A surface-mounted device assembly technique for small optics based on laser reflow soldering

The three-dimensional miniaturized optical surface-mounted device (TRIMO-SMD) is a new flexible and automated assembly technique for small optical components (maximum diameter for a lens is 2 mm) based on laser reflow soldering technique. This technology can be compared to the electronic SMD technique but applied to micro-optical devices. We present some recent developments of TRIMO-SMD in its application to industrial products.     

High Entropy Alloys as Filler Metals for Joining

In the search for applications for alloys developed under the philosophy of the High Entropy Alloy (HEA)-type materials, the focus may be placed on applications where current alloys also use multiple components, albeit at lower levels than those found in HEAs. One such area, where alloys with complex compositions are already found, is in filler metals used for joining. In soldering (<450 °C) and brazing (>450 °C), filler metal alloys are taken above their liquidus temperature and used to form a metallic bond between two components, which remain both unmelted and largely unchanged throughout the process. These joining methods are widely used in applications from electronics to aerospace and energy, and filler metals are highly diverse, to allow compatibility with a broad range of base materials (including the capability to join ceramics to metals) and a large range of processing temperatures. Here, we review recent developments in filler metals relevant to High Entropy materials, and argue that such alloys merit further exploration to help overcome a number of current challenges that need to be solved for filler metal-based joining methods.     

Control Al/Mg intermetallic compound formation during ultrasonic-assisted soldering Mg to Al

To prevent the formation of Al/Mg intermetallic compounds (IMCs) of Al₃Mg₂ and Al₁₂Mg₁₇, dissimilar Al/Mg were ultrasonic-assisted soldered using Sn-based filler metals. A new IMC of Mg₂Sn formed in the soldered joints during this process and it was prone to crack at large thickness. The thickness of Mg₂Sn was reduced to 22 μm at 285 °C when using Sn-3Cu as the filler metal. Cracks were still observed inside the blocky Mg₂Sn. The thickness of Mg₂Sn was significantly reduced when using Sn-9Zn as the filler metal. A 17 μm Mg₂Sn layer without crack was obtained at a temperature of 200 °C, ultrasonic power of Mode I, and ultrasonic time of 2 s. The shear strengths of the joints using Sn-9Zn was much higher than those using Sn-3Cu because of the thinner Mg₂Sn layer in the former joints. Sn whiskers were prevented by using Sn-9Zn. A cavitation model during ultrasonic assisted soldering was proposed.     

Stress analysis of extensively and partially soldered optical components

Resistance soldering of optical components is an upcoming technology following the trends towards automation and miniaturization with particularly high relevance for high optical power applications. A stress analysis is necessary in order to qualify this technology with regard to the component's optical behavior and its long-term stability. Analytical and FEM-simulative calculations are used to estimate the stresses within the optical element and the solder layer for extensively soldered components. Furthermore partially soldered components are being simulated and optically evaluated using polarization microscopy. To evaluate the long-term stability of the compound multiple series of thermal cycling were performed.     

Interface features of ultrasonic flip chip bonding and reflow soldering in microelectronic packaging

Ultrasonic features in the bonding area are of interest for researchers in the field of microelectronic packaging. In this study, the interface characteristics of bonding were examined using an XD7100 X‐ray instrument and a transmission electron microscope (TEM). It was seen that bubbles were usually detected at the interfaces of the reflow‐soldered flip chip (FC), but they were not found at the interfaces of ultrasonically formed FC, and so ultrasonic FC bonding is more reliable than reflow soldering. The strong mechanical effect of ultrasonic vibration activates the dislocations in the crystalline metal lattice. Dislocation diffusion is more prominent than crystal diffusion when the temperature is relatively low during ultrasonic bonding, and therefore the processes of ultrasonic bonding enhance by several orders of magnitude. This indicates that the mechanism of ultrasonic bonding is different from the melting mechanism of reflow soldering. Copyright © 2007 John Wiley & Sons, Ltd.     

Study of cohesive,electronic and magnetic properties of the Ni–In intermetallic system

Cohesive, electronic and magnetic properties of the intermetallic system Ni–In, specifically the stable phases Ni₃In-hP8, Ni₂In-hP6, NiIn-hP6 and Ni₂In₃-hP5, have been investigated. At present, these materials are of great interest in connection to the application of the In–Sn alloys as lead-free micro-soldering alloys, and considering Ni as the contact material. In spite of this, scarce literature regarding basic thermodynamic properties of the Ni–In intermetallic phases has been found. Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations is used. All the calculations include spin polarization. Structural parameters, formation energies and cohesive properties of the different phases are studied through minimization of internal parameters. The electronic density of states (DOS) is analyzed for each optimized structure. We found that the NiIn-hP6 phase is the most stable one and only the Ni₃In-hP8 phase exhibits magnetic properties.     

激光无铅钎焊速度的影响因素(英文)

为了提高激光无铅钎焊的速度,对影响激光无铅钎焊速度的因素(如激光的参数、所用钎料和基体的特性、钎焊的系统结构等)进行了分析研究。研究认为,在激光器、钎料及基体等已定的情况下,相对于那些受到机械惯性制约的移动激光加工头或移动工作台的激光钎焊系统,一种配备了振镜扫描系统和f-theta聚焦透镜的激光钎焊系统具有更高的钎焊速度。另外,对激光钎焊过程中激光束的扫描路径进行了优化,这种优化能在不增加硬件成本的基础上大大缩短总扫描路程,较大程度地提高激光钎焊速度。最后通过实例对激光钎焊的快速性进行了验证。     

Characterization of nitrogen-blanketed wave soldering reactions using thermal analysis

Thermal analysis techniques have been employed to elucidate the mechanism of low solids soldering flux activation. Metal oxides (SnO, PbO and PbO₂) are converted to carboxylate salts, which are displaced in the solder wave, rendering a solderable metal surface. Neither of the activators tested, namely succinic acid and adipic acid, react with SnO₂ at soldering wave temperatures and therefore cannot yield a solderable surface when SnO₂ is present. Further, adipic acid reacts with SnO to form a salt that can decompose to cyclopentanone, so the preheating of the printed circuit board must be carefully controlled to yield a solderable surface.     

Ultrasonic semi-solid coating soldering 6061 aluminum alloys with Sn–Pb–Zn alloys

In this paper, 6061 aluminum alloys were soldered without a flux by the ultrasonic semi-solid coating soldering at a low temperature. According to the analyses, it could be obtained that the following results. The effect of ultrasound on the coating which promoted processes of metallurgical reaction between the components of the solder and 6061 aluminum alloys due to the thermal effect. Al₂Zn₃ was obtained near the interface. When the solder was in semi-solid state, the connection was completed. Ultimately, the interlayer mainly composed of three kinds of microstructure zones: α-Pb solid solution phases, β-Sn phases and Sn–Pb eutectic phases. The strength of the joints was improved significantly with the minimum shear strength approaching 101 MPa.     

Thermal and gas flow characterization of a fluxless Si solder bonding oven

In this paper the technology of the “Linn” type Si fluxless solder bonding oven and the thermal and gas flow characterization of the oven are discussed. This oven is used for fixing silicon chips on metal substrates with high temperature solder bonding process. The solder is applied in a foil form which is placed between the Si chip and the metal substrate. This does not contain any flux, therefore a reducing agent has to be applied to avoid the oxidation of the joints during the soldering process. In this technology the reducing agent is the forming gas which is a mixture of 10 vol.% H₂ and 90 vol.% N₂. The key factors of this soldering process was studied; the suitable temperature (350-370 °C for 13-15 min) and the adequate H₂ concentration (8-10 vol.%). A detailed 3D gas flow model of the Linn oven was prepared which is based on the finite volume model (FVM) method. The gas flow circumstances using the basic and a hypothetic oven setting were compared by simulations applied the ANSYS-FLUENT system. The gas flow model was verified by the measurements of the temperature, the H₂ concentration and the pressure inside the oven. Furthermore the heating ability of the oven under full load was characterized by the change of the heating temperature and the time coefficient of the heating.