Papers by Keyword: Solder Joint

Abstract: The effect of electrolytic Ni plating on the Cu electrode on electromigration in the Sn-3.0Ag-0.5Cu (mass%) solder joint was investigated. The energization test was conducted using Ni-plated Cu/Sn-3.0Ag-0.5Cu/Ni-plated Cu joints. For comparison, the same test was done using joints without Ni plating. The scalloped Cu₆Sn₅ layer formed at the joint interface without Ni plating. In the joint with Ni plating, granular (Cu,Ni)₆Sn₅ and (Ni,Cu)₃Sn₄ formed at the joint interface on the solder side and on the Ni side, respectively. Crack propagation was observed on the cathode side in both joints by current load. Crack propagated at the Cu₆Sn₅/solder interface in the joint without Ni plating and at the (Cu,Ni)₆Sn₅/solder interface in the joint with Ni plating, respectively. The Ni plated layer inhibited the diffusion of Cu facilitated by current load so that the growth of the reaction layer on the anode side was also inhibited. Therefore, the Ni plating is expected to improve the EM life.

Abstract: To improve the reliability of solder joint, Ni–Cu alloy plating films with three-dimensional structures were fabricated on Cu substrates via electroplating. By varying the plating potential, the morphology of the Ni–Cu alloy plating films was controlled, and their effect on solder joint microstructure and mechanical properties was investigated. Sn–5Sb lead-free solder was used to join the plated Cu substrates, followed by aging at 200°C for up to 100 h. Surface observations revealed that more negative plating potentials promoted the formation of larger and more numerous three-dimensional structures. Cross-sectional analysis showed that Cu–Ni–Sn and Cu–Sn reaction layers formed at the solder interface and thickened with aging. Shear test showed that the joint strength decreased after 25 h of aging and remained nearly constant thereafter. In addition, joints with Ni–Cu alloy plating exhibited lower shear strength than those without plating. Fractographic analysis showed that fracture initially occurred within the solder and Cu–Ni–Sn reaction layers, whereas prolonged aging induced fracture propagation through the solder, Cu–Ni–Sn, and Cu–Sn reaction layers.

Abstract: Strength of solder joints is usually evaluated by a shear test and a pull test. The reliability of the solder joint is evaluated by the repetitive pull tests of solder bulk specimens. However, the stress and strain field that caused by thermal load on the solder joint of the product model for estimating the reliability is different from these tests. Therefore, we proposed a repetitive bending test as a reliability test of solder joints producing the stress and strain field caused at the solder joint of product model. We proposed a repetitive multi-point bending test as a method to predict the fatigue life of the solder joint in the thermal cycle test in a short period of time. The influence of strain gradient on the inelastic strain amplitude used for lifetime evaluation is estimated. The controllability of the strain gradient by the three-point bending test parameters is investigated. The effect of residual stress on inelastic strain amplitude during sample preparation for thermal cycle test is also evaluated.

Abstract: Coloured solders offer wide range of possible application on top of conventional usage related to solder and soldering. Coloured solder can be produced by adding colour pigment into solder formulation to form coloured solder composite. The performance of coloured solder joint typically determined by good solderability, which influenced by wetting properties. The objectives of this paper is to investigate the solderability of coloured lead free solder composite with different formulation type of colour pigment and variation of colour pigment composition. Green and “glow in the dark pigment” with composition of 5% and 10% respectively were added into the lead free solder paste. Each coloured solder paste was stencil printed on the PCB and then reflowed using reflow soldering process. The wettability of the solder composite was measured and observed using Infinite Focus Measurements (IFM). The results demonstrated that coloured lead free solder composite have a good wettability. This finding also indicates that use of green pigment into the solder composite has shown greater wettability as compared to glow in the dark pigment. Higher percentage of added colour pigment of 10% has significantly reduced the wettability of solder composite. Wettability of coloured solder composite with small amount of added pigment is in the acceptable range of contact angle, showing good solderability of joining.

Abstract: Considering the size of the natural appearance of the micro alloy components of a SAC solder joint, AFM was used to investigate their mechanical properties in the form of their natural appearance. Contact-mode point-spectroscopy was done to determine the elastic modulus and tapping-mode point-spectroscopy was done to investigate the tip-sample power dissipation.The measured Young’s modulus values of the Cu, IML, Ag₃Sn and Sn components, were 125±9 GPa, 111±20 GPa, 67±11 GPa and 57±16 GPa, respectively. The dissipation measurements were accomplished by Si and diamond probes with different spring constants. The different characteristics of the results are discussed.

Abstract: Recently, Halt (Highly accelerated limit test) is widely employed for evaluation of reliability of electronic products. Halt condition is quite severe. The tested products are subjected to mechanical impacts, thermal shock, and vibration at same time. However, there has not been a reasonable and accurate evaluation method for Halt yet. To construct an accurate evaluation method of Halt, basic deformation mechanism of parts of the electronic products should be clarified from both experimental and theoretical points of view. In this paper, focusing on solder joints of circuit boards of electronic products, ratchetting deformation, especially, biaxial ratchetting deformation of solder joints is revealed from both experimentally and theoretically. The authors have already conducted biaxial ratchetting test combining axial and torsional cyclic loading using a tubular specimen of Type 304 stainless steel. However, as for solders, it is difficult to make tubular specimen. Since size of the solder joints is micron, a small size joint specimen of copper tube and solder is employed in this paper. First, to confirm the quality of the joint specimen such as boundary between copper and solder, both the tensile and cyclic loading tests are conducted at several temperatures using Sn-3Ag-0.5Cu. The basic characteristic of tensile and fatigue failure is obtained from these tests. After the confirmation of the accuracy of the joint specimen, biaxial ratchetting tests are conducted superposing the tensile load on cyclic torsion. The biaxial ratchetting tests are conducted using a biaxial loading testing machine developed for the joint specimens of solder and copper.

Abstract: For accurate evaluation of the reliability of electronic package, FEM analyses considering the creep deformation of solder joint in-situ should be conducted. It is well known that the indentation creep test has an advantage to evaluate the creep deformation in microscopic region although there are the problems. Authors already modified the indentation creep test and proposed the method to estimate the steady state creep deformation by the modified test. For lead free solders generally used for the solder joint, the transient creep deformation should be measured by the indentation test in addition to the steady state creep deformation. The transient creep strain occurs in the indentation process. Therefore, it needs to separate the strain into the elastic-plastic strain and the creep strain. In this paper, the method to obtain the stress-strain relation using the indentation test is proposed. New indentation test used the stepped load was proposed to obtained the stress variation during the indenter was pushed and conducted by the numerical test. The suitable measurement point to obtain the relationship between the stress and the strain was identified. The stress variation estimated by proposed area well coincides with the equivalent stress variation of the nodal solution. Therefore, if the method to obtain the strain variation during the indentation process by the indentation in future is developped, it may be possible to estimate the stress-strain curve expressed the uniaxial deformation in the microscopic region.

Abstract: Environment and the health concerns due to the hazardous effects of lead resulted in significant activities to find a replacement for lead-contained solders for electronics industrial. Majority of the semiconductor industrial are now replacing lead solders with Tin-Silver-Copper (SAC 387) solder balls. However, dropped balls in SAC 387 for Ball Grid Array (BGA) products due to poor solder joint strength caused by high thermal stress are a major concern in the semiconductor industries. Polymer core inside the solder ball (polymer core/Cu/Sn) is thus integrated to improve the solder ball joint strength. The function of polymer core inside the solder ball is to absorb and released the stress better as compared to the SAC 387 solder ball. Since the diffusion rate of Cu is faster than the diffusion rate of Sn, hence, this could caused the Kirkendall voids tends to form in between the Cu and Sn IMC layer. This would affect the solder ball joint strength and causing drop balls issue. By implement with an extra of Ni layer to the polymer core solder ball (core/Cu/Ni/Sn), could reduce the diffusion from Cu to Sn, thus to overcome the Kirkendall voids and to further improve the solder ball joint strength. This research work studies the performance of the solder ball shear strength of the two types of solder balls applied to MAPBGA device. In this research, both SAC 387 and polymer solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester. From the research work results of the two types of solder balls, the ball shear strength were decreased with an increased of aging and cycles. Overall, it can be concluded that the polymer core solder ball with an additional of Ni layer showed better performance than the polymer core without Ni layer and SAC 387 solder balls, after subjected to the AC and TC reliability test.

Abstract: The interfacial reaction and growth of intermetallic compounds (IMCs) between the eutectic Sn-0.7 wt.% Cu solder and Cu substrate during soldering process were investigated experimentally. The Sn-0.7Cu/Cu couples were fabricated with soldering temperature varied at four levels of 300, 340 and 360°C. Microstructural analysis is conducted to analyze the IMCs thickness and morphology using scanning electron microscope. Two intermetallic phases were observed during soldering at the interface: η-phase (Cu₆Sn₅) and ε-phase (Cu₃Sn) IMC layers, except for the solder joints which were fabricated at low temperature. The thickness of the η and ε IMC phases increase with increasing the soldering temperature. It’s found that the increase in total IMC layer thickness obeys a linear relationship with soldering temperature. And the relationship between X and T was given as X = 0.0866×T – 22.5 by means of linear fitting method.

Abstract: Nowadays market demand for storage racks are becoming larger and larger in China, especially in logistics industry. Hold-welding beams are important components in storage racks, and searching for more reasonable solder joint arrangements on them is a problem. On the basis of traditional arrangement, this paper came up with another five schemes with differences in solder joint numbers and location. Then ANSYS was used to analyze the mechanical behavior of the beam in every scheme. According to the numerical analysis results, the most reasonable scheme was recommended.