Flip-Chip Bonding of MEMS Scanner for Laser Display Using Electroplated AuSn Solder Bump

Abstract

A MEMS scanner has been flip-chip bonded by using electroplated AuSn solder bumps. The microelectromechanical systems (MEMS) scanner is mainly composed of two structures having vertical comb fingers. To optimize the bonding condition, the MEMS scanner was flip-chip bonded with various bonding temperatures. Scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX) spectroscopic system was used to observe the microstructures of the joints and analyze the element compositions of them. The die shear strength increased as the bonding temperature increased. During the thermal aging test, the delamination occurred at the interconnection of the MEMS scanner bonded at 340 C. It is inferred that the Au layer serving as pad metallization has been dissolved in the molten AuSn solder totally, and subsequently the Cr layer was directly exposed to the AuSn solder. Judging by the results of both die shear test and thermal aging test, the optimal bonding temperature was found to be approximately 320 C. Finally, using this MEMS scanner, we obtained an optical scanning angle of 32 when driven by the ac control voltage of the resonant frequency in the range of 22.1-24.5 kHz with the 100-V dc bias voltages.Index Terms-AuSn solder, flip-chip bonding, microelectromechanical systems (MEMS), scanning mirror, thermal aging.

Design and fabrication of a highly manufacturable MEMS probe card for high speed testing

“…Ag 3 Sn 96.5 Cu 0.5 and Au 80 Sn 20 solder bonding Generally, a strong mechanical joint is required to guarantee stable electrical interconnection between the top and bottom materials during the assembly as well as in the period of field operation. Therefore, a eutectic solder of lead-tin, silvertin, silver-tin-copper and a gold-tin is commonly used for soldering of microsystems such as optoelectronic, RF and MEMS packaging [17][18][19][20][21][22][23][24][25]. There have been several research studies on AgSn, AgSnCu, AuSn such as Ag-Sn electroplating (Ag-Sn meaning AgSn alloy), Ag/Sn electroplating (Ag/Sn meaning Sn electroplating on Ag electroplating), Ag/Sn evaporation, Ag-Sn-Cu paste, Au-Sn electroplating, Au/Sn plating and Au/Sn evaporation.…”

Flip Chip Bonding of a Quartz MEMS-Based Vibrating Beam Accelerometer

“…Figure 2 shows the self-alignment procedure during the reflow process for flip chip bonding due to the centering force. Recently, flip-chip bonding has been reported for application in packaging MEMS devices [ 16 , 17 , 18 ], such as barometric pressure sensors [ 19 , 20 ], microspring [ 21 ], photonic chips [ 22 ], scanner [ 23 ], microphones [ 24 ] and so on.…”

AuSn20 Eutectic Electrodeposition through Alternative Complexing of Pyrophosphoric Acid: Insights from Electrochemical and DFT Methods

“…AuSn20 eutectic solder is extensively employed in the electronic packaging of optoelectronic and high-powered electronic components − due to its superior mechanical and thermal conduction properties . In addition, it plays a key role in some special technologies, including gas leak sealing treatments, high-powered laser diode packaging, and nonsoldering flux packaging …”