Reflow Characteristics Research Articles

Bonding of 5 μm Cu-Sn Micro Bumps Using Thermal Reflow and Solid-State Pre-Bonding

Copper–tin (Cu–Sn) transient liquid-phase (TLP) bonding has attractive advantages and has been widely used in three-dimensional (3-D) integration to establish electrical connections between stacked chips. However, TLP bonding has technical difficulties in bonding Cu–Sn bumps with small diameters and fine pitches due to the bonding pressure-induced lateral extrusion of the melted Sn layer. As bonding of micro bumps with diameters smaller than 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> is highly desired in future applications, this article reports the TLP bonding of micro bumps using improved reflow and pre-bonding. Due to the large surface-to-volume ratio of micro bumps, the reflow conditions dramatically influence the reflow characteristics, and systematical investigations are performed such that an Sn layer with an optimal thickness has been obtained to avoid lateral extrusion. A new bonding scheme has been developed by combining a solid-state pre-bonding and a TLP final bonding. The new bonding method and the Sn thickness control reflow avoid liquid Sn extrusion under bonding pressure. Using these techniques, Cu–Sn bonding of bumps with a diameter down to 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> has been successfully achieved with a high bonding yield.

Study on liquid-filled structure target with shaped charge vertical penetration

Abstract Based on the characteristic expanded hole of a shaped charge jet (SCJ) for target penetration and the reflow characteristics of liquids, the liquid-filled structure of a target disturbs the stability of the SCJ acquired in two independent parts. The interference jet speed interval, the escape jet speed interval, and the surplus depth are calculated on the basis of the virtual origin theory. The experimental results, including the velocity of the escaped jet tip and the surplus depth of penetration, are consistent with the theoretical results. Experiments show that the theory can describe the interaction process of the target with a shaped charge jet.

Evaluation of Peripheral Blood Circulation Disorder in Scleroderma Patients Using an Optical Sensor with a Pressurization Mechanism.

Blood circulation function of peripheral blood vessels in skin dermis was evaluated employing an optical sensor with a pressurization mechanism using the blood outflow and reflow characteristics. The device contains a light source and an optical sensor. When applied to the skin surface, it first exerts the primary pressure (higher than the systolic blood pressure), causing an outflow of blood from the dermal peripheral blood vessels. After two heartbeats, the pressure is lowered (secondary pressure) and blood reflows into the peripheral blood vessels. Hemoglobin concentration, which changes during blood outflow and reflow, is derived from the received light intensity using the Beer–Lambert law. This method was evaluated in 26 healthy female volunteers and 26 female scleroderma patients. In order to evaluate the blood circulation function of the peripheral blood vessels of scleroderma patients, pressurization sequence which consists of primary pressure followed by secondary pressure was adopted. Blood reflow during the first heartbeat period after applying the secondary pressure of 40mmHg was (mean±SD) 0.059±0.05%mm for scleroderma patients and 0.173±0.104%mm for healthy volunteers. Blood reflow was significantly lower in scleroderma patients than in healthy volunteers (p<0.05). This result indicates that the information necessary for assessing blood circulation disorder of peripheral blood vessels in scleroderma patients is objectively obtained by the proposed method.

Direct Transfer Printing of Water Hydrolyzable Metals onto Silk Fibroin Substrates through Thermal‐Reflow‐Based Adhesion

In recent years, the use of biopolymers as interface materials between inorganic electronics and biological tissues has increased, which has necessitated the integration of micro‐ and nanofabrication techniques with these unconventional materials. This combination has led to devices with intriguing operational characteristics such as so‐called “transient” bioresorbable devices. Here, a method is investigated which leverages the thermal reflow characteristics of non‐beta‐sheet crystallized silk fibroin protein films to transfer print electronic components onto bioresorbable silk substrates. This is accomplished by applying heat and pressure to the interface of the silk and fabricated components, leading to reflow of the silk and transfer of the components from a silicon carrier wafer onto silk. We demonstrate application of this for both traditional (Au) and highly labile transient metals (Mg), over large areas with single micrometer resolution, all while retaining functionality of the transferred components. Additionally, it is shown how control over the reflow characteristics of silk through the process parameters can lead to both water‐stable and water‐soluble device outcomes and retain the efficacy of entrained biological dopants within the silk substrate matrix. Through these means, this method has the potential to improve the number of fabrication options for devices at the biotic/abiotic interface.

Environmental Treatment for Perfect Spray Photoresist Morphology and Analysis

A homogeneous photoresist for IC or read-write data storage head fabrication requires a certain flowing of the resist film on the topography surface for at least few micrometers, thus defining certain minimal resist viscosity for the remaining solvent concentration for spraying technique. The high photoresist solvent evaporates during flight (between spray nozzle and substrate) prevents the droplets from sticking to the substrate and causes a rough surface. The limitation of very low photoresist viscosity for micro droplets spraying is a drawback of the technique. Because of very low viscosity of spray coating resist, nitrogen in spray coating system will act as 2 functions. First is for spread photoresist to be micro droplets. In the same time nitrogen can dry the small droplet before locating to substrate and perform obstacle for UV exposure. The unsatisfied resist was protected UV light during exposure cause pattern deformation. The study was investigated the particles which always found on finished photoresist surface spraying, and aimed to find the solution to decrease or eliminate dry droplet. EDX identified element of the obstacle particles is photoresist. They are dry resist ball about 1 – 6 um size. The selected chemicals for the investigation to dilute or dissolve the resist ball, IPA, acetone and mixing solution between 70% IPA and 30% acetone. Acetone is most effective. The proper time for dissolve dry resist ball with slight photoresist degradation is 40 s, very short because of high vapor pressure of acetone at room temperature. There is a trade-off between resist surface smoothness and reflow characteristics. Final resist thickness with the acetone vaporization condition will be achieved 7.5 um as expectation with less corner coverage problem. SEM and AFM images were confirmed that morphology after acetone vapor exposure was improved. Surface roughness was reduced for 3 times to 8 nm with acetone vaporization environment. The end of this study was include on corrosion characterization for magnetic CoFe alloys underlying photoresist to explore the method to determine photoresist type in future manufacturing which necessary to run the process with sensitive material. With AZ4999 spray photoresist protection indicated corrosion rate of CoFe films was reduced for 100 times compare to bare films.

Highly-enhanced reflow characteristics of sputter deposited Cu interconnections of large scale integrated devices by optimizing sputtering conditions

Improving the reflow characteristics of sputtered Cu films was attempted by optimizing the sputtering conditions. The reflow characteristics of films deposited under various sputtering conditions were evaluated by measuring their filling level in via holes. It was found that the reflow characteristics of the Cu films are strongly influenced by the deposition parameters. Deposition at low temperatures and the addition of H2 or N2 to the Ar sputtering gas had a significant influence on the reflow characteristics. Imperfections in the Cu films before and after the high-temperature, high-pressure treatments were investigated by positron annihilation spectroscopy. The results showed that low temperature and the addition of H2 or N2 led to films containing a large number of mono-vacancies, which accelerate atomic diffusion creep and dislocation core diffusion creep, improving the reflow characteristics of the Cu films.

Sacrificial microchannel sealing by glass‐frit reflow for chip scale atomic magnetometer

AbstractA novel sealing technique using sacrificial microchannels was proposed for control of an atmosphere in a micromachined alkali metal vapor cell for a chip‐scale atomic magnetometer. The microchannels act as a feedthrough connecting the cell to the outside atmosphere during evacuation and gas filling steps, and eventually they are sealed by glass‐frit reflow. A silicon microchannel was designed and sealing by glass‐frit reflow was successfully demonstrated in reflow experiments. Simulation results clarified the glass‐frit reflow characteristics and their dependence on cross‐sectional shapes of the microchannels. Hermeticity of the proposed sealing technique at a leak rate of less than 10−12 Pa·m3/s was verified by a high‐resolution helium leak test. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(5): 58–66, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10432

Characterization of skin dermis microcirculation in flow-mediated dilation using optical sensor with pressurization mechanism

Blood flows out of microvessels in the dermis when pressure higher than arterial blood pressure is applied to the fingertip, and subsequently re-flows into the microcirculation when pressure is released. Both the blood outflow and the reflow characteristics of microcirculation under pressurization are associated with microvasculature, blood and blood pressure. This study describes a novel method of measuring blood inflow and outflow characteristics of dermis microcirculation. An optical sensor, which is furnished with a 571 nm wavelength light source and a photodetector, is pressed to the skin surface using a pressure higher than the human subject's systolic arterial pressure. Hemoglobin concentration by change of the blood flow amount is estimated by the Beer-Lambert law. This method is applied to the measurement of blood inflow and outflow characteristics of microcirculation caused by reactive hyperemia after ischemia with duration of 5 min. Among three parameters evaluated, the one relating to the amplitude of pulsation shows a close correlation with conventional plethysmography, while the other two show varying time responses. Our method provides a new and useful insight into pathophysiology in health and disease conditions and may help researchers better understand the underlying mechanisms of numerous microcirculation-influenced diseases and medical conditions.

Highly-enhanced reflow characteristics of sputter deposited Cu alloy thin films for large scale integrated interconnections

An attempt to improve the reflow characteristics of sputtered Cu films was made by alloying the Cu with various elements. We selected Y, Sb, Nd, Sm, Gd, Dy, In, Sn, Mg, and P for the alloys, and “the elasto-plastic deformation behavior at high temperature” and “the filling level of Cu into via holes” were estimated for Cu films containing each of these elements. From the results, it was found that adding a small amount of Sb or Dy to the sputtered Cu was remarkably effective in improve the reflow characteristics. The microstructure and imperfections in the Cu films before and after high-temperature high-pressure annealing were investigated by secondary ion micrographs and positron annihilation spectroscopy. The results imply that the embedding or deformation mechanism is different for the Cu-Sb alloy films compared to the Cu-Dy alloy films. We consider that the former is embedded by softening or deformation of the Cu matrix, which has a polycrystalline structure, and the latter is embedded by grain boundary sliding.

A Study of Difference in Reflow Characteristics Between Electroplated and Sputtered Cu in a Dual-Damascene Fabrication Process for Silicon Semiconductor Devices

The difference in reflow characteristics between electroplated and sputtered Cu films during high-temperature high-pressure treatment was confirmed, and the basis for this difference was analyzed. Using test element groups containing a number of via holes, it was found that electroplated Cu films had much superior embedding characteristics compared with sputtered Cu films. This was confirmed by measurements of the stress–strain curves of these Cu films, which indicated that the strength at high temperature of the electroplated films was lower than that of sputtered films. Identification of lattice defects and analysis of the microstructure of these films were carried out by positron lifetime measurements and transmission electron microscopy, respectively. The results showed that a large quantity of vacancy clusters was present in the electroplated Cu films, and this increased to a maximum after isochronal annealing at 300°C. From the results, it was shown that Cu atoms in electroplated films with a large number of vacancy clusters diffuse rapidly at around 300°C, and this rapid diffusion contributes greatly to softening of the film and a promotion in reflow behavior. This study revealed that the reflow behavior of Cu films strongly depends on the presence of vacancy clusters within it.

An electrochemical impedance biosensor with aptamer-modified pyrolyzed carbon electrode for label-free protein detection

We present an electrochemical impedance biosensor utilizing pyrolyzed carbon film as a working electrode material for aptamer-based thrombin detection. Batch-fabricated, smooth thin film carbon electrodes, which are fabricated by photolithography and photoresist thermal decomposition at high temperatures in inert ambient, are obtained for integrated electrochemical biosensors. To confirm the suitability of pyrolyzed carbon for use in an electrochemical biosensor, physical and electrical properties of carbon film pyrolyzed with a positive photoresist, AZ9260, were studied. Film thickness after pyrolysis was between 19% and 15% relative to the initial photoresist thickness and the cross-section was changed from rectangular to round shape due to the photoresist reflow characteristics. Resistivity of carbon thin film pyrolyzed at 1000 °C was 3 mΩ cm, which is comparable to that of highly boron-doped polysilicon. The pyrolysis temperature of 1000 °C was chosen in order to obtain carbon film with high conductivity for use as a working electrode. Thrombin aptamer was grafted onto the pyrolyzed carbon surface using carbodiimide-mediated chemistry, followed by Triton-X 100 and BSA treatment to reduce non-specific binding of thrombin. Electron-transfer resistance changes due to thrombin binding onto the carbon surface were measured using electrochemical impedance spectroscopy techniques. Thrombin concentrations between 0.5 nM and 500 nM were detected by electrochemical measurement. Pyrolyzed carbon can provide a new approach for miniaturization, integration, and low-cost fabrication in electrochemical biosensors.

Reflow and Electrical Characteristics of Nanoscale Solder

Soldering nanojoints: Nanowires with a diameter range of 30–200 nm were patterned with solder segments, and the reflow of the solder on these wires was investigated (see Figure). Low-resistance ohmic contacts were observed across solder joints after reflow. Corrosion, oxidation, and intermetallic diffusion play a crucial role in solder reflow and joint formation at the nanoscale.

A systematic procedure for the selection of a lead‐free solder paste in an electronics manufacturing environment

PurposeHistorically, tin‐lead solder has been a commonly used joining material in electronics manufacturing. Environmental and health concerns, due to the leaching of lead from landfills into ground water, have necessitated legislation that restricts the use of lead in electronics. The transition from tin‐lead solder to a lead‐free solder composition is imminent. Several alternative solder alloys (and their fluxes) have been researched for electronics assembly in the last few years. The objective of this research was to develop a systematic selection process for choosing a “preferred” lead‐free solder paste, based on its print and reflow performance.Design/methodology/approachAfter a detailed study of industry preferences, published experimental data, and recommendations of various industrial consortia, a near eutectic tin‐silver‐copper (SAC) composition was selected as the preferred alloy for evaluation. Commercially available SAC solder pastes with a no‐clean chemistry were extensively investigated in a simulated manufacturing environment. A total of nine SAC pastes from seven manufacturers were evaluated in this investigation. A eutectic Sn/Pb solder paste was used as a baseline for comparison. While selecting the best lead‐free paste, it was noted that the selected paste has to perform as good as, if not better than, the current tin‐lead paste configuration used in electronics manufacturing for a particular application. The quality of the solder pastes was characterized by a series of analytical and assembly process tests consisting of, but not limited to, a printability test, a solder ball test, a slump test, and post reflow characteristics such as the tendency to form voids, self‐centring and wetting ability.FindingsEach paste was evaluated for desirable and undesirable properties. The pastes were then scored relative to each other in each individual test. An aggregate of individual test scores determined the best paste.Originality/valueThis paper summarizes a systematic approach adopted to evaluate lead‐free solder pastes for extreme reflow profiles expected to be observed in reflow soldering lead‐free boards.

Reflow Characteristics of Copper in an Oxygen Ambient

Reflow Characteristics of Copper in an Oxygen Ambient

Reflow characteristics of Sn-Ag matrix in-situ composite solders

Reflow characteristics of Sn-Ag matrix in-situ composite solders

Oxidation, grain growth and reflow characteristics of copper thin films prepared by chemical vapor deposition

Oxidation and grain growth characteristics of copper thin films in an oxygen ambient were investigated. In general, reflow characteristics of thin films mainly depend on the surface self-diffusion of the film's material, but we found that the oxidation and grain growth could result in the reflow of copper thin films in an oxidizing atmosphere. Upon post-annealing at higher than 400°C in an oxygen ambient, the normal grain growth and the agglomeration of copper occurred simultaneously and filled the patterns. This behavior was not observed in inert ambient annealings. Copper oxide was formed during the annealing in an oxygen ambient to a thickness of at most 20 nm. The grain growth is attributed to stresses produced during the surface oxidation of the copper.

A simulation study of copper reflow characteristics in vias

The reliable and complete filling of vias and trenches with an appropriate metal is an important process in the fabrication of microelectronic components. Due to its favorable electronic properties and its reliability, copper is a common choice for replacing aluminum as a metallization material. One metallization procedure of interest is the sputter reflow of copper. The sputter reflow process begins with depositing copper via traditional sputter technologies. The films are subsequently made to fill micrometer and submicrometer trenches and vias through surface diffusion enhanced by annealing. This paper studies fundamental considerations such as deposition rates, underlayer material, and transport mechanisms through numerical simulation using the process simulators SIMSPUD and GROFILMS. The simulations are further used to study via filling using Cu reflow and alternative methods including in situ annealing, three-step deposition, and a four-stage deposition-chemical mechanical polishing procedure. Simulation results are presented as depictions of the film on the feature scale. A discussion of the algorithmic solutions to the three-dimensional problems associated with vias is also provided.

Reflow of copper in an oxygen ambient

In order to investigate the reflow characteristics of copper, copper was deposited on hole and trench patterns by metal organic chemical vapor deposition and it was annealed in nitrogen and oxygen ambients with the annealing temperatures ranging from 350 to 550 °C. Upon annealing in an oxygen ambient at higher than 450 °C, copper was reflowed into the trench patterns whose line- width and aspect ratio were 0.2 μm and 4:1, respectively. Copper oxide was found with a thickness of less than a fifth of the total film thickness. The resistivity of the copper film increased when reflow occurred. It is thought that the reflow of copper in an oxygen ambient takes place because of enhanced surface diffusion.

Solder Joint Formation Simulation and Component Tombstoning Prediction During Reflow

The failure of electrical devices associated with solder joints has become one of the most critical reliability issues for surface-mounted devices. Solder joint reliability performance has been found to be highly dependent on the solder joint configuration, which, in turn, is governed by bond pad size, alloy material, and leadframe structure, as well as solder reflow characteristics. To investigate tombstone effects causing solder joint failure during leadless component reflow process, this work has focused on (1) developing a numerical model for the simulations of the solder joint formation during the reflow process, and (2) determining possibility that a tombstone effect for the leadless component may occur by analyzing the force and torque in the problem. Using this methodology, the tombstone effect associated with different pad geometry configurations and solder paste amount has been analyzed through the application of the public domain software tool Surface Evolver. Simulations show that the tombstoning is very sensitive to pad/component geometry design, solder surface tension, solder paste volume, wetting area, and wetting angle. This model simulation can be used to determine optimal solder paste volume, pad geometry configurations, and solder material for avoiding tombstone effects.

スパッタＣｕ膜のリフロー埋め込み特性に与える下地膜の影響

Ti, W, Ta and their nitride films grown by sputtering were evaluated as the under layer of the sputtered Cu film with reflow process. The well nitrided films had good endurance against Cu-Si reaction at the annealing temperature higher than 680°C. The reflow characteristics of Cu film depend on a trench configuration and the Cu film thickness as well as the under layer species. Regardless of the reflow conditions, Cu on WNx revealed good reflow characteristics compared with Cu on TiNx or TaNx. This result shows that WNx is appropriate for the under layer material of reflow Cu. It was also found that the Cu reflow characteristics are highly correlated with the crystallinity of Cu film. The Cu film with (200) preferred orientation showed better reflow characteristics than that with (111) preferred orientation. However, in our experiments, there was no correlation between the reflow characteristics and the wettability of Cu on each under layer material.