Soldering experiments of quad flat package(QFP) devices were carried out by means of diode laser soldering system with Sn-Ag-Cu and Sn-Cu-Ni lead-free solders, and competitive experiments were also carried out not onl...Soldering experiments of quad flat package(QFP) devices were carried out by means of diode laser soldering system with Sn-Ag-Cu and Sn-Cu-Ni lead-free solders, and competitive experiments were also carried out not only with Sn-Pb eutectic solders but also with infrared reflow soldering method. The results indicate that under the conditions of laser continuous scanning mode as well as the fixed laser soldering time, an optimal power exists, while the optimal mechanical properties of QFP micro-joints are gained. Mechanical properties of QFP micro-joints soldered with laser soldering system are better than those of QFP micro-joints soldered with IR reflow soldering method. Fracture morphologies of QFP micro-joints soldered with laser soldering system exhibit the characteristic of tough fracture, and homogeneous and fine dimples appear under the optimal laser output power.展开更多
To investigate the effect of Au thickness on evolution of AuSnx IMCs, pads with 0. 1, 0. 5 and 4. 0 μm thickness of Au surface finish were utilized. Laser reflowed solder joints were aged in 125℃ isothermal ovens. R...To investigate the effect of Au thickness on evolution of AuSnx IMCs, pads with 0. 1, 0. 5 and 4. 0 μm thickness of Au surface finish were utilized. Laser reflowed solder joints were aged in 125℃ isothermal ovens. Results indicated that little IMC formed at the interface of solder and pad with 0. 1 μm thickness of Au. Even in condition of 744 hours aging, thickness of lMCs did not increase obviously. As for the joints with 0. 5 μm thickness of Au, most of AuSn4 IMCs stayed at the inteornce and were in needle-like or dendritic morphology. With the increase of aging time, AuSn4 IMCs beeame flat and changed to a continuous layer. In the joints with 4. 0 μm thickness of Au on pads, AuSn, AuSn2, AuSn4 IMCs and Au2Sn phase formed at the interface. As aging time was increased, more Sn rich IMCs formed at the interface, and evolved to AuSn4 IMCs in condition of long time aging. Thickness of AuSn4 IMCs reached about 30μm.展开更多
In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetr...In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetration or unacceptable welds.Recognition of joint position offset, which describes the deviation between the laser beam focus and the weld joint, is important for adjusting the laser beam focus and obtaining high quality welds. A new method based on the magneto-optical（MO） imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm. The weldments are excited by an external magnetic field, and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images. A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired. By analyzing the MO image characteristics and extracting the weld joint features, the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.展开更多
Tensile strengths of QFP micro-joints with different pitches were tested by means of micro-joints tester. On the basis of those results, the effects of QFP pitches’ numbers on the mechanical properties were studied a...Tensile strengths of QFP micro-joints with different pitches were tested by means of micro-joints tester. On the basis of those results, the effects of QFP pitches’ numbers on the mechanical properties were studied and the microstructures of cracks of micro-joints were analyzed based on facts of SEM and EDS. The results indicate that of tensile strengths micro-joint of 48 pitches are lower than that of 100 pitches and the tensile strength of soldered joint is higher than that of solder itself. The fracture mechanism of QFP soldered joint with Sn-Pb solder acts as the interface cavity impair ductile rupture while the fracture mechanism of QFP soldered joint with lead-free solder shows trans-crystalline toughness rupture which belongs to micro-holes coalescence fracture.展开更多
Nanoindentation method was adopted to investigate the distribution regularities of micro-mechanical properties of 2219 twin wire welded joints, thus providing the necessary theoretical basis and guidance for joint str...Nanoindentation method was adopted to investigate the distribution regularities of micro-mechanical properties of 2219 twin wire welded joints, thus providing the necessary theoretical basis and guidance for joint strengthening and improvement of welding procedure. Experimental results show that in weld zone, micro-mechanical properties are seriously uneven. Both hardness and elastic modulus distribute as uneven sandwich layers, while micro-mechanical properties in bond area are much more uniform than weld zone;In heat-affected zone of 2219 twin wire welded joint, distribution regularity of hardness is similar to elastic modulus. The average hardness in quenching zone is higher than softening zone, and the average elastic modulus in solid solution zone is slightly higher than softening zone. As far as the whole welded joint is concerned, metal in weld possesses the lowest hardness. For welded specimens without reinforcement, fracture position is the weld when tensioning. While for welded specimens with reinforcement, bond area is the poorest position with joint strength coefficient of 61%. So, it is necessary to strengthen the poor positions--weld and bond area of 2219 twin wire welded joint in order to solve joint weakening of welding this kind of alloy.展开更多
Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is ...Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.展开更多
Based on the simulated aerospace thermal cycling tests,the effect of thermal cycle on the void damage evolution mechanism of LF6 aluminum alloy welded joint was investigated.The results show that micro-voids form arou...Based on the simulated aerospace thermal cycling tests,the effect of thermal cycle on the void damage evolution mechanism of LF6 aluminum alloy welded joint was investigated.The results show that micro-voids form around the second phase particles under the thermal cycling tests.The thermal stress coupled with external stress leads to dislocations pile-up around the particles,and when the dislocation density reaches a certain degree,the stress concentration will exceed the bonding strength at the interface between particles and matrix,resulting in the formation of micro-cracks.The numerical simulation is successfully implemented with the finite element to describe the void damage evolution of the welded joint under thermal cycling conditions.展开更多
基金Project(CX07B_087z) supported by Jiangsu General Colleges and Universities Postgraduate Scientific Research Innovative Plan, ChinaProject(06-E-020) supported by the Six Kind Skilled Personnel Project of Jiangsu Province, China
文摘Soldering experiments of quad flat package(QFP) devices were carried out by means of diode laser soldering system with Sn-Ag-Cu and Sn-Cu-Ni lead-free solders, and competitive experiments were also carried out not only with Sn-Pb eutectic solders but also with infrared reflow soldering method. The results indicate that under the conditions of laser continuous scanning mode as well as the fixed laser soldering time, an optimal power exists, while the optimal mechanical properties of QFP micro-joints are gained. Mechanical properties of QFP micro-joints soldered with laser soldering system are better than those of QFP micro-joints soldered with IR reflow soldering method. Fracture morphologies of QFP micro-joints soldered with laser soldering system exhibit the characteristic of tough fracture, and homogeneous and fine dimples appear under the optimal laser output power.
基金Acknowledgement This work is finaneially supported by the National Natural Science Foundation of China （Grant No. 51005058）, National Hight- eeh R＆D Program （863 Program ） of China （Grant No. 2007AA04Z314） and Natural Scientific Research Innovation Foundation in Harbin Institute of Technology （ HIT. NSRIF. 2009037 ）.
文摘To investigate the effect of Au thickness on evolution of AuSnx IMCs, pads with 0. 1, 0. 5 and 4. 0 μm thickness of Au surface finish were utilized. Laser reflowed solder joints were aged in 125℃ isothermal ovens. Results indicated that little IMC formed at the interface of solder and pad with 0. 1 μm thickness of Au. Even in condition of 744 hours aging, thickness of lMCs did not increase obviously. As for the joints with 0. 5 μm thickness of Au, most of AuSn4 IMCs stayed at the inteornce and were in needle-like or dendritic morphology. With the increase of aging time, AuSn4 IMCs beeame flat and changed to a continuous layer. In the joints with 4. 0 μm thickness of Au on pads, AuSn, AuSn2, AuSn4 IMCs and Au2Sn phase formed at the interface. As aging time was increased, more Sn rich IMCs formed at the interface, and evolved to AuSn4 IMCs in condition of long time aging. Thickness of AuSn4 IMCs reached about 30μm.
基金Project supported by the National Natural Science Foundation of China(Grant No.51175095)the Natural Science Foundation of Guangdong Province,China(Grant No.10251009001000001)+1 种基金the Guangdong Provincial Project of Science and Technology Innovation of Discipline Construction,China(Grant No.2013KJCX0063)the Science and Technology Plan Project of Guangzhou City,China(Grant No.1563000554)
文摘In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetration or unacceptable welds.Recognition of joint position offset, which describes the deviation between the laser beam focus and the weld joint, is important for adjusting the laser beam focus and obtaining high quality welds. A new method based on the magneto-optical（MO） imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm. The weldments are excited by an external magnetic field, and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images. A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired. By analyzing the MO image characteristics and extracting the weld joint features, the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.
文摘Tensile strengths of QFP micro-joints with different pitches were tested by means of micro-joints tester. On the basis of those results, the effects of QFP pitches’ numbers on the mechanical properties were studied and the microstructures of cracks of micro-joints were analyzed based on facts of SEM and EDS. The results indicate that of tensile strengths micro-joint of 48 pitches are lower than that of 100 pitches and the tensile strength of soldered joint is higher than that of solder itself. The fracture mechanism of QFP soldered joint with Sn-Pb solder acts as the interface cavity impair ductile rupture while the fracture mechanism of QFP soldered joint with lead-free solder shows trans-crystalline toughness rupture which belongs to micro-holes coalescence fracture.
基金The project is supported by Postdoctoral Science Fund of China and Postdoctoral Fund of Heilongjiang Province.
文摘Nanoindentation method was adopted to investigate the distribution regularities of micro-mechanical properties of 2219 twin wire welded joints, thus providing the necessary theoretical basis and guidance for joint strengthening and improvement of welding procedure. Experimental results show that in weld zone, micro-mechanical properties are seriously uneven. Both hardness and elastic modulus distribute as uneven sandwich layers, while micro-mechanical properties in bond area are much more uniform than weld zone;In heat-affected zone of 2219 twin wire welded joint, distribution regularity of hardness is similar to elastic modulus. The average hardness in quenching zone is higher than softening zone, and the average elastic modulus in solid solution zone is slightly higher than softening zone. As far as the whole welded joint is concerned, metal in weld possesses the lowest hardness. For welded specimens without reinforcement, fracture position is the weld when tensioning. While for welded specimens with reinforcement, bond area is the poorest position with joint strength coefficient of 61%. So, it is necessary to strengthen the poor positions--weld and bond area of 2219 twin wire welded joint in order to solve joint weakening of welding this kind of alloy.
基金supported by the opening fund of National Key Research and Development Program of China(No.2020YFE0205300)Key Laboratory of Science and Technology on Silicon Devices,Chinese Academy of Sciences(No.KLSDTJJ2022-5)+1 种基金Chongqing Natural Science Foundation of China(No.cstc2021jcyj-msxmX1002)the Fundamental Research Funds for the Central Universities(No.AUGA5710051221).
文摘Sn/ENIG has recently been used in flexible interconnects to form a more stable micron-sized metallurgical joint,due to high power capability which causes solder joints to heat up to 200℃.However,Cu_(6)Sn_(5)which is critical for a microelectronic interconnection,will go through a phase transition at temperatures between 186 and 189℃.This research conducted an in-situ TEM study of a micro Cu/ENIG/Sn solder joint under isothermal aging test and proposed a model to illustrate the mechanism of the microstructural evolution.The results showed that part of the Sn solder reacted with Cu diffused from the electrode to formη´-Cu_(6)Sn_(5)during the ultrasonic bonding process,while the rest of Sn was left and enriched in a region in the solder joint.But the enriched Sn quickly diffused to both sides when the temperature reached 100℃,reacting with the ENIG coating and Cu to form(Ni_(x)Cu_(1-x))_(3)Sn_(4),AuSn_(4),and Cu_(6)Sn_(5)IMCs.After entering the heat preservation process,the diffusion of Cu from the electrode to the joint became more intense,resulting in the formation of Cu_(3)Sn.The scallop-type Cu_(6)Sn_(5)and the seahorse-type Cu_(3)Sn constituted a typical two-layered structure in the solder joint.Most importantly,the transition betweenηandη’was captured near the phase transition temperature for Cu_(6)Sn_(5)during both the heating and cooling process,which was accompanied by a volume shifting,and the transition process was further studied.This research is expected to serve as a reference for the service of micro Cu/ENIG/Sn solder joints in the electronic industry.
基金Project(90205035) supported by the National Natural Science Foundation of China
文摘Based on the simulated aerospace thermal cycling tests,the effect of thermal cycle on the void damage evolution mechanism of LF6 aluminum alloy welded joint was investigated.The results show that micro-voids form around the second phase particles under the thermal cycling tests.The thermal stress coupled with external stress leads to dislocations pile-up around the particles,and when the dislocation density reaches a certain degree,the stress concentration will exceed the bonding strength at the interface between particles and matrix,resulting in the formation of micro-cracks.The numerical simulation is successfully implemented with the finite element to describe the void damage evolution of the welded joint under thermal cycling conditions.
