigue crack growth resistance was slightly better for Ti-62222 than β-21S at 25 and 175 °C. The presence of crack closure under various conditions caused moderate shifts in the fatigue crack growth data. Under miniTWIST flight spectra loading, Ti-62222 exhibited a greater extension in life in comparison to the β-21S at elevated temperature, consistent with the NASA/FLAGRO calculations. This was also consistent with the single tensile overloads where 25 °C tests were comparable for both materials, while at 175 °C, delay cycles were greater by a factor of almost three for Ti-62222. Extensive secondary cracking in Ti-62222 at elevated temperature accounted for the extended fatigue lives.     

Thermal emission from undoped and degenerate silicon structures and from a metallic grating structure

The thermal spectral emission properties of three types of periodic grating structure were investigated: (1) a lightly doped (intrinsic-like) silicon grating, (2) a degenerate (metallic-like) silicon grating, and (3) silicon gratings coated with nickel metal. The structural dimensions of all samples were the same, with feature sizes comparable to the measurement wavelengths (2.5–25 μm). The measurement temperatures for all samples were in the range 27–740 °C. In general, it was found that the spectral emission of the metallic-like gratings depended on the parameters of the grating material and on the structural dimensions. A spectral oscillation in the wavelength range comparable to the structural dimension was observed.     

灵敏度可调型光纤FBG倾角传感器研究

提出了一种基于等截面梁弯曲变形原理的灵敏度可调型光纤布拉格光栅(FBG)倾角传感器,通过FBG光栅感受因结构倾角改变而引起的等截面梁弯曲变形,进而实现对结构倾斜角度的测量,并构建了灵敏度可调型光纤FBG光栅倾角检测系统。实验结果表明,该FBG倾角传感器测量范围为±35°,最高灵敏度达到56.93pm/(°),测量精度为0.02°。该传感器可通过改变等截面梁的宽度还可实现对倾角检测灵敏度的有效调节。     

The permeability and stability of microencapsulated epoxy resins

Microcapsules containing self-healing agents have been introduced into polymer to self-heal the microcracks and toughen the brittle matrix. Poly(urea–formaldehyde) (PUF) microcapsules containing epoxy resins are potential for the self-healing and toughening polymer. The resistance to medium surroundings of microcapsules is required. In the present study, PUF microcapsules containing epoxy resins were prepared by in situ polymerization. The effects of diameter, surface morphology and wall thickness on the permeability and stability of microcapsules in thermal and solvent surroundings were investigated. The morphology of microcapsule was investigated using optical microscope (OM), metalloscope (MS) and scanning electron microscope (SEM), respectively. The composition on the surface of microcapsule was analyzed by using energy dispersive analysis of X-ray (EDAX). The thermal properties of microcapsules were investigated using differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The thermal permeability of core increases and the stability of microcapsule decreases with the enhancement of heating temperature mainly due to the expansion of epoxy resins below 251 °C and the decomposition of PUF above 251 °C. At room temperature, the permeability constants of core materials of microcapsules in acetone solvent are small and they are 1.20 × 10⁻³ m s⁻¹, 1.39 × 10⁻³ m s⁻¹ and 1.60 × 10⁻³ m s⁻¹ corresponding to the microcapsules with diameters of 400 ± 50 μm, 230 ± 40 μm and 120 ± 30 μm. Increasing the surface smoothness, diameter and wall thickness can decrease the permeability and improve the stability of microcapsules in thermal and solvent surroundings.