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Formation of Cu-Sn intermetallic compounds has been studied with thin Sn and Cu films deposited by physical vapor deposition. The influence of annealing time at 250°C and 320°C highlights a rapid interdiffusion of copper and tin, leading to the formation of Cu6Sn5 and Cu3Sn phases. Application to 100 mm wafer bonding has been implemented at 250°C and 320°C, which shows that stress induced by the deposits...
Emerging 2.5D and 3D package-integration technologies for mobile and high-performance applications are primarily limited by advances in ultra-short and fine-pitch off-chip interconnections. A range of technologies are being pursued to advance interconnections, most notably with direct Cu-Cu interconnections or Cu pillars with solder caps. While manufacturability is still a major concern for the Cu-Cu...
This Paper reports an emerging lead-free joining technology for high temperature application, which can be used for operating temperatures above 200 °C. It is called: “Transient Liquid Phase Soldering (TLPS)”. The TLPS paste used contains a tin-copper powder mixture and is almost completely transformed into Cu6Sn5 and Cu3Sn intermetallic phases after soldering. Due to the reaction between the liquid...
Electroplated Ni/Au over Cu is a popular metallization for printed circuit board (PCB) finish as well as for component leads, especially for wire-bondable high frequency packages, where the gold thickness requirement is high (≥ 20 µinches) for wire bonding. This study examines the effect of redeposition of bulk AuSn4 IMC as a function of varying gold content (2–5 nominal weight-%) in the solder joint...
Low temperature transient liquid phase sintering (LT-TLPS) pastes, based on copper-tin, have been developed for high temperature attachment of wide band gap semiconductor dice to substrates for power electronics. The LT-TLPS attach process enables pressure-less joining at low temperatures in air. An organic binder has been used to form a stencil-printable paste that prevents oxidation of the copper...
Fine pitch vertical interconnect has been extensively studied to meet the demand of next generation 3D packaging requirements. Copper pillar bump has received much of attentions as the choice for connecting chips due to its fine pitch and favorable reliability. Typical process involves copper pillar bump on one chip, CuNiAu, NiAu or Cu pad on the other chip, and interconnect is made through either...
The uni-directional Cu with surface covered by (111) plane can be made by electroplating. The shape of Cu grain was columnar. The diameters of these columnar grains were 2 – 5 µm. After electroplating SnAg2.3 on the Cu pad and then reflowed at 260 oC, the ?-Cu6Sn5s have shown a preferential growth relationship on the uni-directional Cu. At the early stage of reflowing, the orientations of Cu6Sn5 were...
Joint properties of Au stud bumps joined with Sn-3.5Ag solder by flip chip bonding were investigated. Au stud bumps were bonded on SOP (solder on pad) at bonding temperature of 260°C and 300°C for 10sec, respectively. Aging treatment was carried out at 150°C for 100 and 300 hrs. After flip chip bonding, intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 were formed at interface between Au stud...
White tin (or β-Sn) has a body-center tetragonal (BCT) crystal structure with lattice parameters of a = b = 5.83 Å and c = 3.18 Å. We found that the orientation of the β-Sn phase strongly correlated with the Ag content in the Sn-Ag-Cu solder joints. When the Ag content is equal to or greater than 3 wt.%, the Sn grains display a strong preferred orientation of the c-axes in the direction parallel with...
The corrosion of Sn-0.75Cu solder and Sn-0.75Cu/Cu joint in 3.5% NaCl, l%NaCl-2%Na2S04 and l%NaCl-0.6%Na2SO4-3%Na2CO3 solutions were investigated using leaching test. The leaching of Sn from the solder in l%NaCl-0.6%Na2SO4-3%Na2CO3 solution was relatively serious, compared to that in the other two solutions. The amount of Sn leached from the joint was the largest in NaCl solution. Loosen corroded...
The mechanical properties and interfacial microstructure of Cu/Sn3Ag0.5Cu3Bi0.05Cr/Cu (Cu/SACBC/Cu) and Cu/Sn3.0Ag0.5Cu/Cu (Cu/SAC/Cu) joints were comparatively investigated after isothermal aging at 85 °C, 120°C and 150°C for 24, 168, 500 and 1000 h, respectively. The mechanism of Bi addition affecting the intermetallic compounds (IMCs) growth was discussed. Results show that the tensile strength...
This study, mainly emphasis on effects of solder volume on interfacial diffusion kinetics and mechanical properties of Sn/Cu microbump solder joints. Different thicknesses i.e. 12 μm Sn (electrodeposited) and 100 and 200μm Sn is screen printed over 14 μm thickness Cu under bump metallization (UBM). The diameter of Cu UBM used in this study is 50, 110 and 240μm respectively. Solder joints are subjected...
2nd level reliability performance during drop impact is critical for Wafer Level Packages (WLP). Accompanying the popularization of portable and mobile phone products, high reliability under board level drop test is a great concern to semiconductor manufacturers. A 0.4mm pitch Cu under bump metallization (UBM) type has been developed for mobile computing application. In this paper presents the impact...
This study was conducted to the Ni and Cu dissolution behaviors, and the cross-interaction during Ni/Sn3.5Ag/Cu joints fabrication. To form such joint structure, two common soldering sequences were employed: an as-reflow Cu/Sn3.5Ag solder bump jointed to Ni (Seq. I), and an as-reflow Ni/Sn3.5Ag solder bump jointed to Cu (Seq. II). The research results revealed that a ternary compound, (Cu, Ni)6Sn5...
In this work, two different reliability experiments, thermal cycling and electromigration, are performed on fully packaged Si-to-Si stacks bonded with Cu-Sn intermetallic (IMC) micro-bumps. These experiments investigate both the more critical thermo-mechanical behavior as well as the expected positive thermal-electrical behavior. The Cu-Sn IMC bumps survive thermal cycling for more than 3900 cycles...
In flip chip technology, Cu thin-film is a widely used under bump metallization (UBM). However, the major disadvantages of Cu UBM are fast consumption of copper, rapid growth of IMCs and easy formation of Kirkendall voids. Many efforts have been focused on suppression of Kirkendall voids which are detrimental to solder joints reliability in the microelectronics industry. In this study, a novel Cu(Mn)...
A number of new bonding techniques are emerging with the development of three dimensional (3D) stacking packaging. High temperature joint generated by low temperature process with traditional soldering process was one of the approaches to meet the bonding requirement for 3D packaging. Cu/Cu was bonded with joint gap of 100 micros and 60 micros via a layer of Sn plated on the Cu surface. Coupons were...
The formation and growth of intermetallic compounds (IMC) is a key factor to the reliability of soldering joints in modern electronic mounting and packaging industry. In this paper, by means of Olympus, scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) analysis methods, the morphology and growth mechanisms of IMCs between SAC305-xNi and Cu joint during soldering as well as aging...
Cure Induced Micro-Anomaly (CIMA) are worm like hollow microstructures found within resin rich region of underfill after curing within a BGA package with combination of copper die bumps and Sn-Ag substrate bumps. CIMA leads to solder extrusion during secondary reflow. Root cause of CIMA has been identified to be from thermal mechanical stress induced by the stiffness of the joints formed between the...
The combined effects of thermomigration (TM) and electromigration (EM) were investigated in Cu/Sn3.0Ag0.5Cu/Ni solder joints by applying a 5×103A/cm2 DC current to the joints. With a thermal gradient, the Cu atoms and Ni atoms were found to migrate towards the lower temperature side while the Sn atoms were found to migrate towards the higher temperature side. For the solder joint stressed with a 5×10...
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