Au-Sn SLID Bonding: A Reliable HT Interconnect and Die Attach Technology (original) (raw)
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High-Temperature Mechanical Integrity of Cu-Sn SLID Wafer-Level Bonds
Metallurgical and Materials Transactions A, 2015
Wafer-level Cu-Sn SLID (Solid-Liquid Interdiffusion)-bonded devices have been evaluated at high temperature. The bonding process was performed at 553 K (280°C) and the mechanical integrity of the bonded samples was investigated at elevated temperatures. The die shear strength of Cu-Sn systems shows a constant behavior (42 MPa) for shear tests performed from room temperature [RT-298 K (25°C)] to 573 K (to 300°C). This confirms experimentally the high-temperature stability of Cu-Sn SLID bonding predicted from phase diagrams. The fractography of sheared samples indicates brittle-fracture mode for all samples shear tested from RT to 573 K (300°C). The two dominating failure modes are Adhesive fracture between the Ti-W adhesion layer and the Si, and interface fracture at the original bond interface. This indicates that the bonding material itself is stronger than the observed shear strength values, and since these interfaces can be improved with process optimization even stronger bonds can be achieved. The presented work offers fundamental evidence of the Cu-Sn SLID bonding process for operating microelectronics and MEMS at high temperature.
Evaluation of High Temperature Joining Technologies for Semiconductor Die Attach
Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT), 2017
The development of novel high temperature die attach methods for semiconductor packaging enables use in harsh environments and unique opportunities for demanding industrial applications such as controls and monitoring for next generation engine and airframe platforms. Traditional die attach materials including lead solders and conductive adhesives cannot meet requirements of operation temperatures up to and exceeding 300°C due to their limited melting and glass transition temperatures [1]. The Manufacturing Technology Centre Ltd (MTC) has evaluated a range of high temperature die attach materials and processes for silicon and silicon carbide (SiC) semiconductors. Assembly processes were explored for bonding components with and without a back metallisation and with capability to support electrical back contact if required. Die attach methods evaluated include:Sinterable silver materials for back metallised semiconductor componentsSilver glass for non-back metallised semiconductor com...
Au-Sn Solders Applied in Transient Liquid Phase Bonding: Microstructure and Mechanical Behavior
Social Science Research Network, 2019
Transient liquid phase bonding offers one option to generate a robust lead-free die attach with sound thermal and electrical conductivity in microelectronic packages. However, it is a challenge to characterize the microstructure and mechanical behavior of the bonding layer because of its ultra-thin thickness and its nano-sized constituents. We show that microstructures and local mechanical properties of such a modern solder systems are accessible with state-of-the-art methods including transmission electron microscope, synchrotron X-ray nano-beam diffraction as well as micro-scale mechanical testing. Three sub-regions with different morphologies have been identified within the bonding area, and their contained phases have been mapped. Two of the sub-regions contain nanosized intermetallic compounds (IMC) while the third one is mostly composed of an FCC Au-Cu solid solution with a Cu concentration gradient. On top of that, micro-cantilever bending testing has been conducted to investigate the mechanical behavior of the bonding region. The two IMC sub-regions show brittle behavior while the Au-Cu sub-region is ductile.
SLID Bonding for Energy Dense Applications – Thermo-Mechanics
Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT), 2012
Solid-Liquid Inter-Diffusion (SLID) bonding is traditionally a technology used for high performance and high reliable die attach/interconnect applications. The generic properties of SLID allows the bonding to occur at a relatively low process temperature. However, when the bond is completed, the final joint has a melting point well above the process temperature. This makes it well suited as for high performance electronic assemblies. The typical bonding temperature of Cu-Sn SLID and Au-Sn SLID are 250–300 °C and 320–350 °C respectively. These temperatures compare to that of other high temperature (HT) electronic adhesives e.g. Staystik® 101G. The thermal performance of the SLID bond is superior to other electronic interface materials. This is due to the thin joint (∼ 10 μm) and the high thermal conductivity (∼ 60 W/m·K for Au-Sn). Thus, the thermal resistance of a SLID joint, about 2×10−3 cm2·K/W, is significantly lower than most other thermo-mechanical joints suitable for use in el...
Influence of fabrication parameters on bond strength of adhesively bonded flip-chip interconnects
The push for miniaturization in microelectronics, coupled with conversion towards Pb-free electronics has led to increasing interest in adhesive bonding of flip-chip dies directly to printed wiring boards (PWBs). However, the interconnect strength and durability have not been adequately studied, which hampers proper reliability assessment. This paper focuses on the integrity of joints made with non-conducting adhesives (NCAs). The durability of such joints comes partly from the residual compressive stresses generated by the curing-induced shrinkage of the adhesive and partly from direct metal-to-metal bonding between the mating bond pads. The focus in this paper is specifically on the nature of the second mechanism, viz. metal-to-metal bonding and its dependence on the bonding parameters. To further explore this issue, detailed experiments are conducted on specially fabricated test specimens that consist of a pair of gold-bumped flip-chip dies that are bonded to each other without any adhesive between them. An experimental matrix is designed, where the bonding pressure, bonding temperature, and bonding time are systematically varied in order to understand the metal-to-metal bonding mechanism(s). The bond strength is found to increase with increase in bonding pressure, bonding temperature, and bonding time. The results suggest that bonding occurs by a sequence of plastic flattening at the Au–Au interfacial asperities followed by a time-dependent bonding mechanism. Since the temperature is too low for classical diffusion bonding between Au, a possible explanation is that the growth of bonding strength with bonding time/temperature could be a ‘cold-welding’ phenomenon, partially due to creep-assisted growth of the area of atomistically flat contact regions. This hypothesis is supported by the fact that the experimental data agree well with: (i) theoretical diffusion models, commonly used in the literature for solid-state diffusion bonding studies; and (ii) computational creep models of time-dependent deformation and flattening at the contact asperities.
Intermetallic Compounds - Formation and Applications, 2018
Solid-liquid interdiffusion (SLID) bonding for microelectronics and microsystems is a bonding technique relying on intermetallics. The high-melting temperature of intermetallics allows for system operation at far higher temperatures than what solder-bonded systems can do, while still using similar process temperatures as in common solder processes. Additional benefits of SLID bonding are possibilities of fine-pitch bonding, as well as thin-layer metallurgical bonding. Our group has worked on a number of SLID metal systems. We have optimized wafer-level Cu-Sn SLID bonding to become an industrially feasible process, and we have verified the reliability of Au-Sn SLID bonding in a thermally mismatched system, as well as determined the actual phases present in an Au-Sn SLID bond. We have demonstrated SLID bonding for very high temperatures (Ni-Sn, having intermetallics with melting points up to 1280°C), as well as SLID with low process temperatures (Au-In, processed at 180°C, and Au-In-Bi, processed at 90-115°C). We have verified experimentally the high-temperature stability for our systems, with quantified strength at temperatures up to 300°C for three of the systems: Cu-Sn, Au-Sn and Au-In.
Die Attach for High Temperature Electronics Packaging
AuSi, patterned Au and off-eutectic Sn-Au-Sn die attach materials and processes have been investigated for SiC die attach for high temperature applications. AuSi shear test results after 3000 hours of aging at 325 o C in air showed only a slight decrease in shear strength when assembled on Mo:Mn/Pd/Au metallized AlN. However, when assembled on Mo:Mn/Ni/Au metallized AlN, the die shear strength decreased dramatically after only 500 hours at 325 o C in flowing nitrogen. The patterned Au die attach showed a decrease in shear strength and a change in failure mode after storage at 500 o C in air. The initial failure mode was in the Au bump, but after 500 hours at 500 o C, the failure mode shifted to failure near the SiC die interface. A similar change in failure mode was observed with off-eutectic Sn-Au-Sn die attach stored at 500 o C. In both cases there was evidence of Ti diffusion from the Ti/Ti:W/Au thin film metallization stack on the backside of the SiC die.
A review: Application of adhesive bonding on semiconductor interconnection joints
A comprehensive review on adhesive die bonding is presented in this paper. Adhesive bonding technique involved electrically conductive adhesives that bond by evaporation of a solvent or by curing a bonding agent with three main parameters; heat, pressure, and time. Isotropic conductive adhesive (ICA) and anisotropic conductive adhesive (ACA) are the commonly used adhesive in this technique. In order to achieve and promote a better adhesion of die on the substrate, surface cleaning steps and methods were very crucial. The major challenge faced by this technique is entrapment of the conductive particles between the die and substrate. An adequate amount of conductive particle is needed between the die and substrate in order to avoid increase in contact resistance.
Journal of Materials Science: Materials in Electronics
Micron Ag paste had a more affordable price, feasible large-scale synthesis, and longer storage life compared to nano Ag paste, thus it attracts much industrial interest for die attachment of high-power devices. However, the previous studies of hightemperature reliability were mainly focused on nano Ag joints, the research about reliability of micron Ag joints, especially low-temperature and pressureless, was very limited. Therefore, we evaluated high-temperature stability of low-temperature and pressureless micron Ag joint, involving in the changes of mechanical behaviors, evolution of microstructure and interfacial reliability. The average joint strength of micron Ag joints was independent of aging time and kept approximately 35 MPa after aging for 1000 h. The fracture of the micron joint was dominated by the ductile deformation of Ag grains during the fracture process. On the other hand, the microstructure of porous structure evolved greatly during aging process. Ag grains were oriented randomly before and after aging process, but the Ag grains increased slightly from 827.2 nm initially to 1178.4 nm after 1000 h aging. Meanwhile, the pores size in porous structure increased, the number decreased significantly, and the porosity also decreased slightly. Moreover, the barrier layers at interfaces of micron Ag joint remained stable and reliable during aging at 250 °C. The results would promote the large-scale application of the commercially available micron Ag paste in high-power devices.