-
[show abstract]
[hide abstract]
ABSTRACT: Low-temperature solders have wide applications in integrated circuits and micro-electromechanical systems packaging. In this
article, a study on Ag-In solder for chip-to-chip thermocompression bonding was carried out. The resulting joint consists
of AgIn2 and Ag9In4 phases, with the latter phase having a melting temperature higher than 400°C. Complete consumption of In solder into a Ag-rich
intermetallic compound is achieved by applying a bond pressure of 1.4MPa at 180°C for 40min. We also observe that the bonding
pressure effect enables a Ag-rich phase to be formed within a shorter bonding duration (10min) at a higher pressure of 1.6MPa.
Finally, prolonged aging leads to the formation of the final phase of Ag9In4 in the bonded joints.
Journal of Electronic Materials 04/2012; 38(2):365-371. · 1.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents micro fabrication process and wafer-level integration of a silicon carrier, which consists of two Si chips that are bonded together with evaporated AuSn-solder. There are micro fins and channels fabricated in the Si chip and form the embedded cooling layer after bonding. The embedded cooling layer is connected with an inlet and an outlet to form a fluidic path for heat transfer enhancement. Besides, in the silicon carrier, there are through silicon vias (TSVs) with metal film on sidewall for electrical interconnection. Two or more carriers can then be stacked together with a silicon interposer in between to make up of a stacked cooling module for high power heat dissipation. The advantage of this 3-D stacking method is that it provides a method of simultaneously realizing electrical interconnection and fluidic path and it can extract heat from the constraints of 3-D silicon module chips to surface without external liquid circulation.
IEEE Transactions on Components and Packaging Technologies 10/2009; · 0.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Developments of ultra fine pitch and high density solder microbumps and assembly process for low cost 3D stacking technologies are discussed in this paper. The solder microbumps developed in this work consist of Cu and Sn, which are electroplated in sequential with total thickness of 10 mum; The under bump metallurgy (UBM) pads used here is electroless plated nickel and immersion gold (ENIG) with thickness of 2 mum. Accordingly, joining of the two Si chips can be conducted by joining CuSn solder microbumps to ENIG UBM pads or CuSn solder microbumps to CuSn solder microbumps. The first joining can only be done with chip to chip assembly whereas the second joining has the potential for chip to wafer assembly. Assembly of the Si chips is conducted with the FC150 flip chip bonder at different temperatures, times, and pressures and the optimized bonding conditions are obtained. After assembly, underfill process is carried out to fill the gap and a void free underfilling is achieved using an underfill material with fine filler size.
Electronic Components and Technology Conference, 2009. ECTC 2009. 59th; 06/2009
-
[show abstract]
[hide abstract]
ABSTRACT: Bonding of multiple indium-silver intermediate layers facilitates precise control of the formed alloy composition and the joint thickness. The bonding temperature and post-bonding re-melting temperature can thus be easily designed by controlling the multilayer materials and structure thicknesses. However, joining different materials involves the formation of intermetallics, which is known to be brittle. In this paper, In-Ag intermetallic phase formation under different applied pressure is studied.
Physical and Failure Analysis of Integrated Circuits, 2008. IPFA 2008. 15th International Symposium on the; 08/2008
-
[show abstract]
[hide abstract]
ABSTRACT: A bonding joint between Cu metallization and evaporated Sn/In composite solder was produced at temperature lower than 200degC in air in this work. The isothermal solidification and subsequent interdiffusion of Cu and Sn/In took place along the bonding couples held at 180degC for 20 minutes. The interfacial reaction and the bonding quality is studied and evaluated. Scanning electron microscopy (SEM) exhibits the joint is uniform along the bonding interface and no crack or voids present, which has an interfacial tensile strength of 52 kg/cm<sup>2</sup>. The overall bonding is examined by C-mode scanning acoustic microscope (C-SAM). Fine leak rate test shows the leak rate is about 5.8x10<sup>-9</sup> arm-cc/s which indicates a hermetic sealing. Intermetallic compounds (IMCs) such as Auln<sub>2</sub>, Cu<sub>6</sub>Sn<sub>5</sub> and Cu<sub>11</sub>ln<sub>9</sub> have been detected by means of X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) accompanied with energy dispersive X-ray (EDX). The chemical composition analysis also reveals that solder interlayers, Sn and In, have been completely converted into IMCs by reacting with Cu. All IMCs formed in the joints have re-melting temperature above 300degC according to Cu-In, Cu-Sn and Au-In phase diagrams. Therefore, the joint can sustain high service temperature due to the presence of IMCs. Such technique producing the joints with the good bond quality and high re-melting point has great potential in electronics and microelectronics packaging such as MEMS packaging and photonic packaging.
Electronic Components and Technology Conference, 2008. ECTC 2008. 58th; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents micro fabrication process and wafer level integration of a silicon carrier, in which optimized liquid cooling layers are embedded. Two or more carriers can then be stacked together with a silicon interposer in between to make up of a stacked cooling module for high power heat dissipation. Wafer bonding are carried out with AuSn-solder which deposited by evaporation and the shear strength is higher than 27.2 MPa after bonding, which is high enough for application. The advantage of this 3-D stacking method is that it provides a method of simultaneous realizing electrical interconnection and fluidic path between two carriers and it can extract heat from the constraints of 3-D silicon module chips to surface without external liquid circulation.
Electronic Components and Technology Conference, 2008. ECTC 2008. 58th; 06/2008
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a reconfigurable filter using micromachined switches is designed, fabricated, and experimented. An equivalent-circuit model is derived for the reconfigurable cell structure. Extracted parameters show the characteristics of both bandpass and bandstop filters, which can be accurately analyzed using circuit analysis. Coplanar waveguide transmission lines for the reconfigurable filter are also analyzed. The bandpass filter is formed by cascading the unit cell structure. This bandpass filter can be switched to bandstop filter using the micromachined switches and p-i-n diode. Dispersion characteristics are obtained to investigate the electromagnetic wave behavior within the unit cell using Floquet's theorem. Measurement results with micromachined switches show that insertion loss is 1.55 dB for the bandpass filter whereas band rejection level is >20 dB and the insertion loss in the passband is 1.2 dB for the bandstop filter. With the p-i-n diode, the insertion loss is 2.1 dB and the 3-dB bandwidth is 5.2 GHz for the bandpass filter, the 20-dB rejection bandwidth is 5.3 GHz, and the insertion loss in the passband is 1.6 dB for the bandstop filter.
IEEE Transactions on Microwave Theory and Techniques 07/2007; · 1.85 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Indium-silver as solder materials for low temperature bonding had been introduced earlier. In theory the final bonding interface composition is determined by the overall materials composition. Wafer bonding based multiple intermediate layers facilitates precise control of the formed alloy composition and the joint thickness. Thus the bonding temperature and post-bonding re-melting temperature could be easily designed by controlling the multilayer materials. In this paper, a more fundamental study of In-Ag solder materials is carried out in chip-to-chip level by using flip-chip based thermocompression bonding. Bonding at 180 o C for various time duration under various bonding pressure is studied. Approaches of forming Ag 2 In with re-melting temperature higher than 400ºC at the bonding interface are proposed and discussed. Knowledge learned in this process technology can support us to develop sophisticated wafer level packaging process based wafer bonding for applications of MEMS and IC packages.
-
[show abstract]
[hide abstract]
ABSTRACT: Radio-frequency microelectromechanical systems (RF MEMS) are highly miniaturized devices intended to switch, modulate, filter or tune electrical signal from DC to microwave frequencies. The micromachining techniques used to fabricate these components are based on the standard CMOS techniques for high-volume integrated semiconductor circuits. RF MEMS switches are characterized by their low insertion loss, high return loss and isolation, large bandwidth, good linearity, negligible power consumption, low actuation voltage. In this project, new RF MEMS switches that could play key roles in MEMS have been developed.
-
[show abstract]
[hide abstract]
ABSTRACT: A tunable bandstop filter using fractal electromagnetic bandgap (EBG) structure is designed, simulated and fabricated. The uniform fractal EBG (U-FEBG) structure is realized by replacing the etched rectangular holes with a Minkowski loop generator. A new technique of doubly tapered fractal EBG (DT-FEBG) structure is designed by non-uniform Kaiser distribution on the fractal structures. The Kaiser distribution improves the pass band performance and generates two distant bandgaps. The tunable bandstop filter is tuned by micromachined capacitive bridges. The propagation characteristic of the periodic microelectromechanical system (MEMS) bridges is determined by the dispersion behavior. Different types of parametric analysis are applied to investigate the performance of the MEMS bridges. Surface micromachining fabrication process is employed on the high resistivity silicon substrate to fabricate the filter. The measurement results for the DT-FEBG structure show insertion loss of 1.2 dB and the stop-band rejection of 44 dB. The tuning range of the U-FEBG structure is 1.1 GHz with insertion loss of 1.7–2.5 dB.
Sensors and Actuators A: Physical.
-
[show abstract]
[hide abstract]
ABSTRACT: Low temperature fluxless solder for wafer bonding has received a lot of attention due to its great potential in hermetic MEMS packaging. Previous research activities mainly deploy solder alloy of eutectic composition to achieve low bonding temperature. We proposed new intermediate bonding layers (IBLs) of rich Ag composition in In–Ag materials systems. In this study, we investigated the intermetallic compounds (IMCs) at the bonding interface with respect to the bonding condition, post-bonding room temperature storage and post-bonding heat treatment. With this IBL, the IMCs of Ag2In and Ag9In4 with high temperature resist to post-bonding process are derived under process condition of wafer bonding at 180 °C, 40 min and subsequent 120–130 °C annealing for 24 h. Low melting temperature IMC phase of AgIn2 is formed in the interface after long term room temperature storage or 70 °C aging treatment. This low melting temperature IMC phase can be completely converted into high melting temperature IMCs of Ag2In and Ag9In4 after 120 °C additional annealing. Based on our results, we can design the packaging process flow so as to get reliable hermetic packaged MEMS devices by using low temperature fluxless In–Ag wafer bonding.
Sensors and Actuators A: Physical.
