Wire Bond Research Articles

Fabrication and Characterization of Ferrofluidic-Based Wire-Wound and Wire-Bonded Type Inductor for Continuous RF Tunable Inductor

This paper reports on the novel implementation of a tunable solenoid inductor using the fluid-based inductance varying technique. The concept utilized material permeability variation that directly modifies self-induced magnetic flow density inside the coil, which in turn creates a variation of the inductance value. The core is formed by a channel which allows the circulation of a liquid through it. The liquid proposed for this technique has ferromagnetic behavior, called ferrofluid, with a magnetic permeability higher than unity. To evaluate the proposed technique, two different types of solenoid inductor were designed, simulated and measured. The two structures are wire-wound and wire bond solenoid inductors. The structures are simulated in a 3D EM analysis tool followed by fabrication, test and measurement. The wire-bonded-based inductor showed a quality factor of 12.7 at 310 MHz, with 81% tuning ratio, by using ferrofluid EMG 901. The wire-wound-based inductor showed that the maximum tuning ratio is 90.6% with quality factor 31.3 at 300 MHz for ferro fluidic EMG 901. The maximum measured tuning ranges were equal to 83.5% and 56.2% for the wire-wound type and the wire-bonded one, respectively. The measurement results for the proposed technique showed a very high tuning range, as well as high quality factor and continuous tunability.

Measurement of thermal conductivity of millimeter-sized wires using the fin effect

Measurement of thermal conductivity of thin wires is critical for multiple engineering applications that involve heat transfer in thin wires. While well-established experimental methods are available for thermal conductivity measurements on large as well as microscale samples, these methods do not work well for thin wires of around a few mm diameter. This paper presents a comparative method for measuring thermal conductivity of a thin wire. The method is based on infrared thermography of the wire of interest suspended from a high temperature base. Through comparison of thermal response of the wire with that of a standard wire of known properties, thermal conductivity is measured for a number of wires in a broad range of thermal conductivity. Measurements are reported for both low thermal conductivity polymer wires and high thermal conductivity metal wires. Results are found to be in good agreement with expected values of thermal conductivity. The effect of wire diameter and base temperature on the accuracy of measurements is investigated. The method is used for measurement of thermal conductivity of solder wires. Results presented in this work contribute towards addressing an important thermal metrology need, and may help improve thermal design of a broad range of engineering applications that utilize thin wires.

Optical receiver module design that improves link gain of 28 GHz RF signal over a multi-mode fiber

We investigate the impact of photodetector (PD) aperture size and wire bond length on the performance of analog radio over multi-mode fiber (A-RoMMF) systems using high-frequency bands up to 28GHz. It is realized that transmission characteristics of A-RoMMF is affected by the change of frequency response due to the PD aperture size and the bonding wire length. We also demonstrate A-RoMMF transmission using an optical receiver mounted PD and a low noise amplifier (LNA) on one printed circuit board (PCB) to improve size, link gain, and transmission characteristics.

A Lifetime Prediction Method for IGBT Modules Considering the Self-Accelerating Effect of Bond Wire Damage

As core components of power converters, the insulated gate bipolar transistor (IGBT) module is required to have long-term reliability in increasingly more applications. To assess and improve the reliability, power cycling (PC) tests are conducted to determine the lifetime of IGBT modules; these tests are very time-consuming and may take a couple of weeks or even months for a single sample. Therefore, an urgent need in the industrial community is to develop an accurate and efficient method to predict the lifetime of the IGBT modules. In this article, we present a lifetime prediction method, in which the self-accelerating effect of bond wire damage on the lifetime is considered by using the feedback from the collector-emitter ON-resistance degradation into the power loss model, and a degradation model is proposed to describe the degradation process of the collector-emitter ON-resistance. Base on the physical PC tests of IGBT modules, we demonstrate that the proposed method accurately and efficiently predicts the lifetime of IGBT modules.

A Novel Approach to Control of Piezo-Transducer in Microelectronics Packaging: PSO-PID and Editing Trajectory Optimization

This article presents a novel optimization algorithm to control the ultrasonic vibration of piezo-transducer in microelectronics packaging. The control of resonant frequency tracking to piezo-transducer is significant to the bonding quality. A conventional PID controller is applied to track the resonant frequency of piezo-transducer dynamically; however, there are shortcomings, such as tedious parameter tuning and uncertain optimal parameters. This article proposes the particle swarm optimization (PSO) to search the PID parameters intelligently. The MATLAB-Simulink model of PSO-PID is established to analyze the phase and frequency response of the piezo-transducer by a closed loop, where the optimal control parameters are determined by the PSO search. To solve the conventional abrupt ultrasonic power, an editable voltage trajectory with analytical geometry is proposed to provide various driving voltage trajectories. Finally, the control experiments with the proposed optimization are carried out in ultrasonic wire bonder. The results validate that the PSO-PID and editing trajectory optimizations can attain competitive bonding quality, stability, and robustness.

Electrochemical Express Analysis of Organic Additives in Lead-Free Wafer Level Packaging Plating Baths

Semiconductor packaging migrated from wire bond to flip chip level interconnect to meet size, weight and electrical performance requirements. Lead-free alloys for flip chip attachment has become a common material in electronics. Alloys containing Sn and Ag as well as pure Sn are the most common ones. The mechanical strength, wetting, and fatigue resistance of these alloys and pure Sn is either comparable or surpass lead contained alloys. Electroplating with lead-free alloys is the most desirable technique due to its low cost and usefulness in building fine pitch solder bumps [1].The new generation of lead free plating systems targeting faster deposition rates, better uniformity with-in die and longer bath life. The co-deposition of elements may be complicated by the large difference in the electrode potentials of tin and alloying metals (e.g. silver, bismuth). To produce uniform and dense deposits, these plating baths include organic additives that are typically separated for two groups with different functions: polarizers that significantly affect the plating rate and control the uniformity of deposit; and grain refiners [2]. For desired properties of deposit, the bath components must be kept within specific concentration ranges. In some cases, the analytical results for bath components should be available more frequently in order to provide feedback to dosing system [3]. To develop most accurate and repeatable analytical methods, the interactions between lead free plating bath components were previously investigated and understood [2]. That allowed to develop efficient analytical techniques for analysis of lead free plating bath components. However, faster analytical methods are required for control of high speed plating baths. The effect of changes in the concentration of organic components on the structure of deposit were studied more recently and will be reported in this work.When the speed of analyses increases, it is critical to keep reproducible state of all electrodes. Therefore, new regeneration method for electrodes was developed. For development of new express analytical methods, we utilized an electrochemical cell with three electrodes connected to a potentiostat/galvanostat. RDE working and counter platinum electrodes were used as well as Ag/AgCl double junction reference electrode. It has been found that multiple factors can reduce the speed of electrochemical analysis. One of the most potent parameters that affect speed of analysis was a scan rate. Fig. 1 shows the electrochemical responses of polarizer at different scan rates.Other parameters and steps of analysis were also evaluated for potential reduction the analysis time. This presentation will provide more information related to the electrochemical behavior of organic additives at specific conditions when the analysis is performed with different speed. Results for other bath components will be also presented. The concentration of inorganic components and silver complexing agent can be determined via non-reagent and virtually real time spectroscopic analytical methods. The presentation will be concluded with a discussion of analytical results for several organic additives at different concentration levels.

Controllable Transfer of MOx Nanowires on Microhotplate-Based Gas Sensing Devices

Introduction SnO2 nanowires (NWs) have been synthesized and implemented on CMOS-based gas sensors devices with gold inter-digital electrode structures (IDES). For the implementation process of NWs a polydimethylsiloxane-based stamping transfer was employed with help of a Condor Sigma bond tester. The multi-nanowire gas sensor has demonstrated sensitivity for toluene concentrations as low as 100 ppb. The transfer method applied in this work is one step further from previous manual transfer [1] to the industrial adaptation of the process. Materials and substrates A two-step synthesis was applied to prepare SnO2 nanowires, as described elsewhere [2]. The gas sensing substrate was a commercial chemical sensor platform provided by ams AG, Austria - a 2x2 mm micro-hotplate chip with a Pt-based microheater and Pt-IDES with an electrode width and the distance between the electrode fingers both 5 µm. SnO2 NWs were transferred on the IDES-structure with a PDMS stamp, prepared by 1:10 standard recipe and cut into 3x3mm pieces. Transfer of SnO2 NWs A Condor Sigma bond tester tool was employed to transfer SnO2 NWs. The PDMS-stamp was glued on a specific tool of the bond tester, which is usually employed for testing wire bond connections. The PDMS stamp was pressed with well controlled parameters (force, distance and position) onto the substrate with MOx NWs in order to collect the NWs with the stamp. Afterwards the NWs were transferred onto the gas sensing substrate with maximal force of 0.7N and 10s time of contact between the stamp and the micro-hotplate substrate, which resulted in NW transfer and interconnection to the electrodes. Gas measurement Gas measurements were performed by an automatized setup, with synthetic air (80% N2, 20% O2) as a background gas and a constant flow rate of 1000 sccm. Three different humidity levels of 25, 50 and 75% were investigated in the presence of 5 different toluene concentrations – 0.05, 0.1, 0.5, 1 and 5 ppm. The temperature of the microhotplate was kept constant at 300°C. Response was calculated as follows:R = (Rair -Rgas)/Rair *100%where Rair is a resistance of the sensor in synthetic air before the gas pulse and Rgas is a resistance of the sensor in the presence of a test gas at the end of a gas pulse. Two independent sensors were measured, prepared by the same technique. Results and Conclusions The Condor Sigma bond tester enabled precise manipulation of the PDMS NW transfer stamp not only in all 3 axis but also by using force sensor. Due to the high precision of the machine the transfer process could be performed with high precision and control without damage to the micro-hotplate. This demonstrates that such a NW transfer process is suited for realization of a NW-based chemical sensor devices. The response towards toluene is shown in Fig.1. The multi-nanowire based devices are able to sense a gas concentration as low as 100 ppb (where the threshold limit value for Switzerland is 50 ppm [3]). There is also visible dependence towards humidity – but it is not as high as for toluene – i.e. for 5 ppm of toluene the mean response for both sensors is 9%, 8% and 8% for 25, 50 and 75% rH levels, respectively. Presently the work is focused on the NWs transfer on CMOS-based microhotplate array chips. Acknowledgements This work was partly performed within the project “FunkyNano – Optimized Functionalization of Nanosensors for Gas Detection by Screening of Hybrid Nanoparticles” funded by the FFG - Austrian Research Promotion Agency (Project No. 858637).

Multi-chip assemblies combining wire bond and flip-chip package technologies

The paper considers technological solutions for the production of multi-chip package-on-package assemblies. To evaluate the capabilities of the manufacturer product line the PoP prototype samples were produced. The results of qualification tests of PoP prototype samples are presented. Conclusions have been drawn on the applicability of systems in package, combining the installation technologies of Wire Bond and Flip-Chip crystals.

Hybrid multi-chip assembly of optical communication engines by in situ 3D nano-lithography

Three-dimensional (3D) nano-printing of freeform optical waveguides, also referred to as photonic wire bonding, allows for efficient coupling between photonic chips and can greatly simplify optical system assembly. As a key advantage, the shape and the trajectory of photonic wire bonds can be adapted to the mode-field profiles and the positions of the chips, thereby offering an attractive alternative to conventional optical assembly techniques that rely on technically complex and costly high-precision alignment. However, while the fundamental advantages of the photonic wire bonding concept have been shown in proof-of-concept experiments, it has so far been unclear whether the technique can also be leveraged for practically relevant use cases with stringent reproducibility and reliability requirements. In this paper, we demonstrate optical communication engines that rely on photonic wire bonding for connecting arrays of silicon photonic modulators to InP lasers and single-mode fibres. In a first experiment, we show an eight-channel transmitter offering an aggregate line rate of 448 Gbit/s by low-complexity intensity modulation. A second experiment is dedicated to a four-channel coherent transmitter, operating at a net data rate of 732.7 Gbit/s – a record for coherent silicon photonic transmitters with co-packaged lasers. Using dedicated test chips, we further demonstrate automated mass production of photonic wire bonds with insertion losses of (0.7 ± 0.15) dB, and we show their resilience in environmental-stability tests and at high optical power. These results might form the basis for simplified assembly of advanced photonic multi-chip systems that combine the distinct advantages of different integration platforms.

Effects of Temperature and Pd Concentration on the Corrosion Behavior of Pd-Doped Cu and Cu9Al4 at the Cu–Al Ball-Bond Interface

Corrosion-induced failure along the Cu and Cu9Al4 interface is a major reliability concern for the Cu-wire-bonded packages. The open circuit potential, $E_{\text {oc}}$ , and the corrosion current density, $i_{\text {corr}}$ , of Cu and Cu9Al4 with varying amounts of Pd addition were characterized using the potentiodynamic polarization method at 25 °C, 45 °C, and 65 °C. At a given temperature, Pd addition to Cu caused the value of $E_{\text {oc}}$ to increase and the value of $i_{\text {corr}}$ to decrease due to the higher nobility of Pd. For the Cu9Al4 intermetallics, although Pd addition caused an increase in the value of $E_{\text {oc}}$ attributed to the high nobility of Pd, the value of $i_{\text {corr}}$ increases with small amounts of Pd addition due to high cathodic activity of Pd. To further evaluate the effect of Pd addition in preventing the corrosion of Cu wire bonds, galvanic current densities, $i_{g}$ , between Cu and Cu9Al4 and their Pd-doped couples were also measured. At 25 °C and 45 °C, the stabilized value of $i_{g}$ decreases with an increasing amount of Pd addition. At 65 °C, the stabilized value of $i_{g}$ was not lower until 9 wt.% Pd was added. The results of both self-corrosion and galvanic corrosion suggest that the amount of Pd needs to be above a critical value to effectively prevent Cu wire corrosion regardless of the operating temperature.

Hybrid technology for the production of highly integrated multi-chip microcircuits: problems and solutions

Innovative technologies in the field of microelectronics provide technological transformation of the crystal and multichip microcircuit industry, combining various methods of crystal mounting and packaging processes. An increase in the integration of electronic circuits, an increase in the number of peripheral elements and, as a result, an increase in the energy consumption of the crystal, lead to a significant increase in the complexity of solving the problems of packaging when the case is converted into a complex electronic device.Chip crystals, according to current technological standards, are produced by a small number of specialized companies owned by transnational corporations. At the same time, in a number of countries there are qualified personnel specializing in the design of integrated circuits. One of the trends in the Russian market of multifunctional miniature devices is import substitution. A patent information search was conducted to identify trends and directions in the development of technologies in the field of packaging integrated circuits. A detailed analysis of the problem of the production of multi-chip microcircuits, systems in a package combining various packaging processes is shown; ways to solve it are shown, including applied research aimed at creating a hybrid multi-chip packaging technology combining crystals installed in a single package and on a single substrate using various methods installation - Wire bond and Flip chip.

High-Temperature Electronics Packaging for Simulated Venus Condition

Abstract An electronic packaging technology that survives the simulated Venusian surface temperature of 465°C and 96 bar pressure in carbon dioxide (CO2) and nitrogen environments, without the corrosive trace gases, was developed. Alumina ceramic substrates and gold conductors on alumina were evaluated for electrical and mechanical performance. The most promising die-attach materials are thick-film gold and alumina-based ceramic pastes. Alumina, sapphire, silicon, and silicon carbide dies were attached to the alumina substrates using these die-attach materials and exposed to 96 bar pressure in a CO2 environment at 465°C for 244 h. The ceramic die-attach material showed consistent shear strengths before and after the test. An alumina ceramic encapsulation material was also evaluated for thermomechanical stability. The devices on the packaging substrates were encapsulated by a ceramic encapsulation with no significant increase in cracks and voids after the Venusian simulator test. Wire pull strength tests were conducted on the gold bond wire to evaluate mechanical durability before and after the Venusian simulator exposure. The average gold bond wire pull strengths before and after exposure were 5.78 g-F and 4 g-F for 1-mil gold bond wires, respectively, meeting the minimum MIL-STD-885 2011.9 standard. The overall wire bond daisy chain resistance change was .47% after the Venus simulator test, indicating a promising wire bond integrity. A titanium package was fabricated to house the ceramic packaging substrate and a two-level metalized feedthrough was fabricated to provide electrical interfaces to the package.

Electrical testing of small-series multi-chip microcircuit samples combining Wire Bond and Flip-Chip technologies

The paper provides a technical solution and methodology for conducting automated electrical and functional testing of small series samples of multi-chip assemblies. The results of multi-chip assembly samples testing combining Wire Bond and Flip-Chip technologies are presented. Based on the test results, defects that occur during the packaging process are localized and the assembly stages at which these defects occur are determined.

Relative Contributions of Packaging Elements to the Thermal Hysteresis of a MEMS Pressure Sensor

Piezoresistive silicon pressure sensor samples were thermally cycled after being consecutively packaged to three different levels. These started with the absolute minimum to allow measurement of the output and with each subsequent level incorporating additional packaging elements within the build. Fitting the data to a mathematical function was necessary both to correct for any testing uncertainties within the pressure and temperature controllers, and to enable the identification and quantification of any hysteresis. Without being subjected to any previous thermal preconditioning, the sensors were characterized over three different temperature ranges and for multiple cycles, in order to determine the relative contributions of each packaging level toward thermal hysteresis. After reaching a stabilised hysteretic behaviour, 88.5% of the thermal hysteresis was determined to be related to the bond pads and wire bonds, which is likely to be due to the large thermal mismatch between the silicon and bond pad metallisation. The fluid-fill and isolation membrane contributed just 7.2% of the total hysteresis and the remaining 4.3% was related to the adhesive used for attachment of the sensing element to the housing. This novel sequential packaging evaluation methodology is independent of sensor design and is useful in identifying those packaging elements contributing the most to hysteresis.

Effect of manufacturing technics on the microstructure and temperature-affected electrical performance of D-type latch devices

In this study, the D-type latch devices with Ceramic Flat Package (CFP) and Shrink Small-Outline Package (SSOP) were tested and analyzed by experimental means. The effects of manufacturing technics on the pin structure, wire bond, chip layout design, die attach and temperature-affected electrical performance were subsequently investigated. Results show that manufacturing technics with CFP package possesses thicker special pin coatings, thicker different wire bond, stable and effective die attach compared with SSOP package. Meanwhile, the bare dies of two devices exhibit same layout structure design but different longitudinal dimensions. The temperature-affected electrical performances including voltage, current and propagation delay time reveal that the temperature sensitive parameters of CFP latch (variation about 1%) display 12 times better stability than that of SSOP latch (distinct variation about 12%) from −55 ​°C to 125 ​°C. Meanwhile, the SSOP latch displays 41.8% better switching speed and working frequency than CFP latch with similar other electrical parameters at room temperature.

Small chamber study of lead exposures from manual soldering of microelectronics

Airborne and surface Pb concentrations were measured inside a glovebox chamber with controlled inflow rate at 1.0 L/min of ultrapure air over a 4-hour period while an operator completed 1,680 solder connections using Sn63:Pb37 solder with rosin flux core. Chamber atmosphere showed released mean Pb mass of 0.0238 ± 0.011 μg and mean airborne concentration of 0.176 ± 0.085 μg/m3. Of the total solder mass used in two trials, on average 4.65% was recovered from the tip cleaning sponge and 0.14% dropped onto the work surface, with a surface loading rate of 0.30–0.45 μg/cm2. The estimated fingertip surface area in contact with solder wire was 14.7 cm2, with a measured average Pb mass of 14.9 μg, and a corresponding dermal loading rate of 1.01 μg/cm2. The waste solder dross surface area determined from digital micrographs in each trial were 1.65 and 2.43 cm2, with corresponding Pb density of 714 and 610 mg/cm2 and >90% of the detected dross mass comprising particles >100 μm in the widest dimension. Corresponding increases in blood Pb levels estimated using physiologically-based pharmacokinetic modeling were negligible compared with background. These findings demonstrate very low Pb emissions to air and surfaces during intensive manual microelectronic soldering activities.

Versatile Dual-Receiver 94-GHz FMCW Radar System With High Output Power and 26-GHz Tuning Range for High Distance Applications

Airborne applications demand exceptional overall radar system performance and eminently high output power for high range target detection. The frequency modulated continuous wave (FMCW) radar system presented in this article is capable of achieving this task due to its high output power at 94-GHz center frequency with over 26-GHz tuning range. Nevertheless, the radar still provides a small form factor and low power consumption of 4.25 W at 5 V single Universal Serial Bus (USB) supply. The key system component is a Silicon Germanium (SiGe) bipolar complementary metal-oxide-semiconductor (BiCMOS) monolithic microwave integrated circuit (MMIC) that contains a 94-GHz voltage-controlled oscillator (VCO), and a 27-GHz VCO for dual-loop phase-locked loop (PLL) stabilization, a power amplifier (PA), and two receive mixers. It generates frequency ramps between 83- and 109-GHz with a maximum output power of 19.7 dBm at its output after the bond wires on the printed circuit board (PCB) and 14.8-dBm output power at the radar’s transmit (TX)-waveguide WR-10-flange. The sensor was also tested in a temperature range from −40 °C to +70 °C with menial deviation. Thus, the system offers high system dynamic range and far distance target detection range. Following a detailed system description, we finally present the FMCW range and Doppler measurements performed with the presented radar sensor as well as the application on unmanned aerial vehicles (UAVs) for flight altitude control and as airborne collision avoidance system (ACAS).

Vertical integration of microchips by magnetic assembly and edge wire bonding

The out-of-plane integration of microfabricated planar microchips into functional three-dimensional (3D) devices is a challenge in various emerging MEMS applications such as advanced biosensors and flow sensors. However, no conventional approach currently provides a versatile solution to vertically assemble sensitive or fragile microchips into a separate receiving substrate and to create electrical connections. In this study, we present a method to realize vertical magnetic-field-assisted assembly of discrete silicon microchips into a target receiving substrate and subsequent electrical contacting of the microchips by edge wire bonding, to create interconnections between the receiving substrate and the vertically oriented microchips. Vertical assembly is achieved by combining carefully designed microchip geometries for shape matching and striped patterns of the ferromagnetic material (nickel) on the backside of the microchips, enabling controlled vertical lifting directionality independently of the microchip’s aspect ratio. To form electrical connections between the receiving substrate and a vertically assembled microchip, featuring standard metallic contact electrodes only on its frontside, an edge wire bonding process was developed to realize ball bonds on the top sidewall of the vertically placed microchip. The top sidewall features silicon trenches in correspondence to the frontside electrodes, which induce deformation of the free air balls and result in both mechanical ball bond fixation and around-the-edge metallic connections. The edge wire bonds are realized at room temperature and show minimal contact resistance (<0.2 Ω) and excellent mechanical robustness (>168 mN in pull tests). In our approach, the microchips and the receiving substrate are independently manufactured using standard silicon micromachining processes and materials, with a subsequent heterogeneous integration of the components. Thus, this integration technology potentially enables emerging MEMS applications that require 3D out-of-plane assembly of microchips.

Transesterification activity by a zinc(II)-Schiff base complex with theoretical interpretation

The article demonstrates the synthesis, structural characterization and transesterification activity of a mononuclear zinc(II) complex, [Zn(HL)(H2O)]·(H2O) (1) containing a previously reported Schiff base ligand, H3L = N,N′-bis(salicylidene)-1,3-diamino-2-propanol]. X-ray structural analysis of 1 reveals that Zn(II)-Schiff base complex crystallizes in hexagonal crystal system with P61 space group and adopts a distorted tetrapyramidal geometry. Self-assembled molecular units of 1 exhibit a beautiful construction of 3D crystalline architecture through intermolecular hydrogen bond wire. Zinc(II) complex displays an enhancement of fluorescence intensity in comparison to HL in methanol medium. Catalytic behaviour of 1 towards disodium salt of 2,4-dinitrophenylphosphate (PNPP) in aqueous-methanol medium exhibits good transesterification activity with initial rate constant value of 1.73 × 10−4 min−1. Detailed DFT calculations are also employed to cope with the geometrical parameters of 1 as well as to explore the proposed catalytic mechanism of transesterification activity.

Monitoring Bond Wire Defects of IGBT Module Using Module Transconductance

Monitoring the defective insulated gate bipolar transistor (IGBT) module is a cost-effective approach to improve the quality of customer service. In general, the parasitic parameters of bond wires inside the IGBT module are affected by aging. Module transconductance reflects the characteristics of the IGBT module and contains information about bond wire health status. It is investigated as a precursor parameter to monitor the bond wire defects in this article. The mathematical model of module transconductance is deduced to establish the relationship between module transconductance and the parameter of bond wires, which indicates that the module transconductance decreases with the increase of bond wire defects. For accurate and safe measurement, the influence of temperature difference caused by bond wire defects during measurement and safety measurement area where the module operates in the active region are discussed. Based on the safety measurement area and the method to eliminate the difference in temperature, a pulse ramp drive circuit is proposed to extract module transconductance. The simulation and experiments are carried out to validate the feasibility of the measurement method and correctness of the theoretical analysis.