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Cu pillar bumps were mechanically enhanced using electroless Ni plating for fine-pitch electronic packaging applications. The interfacial reaction and mechanical properties of the Ni-plated Cu pillar bump joints were evaluated. After reflowing, the plated Ni layer dissolved into the Sn-Ag solder caps. The Ni was incorporated into the interfacial reactions, forming a (Cu,Ni) 6 Sn 5 intermetallic compound on the Cu pillar bumps. Adding Ni to the Cu pillar bumps significantly affected the mechanical properties of the joint and increased the bump shear strength of the solder cap. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural evolution and interfacial reactions of Au/Sn/Au/Au/Ni/Kovar joint were investigated during aging at 180 and 250°C for up to 1000h. The Au/Sn combination formed a rapid diffusion system. Even in non-annealed joint, three phases such as AuSn, AuSn2 and AuSn4 were formed. After initial aging at 180°C, the AuSn, AuSn2, AuSn4, Au and Sn phases, which were formed after plating, were fully transformed into ζ-phase and δ-phase, and (Ni,Au)3Sn2 intermetallic compound (IMC) layer was observed between the ζ-phase and Kovar. As a whole, the microstructure of the joint was stable during aging at 180°C. On the other hand, the solid-state interfacial reaction was much faster at 250°C than at 180°C. During aging at 250°C, the Ni layer on the Kovar reacted primarily with the δ-phase in the solder, resulting in the formation and growth of the (Au,Ni)Sn IMC layer at the interface. After aging for 48h, the Fe–Co–Ni–Au–Sn phase was formed underneath the (Au,Ni)Sn IMC layer. Furthermore, cracks were observed inside the interfacial layers after complete consumption of the Ni layer. The study results clearly demonstrate the need for either a thicker Ni layer or an alternative surface finish on Ni, in order to ensure the high temperature reliability of the Au/Sn/Au/Au/Ni/Kovar joint above 250°C. [Copyright &y& Elsevier]

Abstract: The shear test for flip chip solder bump was investigated in terms of effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear 3-dimensional finite element analysis for evaluating the solder joint integrity of area array packages. A representative Pb-free, Sn–3.0Ag–0.5Cu, was examined in this study. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Relatively high shear height exceeding about 20% of the solder bump height could cause some unfavorable effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder bump surface. The low shear height conditions were favorable for screening the type of premature brittle interfacial fractures or the degraded layers in the interfaces. The increase in shear force with the shear speed is highly related with the stress values of the von Mises stress contours within the solder bump. [Copyright &y& Elsevier]

Abstract: The microstructural evolutions and shear properties of the Sn–3.5Ag (in wt%) BGA solder joints were investigated in terms of the effects of various substrate metallization methods with multiple reflows. A continuous scallop-shaped Cu6Sn5 intermetallic compound (IMC) layer was formed at the solder/Cu interface, whereas a reaction layer between the solder and electrolytic Ni/Au substrate was analyzed to be a continuous Ni3Sn4 IMC layer. The thickness of the IMC layers increased with the number of reflows. The reaction products between the solder and electroless Ni/immersion Au (ENIG) substrate were three distinctive layers consisting of Ni3Sn4, Ni–Sn–P and Ni3P. The spalling of the Ni3Sn4 IMC and the growth of Ni–Sn–P and Ni3P layers were observed with the number of reflows. The shear properties of the Sn–3.5Ag/Cu solder joints were nearly consistent with the multiple reflows. The electrolytic Ni/Au substrate provided the excellent mechanical properties of the Sn–3.5Ag BGA solder joints. The shear properties of the Sn–3.5Ag/ENIG solder joints significantly decreased with the multiple reflows. [Copyright &y& Elsevier]

Abstract Intense pulsed light sintering of printed metallic circuits on polymer substrates is an attractive technique. However it still does not yield the mechanical quality required for industrial applications. This technology must improve adhesion and flexibility to produce highly reliable flexible electronic devices. The effects of atmospheric pressure oxygen plasma and acrylic acid polymerization treatments upon the adhesion and flexibility properties were investigated. Modified polyimide surfaces were characterized by surface free energy measurements, and adhesion and flexibility properties were evaluated by means of roll-type 90° peel tests and IPC sliding tests. The strength of adhesion with oxygen-treated and acrylic acid polymerized samples increased about 17- and 20-fold compared with that of untreated samples, and the flexibility was improved by about 2 fold, respectively. The evident improvements in surface free energy, adhesion and flexibility were attributed to the creation of oxygen functional groups on the polyimide surface after atmospheric pressure plasma treatment. Graphical abstract Unlabelled Image Highlights • Our group has studied modifying surface characteristic to enhance the adhesion of photonic sintered Ag printed circuit. • An acrylic acid polymerization using APP was proposed as an effective method for modifying surface of substrate. • We suggest the surface free energy, XPS spectra contrast, and peel strength after the APP treatment. [ABSTRACT FROM AUTHOR]

Abstract A micro-sized Ag paste was fabricated with the metal content of approximately 85% as a sinter-bonding material in this study. The sintering reactions and joint strengths of Ag sintered joints with three different surface finishes of Cu, Ag, and electroless Ni-immersion Au (ENIG) were evaluated at different sinter bonding times during the sintering process. Stable interfacial microstructures and relatively dense Ag sintered layers were formed in the three Ag sintered joints, and the interdiffusion behaviors between the Ag paste and substrate metals promoted in the formation of good metallurgical bonding during the Ag sintering process, regardless of surface finish. The bonding time of 10 min was sufficient for full sintering reactions between the chip and different substrate finishes. The shear strength did not increase with increased sintering time regardless of surface finish. The substrate metals strongly affected the die shear strengths of the Ag sintered joints, and the Ag-finished joint had a more stable interfacial microstructure and superior shear strength compared to the other metal-finished joints. Graphical abstract Unlabelled Image Highlights • Ag paste with 85% metal content and 2–3 μm particles was fabricated. • Bare, Ag-coated, and ENIG-treated DBC substrates were sintered using paste. • Joint strengths of Ag-coated Si chips to metallized DBC substrates were tested. • Ag-coated DBC substrates allowed the best atomic interdiffusion and joint strength. [ABSTRACT FROM AUTHOR]

Highlights: [•] Screen printing enables for metallization of stretchable electronics. [•] Various circuit designs were employed for stretchable interconnects. [•] Horseshoe-type circuit shows the greatest extensibility of about 8%. [ABSTRACT FROM AUTHOR]

Abstract: The adhesion strength of a Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL), was evaluated according to the thickness of the Ni–Cr (Ni:Cr=95:5 ratio) seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by SEM, AFM and XPS. The peel strength of the FCCL increased with increasing thickness of the Ni–Cr seed layer, due to the increase in the ion bombardment caused by the higher power used in the Ni–Cr sputtering process. This increase in the FCCL peel strength was attributed to the lower proportion of C–N bonds and higher proportion of C–O bonds in the polyimide surface. The adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide. [Copyright &y& Elsevier]

Abstract: The radio frequency (RF) and high frequency performance of the flip chip interconnects with anisotropic conductive film (ACF) and non-conductive film (NCF) was investigated and compared by measuring the scattering parameters (S-parameters) of the flip chip modules. Low cost electroless-Ni immersion-Au (ENIG) plating was employed to form the bumps for the adhesive bonding. To compare the accurate intrinsic RF performance of the ACF and NCF interconnect without lossy effect of chip and substrate, a de-embedding modeling algorithm was employed. The effects of two chip materials (Si and GaAs), the height of ENIG bumps, and the metal pattern gap between the signal line and ground plane in the coplanar waveguide (CPW) on the RF performance of the flip chip module were also investigated. The transmission properties of the GaAs were markedly improved on those of the Si chip, which was not suitable for the measurement of the S-parameters of the flip chip interconnect. Extracted impedance parameters showed that the RF performance of the flip chip interconnect with NCF was slightly better than that of the interconnect with ACF, mainly due to the capacitive component between the bump and substrate and self inductance of the conductive particle surface in the ACF interconnect. [Copyright &y& Elsevier]

Abstract: The flip chip solder bump was investigated in situ with current stressing in an ambient temperature of 423K. For the in situ investigation of the solder joints, a single flip chip package was examined during whole investigation time. Cross-sectional studies were conducted with the scanning electron microscope (SEM). Cu mini bumps were formed on a Si chip for the solder bumping and electroless Ni-immersion Au (ENIG) surface treatment was conducted on the Cu pads in substrate side. Cu6Sn5 and Ni3Sn4 intermetallic compound (IMC) layers were formed in the both interface, while a typical eutectic structure of Pb-rich and Sn-rich phases were formed within the solder region. After current stressing of 6h, separation of the Pb-rich and Sn-rich phases were occurred in the left solder bump, while a void was formed under the Cu6Sn5 IMC layer in the right side solder bump. After current stressing of 7.5h, the solder joints were catastrophically failed due to the remelting of the solder bump. [Copyright &y& Elsevier]

Abstract: Effects of reflow process on the thermo-mechanical reliability of the anisotropic conductive film (ACF) joints were investigated. Cross-sectional studies were carried out to investigate the effects using a scanning electron microscope (SEM). Swelling of ACF matrix in z-direction and formation of a conduction gap were observed in the reflowed ACF joints which were bonded in lower flip chip bonding pressures than 60N. However, a delamination as well as the formation of a conduction gap was occurred between the ACF and Cu pad on flexible printed circuits (FPC) when ACF joints bonded in higher bonding pressures than 70N were reflowed. This difference of failure mode was mainly due to the divergence of adhesive matrix thickness between the Au bump on Si chip and Cu pad on FPC. Finite element analyses were also conducted to interpret the failure behaviors of the ACF joints. [Copyright &y& Elsevier]

Abstract: The interfacial reaction of the ENIG/Sn–3.5Ag–0.7Cu/ENIG sandwich solder joint was studied during aging at 150°C for up to 1000h. (Ni,Cu)3Sn4 intermetallic compounds (IMCs) formed at both ENIG/Sn–Ag–Cu/ENIG interfaces after reflowing. After aging for 24h, IMCs changed from (Ni,Cu)3Sn4 to (Cu,Ni)6Sn5. Until the aging for 250h, the (Cu,Ni)6Sn5 IMC layers grew thicker with increasing aging time. After aging for 500h, the IMCs changed from (Cu,Ni)6Sn5 to (Ni,Cu)3Sn4 once again. The phase transition could be significantly related to the diffusion and content of available Cu atoms from the solder to interface during aging. On the other hand, the results of the analyses of the interfacial reactions of the ENIG/Sn–Ag–Cu/ENIG and Cu/Sn–Ag–Cu/ENIG joints showed that the interfacial reaction on the lower Ni–P side was strongly affected by the interfacial reaction on the opposite pad. In the case of the Cu/Sn–Ag–Cu/ENIG joint, only a (Cu,Ni)6Sn5 IMC layer was observed at the lower Sn–Ag–Cu/ENIG interface during aging. A coupling effect occurred between Cu/Sn–Ag–Cu and Sn–Ag–Cu/ENIG interfaces of the Cu/Sn–Ag–Cu/ENIG joint. [Copyright &y& Elsevier]

Abstract: The microstructural investigation and thermo-mechanical reliability evaluation of the Sn–37Pb solder bumped flip chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction product between the solder and Cu mini bump of the chip side was Cu6Sn5 IMC layer, while a layer of Ni3Sn4 was formed between the solder and electroless Ni–P layer of the package side. The primary failure mechanism of the solder joints in this type of test method and package was confirmed to be thermally activated solder fatigue failure. The brittle interfacial failure mode was sometimes detected from the cross-sectional studies, but nearly whole of the failed packages showed the occurrence of the typical fatigue cracks. The finite element analyses were conducted to interpret the failure mechanisms of the packages. The finite element analyses revealed that the cracks were induced by the accumulation of the plastic work. [Copyright &y& Elsevier]

Stretchable electronic devices are desirable for the next application of electronic devices such as stretchable sensors, stretchable energy storage devices, and humanmachine interfaces. Also, stretchable electronic systems require a stretchable metal circuit on the elastomeric substrate for electrical connection to components. The stretchable circuits fabricated by Cu foil lamination on the thermoplastic polyurethane (TPU) film are investigated with various zigzag-patterned circuit designs. The various circuit designs are simulated by finite element analysis (FEA) for fatigue life prediction and the simulation results are compared with experimental results. The 6 types of zigzag-shaped circuit designs with different corner patterns are investigated. The thicknesses of the Cu electrode and TPU substrate are 18 μm and 50 μm, respectively. The stretchability of Cu stretchable circuits is evaluated by the uniaxial tensile test with 10% elongation. Also, the equivalent plastic strain is calculated for fatigue life prediction. The number of stretch cycles to failure increased as decreasing the equivalent plastic strain obtained by FEA. The tendency of crack propagation and fatigue life prediction are well agreed with FEA results. Thus, it is considered that modifying the circuit patterns of the strain concentration area is the most important to enhance the mechanical reliability of stretchable circuits. Unlabelled Image • Cu Stretchable circuits on TPU film were fabricated by Cu foil lamination process. • Various Cu stretchable circuit design by finite element analysis. • 10% elongation uniaxial tensile test was conducted with various designs. [ABSTRACT FROM AUTHOR]

The effect of black residue (BR) formation on the mechanical properties of Sn-58Bi epoxy solder surface finished with an electroless nickel-immersion gold (ENIG) were evaluated with various reflow process conditions. The BR was formed around the solder ball after reflow process, and their area were variated with ramp time and peak temperatures. As peak temperature increased from 160 to 190 °C, the area ratio of the BR decreased from 50.3 to 18.0%. According to XRD, FT-IR, and XPS analyses, we assumed the most probable composition of the BR was epoxy or flux residue with Sn and Bi as well as carboxylate salts such as Bi(RCOO) 3 and Sn(RCOO) 2. These were generated by the carboxyl-based flux to prevent oxidation and reduce the surface tension of the molten solder in the epoxy-based Sn-58Bi soldering. The shear strength increased by 31.3% as the peak temperatures increased from 160 °C to 190 °C, while the fracture energy increased by 18.3%. We also investigated the effects of the addition of epoxy on the mechanical properties of Sn-58Bi solder joints under various reflow conditions. The bonding characteristic of the Sn-58Bi epoxy solder joints were elucidated via chemical analysis and by observing the fractures. The effect of black residue formation on the mechanical properties of Sn—58Bi epoxy solder surface finished with an electroless nickel-immersion gold were evaluated with various reflow process conditions. Unlabelled Image • The effect of black residue on the Sn—58Bi epoxy solder were evaluated. • The reflow profile affected on formation of black residue and mechanical property. • Remaining flux and epoxy were attributed to the formation of black residue. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied the failure behavior induced by EM test on the Sn–Bi solder joint. [•] We evaluated the EM reliability of Sn–Bi solder joint on various surface finishes. [•] The Bi was segregated from cathode to anode side. [•] The OSP surface finish showed longer time to failure than others. [ABSTRACT FROM AUTHOR]

Abstract: There are two main technologies for the commercialization of printable and flexible electronic devices. One is the manufacture of nanomaterials such as nanoinks and nanopastes that include conducting nanoparticles, and another is heat treatment at lower temperatures. Copper (Cu) nanopaste and atmospheric-pressure plasma (APP) sintering is highly adoptable for mass production of printable and flexible electronic devices at low cost. The relation between the microstructure of screen-printed Cu nanopaste and its electrical properties was investigated. The characteristics of Cu patterns sintered by APP were compared to those sintered by conventional radiation–conduction–convection heating. The Cu patterns sintered at 250W for 40min showed the lowest electrical resistivity of 21.06μΩcm, which is around 12.61 times of the bulk Cu. All of the Cu pattern surfaces sintered by APP showed lower oxygen concentrations than those sintered by conventional heating. [Copyright &y& Elsevier]

To investigate the effect of the sintering temperature on the electrical properties of a chip on glass (COG) module, a screen-printed conductive circuit was sintered at various temperatures, viz. 150, 200, 250 and 300°C for 30min. An anisotropic conductive film (ACF) is a suitable bonding material for the interconnection between a device and printed circuit, because of the conductive particles within it. We expected that the conductive particles in the ACF would provide a good electrical connection and reliability in our study. The electrical properties of the printed Ag circuits improved with increasing sintering temperature. The conductive particles in the ACF were well deformed in between the Au bumps and printed Ag pads after the bonding process. The resistances of the interconnections drastically decreased with increasing sintering temperature. Also, the temperature–humidity reliability of the ACF was investigated by measuring the resistance after the temperature–humidity test (THT) at 85°C and 85% relative humidity. After the THT, the resistance shows a tendency to decrease when sintered below 200°C, whereas it increases when sintered over 250°C. The increase in the resistance due to the effect of surface oxidation is negligible. [ABSTRACT FROM AUTHOR]

Abstract: Highly contrasting surface energies were induced on polyimide (PI) substrates using atmospheric-pressure plasma (APP) to allow precise printing of Ag electrodes that showed mitigated electrochemical migration (ECM). The substrate surface was made uniformly hydrophobic via APP tetraethyl orthosilicate (TEOS) polymerization. Selected areas were then made hydrophilic via oxygen APP applied through a patterned metal mask. Ag nanoink was then inkjet-printed onto the hydrophilic portions and sintered for 30min at various temperatures ranging from 100 to 250°C. The resulting Ag patterned electrodes were of the desired dimensions and showed sharp edges. The Ag ECM dendrites deposited at the cathode took ca. 39% longer than in similar patterns printed on pristine substrates. The contrasting surface-energies induced by the plasma allowed precise control of the Ag electrodes’ edges, which led to reduce ECM. [Copyright &y& Elsevier]

Abstract: In this study, we investigated the phenomena of electrochemical migration (ECM) on a silicon (Si) substrate with directly printed Ag paste with epoxy binder (7wt.%) using a screen-printing method. The microstructure and electrical characteristics of the directly printed Ag patterns under different sintering conditions were estimated. In addition, the ECM characteristics of the directly patterned Ag circuits on Si substrates were evaluated according to the sintering conditions. The ECM characteristics of the Ag paste with epoxy binder were compared with the ECM characteristics of Ag paste without epoxy binder. Clusters were formed by interparticle necking during the sintering process; the cluster size in the patterns increased as the sintering temperature and time increased. Granular Ag films, which were sintered at high temperatures and for long time periods of time, had excellent electrical characteristics as a result of the formation of interparticle necking of sufficient size. The directly printed Ag patterns that were exposed to higher sintering temperatures and longer sintering times had higher resistances to ECM than those that were exposed to lower sintering temperatures and shorter sintering times. Also, the directly printed Ag pattern with epoxy binder had a higher resistance to ECM phenomenon than the pattern without epoxy binder. [Copyright &y& Elsevier]

Abstract: This study provides a framework for evaluating the drop reliability of solder joints using a high-speed lap-shear test. The test specimens employed here were Sn–37Pb/Cu under bump metallization (UBM) solder joints and were aged for 120h at different temperatures (120, 150, and 170°С) to examine the effects of aging. We tested them at different loading speeds in the range of 0.01–500mm/s. A careful analysis of the stress–strain graphs attained from the tests, coupled with characterization of the fracture surfaces, discloses that the fracture mode shifts from ductile to brittle as the loading speed escalates. A map of the fracture mode shows that how readily the mode transition with the loading speed occurs can be directly translated into the drop reliability of the solder joint, disclosing that the drop reliability would deteriorate as the aging temperature increases possibly due to the increased IMC thickness. These results underscore the utility of the experimental methodology adopted in this study to evaluate the drop reliability of solder joints. [Copyright &y& Elsevier]

Abstract: In this study, the effect of a Ni–Cr seed layer on the adhesion strength of flexible copper clad laminate (FCCL) was evaluated after thermal treatment. The changes in the chemical composition, morphology and adhesion property were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron probe micro analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and 90° peel test. The peel strength of the FCCLs was significantly affected by the thermal treatment and the FCCL with a higher peel strength had a higher thermal stability than that with a lower peel strength. The roughness of the fracture surface for the FCCLs decreased with increasing thermal treatment temperature and holding time. The thermal treatment of the FCCL increased the ratio of the C–N bonds and reduced that of the C–O and carbonyl (Cin the polyimide. [Copyright &y& Elsevier]

Abstract: Printed electronics is expected to increase its market share significantly in near future on account of its high material usage efficiency, environmental friendliness, the avoidness of expensive process steps, and the ability to rapidly change circuit designs in real time in a highly cost effective fashion. Herein, we tried to examine the physical characteristics of the two types of selected Ag nanopastes and electrical characteristics of screen printed Ag patterns on a Si substrate sintered at 200°C for varying sintering times. The first type of the paste had no binder material and the second one was formulated with an addition of a polymeric binder. They had different thermal behaviors, i.e., the paste with a binder showed a continuous small reaction well beyond the temperature for the main reaction of the paste without any binder. The microstructure of the Ag tracks after sintering was also different between the two cases, which verified the poor electrical characteristics of the paste containing a binder than the one without any binder. We also measured the insertion losses of the Ag tracks with a design for the high frequency transmission, and the observed electrical behaviors were discussed with the physical properties of the pastes measured in this study. [Copyright &y& Elsevier]

Abstract: In this study, we investigated the effect of the current density on the interfacial reaction and mechanical reliability of an electroless Ni/immersion Au (ENIG) substrate with Sn–3.5Ag solder. We first evaluated the interfacial reactions of the solder joint under aging for up to 800h and current stressing with current densities of 3×102 A/cm2 and 5×103 A/cm2. Also, we successfully revealed the correlation between the interfacial reaction behavior and mechanical reliability under current stressing. With increasing aging time, the thickness of the Ni3Sn4 layer increased. At both low and high current densities, the thickness of the Ni3Sn4 layer increased up to 400h and decreased thereafter at the cathode, while that of the IMC increased up to 800h at the anode. After the die shear test, the ductile fracture was observed in the as-reflowed joint without current stressing. The fracture mode changed from ductile fracture to brittle fracture when thermal aging and current flow were simultaneously applied. The combination of the current stressing and isothermal aging at high temperature significantly deteriorated the mechanical reliability of the solder joint. [Copyright &y& Elsevier]

Abstract: The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn–2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu6Sn5 IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu6Sn5 phase and a planar Cu3Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number. [Copyright &y& Elsevier]

Abstract: We investigated the effects of sintering temperature on microstructural evolution and electrical characteristics of screen printed Ag patterns. A commercial conducting paste containing Ag nanoparticles was screen printed onto a Si substrate passivated with SiO2 and sintered under a sintering temperature range from 150°C to 300°C. Four point probe method was used to measure the DC resistance, while a network analyzer and Cascade’s probe system in the frequency range from 10MHz to 30GHz were employed to measure the S-parameters of the sintered Ag conducting patterns. The resistivity under the application of a DC decreased from 398μΩcm to 9μΩcm with increasing sintering temperature from 150°C to 300°C. From the measured S-parameters, the electrical losses in high frequencies also decreased with increasing sintering temperature (about 1.2dB at 30GHz) due to the formation of an interparticle neck after heat treatment at high temperatures. [Copyright &y& Elsevier]

Abstract: This study utilized a high speed lap-shear test to evaluate the mechanical behavior of Sn-37Pb/Cu under bump metallization (UBM) solder joints under high speed loading and hence the drop reliability. The samples were aged for 120h at different temperatures (150°С, 180°С) and then tested at different displacement rates in the range of 0.01mm/s to 500mm/s to examine the effects of aging on the drop reliability. The combination of the stress-strain graphs captured from the shear tests and the fracture morphology analysis discloses that the aging at high temperatures has influenced critically the deformation behavior of the solder joints and the effects appears more significant at high strain rates. This study demonstrates a unique capability of a drop reliability evaluation method that utilizes a high speed lap-shear test. [Copyright &y& Elsevier]

Abstract: The reliability of adhesive interconnections using anisotropic conductive film (ACF) and non-conductive film (NCF) was evaluated by measuring connection resistance during 500cycles of thermal shock testing. The four-point probe method was used to measure the connection resistance of the adhesive joints constructed with Au bump on Si chip and Cu pad on flexible printed circuit (FPC). The connection resistance of the ACF joints was markedly higher than that of the NCF joints, mainly due to the constriction of the current flow and the intrinsic resistance of the conductive particles in the ACF joints. The connection resistances of both interconnections decreased with increasing bonding force, and subsequently converged to about 10 and 1mΩ at a bonding force of 70 and 80N, for the ACF and NCF joints, respectively. During the thermal shock testing, two different conduction behaviors were observed: increased connection resistance and the termination of Ohmic behavior. The former was due to the decreased contact area caused by z-directional swelling of the adhesives, whereas the latter was caused by either contact opening in the adhesive joints or interface cracking. [Copyright &y& Elsevier]

Abstract: This study focused on the feasibility of using Ni flip chip bumps with a Sn–2.5Ag (wt.%) solder encapsulation. The interfacial reaction and die shear property of the Ni flip chip bump with a Sn–Ag solder cap bonded on the electroplated Cu/Sn–Ag substrate were investigated with increasing bonding time. After bonding for 1s (Cu x Ni1−x )6Sn5 and Cu6Sn5 intermetallic compound (IMC) layers were formed at the upper and lower interfaces, respectively, with the former IMC being the predominant phase during bonding. The transformation of the solder cap into the (Cu x Ni1−x )6Sn5 IMC depleted the solder after bonding for 30s, and then the Ni concentration in the IMC gradually decreased with increasing bonding time. The shear property peaked after 30s, and then decreased with increasing bonding time. The fractures occurred at the solder/Cu6Sn5 interface and inside the (Cu x Ni1−x )6Sn5 IMC after bonding for 1s and 30s, respectively, after which the fracture location shifted toward the (Ni x Cu1−x )3Sn4/(Cu x Ni1−x )6Sn5 interface with increasing bonding time. [Copyright &y& Elsevier]

Abstract: Rolled copper foil of 18μm thickness underwent nodule treatment via electro plating in a solution containing dissolved CuSO4 and NiSO4. The product formed on the surface of the copper foil varied from copper oxides to nickel compounds of the sphere type with increasing current density and plating time. The highest surface roughness and maximum peel strength of 680gf/cm were obtained with the formation of nickel compounds at a current density of 1.5A/dm2 and plating time of 30s. In addition, the fracture location varied according to the plating parameters and occurred at the interface between the polyimide film and adhesive layer at the condition of the maximum adhesion strength. [Copyright &y& Elsevier]

Abstract: This study was focused on the formation and reliability evaluation of solder joints with different diameters and pitches for flip chip applications. We investigated the interfacial reaction and shear strength between two different solders (Sn–37Pb and Sn–3.0Ag–0.5Cu, in wt.%) and ENIG (Electroless Nickel Immersion Gold) UBM (Under Bump Metallurgy) during multiple reflow. Firstly, we formed the flip chip solder bumps on the Ti/Cu/ENIG metallized Si wafer using a stencil printing method. After reflow, the average solder bump diameters were about 130, 160 and 190μm, respectively. After multiple reflows, Ni3Sn4 intermetallic compound (IMC) layer formed at the Sn–37Pb solder/ENIG UBM interface. On the other hand, in the case of Sn–3.0Ag–0.5Cu solder, (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 IMCs were formed at the interface. The shear force of the Pb-free Sn–3.0Ag–0.5Cu flip chip solder bump was higher than that of the conventional Sn–37Pb flip chip solder bump. [Copyright &y& Elsevier]

Abstract: The surface morphology, electrical property and reaction with solder alloy of two electroless nickel-phosphorus (EN–P) deposits (Ni–7wt.%P and Ni–10wt.%P) were investigated in this study. The P content of the EN–P layer decreased with increasing pH value. The EN–P plating layers had an amorphous structure and the electrical resistivity of the layer increased with increasing P content. Reaction layers of Ni3Sn4, Ni2SnP and Ni3P formed at the interfaces between the Sn–3.5Ag solder and the two EN–P deposit layers. The thickness of the interfacial Ni3Sn4 intermetallic compound (IMC) layer in the Sn–3.5Ag/Ni–7wt.%P joint was thicker than that in the Sn–3.5Ag/Ni–10wt.%P joint, whereas the thickness of the Ni3P layer increased with increasing P content. These study results confirmed that the interfacial reaction between solder and the EN–P layer is significantly affected by the composition (P content) of the EN–P layer. [Copyright &y& Elsevier]

Abstract: The interfacial reactions and shear strength of joints between Sn–9Zn solder and two different kinds of BGA (ball-grid-array) substrates (Cu and Au/Ni–P/Cu) were investigated for reflow conditions of 230°C up to 60min. For the Cu substrate, only Cu5Zn8 intermetallic compound was observed and other Cu–Sn IMCs were not observed. For the Au/Ni/Cu substrate, an AuZn3 IMC layer formed at the interface due to the fast reaction between Au and Zn. In addition, some of the AuZn3 IMC layer was detached from the interface after reflow. The thickness of the AuZn3 layer did not change with reflow time because the Au was consumed during the initial reflow process. After being reflowed for 60min, a Ni5Zn21 IMC formed between AuZn3 IMC and Ni substrate. Also, many voids existed inside the upper AuZn3 IMC layer. Ball shear tests for the Cu substrate showed the shear strength significantly decreased after reflow for 60min. A Cu5Zn8 IMC was also observed on the fracture surface. For the Au/Ni/Cu substrate, the shear strength value did not change much as a function of reflow time and fractures occurred within the solder. [Copyright &y& Elsevier]

Abstract: System-on-Chip and System-on-Package technologies have advantages depending on application needs. As a number of electrical and electronic equipment manufacturers have an interest in increasing CMOS technology densities, a range of two- and three-dimensional silicon integration technologies are emerging which will support next-generation high-end semiconductors such as high speed microprocessors and high speed memories. However, there are many issues regarding process integration, thermal management, and reliability of 3D stacked package. In this study, the printed circuit board (PCB), silicon carrier and silicon chip are integrated with ultrasonic vibration. Die shear tests of the joints were carried out with increasing bonding time and input power to optimize the bonding condition. The integrated chips were successfully bonded to the PCB with and without NCF using a transverse ultrasonic bonding. Electrical resistance of multi-chip bonded with NCF (10mΩ) measures lower than that bonded without NCF (28.9mΩ). The voids and delamination were easily found on the joint bonded without NCF that caused lower shear strength. [Copyright &y& Elsevier]