Ultrasonic-assisted Soldering Research Articles

A novel packaging method for FBG temperature sensors based on ultrasonic-assisted soldering technology

The packaging technology of fiber Bragg grating (FBG) sensors is the key to determining their operational performance. A method for encapsulating FBG temperature sensors using ultrasonic-assisted soldering technology has been proposed and attempted. This packaging method is based on the successful connection between SiO2 quartz glass and Invar alloy. Implementing this soldering connection depends on the active components in the solder, which are dispersed into SiO2 and metal alloys to form more stable substances. The FBG with the removed coating is reliably connected to the metal capillary through ultrasonic soldering. The fragile FBG is adequately protected in the capillary. Sn-based solder with a melting point of 297 ℃ has been selected. The soldering temperature of 330 ℃ avoids significant residual stress caused by the difference in the thermal expansion coefficient of the material at the joint. Excellent bonding strength between optical fibers, solder, and capillaries is necessary for encapsulating sensors. Compared to adhesive, solder packaging is no longer affected by the creep of the sealant. The results show that the working range of FBG temperature sensors encapsulated in epoxy resin is −25 ℃ −115 ℃, while temperature sensors encapsulated by welding can operate stably at −50 ℃ −280 ℃. Sensors packaged using ultrasonic-assisted soldering technology have the potential to be embedded in metal substrates, creating favorable conditions for the development of intelligent electromechanical components.

Inhibition of intermetallic compounds using pure Ni or Ni–Al2O3 nanocomposite coating during the ultrasonic-assisted soldering of Mg/Al dissimilar metals

The widespread utilization of lightweight Mg and Al alloys underscores the importance of establishing reliable connections between them. However, joining dissimilar Mg/Al alloys presents challenges, primarily due to uncontrolled formation of intermetallic compounds during the process, leading to weakened joint performance. To inhibit its formation, a Ni or Ni–Al2O3 nanocomposite coating served as a barrier layer during ultrasonic-assisted soldering AZ31 Mg/6061 Al using Sn–3.0Ag–0.5Cu solder. By investigating the impacts of Ni/Ni–Al2O3 composite coating on microstructure, intermetallic compounds formation, and joint performance, we found that the Ni coating partially inhibited Mg diffusion into the solder at 260 °C for 20 min, thus limiting excessive Mg2Sn compound formation and increasing shear strength by approximately 110% compared to uncoated joints. However, with an extension of the holding time to 30 min, block-shaped Mg2Sn compound reemerged as the primary cause of joint failure. Using Ni–Al2O3 composite coating further broadened the process window of Mg/Al soldering, eliminating block-shaped Mg2Sn compound in the joint at 260 °C for 40 min. The incorporation of Al2O3 further enhanced joint properties, with the maximum shear strength of the Mg(Ni–Al2O3)/SAC/Al joint reaching approximately 66.6 MPa, an improvement of 18.3% compared to the joint with Ni coating. This enhancement shifted the fracture position from the Ni/SAC interface to the SAC solder. Additionally, due to grain refinement in the Ni matrix, the microhardness of the Ni–Al2O3 composite coating surpassed that of the Ni coating. A model of Ni/Ni–Al2O3 composite coating preventing intermetallic compounds formation of was proposed. This nanocomposite coating-ultrasonic assisted soldering method effectively avoids the issue of excessive intermetallic compounds formation when joining dissimilar metals.

Development of an ultrasonic-assisted soldering system for Fe-based lead frame surface coating

Development of an ultrasonic-assisted soldering system for Fe-based lead frame surface coating

Ceramic-to-metal bonding using rare-earth containing Sn–Bi solder

With the increasing miniaturization and power of optoelectronic devices, direct bonding of optical substrates like semiconductors and ceramics to metal heat sinks using low melting-point solder has gained significant interest. In this study, we demonstrated the bonding of glass to copper using Sn-58 wt% Bi solder (SB solder) doped with a small amount of rare earth (RE) elements. The RE elements act as active agents that facilitate the bonding to glasses without glass metallization. By optimizing the bonding parameters, such as reflow temperature and time, and employing an inert gas atmosphere to prevent solder or RE oxidation, we successfully achieved the highest shear strength in glass-copper solder joints using SB-RE solder, without the need for ultrasonic-assisted soldering (UAS). These results demonstrate the potential of using RE-containing solder for bonding unmetallized glass and ceramics in optoelectronic devices with metals at low soldering temperatures (< 200 °C). Furthermore, analysis of the shear strength and failure morphology of solder joints revealed only small degradation, primarily originating from the bulk solder region rather than the solder-glass interface, after both thermal aging (100 h) and cycling tests (100 cycles). The establishment of low-melting point RE-containing solders opens the possibility of direct jointing ceramic optoelectronic substrates to metal heat sinks for more efficient heat dissipation. In the meantime, our work also suggests that further optimization studies are necessary to explore its performance under more extreme working conditions.

Ultrasonic-assisted soldering of Si and Cu joint with SnAgTi solder in air

The reliable connection of single crystal Si and Cu at low temperature is widely utilized and plays a crucial role in the field of electronic packaging. In this study, Sn–Ag–Ti active filler is ultrasonically coated onto the Si surface to facilitate the subsequent ultrasonic soldering process to realize the bonding of Cu to pre-metallized Si. Furthermore, a detailed analysis was conducted on the influence of ultrasonic time on both the bonding mechanism and mechanical properties of the joint. The results revealed that Ti–Sn compound within the solder decomposed with ultrasonic action duration time of 20 s, resulting that Ti elements enriched at the Si/solder interface and reacted with SiO2 to form a mixture comprising TiO2 and SiTi phase. It contributed to higher strength (43.9 MPa) at the Si/solder interface. Additionally, it has been found that microstructure and property at the Cu/solder interface were directly affected by ultrasonic time. Specifically, when subjected to 3 s of ultrasonic action, poor load-bearing capacity exhibited by thin infiltration layers caused fracture at the Cu/solder interface; When the ultrasonic action time is 6 s, the joint strength reaches its maximum value of 41.3 MPa, leading to fracture occurring within the Si material. However, when the ultrasonic holding time is extended to 20 s, the joint strength decreases to 20.3 MPa. This phenomenon arises from impaired plasticity of Cu6Sn5 near the Cu–Sn layer, which is attributed to the presence of attached dendritic Cu6Sn5 phases and shed bulk Cu6Sn5 that are prone to crack initiation. This research presents a promising approach for ceramic/metal heterogeneous joining.

Orthogonal design optimization for Cu/Sn58Bi-0.4Mg/Cu solder joint strength in ultrasonic-assisted soldering

This study investigated the influence of three ultrasonic-assisted soldering process parameters, namely soldering temperature, ultrasonic duration, and ultrasonic power, on the strength of Cu/Sn58Bi-0.4Mg/Cu solder joints. A three-factor, three-level orthogonal experiment was conducted by us using an L9 (34) orthogonal design, and the research outcome was evaluated in terms of solder joints shear strength. The optimal experimental design was determined through range analysis, and the Analysis of Variance (ANOVA) was performed to assess the individual impacts of each factor on the experimental results. Furthermore, we employed scanning electron microscopy (SEM) to examine the microstructures of the solder joints, investigate the progression of intermetallic compounds (IMC), and analyze the fracture surface morphology. Furthermore, we conducted essential Energy Dispersive Spectroscopy (EDS) elemental analysis to study the diffusion and distribution of elements. Finally, validation experiments were performed to compare the optimal design from the orthogonal experiment with the design derived from theoretical analysis, revealing that the latter yielded superior results. This study has identified an excellent set of parameters for ultrasonically assisted Cu/Sn58Bi-0.4Mg/Cu bonding. It offers novel insights into parameter selection for ultrasonic-assisted soldering, with potential energy conservation and efficiency improvement benefits.

Ultrasonic-assisted soldering of SiC ceramic and aluminum alloy with a commercial inactive Sn3.0Ag0.5Cu solder

Achieving the joining of SiC ceramic and Al alloy will be potential for the broad application of high-power IGBT packages. This work proposes a novel strategy of using the commercial Sn3.0Ag0.5Cu inactive solder to achieve an active bonding between SiC ceramics and 6063Al alloy. The ultrasound promotes the intensive dissolution of Al into the solder, resulting in the solder being activated and the interfacial reaction between the SiC ceramic and solder triggered by the acoustic cavitation effect. At a shorter ultrasonic action, The dissolution of Al-based metal by the Sn3.0Ag0.5Cu solder was low, and the Al/solder interface became uneven and precipitated fine Ag3Al2 and Al2Cu compounds in the solder. While the amount of Al dissolved by the Sn3.0Ag0.5Cu solder increased sharply, obvious notches were found at the Al/solder interface, and a large amount of α-Al precipitates in the solder under a longer ultrasonic duration (>10 s). The SiC/solder interface evolved from partial bonding to full metallurgical bonding with the prolongation of ultrasonic actions. The shear strength of the obtained SiC and 6063Al joints reached 35 MPa at the ultrasonic time of 40 s. The amorphous Al2O3 mixed with γ-Al2O3 grains was formed in the SiC/solder interface and 6063Al/solder interface. Based on the effect of acoustics cavitation and thermodynamics, the formation mechanism of the interfacial reaction layer was discussed in detail.

Preventing formation of intermetallic compounds in ultrasonic-assisted Sn soldering of Mg/Al alloys through pre-plating a Ni coating layer on the Mg substrate

Magnesium and aluminum alloys are widely used in various industries because of their excellent properties, and their reliable connection may increase application of materials. Intermetallic compounds (IMCs) affect the joint performance of Mg/Al. In this study, AZ31 Mg alloy with/without a nickel (Ni) coating layer and 6061 Al alloy were joined by ultrasonic-assisted soldering with Sn-3.0Ag-0.5Cu (SAC) filler. The effects of the Ni coating layer on the microstructure and mechanical properties of Mg/Al joints were systematically investigated. The Ni coating layer had a significant effect on formation of the Mg2Sn IMC and the mechanical properties of Mg/Al joints. The blocky Mg2Sn IMC formed in the Mg/SAC/Al joints without a Ni coating layer. The content of the Mg2Sn IMC increased with increasing soldering temperature, but the joint strength decreased. The joint without a Ni coating layer fractured at the blocky Mg2Sn IMC in the solder, and the maximum shear strength was 32.2 MPa. By pre-plating Ni on the Mg substrate, formation of the blocky Mg2Sn IMC was inhibited in the soldering temperature range 240–280 °C and the joint strength increased. However, when the soldering temperature increased to 310 °C, the blocky Mg2Sn IMC precipitated again in the solder. Transmission electron microscopy showed that some nano-sized Mg2Sn IMC and the (Cu, Ni)6Sn5 phase formed in the Mg(Ni)/SAC/Al joint soldered at 280 °C, indicating that the Ni coating layer could no longer prevent diffusion of Mg into the solder when the soldering temperature was higher than 280 °C. The maximum shear strength of the Mg(Ni)/SAC/Al joint was 58.2 MPa for a soldering temperature of 280 °C, which was 80.7% higher than that of the Mg/SAC/Al joint, and the joint was broken at the Mg(Ni)/SAC interface. Pre-plating Ni is a feasible way to inhibit formation of IMCs when joining dissimilar metals.

Ultrasonic-assisted soldering W90 Tungsten heavy alloy to AZ31B Mg alloy using Sn-xAl alloy

A double-layered W/Mg structure is expected to be a new generation of nuclear radiation shielding material. The tungsten heavy alloy (W90) and AZ31B Mg alloy were firstly bonded by ultrasonic-assisted soldering using pure Sn and Sn-Al filler metal in an atmospheric environment. The influence of ultrasonication time on the microstructure and mechanical properties of the joint was investigated. The typical microstructure of the W90/Sn/Mg joint was W90/Mg2Sn + Sn/Mg2Sn layer/Mg. As the ultrasonication time increased from 2 s to 10 s, the joint width reduced and the thickness of the Mg2Sn layer increased. The shear strength of the joint firstly increased, then flattened, and finally decreased. The joint strength reached the maximum value of 10.5 MPa. The fracture position of the joint changed from the W90/filler metal interface to the Mg2Sn layer. The addition of Al in Sn resulted in the formation of the Al4W phase at the W/Sn-1Al interface. The W/filler metal interface changed from the semi-coherent interface to the coherent interface and the joint strength increased. As the ultrasonication time was 6 s, the shear strength W90/Sn-1Al/Mg joint reached the maximum value of 24.6 MPa and the joint fractured at two positions: W90/filler metal interface and filler metal. With the further increase of ultrasonication time, the joint strength decreased and the joint fractured in the Mg2Sn layer.

Ultrasonic-induced metallurgical bonding between W90 tungsten heavy alloy and AZ31B Mg alloy using Sn

W90 tungsten heavy alloy (W90) and AZ31B Mg alloy were firstly bonded by ultrasonic-assisted soldering using Sn in atmospheric environment. The wetting angle of Sn on W90 decreased to 130.7° under the action of ultrasound. The microstructure of W90/Sn/Mg joint treated with 2 s of ultrasounication time was W90/Mg2Sn + Sn/Mg2Sn layer/Mg. As the ultrasonication time increased to 4 s, the joint width reduced and the thickness of Mg2Sn layer increased. The joint strength decreased from 10.4 MPa to 5.1 MPa as the ultrasonication time increased from 2 s to 4 s. A semi-coherent interface formed at the Sn/W interface as the ultrasound was applied.

High-strength joining of silica glass and 2024 aluminum alloy by ultrasonic-assisted soldering with Sn-Bi low temperature solder

To alleviate the problem of residual stress in silica glass/2024Al soldered joints, ultrasonic-assisted soldering of silicon glass and 2024Al was carried out using SnBi low-temperature solders. The impact of the soldering temperature and Bi content of the solder on the soldered joints were studied. Powder-reinforced solders were utilized to further improve the joint shearing strength, and the stirring time of the composite solder was also researched. The results showed that the joint strength stabilized after the soldering temperature reached 260 °C. For solders with different Bi content, the highest joint strength (27.3 MPa) was achieved with Sn28Bi solder. The composite solder could further increase the joint strength to 32.1 MPa. In addition, 10 min of ultrasonic vibration and mechanical stirring were recommended to obtain a high-quality composite solder.

Effect of the ultrasonic-assisted soldering on the interfacial reaction and IMC growth behavior of SAC305 solder with Cu alloy substrates

Effect of the ultrasonic-assisted soldering on the interfacial reaction and IMC growth behavior of SAC305 solder with Cu alloy substrates

The Horizontal Sonocapillary Effect in UltrasonicAssisted Soldering

In this work, the horizontal sonocapillary effect in ultrasonic-assisted soldering was investigated via numerical simulations and experiments. The numerical simulation results indicated that acoustic pressures in the liquid solder exhibited distinct sinusoidal features with negative offsets, forming a negative average acoustic pressure. When the ultrasonic vibrations were transmitted to the lower substrate in the joint clearance, the average acoustic pressures decreased from the acoustic pressure center to the filling front, forming a negative acoustic pressure gradient in the horizontal direction. As a result, the solder was sucked into the joint clearance by a large negative acoustic pressure. This sonocapillary effect was verified with experiments. In the calculation model, a high ultrasonic amplitude, a small joint clearance width, and a high base material stiffness increased the acoustic pressure and its average difference on the horizontal direction in the solder, which further improved the driving force of the sonocapillary effect. However, the wetting angle had a small influence on the sonocapillary effect.

Review of ultrasonic-assisted soldering in Sn-based solder alloys

Review of ultrasonic-assisted soldering in Sn-based solder alloys

Interfacial IMC growth behavior and mechanical properties of Cu/Sn58Bi/Cu and Cu/Sn58Bi–0.05AlN/Cu solder joints under ultrasonic-assisted soldering

Interfacial IMC growth behavior and mechanical properties of Cu/Sn58Bi/Cu and Cu/Sn58Bi–0.05AlN/Cu solder joints under ultrasonic-assisted soldering

Microstructure evolution and grain refinement of ultrasonic-assisted soldering joint by using Ni foam reinforced Sn composite solder.

In this investigation, ultrasonic-assisted soldering at 260°C in air produced high strength and high melting point Cu connections in 60s using Ni foam reinforced Sn composite solder. Systematically examined were the microstructure, grain morphology, and shear strength of connections made with various porosities of Ni foam composite solders. Results shown that Ni foams as strengthening phases could reinforce Sn solder effectively. The addition of Ni foam accelerated the metallurgical reaction due to great amount of liquid/solid interfaces, and refined the intermetallic compounds (IMCs) grains by ultrasonic cavitation. The joints had different IMCs by using Ni foam with different porosity. Layered (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 phases both existed in Cu/Ni60-Sn/Cu joint while only (Cu,Ni)6Sn5 IMCs grew in Cu/Ni98-Sn/Cu joint. As ultrasonic time increasing, Ni skeletons were dissolved and the IMCs were peeled off from substrates and broken into small particles. And then, the IMCs gradually dissociated into refined particles and distributed homogeneously in the whole soldering seam under cavitation effects. Herein, the Cu/Ni60-Sn/Cu joint ultrasonically soldered for 60s exhibited the highest shear strength of 86.9MPa, as well as a high melting point about 800℃ for the solder seam composed of Ni skeletons and Ni-Cu-Sn IMCs. The characterization indicated that the shearing failure mainly occurred in the interlayer of the soldering seam. The homogeneous distributed granular IMCs and Ni skeletons hindered the crack propagation and improved the strength of Cu alloy joints.

Microstructure and shear strength on ultrasonic-assisted soldered the Si/Cu joint using Sn-3.5Ag solder

The thermal stress, resulting from the big difference of CTE between Si and Cu, could reduce the strength of joints. In this study, Silicon and Cu were soldered by a two-step process (pre-metallization and brazing), which could alleviate the stress. Firstly, a Al-Si metallization layer (consisting α-Al matrix and Si phase) was prepared on the surface of monocrystalline Si by using Al metal powder at 900 ℃. Then the joint of pre-metallized Si and Cu was successfully achieved by ultrasonic-assisted soldering method with Sn-3.5Ag filler at 250 ℃ in air. The effects of ultrasonic time on microstructure and shear strength of the Si/Cu joints were investigated in details. It was found that the oxide layer was broken and gradually dissolved with the ultrasonic action, which was attributed to the high velocity (3055 m/s), high pressure (2.32×108 Pa), and the high temperature (5700 K) generated by the cavitation bubble collapse. Besides, the Ag2Al compounds and Si phases at the solder/metallization layer interface were observed. And the Cu6Sn5+Cu3Sn compounds were detected forming at the solder/Cu interface. As the ultrasonic vibration duration time increased, Ag2Al compounds attached to the Al-Si layer gradually increased, and ultimately entered into the filler. Attentionly, the maximum strength of Si/Cu joint was 32.4 MPa with the ultrasonic time of 6 s, and the fracture occurred inside the monocrystalline Si. The results show that ultrasonic action affects the distribution of Ag2Al compound and Si phase, which has an important influence on the joint strength.

In-situ formation of amorphous Al2O3 interphase during ultrasonic-assisted soldering process of ZrO2 ceramic and 1060Al using Sn filler at low temperature

The dissimilar ZrO2/Sn/Al butt joints were successfully achieved by ultrasonic-assisted soldering using a needle-shape acoustic horn at 350 °C. It was found that the bonding mechanism of the dissimilar butt joints was based on the interfacial sono-oxidation reactions leading to the formation of the amorphous Al2O3 layers of 6 nm and 12 nm thickness at the ZrO2/Sn and Al/Sn interfaces, respectively. The average tensile strength of the ZrO2/Sn/Al butt joints was tested to be 29.2 MPa.

Control of intermetallic compounds in Ultrasonic-Assisted Sn soldering of Mg/Al alloys

Magnesium and aluminum alloys are widely used in various industries because of their light weight and other properties. However, Mg–Al intermetallic compounds (IMCs) decrease the joint properties of Mg/Al, which limits its applications. Here, the alloys AZ31 Mg and 6061 Al are soldered together with Sn and Sn–9Zn solders though different cooling rates via ultrasonic-assisted soldering to control IMC formation and growth. Results show that this prevents formation of Mg–Al IMCs such as Al3Mg2 and Al12Mg17; however, Mg2Sn forms in the soldered joints. The Mg2Sn thickness increases with soldering temperature, which reduces joint strength. The thickness is reduced using the Sn–9Zn solder, and the effect of Zn is analyzed. With the use of water-cooling, the Mg2Sn formation and growth are inhibited, the Mg2Sn thickness is kept below 5 μm, and the shear strength peaks at 53.2 MPa. A soldering model of Mg2Sn formation is proposed to reveal the evolution and inhibition mechanism of Mg2Sn. This study well controls IMC thickness and improves joint strength, thus expanding industrial application of Mg–Al dissimilar metals and providing a feasible method for controlling IMCs in dissimilar metal joining.

Ultrasonic-assisted soldering of sapphire through metallic transition layers of Al and Zn using Sn-xZn-2Al solder alloys

Ultrasonic-assisted soldering has potential in the electrical industry especially for the joining of ceramics. The Al-activated Sn-based alloys are promising ultrasonic solders due to simple preparation, while the current approaches required long ultrasonic action. In order to increase the efficiency and reduce ultrasonic-induced damage, this study investigated the soldering of sapphire (monocrystalline α-Al2O3) performed under an ultrasonic action for 0.5 s by using Sn-xZn-2Al(x = 9, 25, 45) solder alloys. Microstructures of interfacial transition layers between the sapphire and solders were focused on. It has been found that at the interfaces no interfacial reaction phases formed and the interfacial bonding was realized via metallic transition layers. Three kinds of interfacial structures existed, that is, sapphire/Al atomic layer/β-Sn, sapphire/Al atomic layer/(Zn enrichment layer)/β-Sn and sapphire/Al atomic layer/Zn nanocrystalline clusters/β-Sn. The elements of Al and Zn in the solder alloys underwent a selective and asynchronous adsorption process during the ultrasonic action. An Al atomic layer formed on the sapphire surface by the stronger chemical adsorption and acted as a transition layer between sapphire and β-Sn. The Zn enrichment layer was distributed locally along the interface and as the Zn content increased in the solder alloys, more localized Zn nanocrystalline clusters formed. These Zn transition structures strengthened the interfacial bonding by transforming the Al atomic layer/β-Sn interface into the Al atomic layer/Zn transition structures/β-Sn interfaces. The joints possessed a shear strength of up to 28 MPa when soldering with Sn–45Zn–2Al at 350 °C.