Effects of SU-8 Cross-linking on Flip-Chip Bond Strength when Assembling and Packaging MEMS (original) (raw)

Wafer-level SLID bonding for MEMS encapsulation

Advances in Manufacturing, 2013

Hermetic packaging is often an essential requirement to enable proper functionality throughout the device's lifetime and ensure the optimal performance of a micro electronic mechanical system (MEMS) device. Solid-liquid interdiffusion (SLID) bonding is a novel and attractive way to encapsulate MEMS devices at a wafer level. SLID bonding utilizes a low-melting-point metal to reduce the bonding process temperature; and metallic seal rings take out less of the valuable surface area and have a lower gas permeability compared to polymer or glassbased sealing materials. In addition, ductile metals can adopt mechanical and thermo-mechanical stresses during their service lifetime, which improves their reliability. In this study, the principles of Au-Sn and Cu-Sn SLID bonding are presented, which are meant to be used for wafer-level hermetic sealing of MEMS resonators. Seal rings in 15.24 cm silicon wafers were bonded at a width of 60 lm, electroplated, and used with Au-Sn and Cu-Sn layer structures. The wafer bonding temperature varied between 300°C and 350°C, and the bonding force was 3.5 kN under the ambient pressure, that is, it was less than 0.1 Pa. A shear test was used to compare the mechanical properties of the interconnections between both material systems. In addition, important factors pertaining to bond ring design are discussed according to their effects on the failure mechanisms. The results show that the design of metal structures can significantly affect the reliability of bond rings.

Novel SU8 based vacuum wafer-level packaging for MEMS devices

Microelectronic Engineering, 2010

This work presents a simple and low-cost SU-8 based wafer-level vacuum packaging method which is CMOS and MEMS compatible. Different approaches have been investigated by taking advantage of the properties of SU-8, such as chemical resistance, optical transparence, mechanical reliability and versatility. A novel technique of wafer level adhesive bonding, which uses SU-8 as structural and adhesive material, has been

BETTS: bonding, exposing and transferring technique in SU-8 for microsystems fabrication

Journal of Micromechanics and Microengineering, 2010

A novel fabrication process called BETTS (bonding, UV exposing and transferring technique in SU-8) is presented in this paper. SU-8 layers can be transferred and patterned over SU-8 microstructures by means of a removable, flexible and transparent substrate. This substrate is composed of a thin acetate film, which can be also used as a mask, and a cured PDMS layer deposited over it. SU-8 is then spin coated and transferred to the SU-8 structures performing simultaneously the steps of bonding and transferring by UV exposure. Due to the low adhesion between PDMS and SU-8, acetate film removal can be easily performed. BETTS provides easy, irreversible and robust SU-8 to SU-8 bonding, where the absence of oxygen plasma equipment or vacuum systems decreases drastically the fabrication cost and time involved. The reported fabrication process makes it possible to fabricate complex SU-8 three-dimensional structures using a simple and inexpensive procedure and also ensures its compatibility and integration with microfluidic and PCB-MEMS devices. Some specific applications such as multilevel microchannel network, patterned membranes, microchambers and microvalves are reported to demonstrate the potential of the proposed process.

Investigation of Flip-Chip Bonding for MEMS Applications

Journal of Electronic Packaging, 2004

An investigation of the flip-chip bonding process for application in MEMS devices was carried out. Finite element analyses of axisymmetric and non-axisymmetric solder joint geometries were performed. It was found that in typical cases of MEMS devices in which the solder volume is small (Bo≪1, where Bo is the Bond number), the finite element solution of the axisymmetric solder joint is well approximated by a surface of revolution whose generating meridian is a circular arc. Experimental results of solder joints in flip-chip assembly were found to correlate well with simulation results.

A study of multi-stack silicon-direct wafer bonding for MEMS manufacturing

Technical Digest. MEMS 2002 IEEE International Conference. Fifteenth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.02CH37266), 2002

Multi-stack wafer bonding is one of the most promising fabrication techniques for creating three-dimensional (3D) microstructures. However, there are several bonding issues that have to be faced and overcome to build multilayered structures successfully. Among these are:

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.

Wafer Level Surface Activated Bonding Tool for MEMS Packaging

Journal of The Electrochemical Society, 2004

A wafer level surface activated bonding ͑SAB͒ tool has been developed for microelectromechanical systems ͑MEMS͒ packaging at low temperature. The tool accommodates 8 in. diam wafers. The principle features of the tool are the automatic parallel adjustment for 8 in. wafers to a margin of error within Ϯ1 m and the X, Y, and axis alignments with an accuracy of Ϯ0.5 m. We have approached a new integration technique for the integration of ionic crystals with transparent and nontransparent thin intermediate layers using this tool. Various sizes of patterned and bare silicon, Al silicate glass, and quartz wafers cleaned by a low energy argon ion source in a vacuum have been successfully bonded by this technique at low temperature. Radioisotope fine leak and vacuum seal tests of sealed silicon cavities show leak rates of 1.0 ϫ 10 Ϫ9 and 2.6 ϫ 10 Ϫ16 Pa/m 3 s, respectively, which are lower than the American military standard encapsulation requirements for MEMS devices in harsh environments. Void-free interfaces with bonding strengths comparable to bulk materials are found. Low adhesion between SAB-processed ionic crystals without adhesive layers is believed to be due to radiation-induced discontinuous polarization.

Low temperature silicon wafer bonding for MEMS applications

2002

Abstract This paper reports the investigation of low-temperature silicon wafer fusion bonding for MEMS applications. A bonding process utilizing annealing temperatures between 400 C and 1100 C was characterized. The silicon-silicon bonded interface was analyzed by Infrared Transmission (IT) and Transmission Electron Microscopy (TEM) and the bond strength was quantified by a four-point bending-delamination technique

Process Integration and Reliability of Wafer Level SLID Bonding for Poly-Si TSV capped MEMS

2018 7th Electronic System-Integration Technology Conference (ESTC), 2018

The objective of this study was to develop a fully integrated process for wafer level MEMS packaging utilizing Poly-Si through silicon via (TSV) capped MEMS devices. First, interconnection metallurgy and Solid Liquid Interdiffusion (SLID) bonding process was optimized. Then sc. "vias before bonding" capping process and contact metallizations for Poly-Si TSVs were developed. Finally, the process integration was demonstrated by using piezoelectrically driven MEMS actuators. However, several design and manufacturing related challenges were observed and detailed failure analysis were carried out to resolve these problems.