The Experts below are selected from a list of 14100 Experts worldwide ranked by ideXlab platform
Zhuoshen Shen - One of the best experts on this subject based on the ideXlab platform.
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wetting and spreading behavior of borosilicate glass on Kovar
Journal of Alloys and Compounds, 2009Co-Authors: Zhuoshen ShenAbstract:Abstract The wetting and spreading behavior of borosilicate glass on Kovar with oxides of FeO + Fe 3 O 4 was investigated as a function of wetting time by the sessile drop method. The contact angle and drop base diameter were measured by the VHX-100K digital microscopy. The top view of spreading and cross-sectional microstructure of glass/Kovar was investigated by SEM, and elements distribution of Fe, Co, Ni and Si in interfacial regions was characterized by EDS line scanning. The results showed two halos were formed at the fringe of glass base in the wetting process. By analyzing the change of contact angle and drop base diameter, wetting process could be divided into three stages: incubation period, reaction period and equilibrium period. Chemical reaction is occurred between glass and oxides, and the reaction product is Fe 2 SiO 4 . Chemical and mechanical bonding effects are all present in the wetting of glass to Kovar.
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effect of Kovar alloy oxidized in simulated n2 h2o atmosphere on its sealing with glass
Journal of University of Science and Technology Beijing Mineral Metallurgy Material, 2008Co-Authors: Wenbo Leng, Zhuoshen ShenAbstract:Abstract The effect of Kovar alloy oxidized in simulated field atmosphere on its sealing with glass was studied in this article. After Kovar plates and pins were preoxidized in N 2 with 0°C, 10°C and 20°C dew points at 1000°C for different times, Fe 3 O 4 and Fe 2 O 3 existed in the oxidation products on Kovar surface, and the quantity of Fe 2 O 3 increased with increasing dew point and oxidation time. Then they were sealed with borosilicate glass insulator at 1030°C for 20 min. The results indicated that the type and quantity of oxidation products would directly influence the quality of glass-to-metal seals. With the increase of oxidation products, gas bubbles in the glass insulator were more serious, the climbing height of glass along the pins was higher, and corrosion of Kovar pins caused from the molten glass was transformed from uniform to the localized.
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Effect of Kovar alloy oxidized in simulated N2/H2O atmosphere on its sealing with glass
Journal of University of Science and Technology Beijing Mineral Metallurgy Material, 2008Co-Authors: Wenbo Leng, Zhuoshen ShenAbstract:Abstract The effect of Kovar alloy oxidized in simulated field atmosphere on its sealing with glass was studied in this article. After Kovar plates and pins were preoxidized in N 2 with 0°C, 10°C and 20°C dew points at 1000°C for different times, Fe 3 O 4 and Fe 2 O 3 existed in the oxidation products on Kovar surface, and the quantity of Fe 2 O 3 increased with increasing dew point and oxidation time. Then they were sealed with borosilicate glass insulator at 1030°C for 20 min. The results indicated that the type and quantity of oxidation products would directly influence the quality of glass-to-metal seals. With the increase of oxidation products, gas bubbles in the glass insulator were more serious, the climbing height of glass along the pins was higher, and corrosion of Kovar pins caused from the molten glass was transformed from uniform to the localized.
Ning Li - One of the best experts on this subject based on the ideXlab platform.
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microstructural evolution in the braze joint of sapphire to Kovar alloy by ti cu metallization layer
Journal of Materials Processing Technology, 2017Co-Authors: Ning LiAbstract:Abstract Sapphire was metallized by magnetron sputtering Ti-Cu bilayer films on the surface and was brazed to Kovar alloy (Fe-Ni-Co) using Ag-Cu eutectic alloy. The microstructures of these joints were investigated. The correlation between the Al2O3/Kovar joining strength and the microstructures of the braze joints was discussed. The results show that Ni atoms in Kovar alloy diffused towards the Ti-Cu metallizaton layer and remained as (Ni, Cu) solution during the solidification process. The metallization layer became thicker and evolved into a reaction layer which consisted of (Ni, Cu) solution, Cu-Ti-O and TiO. This reaction layer in the joint played an important role in relieving residual stress. Thus the maximal tensile strength of 72.6 ± 4.4 MPa was achieved. However, as the holding time was further prolonged, Ni atoms diffused through the (Ni, Cu) solid solution into the reaction layer resulting in formation of Ni3Ti intermetallic compounds and transformation of TiO to Ti2O3, which leads to the joint strength decreasing.
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metallization of al2o3 ceramic by magnetron sputtering ti mo bilayer thin films for robust brazing to Kovar alloy
Ceramics International, 2016Co-Authors: Ning LiAbstract:Abstract Ti/Mo bilayer thin films were deposited onto Al2O3 ceramic by magnetron sputtering with a subsequent high temperature sintering to ensure the robust brazing of Al2O3 ceramic to Kovar (Fe–Ni–Co) alloy. The interface reaction process between Ti film and Al2O3 ceramic as well as the joining strength between metallized Al2O3 ceramic and Kovar alloy were investigated systematically using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and electronic universal testing machine. The results show that the active Ti film can react with Al2O3 ceramic to form Ti3Al and TiO during high-temperature sintering process, in which the amount, size and morphology of TiO crucially depend on the sintering temperature. As the sintering temperature reaches 1200 °C, a plenty of spherical TiO nanoparticles with ~ 150 nm in diameter and metallic nature can be created across the Ti/Al2O3 interfaces, which can effectively act as ‘bridges’ to join Ti film to Al2O3 substrate firmly. Hence, the optimal joining strength of 69.6±3.1 MPa between metallized Al2O3 ceramic and Kovar alloy can be obtained, much better than those counterparts metallized at 900 °C and 1050 °C almost without the existence of observable TiO.
John A Fernie - One of the best experts on this subject based on the ideXlab platform.
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active metal brazing of al _ 2 o _ 3 to Kovar fe 29ni 17co wt using copper aba cu 3 0si 2 3ti 2 0al wt
Philosophical Magazine, 2018Co-Authors: Kevin M Knowles, Phillip M Mallinson, John A FernieAbstract:AbstractThe application of an active braze alloy (ABA) known as Copper ABA® (Cu–3.0Si–2.3Ti–2.0Al wt.%) to join Al2O3 to Kovar® (Fe–29Ni–17Co wt.%) has been investigated. This ABA was selected to increase the operating temperature of the joint beyond the capabilities of typically used ABAs such as Ag–Cu–Ti-based alloys. Silica present as a secondary phase in the Al2O3 at a level of ~5 wt.% enabled the ceramic component to bond to the ABA chemically by forming a layer of Si3Ti5 at the ABA/Al2O3 interface. Appropriate brazing conditions to preserve a near-continuous Si3Ti5 layer on the Al2O3 and a continuous Fe3Si layer on the Kovar® were found to be a brazing time of ≤15 min at 1025 °C or ≤2 min at 1050 °C. These conditions produced joints that did not break on handling and could be prepared easily for microscopy. Brazing for longer periods of time, up to 45 min, at these temperatures broke down the Si3Ti5 layer on the Al2O3, while brazing at ≥1075 °C for 2–45 min broke down the Fe3Si layer on the Kovar® s...
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Evolution of the interfacial phases in Al$_{2}$O$_{3}$–Kovar joints$^{®}$ brazed using a Ag–Cu–Ti-based alloy
Philosophical Magazine, 2017Co-Authors: Kevin M Knowles, Phillip M Mallinson, John A FernieAbstract:AbstractA systematic investigation of the brazing of Al2O3 to Kovar® (Fe–29Ni–17Co wt.%) using the active braze alloy (ABA) Ag–35.25Cu–1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary phases in the Al2O3 participate in the reactions at the ABA/Al2O3 interface has been clarified. Another aspect of this work has been to determine the influence of various brazing parameters, such as the peak temperature, Tp, and time at Tp, τ, on the resultant microstructure. As a consequence, the microstructural evolution of the joints as a function of Tp and τ is discussed in some detail. The formation of a Fe2Ti layer on the Kovar® and its growth, along with adjacent Ni3Ti particles in the ABA, dominate the microstructural developments at the ABA/Kovar® interface. The presence of Kovar® next to the ABA does not change the intrinsic chemical reactions occurring at the ABA/Al2O3 interface. However, the extent of these reactions is lim...
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evolution of the interfacial phases in al _ 2 o _ 3 Kovar joints brazed using a ag cu ti based alloy
Philosophical Magazine, 2017Co-Authors: Kevin M Knowles, Phillip M Mallinson, John A FernieAbstract:AbstractA systematic investigation of the brazing of Al2O3 to Kovar® (Fe–29Ni–17Co wt.%) using the active braze alloy (ABA) Ag–35.25Cu–1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary phases in the Al2O3 participate in the reactions at the ABA/Al2O3 interface has been clarified. Another aspect of this work has been to determine the influence of various brazing parameters, such as the peak temperature, Tp, and time at Tp, τ, on the resultant microstructure. As a consequence, the microstructural evolution of the joints as a function of Tp and τ is discussed in some detail. The formation of a Fe2Ti layer on the Kovar® and its growth, along with adjacent Ni3Ti particles in the ABA, dominate the microstructural developments at the ABA/Kovar® interface. The presence of Kovar® next to the ABA does not change the intrinsic chemical reactions occurring at the ABA/Al2O3 interface. However, the extent of these reactions is lim...
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xps examination of the oxide layer formed on Kovar following pre oxidation
Surface Science Spectra, 2015Co-Authors: Christopher F Mallinson, Sabrina Tardio, Paul M Yates, Martyn T Staff, John A Fernie, John F WattsAbstract:Kovar (Fe-29 Ni-17 Co wt%) is widely used in electrical components. For applications such as feed-throughs there is a requirement to join it to glass, forming a glass-to-metal seal. A controlled thickness, well adhered, oxide is desired on the Kovar to form a strong bond. The oxides formed on Kovar pre-oxidized, at 700 and 800 °C for ten min, have been analyzed. Each sample showed the presence of Fe2O3, CoO and NiO. XPS survey spectra and high resolution spectra were collected and are presented.
Paul T Vianco - One of the best experts on this subject based on the ideXlab platform.
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solderability testing of sn ag xcu pb free solders on copper and au ni plated Kovar substrates
Journal of Electronic Materials, 2005Co-Authors: Edwin Paul Lopez, Paul T Vianco, Jerome A RejentAbstract:Solderability was evaluated for four Pb-free alloys: 95.5Sn-4.3Ag-0.2Cu (wt.%), 95.5Sn-4.0Ag-0.5Cu, 95.5Sn-3.9Ag-0.6Cu, and 95.5Sn-3.8Ag-0.7Cu on oxygen-free electronic grade (OFE) Cu and Au-Ni plated Kovar substrates. The solderability metric was the contact angle, θc, as determined by the meniscometer/wetting balance technique. Tests were performed at 230°C, 245°C, and 260°C using rosin-based, mildly activated (RMA) flux, a rosin-based (R) flux, and a low-solids (LS) flux. The Pb-free solders exhibited acceptable to poor solderability (35°<θc<60°) on Cu with the RMA flux. Nonwetting occurred in most tests using the R flux. Wetting was observed with the LS flux, but only at 245°C and 260°C and with high contact angles. The solderability of the Pb-free solders improved at all test temperatures on the Au-Ni plated Kovar substrate when using the RMA flux (30°<θc<50°). Wetting was observed with the R flux (35°<θc<60°) and LS flux (50°<θc<85°) for all temperatures. The Pb-free solders had generally lower wetting rates and longer wetting times on Cu than the 63Sn-37Pb solder. The wetting rate and wetting time data were superior on the Au-Ni plated Kovar substrates. In general, solderability, as measured by θc along with the wetting rate and wetting time, did not exhibit a consistent dependence on the composition of the Sn-Ag-XCu (X=0.2, 0.5, 0.6, and 0.7) alloys. The better performers were 95.5Sn-3.9Ag-0.6Cu alloy with the RMA flux (both Cu and Au-Ni plated Kovar) and 95.5Sn-3.8Ag-0.7Cu with the R and LS fluxes (Au-Ni-Kovar, only). The solder-flux interfacial tension, γLF, had a significant impact on the θc values. The magnitudes of the contact angle θc suggested that the four Pb-free solders would experience higher solderability defect counts at the printed wiring assembly level.
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microstructure and performance of Kovar alumina joints made with silver copper base active metal braze alloys
International Brazing and Soldering Conference Albuquerque NM (US) 04 02 2000--04 05 2000, 1999Co-Authors: John J Stephens, Paul T Vianco, Paul F Hlava, Charles A WalkerAbstract:Poor hermeticity performance was observed for Al{sub 2}O{sub 3}-Al{sub 2}O{sub 3} ceramic-ceramic joints having a Kovar{trademark} alloy interlayer. The active Ag-Cu-Ti filler metal was used to braze the substrates together. The Ti active element was scavenged from the filler metal by the formation of a (Fe, Ni, Co){sub x}Ti phase (x= 2-3) that prevented development of a continuous Ti{sub x}O{sub y} layer at the filler metal/Al{sub 2}O{sub 3} interface. Altering the process parameters did not circumvent the scavenging of Ti. Molybdenum barrier layers 1000, 2500, or 5000 {angstrom} thick on the Kovar{trademark} surfaces successfully allowed Ti{sub x}O{sub y} formation at the filler metal/Al{sub 2}O{sub 3} interface and hermetic joints. The problems with the Ag-Cu-Ti filler metal for Kovar{trademark}/Al{sub 2}O{sub 3} braze joints led to the evaluation of a Ag-Cu-Zr filler metal. The Zr (active element) in Ag-Cu-Zr filler metal was not susceptible to the scavenging problem.
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Microstructure and Performance of Kovar/Alumina Joints Made with Silver-Copper Base Active Metal Braze Alloys
1999Co-Authors: J.j. Stephens, Paul T Vianco, Paul F Hlava, Charles A WalkerAbstract:Poor hermeticity performance was observed for Al{sub 2}O{sub 3}-Al{sub 2}O{sub 3} ceramic-ceramic joints having a Kovar{trademark} alloy interlayer. The active Ag-Cu-Ti filler metal was used to braze the substrates together. The Ti active element was scavenged from the filler metal by the formation of a (Fe, Ni, Co){sub x}Ti phase (x= 2-3) that prevented development of a continuous Ti{sub x}O{sub y} layer at the filler metal/Al{sub 2}O{sub 3} interface. Altering the process parameters did not circumvent the scavenging of Ti. Molybdenum barrier layers 1000, 2500, or 5000 {angstrom} thick on the Kovar{trademark} surfaces successfully allowed Ti{sub x}O{sub y} formation at the filler metal/Al{sub 2}O{sub 3} interface and hermetic joints. The problems with the Ag-Cu-Ti filler metal for Kovar{trademark}/Al{sub 2}O{sub 3} braze joints led to the evaluation of a Ag-Cu-Zr filler metal. The Zr (active element) in Ag-Cu-Zr filler metal was not susceptible to the scavenging problem.
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Solderability of Kovar[trademark]
1992Co-Authors: Paul T Vianco, F.m. HoskingAbstract:The wettability of bare Kovar by liquid 60Sn-40Pb solder was examined as a function of two surface preparation techniques. Adequate solderability was achieved with four organic acid fluxes when the Kovar surfaces were chemically etched in an acid solution; however, wetting was poor with the use of a rosin-based, mildly activated (RMA) flux. Changing to an electropolishing treatment with an acetic acid/perchloric acid electrolyte improved solder wetting, particularly with the RMA flux. Growth of the solder-substrate metallurgical reaction layer was examined after elevated-temperature annealing treatments. Intermetallic compounds grew both along the solder-substrate interface as well as in the solder phases, at rates much less than observed for the copper-solder system.
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Solderability testing of Kovar with 60Sn40Pb solder and organic fluxes
1990Co-Authors: Paul T Vianco, F.m. Hosking, Jerome A RejentAbstract:The solderability of 60Sn40Pb solder on Kovar was examined as a function of surface-cleaning procedure, flux, and solder-bath temperature. Organic-acid fluxes were more effective at lowering the contact angle than was a mildly activated, rosin-based (RMA) flux on chemically etched Kovar. The contact angles were as low as 29{degree} {plus minus} 5{degree} as compared to 61{degree} {plus minus} 11{degree}, respectively. Varying the solder temperature through the range of 215{degree}C to 288{degree}C caused an insignificant change in the contact angle for the RMA flux and a decrease of the contact angle for a candidate water-based, organic-acid flux. The dilution strength of the flux and the elapsed cleaning time significantly influenced the solder-flux interfacial tension, {sub {gamma}LF}. T-peel strengths of Kovar-60Sn40Pb-OFHC copper joints had a low correlation with the contact angle derived from the solderability experiments. The results of the solderability tests and the T-peel mechanical tests, and subsequence microanalysis of the as-soldered and T-peel samples revealed that the best results for the RMA flux were achieved by using an electropolishing procedure and a solder temperature of 240{degree}C to 260{degree}C. A relatively low contact angle of 31{degree} {plus minus} 2{degree} was observed, with no evidence of cracking or thick-film intermetallic formation atmore » the Kovar-solder interface. T-peel strengths were nominally 9.4{degree} {plus minus} 0.5 {times} 10{sup 6} dyn/cm. 21 refs., 36 figs., 11 tabs.« less
Xiao-wu Hu - One of the best experts on this subject based on the ideXlab platform.
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Shear strength and fracture behavior of solder/Kovar joints with electroplated Cu film
Vacuum, 2019Co-Authors: Xiao-wu Hu, Qinglin LiAbstract:Abstract In this study, the effects of isothermal aging on the interfacial reactions, shear strength and failure mode of Sn37Pb/electroplated Cu (EPC)/Kovar solder joints were investigated in detail. Various interfacial intermetallic compound (IMC) layers were formed in all as-reflowed solder joints. The as-reflowed solder joints were aged up to 360 h at 150 °C before single-lap shear tests. The microstructure of interfacial IMCs layers was affected by the isothermal aging, as well as deposited thickness of Cu film on Kovar substrate. Single-lap shear tests results revealed that the introduction of Cu film on Kovar significantly improved the shear strength of Sn37Pb/EPC/Kovar solder joints. This is because the Cu film could act as a sacrificial layer and react with molten solder to form a thin Cu-Sn IMCs layer, which was expected to protect Au/Ni films from further reaction with solder, rendering a enhanced bonding strength of joints. The shear strength of Sn37Pb/EPC/Kovar solder joints with same aging time increased first and then decreased with the increase of deposited Cu film thickness. The shear strength of aged solder joints decreased with increasing aging time, which could be ascribed to the thicker IMC layer generated at the joint interface.
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shear strength and fracture behavior of solder Kovar joints with electroplated cu film
Vacuum, 2019Co-Authors: Xiao-wu Hu, Qinglin LiAbstract:Abstract In this study, the effects of isothermal aging on the interfacial reactions, shear strength and failure mode of Sn37Pb/electroplated Cu (EPC)/Kovar solder joints were investigated in detail. Various interfacial intermetallic compound (IMC) layers were formed in all as-reflowed solder joints. The as-reflowed solder joints were aged up to 360 h at 150 °C before single-lap shear tests. The microstructure of interfacial IMCs layers was affected by the isothermal aging, as well as deposited thickness of Cu film on Kovar substrate. Single-lap shear tests results revealed that the introduction of Cu film on Kovar significantly improved the shear strength of Sn37Pb/EPC/Kovar solder joints. This is because the Cu film could act as a sacrificial layer and react with molten solder to form a thin Cu-Sn IMCs layer, which was expected to protect Au/Ni films from further reaction with solder, rendering a enhanced bonding strength of joints. The shear strength of Sn37Pb/EPC/Kovar solder joints with same aging time increased first and then decreased with the increase of deposited Cu film thickness. The shear strength of aged solder joints decreased with increasing aging time, which could be ascribed to the thicker IMC layer generated at the joint interface.
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investigation of the interfacial reactions and growth behavior of interfacial intermetallic compound between sn37pb solder and au ni Kovar substrate
Materials Research Express, 2019Co-Authors: Xiao-wu Hu, Qinglin LiAbstract:The interfacial reactions and microstructural evolution of Sn37Pb/Kovar with Au/Ni platings solder joints were investigated during isothermal aging at 120 °C, 150 °C and 170 °C for different duration, respectively. The experimental results indicated that a thin interfacial intermetallic compounds (IMCs) layer formed at the Sn37Pb/Kovar interface after reflowing process. The accurate compositions of thin IMCs were double-layers of (Ni, Au)3Sn4 and AuSn4, which were confirmed by utilizing TEM-EDS analysis. However, during the aging process, the compositions of interfacial IMCs of solder joint obviously changed, which transformed from AuSn4/(Ni, Au)3Sn4 to (Au, Ni)Sn4/Ni3Sn4 and the AuSn4 IMC formed in the bulk solder gradually changed to the (Au, Ni)Sn4 IMC. Furthermore, the total IMC thickness increased dramatically with increasing isothermal aging time, as well as aging temperature. The growth process of IMC layer is mainly dominated by the volume diffusion mechanism during the solid-state aging. The square of growth rate constant (K) equals to 2.559 × 10−17, 1.307 × 10−16 and 7.781 × 10−16 m2s−1 for the aging temperature of 120 °C, 150 °C and 170 °C, respectively. The activation energy (Q) value of the Sn37Pb/Kovar couple was calculated to be approximate 95.96 kJmol−1.
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Synergetic effect of strain rate and electroplated Cu film for shear strength of solder/Kovar joints
Journal of Materials Science: Materials in Electronics, 2019Co-Authors: Xiao-wu Hu, Nifa Bao, Zhixian MinAbstract:The effects of strain rate and electroplated Cu on the shear fracture behaviors of Sn37Pb/electroplated Cu (EPC)/Kovar solder joints were investigated after reflowing at 250 °C for 5 min. The Kovar was electroplated with 4.1 µm thick layer of Ni and 1.9 µm thick layer of Au. The copper electroplating time were 2, 5, 10 and 20 min, respectively, resulting in a different deposited thicknesses of Cu film on the Kovar substrate. The shear tests of Sn37Pb/EPC/Kovar joints were performed with different strain rates ranging from 8.3 × 10−2 to 1.6 s−1 to study the shear fracture behavior. Experimental results showed that the shear strength and failure mode of solder joints were affected by the thickness of electroplated Cu film and the applied strain rate. The shear strength of solder joint demonstrated increment at first and then decrement as the applied strain rate increased. It was observed that the shear failure mode of solder joints is well known to have experienced a transition from ductile fracture with the low strain rates (8.33 × 10−2 s−1 and 3.33 × 10− 1 s−1) to a mixed fracture with the intermediate strain rate (6.67 × 10−1 s−1) and high strain rates (1 s−1, 1.33 s−1 and 1.67 s−1). Studies in the shear properties of solder joints with electroplated Cu layer indicated that the electroplated Cu on the Kovar substrate has a significant improvement in the shear strength of solder joints. With increasing in the deposited thickness, the shear strength of solder joints increased when the deposited thickness was no more than 3.3 µm. Subsequently, the shear strength started to drop as the deposited thickness further increased.
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synergetic effect of strain rate and electroplated cu film for shear strength of solder Kovar joints
Journal of Materials Science: Materials in Electronics, 2019Co-Authors: Xiao-wu HuAbstract:The effects of strain rate and electroplated Cu on the shear fracture behaviors of Sn37Pb/electroplated Cu (EPC)/Kovar solder joints were investigated after reflowing at 250 °C for 5 min. The Kovar was electroplated with 4.1 µm thick layer of Ni and 1.9 µm thick layer of Au. The copper electroplating time were 2, 5, 10 and 20 min, respectively, resulting in a different deposited thicknesses of Cu film on the Kovar substrate. The shear tests of Sn37Pb/EPC/Kovar joints were performed with different strain rates ranging from 8.3 × 10−2 to 1.6 s−1 to study the shear fracture behavior. Experimental results showed that the shear strength and failure mode of solder joints were affected by the thickness of electroplated Cu film and the applied strain rate. The shear strength of solder joint demonstrated increment at first and then decrement as the applied strain rate increased. It was observed that the shear failure mode of solder joints is well known to have experienced a transition from ductile fracture with the low strain rates (8.33 × 10−2 s−1 and 3.33 × 10− 1 s−1) to a mixed fracture with the intermediate strain rate (6.67 × 10−1 s−1) and high strain rates (1 s−1, 1.33 s−1 and 1.67 s−1). Studies in the shear properties of solder joints with electroplated Cu layer indicated that the electroplated Cu on the Kovar substrate has a significant improvement in the shear strength of solder joints. With increasing in the deposited thickness, the shear strength of solder joints increased when the deposited thickness was no more than 3.3 µm. Subsequently, the shear strength started to drop as the deposited thickness further increased.
