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Wire bonding is an interconnection technique widely used in semiconductor packaging. Certain packages employ a stacked die configuration for miniaturization. Thus, the advancement of stacking dies leads to the overhanging structure of the staked dies. The complexity of an overhang generates challenges in the wire bonding process, whereby the bonding location has no supporting structure, leading to poor bondability due to die deflection. Thus, this paper studies the wire bonding quality on overhang stacked die structures. The experimental work focuses on the wire bonding process of more than 50 Au (gold) wires on more than 50 Al (aluminum) bonding sites with a variation of overhang distance, t ranged from 5 to 11.7 and wire bonding force, x ranged from 3 to 13. Analysis of the wire bonding quality is focused on die deflection during the wire bonding process. After the wire bonding process, intermetallic compound (IMC) formation was determined between the Au wire and Al bond pad using an optical microscope. The IMC was analyzed to determine the IMC coverage. The findings show that higher overhang distance and bonding force contribute to higher die deflection values during the wire bonding process. The die deflection is higher at the corner region of bonding points compared to the middle region bonding sites. Thus, this work suggests the refined average values to represent the true die deflection values by ignoring the "corner" region values. IMC coverage results show less coverage as the overhang distance and bonding force are increased. This work shows good wire bonding quality can be obtained by using a lower bonding force of 13 x , and lower overhang distance of 11.7 t . This could prevent the non-established wire bonding for overhang structure, at least for a die thickness of 31 µm. [ABSTRACT FROM AUTHOR]

Crack propagation has been observed on the bulk solder area of the reworked fine-pitch ball grid array component with the solder joint type SAC305 (Sn97.18 Ag2.0 Cu0.75 Ni0.07) post 550 cycles thermal cycling test (TCT). Four variables were analyzed; control sample PT0, rework sample RT0, and two samples being exposed to the TCT at 550 cycles: sample without rework PT550 and sample with rework RT550. Nondestructive and destructive tests such as 3D X-ray, dye and pull test, cross-section, optical inspection, field emission scanning electron microscopy, and energy dispersive X-ray analysis (EDX) have been complemented with strain-energy density simulation results to further understand the symptoms. EDX analysis results show that up to 12.04 percent, by weight (wt%) gold content is present in the intermetallic compound particles along the crack propagation area in the bulk solder joint’s area due to the undissolved gold. Strain-energy density up to 3.04 Pa to the solder joints causing thermal fatigue crack as observed in the 3D X-ray, dye and pull test, and cross-section sample. [ABSTRACT FROM AUTHOR]

Potassium ions ( K + ) are crucial for many physiological processes. Here we report on the use of a titanium dioxide (TiO2) extended gate field effect transistor as an ion sensor (ISEGFET). We tested within its critical concentration range in artificial blood serum for this. The TiO2 thin films were prepared via a solvothermal process over the conductive glass (coated with indium-tin oxide (ITO)). The prepared samples were tested by X-ray diffraction, Raman spectroscopy, for their phase structures, electron scanning microscopy, and X-ray photoelectron spectroscopy for their morphology and surface element contents. The TiO2/ITO samples were prepared as electrodes, and the threshold voltage and the drain – source current measurements were recorded against a reference electrode. The potential sensitivity of the electrodes was in the range 42 mV/pK – 47 mV/pK, and its current sensitivity was in the range 0.50–0.71 mA1/2/pK with K+ concentration covers the range between 100 µM and 100 mM. The lower limit of detection was approximately 100 µM. The devices were tested in the concentration range of 3.5 mM–10 mM, where the potential sensitivity was recorded between 7.5 mV/mM and 10 mV/mM in artificial blood serum. The devices reveal a stable performance within two months. [ABSTRACT FROM AUTHOR]

The early corrosion detection of a semiconductor package is the desired goal for industrial semiconductor manufacturing owing to its capability to predict corrosion activity before the product leaves the assembly line. However, the standard procedure for early correction detection always faces great challenges and is yet to be available. Usually, the detected corrosion activities show some degree of failure. Leadframe discoloration provides insights into early corrosion detection in a semiconductor package. This study adopted an unbiased highly accelerated stress test (uHAST) to induce discoloration by promoting the suitable equilibrium moisture content (EMC). The wedge bond of Cu wire onto the Ag-plated Cu leadframe was used. To obtain the actual EMC, dew-point analysis was performed by dry- and wet-bulb data collection. The semiconductor package was subjected to several sets of uHAST condition comprising different combinations of temperature and relative humidity (RH) for 168 h. Mechanical decapsulation was used to expose the wedge bond of Cu wire onto the Ag-plated Cu leadframe followed by qualitative and X-ray photoelectron spectroscopy (XPS) analysis. We found that a higher percentage of EMC facilitated the discoloration of Cu-wedge bond. XPS analysis further confirmed that the discoloration was associated with early corrosion activities. Therefore, uHAST may be used as an early corrosion detection procedure by considering the combination effect of RH and temperature through EMC analysis. [ABSTRACT FROM AUTHOR]

The most common environmental stress tests that are commonly used for corrosion risk assessment study or package integrity qualification qualifier as part of AEC-Q101E requirement are Unbiased highly accelerated stress test (u-HAST) and Unbiased humidity test(Moisture Soak). In this paper, this study is initiated due to abnormal situation whereby the failure could not be detected at 0 h as this corrosion symptom takes place after several months of storage (4 to 6 months) and failure can be only detected during customer board assembly process after subsequent period of storage. Objective of this paper is to develop a novel methodology by identifying an optimum environmental stress test condition which can replicate an early detection method to put in evidence the onset of corroded wedge on Cu-Ag system on a copper wire-bonded semiconductor device. The approach used was by subjecting the components to two different unbiased environmental stress methods, i.e., u-HAST and Moisture Soak. Pre- and post-electrical testing will be done after each interval for each stress tests. In the event if there are no electrical failures observed, post-mechanical decapsulation analysis results will be used instead. Upon mechanical decapsulation, the visual inspection on the wedge surface area and periphery of Ag plating was performed through optical inspection. x-ray Photoelectron Spectroscopy (XPS) will complement the Energy Dispersive x-ray (EDX) analysis to confirm the corrosion product on the wedge surface area and periphery of Ag plating area surrounding the wedge surface. Based on the evaluation results, Moisture Soak, clearly demonstrated a better leading indicator compared to u-HAST for the activation of corrosion. Moisture Soak (55 °C/85%RH) showing a consistent trend of higher corrosion detection on SOT23 package compared to u-HAST. [ABSTRACT FROM AUTHOR]

This study investigated the effectiveness of heat shield placement locations during the rework process to avoid thermal and mechanical damage to adjacent ball grid array components and their solder joints on double-sided printed circuit board assembly. Three types of heat shield placement locations were used: sample X, individual heat shield placement on adjacent components of the rework location; sample Y, a U-shaped, and sample Z, a square-shaped heat shield placed respectively at the heat source location. The dye and pull test results, infrared thermography, and temperature measurements were analysed to understand the relationship between the location of the heat shield and solder joint damage during rework. Heat shield placement at the heat source location on the reworked component can reduce the peak temperatures on the adjacent rework component locations by up to 8.18%. The peak temperatures of the centre and corner of the BGA component can be maintained below 195 °C and 210 °C, respectively to improve the adjacent rework component locations' solder joint quality by reducing solder joint damage by more than 50% solder cracks. This is useful for thermal management during rework involving high-density ball grid array component placements on double-sided printed circuit board assembly. [ABSTRACT FROM AUTHOR]

Electronic applications are now driving packaging technology that is equivalent to primary computer packages for the past 25 years. The electronic application currently shows an ascending market demand due to rapid development of smart and wireless component with mixed technologies that include digital microprocessors. In ensuring the quality of the devices, the reliability of the solder joint is very vital. Attributable to their common uses, radiation particles including gamma ray is considered as one of the primary factors that could degrade the performance of the electronic devices. Thus, in this study, both mechanical and microstructure properties of lead-free solder joints radiated with gamma were investigated. Prior to the evaluation, the solder pastes of tin–silver–copper (SnAg3Cu0.5; SAC305) was manually deposited on the printed circuit board using a stencil printing method and reflow soldering process. Subsequently, the solder was exposed to low doses of gamma radiation. The current finding showed that as the radiation dose increased, the solder sample became softer and more plastic. FESEM and EDS analysis signified that intermetallic layer in the tin (Sn) matrix was dominated by Cu6Sn5 and Ag2Sn compound. According to micromechanical investigation, both hardness and reduced modulus of the solder decreased with increasing the radiation dose that was due to microstructure change and the formation of voids. [ABSTRACT FROM AUTHOR]

Electrolyte-Membrane-Insulator-Semiconductor (EMIS) sensors based on ZnO undoped and doped with a different molar ratio of Mg/Zn are demonstrated to detect calcium ions. The samples grown on the silicon substrates by the hydrothermal method were characterized to explore the impact of Mg content on the structural and compositional characteristics and sensing performance by X-ray diffraction analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The results indicated that the EIMS based on ZnO nanorods doped with 3% Mg had a high Ca2+ ion sensitivity (69 mV/decade) and linearity (99.8%). In addition, the samples have good stability with a low drift rate of 0.398 mV/h and possess great selectivity over other interference ions such as Na+, K+, Mg2+, and Ni2+ due to the employment of an ionophore membrane. [ABSTRACT FROM AUTHOR]

Here, we report a simple, cost-effective and repeatable process to grow copper(II) oxide (CuO) over a Cu wire. Characterization of the prepared CuO structures revealed a pure phase of CuO with high-density nanostructures. By applying dibenzo-18-crown-6 as an ionophore, CuO (as a solid contact, SC) was developed into a calcium (Ca2+) ion-selective electrode (ISE) with a linear activity range between 10 μM and 100 mM, an average Nernstian slope (sensitivity) of 32.3 ± 1.3 mV/decade, and a lower limit of detection (LOD) of 10 μM. When tested for selectivity among three ions (magnesium, nickel, and sodium) in addition to the target ion, the electrode had better selectivity toward Ca2+ ions. We were able to demonstrate that the proposed Cu/CuO electrode was stable within the pH range from 5.0 to 9.0 for a period of 60 days. Our results of the proposed SC-ISE exhibit a good potential response and acceptable stability, and they show a clear indication that Cu/CuO nanostructures (SC-ISE) can be used as an ion-to-electron transducer for low-cost solid-state potentiometric sensors. [ABSTRACT FROM AUTHOR]

Herein, we introduce a low-cost and straightforward method for preparing pH sensors based on parchment-type paper and pencil traces as a base and electrode, respectively. The hydrophobic feature of the parchment paper supports the relatively long life of the proposed pH sensor. The results indicate that the present sensors have a Nernstian response with a Nernstian slope of 52.1 ± 1.5 mV/pH and a good linearity of 0.995 from pH 4 to 10. The stability of the proposed electrode is approximately 0.75 mV/h. The prepared electrodes show a relatively long operating life compared with the published results of ordinary paper-based pH devices. However, the Nernstian factor decreases over time and stabilizes at approximately 28 mV/pH after two months. This approach provides a low-cost and reproducible pH sensor. [ABSTRACT FROM AUTHOR]

This paper highlights the advantages of using the nanoindentation approach over the conventional method for the mechanical characterization of components used in electronic packaging. The limitation of the conventional method has become more critical with the miniaturization of electronic packages, giving inadequate information regarding the mechanical properties of metallurgical interconnections. The load–displacement approach via nanoindentation was used in this study to determine the micromechanical properties of a fine-pitch solder joint subjected to aging for 1000 hours. This approach is more advantageous than tensile testing, as it focuses on the elastic behavior unlike that in conventional mechanical testing. The nanoindentation analysis results showed that the elastic–plastic behavior before failure can be assessed in a wide range of temperatures and thus help study the temperature dependence on the mechanical properties of fine-pitch solder joints. The characterization was done beyond the elastic range beforehand of conventional method. The modulus and hardness of the fine-pitch SAC 0307 solder joint decreased while its plastic and elastic behaviors became pronounced at higher aging temperatures. This implies that solder joints become weaker and less resilient with increasing temperature, at least for a duration of 1000 hours. [ABSTRACT FROM AUTHOR]

A characterization of mechanical and micromechanical properties of SAC305 solder wire under varied strain rates and temperatures was performed using tensile and nanoindentation tests. The evolution of SAC305 lead-free solder wire grains was compared in samples that were subjected to various strain rates and temperatures using tensile tests based on ASTM E12 standards. Different behaviours of mechanical properties, micromechanical properties, and microstructure evolution of SAC305 solder wire were observed when either temperature or strain rate was held constant and the other varied. Both tensile and nanoindentation tests produced qualitative results, such as dynamic recovery and occurrence of pop-in events, that reflected changes of microstructure. It was observed that some of the mechanical properties of SAC305 solder wire, namely yield strength (YS), ultimate tensile strength (UTS) and Young's modulus, showed the same trends, but with lower values, compared to micromechanical properties obtained from nanoindentation tests based upon hardness and reduced modulus. Microstructure examination further confirms that the YS, UTS and hardness values increase with more solder wire grain refinement. SAC305 solder wire also maintained an equiaxed structure under various strain rates and temperatures. [ABSTRACT FROM AUTHOR]

The effect of using different flux on wettability of Sn-Ag-Cu lead free solder were investigated. In this study, solder paste Sn-3.0Ag-0.5Cu (SAC305) was used by introducing two types of no-clean flux with different ingredients. The solders namely as SAC305-A and SAC305-B respectively. Then, the both solder paste manually printed on printed circuit board (PCB) using stencil printing and then reflowed at 260 °C temperature. Wettability of Sn-Ag-Cu solder using different flux was determined by contact angle measurement using Alicona ® IFM software. Results show the SAC305-A solder alloys have a good and better wettability with lower contact angle compared to SAC305-B. Functional groups of both solder flux was identified by FTIR analysis. Meanwhile XPS analysis was performed in characterizing the studied fluxes. It was found that no-clean flux solder with aromatic functional groups showed lower contact angle value and better wettability than aliphatic contained functional groups. [ABSTRACT FROM AUTHOR]

Wire bonding processes has been widely adopted in micro-electromechanical systems (MEMS) packaging especially in biomedical devices for the integration of components. In the first process sequence in wire bonding, the zone along the wire near the melted tips is called the heat-affected zone (HAZ). The HAZ plays an important factor that influenced the looping profiles of wire bonding process. This paper investigates the effect of dopants on microstructures in the HAZ. One precent palladium (Pd) was added to the as-drawn 4N gold wire and annealed at 600°C. The addition of Pd was able to moderate the grain growth in the HAZ by retarding the heat propagation to the wire. In the formation of the looping profile, the first bending point of the looping is highly associated with the length of the HAZ. The alloyed gold wire (2N gold) has a sharp angle at a distance of about 30 m from the neck of the wire with a measured bending radius of about 40 mm and bending angle of about 40° clockwise from vertical axis, while the 4N gold wire bends at a longer distance. It also shows that the HAZ for 4N gold is longer than 2N gold wire. [ABSTRACT FROM AUTHOR]

The structural changes of radiolytically prepared aluminium-copper (Al-Cu) bimetallic nanoparticles by adjusting the precursors' mole ratio and gamma radiation dose were investigated by transmission electron microscopy, field emission scanning electron microscopy/energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and X-band continuous wave electron paramagnetic resonance (EPR). The EPR spectrum was also analysed through the simulation of the powder-like EPR spectra. The results note that in prepared samples with higher Al contents, formation of core-shell structure is dominant, whereas in Cu-rich samples, the final structures are primarily in alloy and oxide forms. According to the analysis of data obtained from X-ray diffraction, FTIR, and EPR, we found that the unpaired electron of the Cu ion in various phases play the main role in structural phase transformation of Al-Cu nanoparticles. Additionally, based on the information extracted from simulated EPR peaks of Cu-Cu, the diameter of the Cu core in core-shell structures was obtained. We showed that by increasing the gamma radiation dose from 80 to 120 kGy, the overall size of nanoparticles decreases from 9.47 to 3.75 nm, but the contribution of copper core increases from 11 to 22 % of overall particle size. [ABSTRACT FROM AUTHOR]

We have analyzed the effects of nanoindentation at applied loads of 10 mN and 20 mN on the micromechanical properties of gold (Au) ball bonds with and without cracks. The depth profile and the plastic zone size for each indentation were determined to identify the substrate effect and its relationship with the observed micromechanical properties. The substrate effect occurred for indentations at 20 mN applied load, but did not occur near cracks for either 10 mN or 20 mN loads. Because of the substrate effect and the presence of cracks, the average hardness or yield strength decreased for indentations on Au ball bonds. Therefore, to minimize the substrate effect, an applied load of 10 mN is best for characterizing Au ball bonds. [ABSTRACT FROM AUTHOR]

The bonding mechanisms of gold, to give the desired strength of wire bonding, still require detailed investigation, including establishing adequate and reliable testing procedures. The current practices for analysing the mechanisms of wire bonding are inadequate and do not provide a comprehensive picture. This is because the focus of the tests is not clear, which causes variation in the results obtained, changing the conclusions about the responsible mechanism. Furthermore, as the size of Au wire bonds decreases, the mechanism responsible for thermosonic Au wire bonding may change. This paper provides a comprehensive analysis of the current and possible future methods for elaborating the bonding mechanism and strength of thermosonic Au wire bonds. We discuss the testing methods, their limitations and advantages, and suggest ways in which they can be improved. [ABSTRACT FROM AUTHOR]

The 6XXX series alloy is known to show inferior age-hardening response during the paint-bake cycle due to natural aging prior to the paint-bake. Many researchers have adopted the pre-aging process to offset the detrimental effect of the natural aging process. The alloy used in this study contained excess Si, and it had been reported elsewhere that such alloys do not show positive response to the pre-aging process. The present work is aimed to study the microhardness and tensile strength of the Al-1.2Si-0.5Mg-0.25Fe wrought alloy through Zr additions between 0.02 and 0.30 wt.%. Alloys containing 0.15 wt.% Zr and above heat-treated for 30 min gave higher microhardness and ultimate tensile strength values compared to that of Al-1.2Si-0.5Mg-0.25Fe without Zr which was heat-treated for 11 h. It was found that mechanical properties improved when the Zr content in the alloys increased. The improvement of mechanical properties was mainly attributed to formation of Zr-bearing intermetallic compounds formed in the alloy. [ABSTRACT FROM AUTHOR]