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Ni decorated multi-walled carbon nanotube (Ni-MWCNT) composite solders have been fabricated using Ni-MWCNT composite materials and Sn58Bi solder alloys. Ni-MWCNT composite materials were synthesized with functionalization, reduction and electroless plating. The Ni-MWCNT composite solders were fabricated at various weight percentages (0, 0.05, 0.1 and 0.2 wt.%) of Ni-MWCNT. The mechanical properties of Ni-MWCNT composite solder were evaluated using ball shear tests. The shear strength and fracture energy were improved about 16.02% and 12.60%, respectively, by adding 0.1 wt.% of Ni-MWCNTs, which released the stress in the solder alloy. The environmental reliability was examined at 85°C with 85% relative humidity at various holding times. After environmental reliability testing, the microstructure was analyzed to characterize the grain and intermetallic layers. The growth of grains and intermetallic layer thickness were mitigated by Ni-MWCNTs in the solder matrix that affected the mechanical properties. The distribution of Ni-MWCNTs inside the solder joints was confirmed by EPMA and Raman spectroscopy.

Fan-out wafer/panel level package (PLP) is an advanced package. Compared to the conventional package, its thickness is reduced, and electrical and thermal characteristics are improved, through the substitution of a substrate/interposer with a redistribution layer (RDL). However, its thermal and thermomechanical characteristics need to be improved and controlled more elaborately. In this article, six types of Ag patterns were embedded in the upper side of the fan-out package. Thermal emission was improved by building an efficient thermal conductive path, while warpage was improved by vertical symmetry and strain distribution. Overall, the large pattern in both fan-out and fan-in zones reduced the warpage and the pattern embedded in the fan-in zone efficiently improved the thermal emission. However, the pattern area should be designed by considering the overlapped areas with the through via interconnection or the embedded component in the fan-out zone. Because the embedded pattern with a large area is not necessarily a proper approach, an optimum pattern was studied with the simulation and measurement of the thermogram and warpage. The approach of the embedding pattern in the fan-out package is expected to improve its thermal and thermomechanical behaviors.

The development of ball grid array (BGA) packages, such as the chip scale package, wafer level package and package on package, has focused on creating electronics packages that are smaller, thinner, higher-performance and capable of higher functionality, among other desirable traits. Among the interconnection materials used in BGA packages, the Cu-core solder ball (CCSB) has many advantages, such as the use of finer pitch, improved electrical conductivity and better controllability of the coplanarity of the chip. In this study, we evaluated the mechanical properties of the CCSB and Sn-3.0Ag-0.5Cu (SAC) by low-speed shear tests, and the von Mises stress distribution and plastic strain distribution were simulated using a finite element method. The diameter of each solder ball was 280 μm, and the outer layer of the CCSB was a plated SAC layer. The shear strength of the CCSB was about 10% greater than that of SAC. The maximum value of the simulated von Mises stress for the CCSB was higher than that of SAC because the Cu-core is stiffer than SAC. The fracture energy of the CCSB decreased by about 50% compared to that of SAC. The maximum value of simulated plastic strain, which is associated with fracture surfaces, was higher with the CCSB than with SAC. We can thus conclude that the Cu-core in the CCSB affects the shear strength and fracture behavior of solder joints.

Transient liquid phase sintering (TLPS), which is a combined bonding technology of sintering and transient liquid phase bonding, is considered to be a promising sic. die attach material owing to its excellent mechanical properties and low cost. To prevent the oxidation problem, Ni is typically plated onto direct bonded copper and sic. chip. In this study, we investigated the Ni–Ni bonding by adapting TLPS method using Ni and Sn-58Bi. The bonding temperature and time were 220 °C and 60 min, respectively. In addition, the bonding atmosphere was maintained in air without bonding pressure. To confirm the bonding reliability, high-temperature storage test was conducted at 200 °C for 1000 h. With an increase in the remelting temperature to 271 °C, the bonding strength of the TLPS joint of 20 wt% Ni case was about 15 MPa. In addition, the bonding strength decreased by approximately 32% after the high-temperature storage test for 1000 h. In conclusion, Ni–Ni bonding was successfully achieved by the TLPS of Sn-58Bi with Ni. The high-heat endurance bonding between Ni to Ni was achieved by transient liquid phase sintering bonding using Ni and Sn-58Bi. By the sintering reaction between Ni, and the intermetallic reaction of Ni, Sn, and Bi, the remelting temperature increased from 139 to 271 °C. This bonding method can be applied in SiC die attachment technology.

The multifunctional properties of cross-liked carboxymethlycellulose (CMC) and polyethyleneimine (PEI) films with varied CMC:PEI ratios and Ag flake sizes were studied. Both the CMC and PEI were cross-linked through a sonication process to achieve dispersive equilibrium. Fourier-transform infrared spectroscopy (FT-IR) was used to identify the functional groups in the sample material, with thermogravimetric analysis and differential scanning calorimetry used to investigate the overall thermal behavior of the CMC–PEI cross-linked films. Thermal diffusivity and thermal conductivity were also analyzed using laser flash analysis. To analyze the effects of Ag flakes as a filler material, the distribution of the Ag flakes within the film was determined using scanning electron microscopy. The thermal conductivity and resistance of the CMC films increased when cross-linked with 20% PEI. The electrical and thermal properties of the films also improved with the addition of Ag flakes. The multifunctional properties of cross-liked carboxymethlycellulose and polyethyleneimine films with varied CMC:PEI ratios and Ag flake sizes were studied. The thermal, electrical and mechanical properties of solder joints were investigated by using various kinds of tests.

Package structures are continually becoming more complicated to achieve high-performance devices. Thus, the 2D structure of package needs to be modified to a 2.5D or 3D structure. Therefore, standoff properties at the solder joint are required to prevent Si chip damage and electrical shorts when the solder joint is located between the substrate and interposer. Cu-core solder balls (CCSB) are the most popular interconnection choice for a 2.5D package because they have better standoff properties than the general SAC solder. The mechanical properties of CCSBs were evaluated by ball shear tests and measuring bump height as compared with Sn–3.0 wt.%Ag–0.5 wt.% Cu solder. The bump heights of CCSBs and Sn–3.0 wt.%Ag–0.5 wt.% Cu were measured under several compressive pressure conditions at room temperature, 175 °C and 235 °C. The stand-off height of the CCSBs dramatically better than that of Sn–3.0 wt.%Ag–0.5 wt.% Cu solder under high pressure and temperature. The shear strength of the CCSBs was stronger than that of SAC solder at all multiple reflows due to the finer microstructure and higher stacking of dislocations at the interface of the Cu core ball surface.

The microstructures and mechanical reliability of Sn–58Bi solder and epoxy Sn–58Bi composite solder joint were investigated with organic solderability preservative surface finishes. The mechanical reliabilities of Sn58Bi and epoxy Sn58Bi solder were evaluated by the board-level drop test and the 3-point bend test after temperature-humidity storage testing. The microstructure and chemical composition of the solder joints were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The addition of epoxy in solder paste did not affect the morphology of the intermetallic compound. The thickness of the scalloped-shaped Cu6Sn5 intermetallic compound of solder/OSP joint increased with aging time. The drop number until fail for the epoxy Sn58Bi/OSP joint was higher than that for the Sn–58Bi/OSP joint; the average numbers of drops withstood by the Sn–58Bi/OSP joint and epoxy Sn–58Bi/OSP joint following the reflow process were fewer than 10 drops and 180 drops, respectively. The drop number of solder/OSP joints decreased with increasing aging time. The result of the 3-point bend tests shows that the number of bend cycles for the epoxy Sn–58Bi/OSP joint was 30 times higher than that for the Sn–58Bi/OSP joint. The number of bend cycles for solder/OSP joints was decreased with increasing aging time.

As demanding for high performance and miniaturization of electronic devices, interconnection materials required higher reliability in mechanical, thermal and electrical. The importance of electromigration issue has increased because of these trends. We evaluated the electromigration behavior of Sn58Bi solder and Sn58Bi epoxy solder under high temperature and constant current flow. The electromigration test-kit was a designed and fabricated flip chip-type module and the diameter of the solder bump was 250 μm. A current was passed through the two solder joints, producing a current density of 3.0 × 103 A/cm2 at 100 °C. The microstructure of solder joint after electromigration test were investigated with field-emission scanning electron microscopy during electromigration, a Bi-rich layer was observed at the anode side of the solder joint and the formation of Kirkendall voids was observed at the cathode side of the solder joints. Different inorganic materials affect electromigration in the eutectic Sn58Bi solder joints.

An epoxy Sn–58wt.%Bi solder joint was evaluated by a three-point bending test with electroless nickel immersion gold (ENIG) and electroless nickel electroless palladium immersion gold (ENEPIG) surface finishes aged at 85 °C and 85% relative humidity. Scanning electron microscopy and electron probe microanalysis were carried out to study intermetallic compound variation. The morphology, total thickness, and chemical composition of intermetallic compound in epoxy Sn58Bi solder joints were the same as those of Sn–58wt.%Bi solder joints with each surface finish. The average number of bending-to-failure cycles for the epoxy Sn–58wt.%Bi solder/ENIG joints and epoxy Sn–58wt.%Bi solder/ENEPIG was more than 4000 and 5000, respectively. The average number of bending-to-failure cycles of the epoxy Sn–58wt.%Bi solder joint decreased with increasing age. Three-point bending reliability of epoxy Sn–58wt.%Bi solder joints was higher than that of Sn–58wt.%Bi solder with both surface finishes. Cracking of all solder joints subjected to as-reflowed was propagated through the solder matrix. However, after aging for 1000 h, cracking occurred primarily between intermetallic compound layers.

The fan-out wafer level package (FOWLP) is the most common advanced package technology due to its higher I/O density, ultra-thin profile, high electrical performance, and low power consumption. However, warpage induced by the coefficient of thermal expansion (CTE) mismatch between different kinds of materials is a mechanical issue in FOWLPs. We investigated the warpage of fan-out package (FO package) components molded by EMC (with 3 kinds of materials) for two mold thicknesses. The fan-out package component was fabricated with Si chips (three thicknesses). The warpage of the fan-out package component from room temperature to 260 °C decreased with increasing chip thickness and mold thickness. Finite element method (FEM) analysis showed that the warpage of the fan-out package at 25 °C decreased when the CTE mismatch between the EMC and Si chip decreased. The warpage of the fan-out package at 260 °C decreased with decreasing modulus of the EMC due to a lower stress relaxation. The electrical resistance of the FOWLP component increased more than 2.5 times after temperature–humidity and thermal shock testing. The warpage decreased with increasing EMC thickness, decreasing chip thickness, a lower CTE of the EMC, and a lower modulus of the EMC.

High heat-endurance bonding has become an important technology requisite for the demands of SiC die attachment or other high-temperature packaging applications. Transient liquid phase sintering (TLPS), which is a promising candidate among high heat-endurance bonding technologies, has been widely studied in recent years. Because the advantages of TLPS bonding are short bonding time, low bonding pressure, and low cost. In this study, in order to bond in air condition and low temperature, TLPS pastes using Ni, Sn–58Bi, and flux were fabricated with various weight ratios. Pressureless TLPS bonding processes were conducted in an oven at 220 °C for 60 min in air. The thermal behaviors of TLPS pastes (before bonding) and TLPS joints (after bonding) were analyzed by differential scanning calorimetry (DSC). The shear test was conducted for investigate about mechanical properties. The microstructures of cross-sectional and fracture surfaces were analyzed by field emission scanning electron microscopy (FESEM). Also, the atomic distribution of cross-sectional micrographs was analyzed by electron probe micron analyzer (EPMA) and electron dispersive spectrometry (EDS). After bonding, the residual eutectic Sn–Bi lamellar structure was observed only in Ni–90(Sn–58Bi). To verify the reliability of TLPS joints, the samples were stored in an oven at 200 °C for 100, 500, and 1000 h, and the shear test was conducted. The initial shear strengths of Ni–90(Sn–58Bi), Ni–80(Sn–58Bi), and Ni–70(Sn–58Bi) TLPS joints were 23.56, 17.23, and 5.47 MPa, respectively. After the high-temperature storage test, the decrease in shear strength was smallest in Ni–70(Sn–58Bi) and largest in Ni–90(Sn–58Bi). In conclusion, the optimum weight ratio of Ni and Sn–58Bi was Ni–80(Sn–58Bi) because of increased re-melting temperature (270 °C) and high bonding reliability compared to other conditions.

Printed electronics have been used because of various advantages such as low cost, productivity, and eco-friendly processing. However, for fabricating printed electronics, the conventional sintering process conducted at high temperatures has problems such as thermal damage and long processing time. To solve these problems, low-temperature processes such as intensive pulsed light (IPL) have been widely studied. Research of composite materials has become important in supporting these low-temperature processes. We fabricated Ag-decorated, multi-walled carbon nanotubes (Ag-MWCNTs) in composite pastes and sintered printed circuits using IPL energy. We investigated the electrical resistivity, microstructure, and flexibility of the Ag-MWCNT composite circuit with various durations of IPL energy irradiation and Ag-MWCNT content (0, 1, 2, and 3 wt%). The electrical resistivity of the circuit sintered with IPL energy decreased with irradiation time, but it had an unstable microstructure from the drastic sintering process. The Ag-MWCNTs could solve this problem using the net structure of the MWCNTs. The Ag-MWCNT composite nanoparticles could be a solution to overcome the problems in the photonic sintering process using IPL energy.

Flip-chip light-emitting diode (FCLED) packages were interconnected with various contents of Sn-decorated multi-walled carbon nanotube (Sn–MWCNT) composite solder. The Sn–MWCNT was synthesized with a Sn solution using polyol to decorate Sn nanoparticle on the surface of MWCNTs. The Sn-58Bi solder pastes containing Sn–MWCNTs were printed on the metal-printed circuit boards, and then bonded with a flip-chip bonder. The mechanical property of FCLED packages with various contents of Sn–MWCNTs were evaluated with a bond tester. Thermal property was measured with IR Camera and laser flash analysis. The shear strength of an LED chip with 0.1 wt% Sn–MWCNT solder increased about 25% over that without Sn–MWCNT. The LED chip temperature with 0.1 wt% Sn–MWCNT nanocomposite solder decreased about 7% compared to that of the Sn-58Bi solder.

Microstructures and mechanical property of Sn-3.0Ag-0.5Cu (SAC305) and epoxy Sn-3.0Ag-0.5Cu (epoxy SAC) solder joints were investigated with various surface finishes; organic solderability preservative (OSP), electroless nickel immersion gold (ENIG) and electroless nickel electroless palladium immersion gold (ENEPIG). Bending property of solder joints was evaluated by 3-point bend test method. Microstructure and chemical composition of solder joints was characterized by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. Epoxy did not effect on intermetallic compound (IMC) morphology. Scalloped shaped Cu6Sn5 IMC was observed at OSP surface finish. Chunky-like shaped and needle-like shaped (Ni,Cu)6Sn5 IMC were observed at the solder/ENIG joint and solder/ENEPIG joint, respectively. The bending cycles of SAC305/OSP joint, SAC305/ENIG joints and SAC305/ENEPIG joints were 720, 440 and 481 cycle numbers. The bending cycles of epoxy SAC and three types surface finished solder joints were over 1000 bending cycles. Under OSP surface finish, bending cycles of epoxy SAC solder was approximately 1.5 times higher than those of SAC305 solder joint. Bending cycles of epoxy SAC solder was over twice times higher than those of SAC305 solder with ENIG and ENEPIG surface finishes. The bending property of epoxy solder joint was enhanced due to epoxy fillet held the solder joint.

The effect of thermal shock on the mechanical reliability of epoxy Sn-58wt.%Bi composite (epoxy Sn-58wt.%Bi) solder joints was investigated with different surface-finished substrates. Sn-58wt.%Bi-based solder has been considered as a promising candidate for low-temperature solder among various lead-free solders. However, Sn-58wt.%Bi solder joints can be easily broken under impact conditions such as mechanical shock, drop tests, and bending tests because of their poor ductility. Therefore, previous researchers have tried to improve the mechanical property of Sn-58wt.%Bi solder by additional elements and mixtures of metal powder and epoxy resin. Epoxy Sn-58wt.%Bi solder paste was fabricated by mixing epoxy resin and Sn-58wt.%Bi solder powder to enhance the mechanical reliability of Sn-58wt.%Bi solder joints. The epoxy Sn-58wt.%Bi solder paste was screen-printed onto various printed circuit board surfaces finished with organic solder preservatives (OSP), electroless nickel immersion gold (ENIG), and electroless nickel electroless palladium immersion gold (ENEPIG). The test components were prepared by a reflow process at a peak temperature of 190°C. The thermal shock test was carried out under the temperature range of − 40 to 125°C to evaluate the reliability of Sn-58wt.%Bi and epoxy Sn-58wt.%Bi solder joints. The OSP-finished sample showed a relatively higher mechanical property than those of ENIG and ENEPIG after thermal shock. The average number of cycles for epoxy Sn-58wt.%Bi solder with the OSP surface finish were 6 times higher than that for Sn-58wt.%Bi solder with the same finish. The microstructures of the solder joints were investigated by scanning electron microscopy, and the composition of the intermetallic compound (IMC) layer was analyzed by using energy dispersive spectrometry. Cu6Sn5 IMC was formed by the reaction between Sn-58wt.%Bi solder and a OSP surface-finished Cu after the reflow process. Ni3Sn4 IMC and (Ni, Pd)3Sn4 IMC were formed at the solder joints between the ENIG and solder, and between ENEPIG surface finish and solders, respectively.

Nowadays, 2D structure of PKG needs to change to 2.5D or 3D structure for high performance of PKG. The standoff property was required to prevent the Si chip damage and electrical short when solder joint is located between substrate and interposer. So, CCSB (Cu Core Solder Ball) is the most popular candidate of interconnection material for 2.5D PKG. However, controlling of plated solder composition has limitation due to difficult deposition over 3 elements by electroplating system. So, SAC305 composition was plated for CCSB product. In this paper, we studied Cu bump formation of new concept. At first, Cu bump was formed with combination with 1st reflowed solder bump and specially controlled Cu ball which is the surface treatment layer to get good wetting property of liquid solder by additional reflow. The applied solder is the Sn-2.5Ag-0.8Cu-0.05Ni-1Bi (MXT02) for high reliability. New concept Cu bump showed higher joint strength than general CCSB product. Therefore, new concept of Cu core ball will show higher reliability, easy application and more fine pitch then general CCSB product.

Fan-out package has advantages such as higher I/O density, higher electrical performance, ultra-thin and low power consumption. However, Fan-out package have some issues caused by warpage induced by difference of coefficient of thermal expansion between epoxy mold compound (EMC) and Si die. Therefore, the warpage behavior of the FOWLP component molded with three kinds of EMCs were investigated by using shadow moire method and finite element method analysis. The environmental reliability of fan-out package component was evaluated by thermal shock test and temperature-humidity test. The warpage behavior of fan-out package component changed from convex to concave with increasing the temperature. The warpage of fan-out package component molded by EMC with lower CTE was reduced because of smaller CTE mismatch between chip and EMC at room temperature. However, the warpage of FOWLP component molded by EMC with lower modulus was reduced the warpage even though CTE of EMC was higher than others due to stress-strain relaxation at 260°C. The electrical resistance of fan-out package component increased with increasing aging time and cycles during temperature-humidity test and thermal shock test.

A Cu-cored solder ball (CCSB) is often used as the interconnection material for 3D package. The CCSB has a Cu core surrounded by Sn-Ag-Cu alloy. The effect of the Cu core on mechanical reliability of the CCSB was investigated using thermal shock test. Microstructure and thermal shock reliability of the CCSB with organic solderability preservative (OSP) surface finish was compared with that of Sn-3.0wt.%Ag-0.5wt.%Cu (SAC) solder. The thermal shock test was performed in the temperature range of −40 °C to 125 °C in compliance with JESD22-A104. Failure mechanism was analyzed by finite element method analysis. Average number of thermal shock cycles for the CCSB/OSP joints was 1.15 times higher than that for SAC/OSP joints. Maximum value of simulated plastic strain for the SAC/OSP joints was 1.25 times higher than that for the CCSB/OSP joints because the stand-off height of the CCSB/OSP joints could be maintained by the Cu core.

Ag particles have been attractive candidates for highly reliable interconnections in electronic packages due to an absence of IMCs, high melting temperature, and high electrical and thermal conductivity. We fabricated various Ag-nanoparticle (NP) pastes containing different epoxy/binder percent weight (epoxy: 4.5, 9.0, 13.5, and 18 wt%) to investigate the effect on the bonding strength and electrical performance of multilayer ceramic capacitor (MLCC) components. MLCC joints were obtained by stencil printing Ag NP pastes on an Al2O3 substrate with Cu electrodes followed by pressureless bonding at 250 °C for 15 min. When using Ag NP pastes containing higher epoxy compositions, more residues were identified while the other organic additives, such as the binder and dispersant, were removed by debinding during the bonding process. The Ag NP-18 wt% epoxy paste showed bonding strength approximately 8.6 times that of the paste containing 4.5 wt% epoxy. However, the electrical resistivity of MLCC components of 18 wt% epoxy paste showed an electrical resistance of 3.5 Ω, which was about 1.8 times that with the 4.5 wt% epoxy paste. We designed Ag NP pastes with varying epoxy ratio, and studied their chemical, bonding, and electrical characteristics for the development of advanced interconnection.