A Hermetic Seal Using Composite Thin-Film In/Sn Solder as an Intermediate Layer and Its Interdiffusion Reaction with Cu

Abstract

A bonding joint between Cu metallization and evaporated In/Sn composite solder is produced at a temperature lower than 200°C in air. The effects of bonding temperature and duration on the interfacial bonding strength are studied herein. Cross sections of bonding joints processed at different bonding conditions were examined by scanning electron microscopy (SEM). The optimal condition, i.e., bonding temperature of 180°C for 20 min, was chosen because it gave rise to the highest average bonding strength of 6.5 MPa, and a uniform bonding interface with minimum voids or cracks. Good bond formation was also evidenced by scanning acoustic imaging. For bonding couples of patterned dies, a helium leak rate of 5.8 9 10 -9 atm cc/s was measured, indicating a hermetic seal. The interfacial reaction between Cu and In/Sn was also studied. Intermetallic compounds (IMCs) such as AuIn 2 , Cu 6 Sn 5 , and Cu 11 In 9 were detected by means of x-ray diffraction analysis (XRD), and transmission electron microscopy (TEM) accompanied by energy-dispersive x-ray (EDX) spectroscopy. Chemical composition analysis also revealed that solder interlayers, Sn, and In were completely converted into IMCs by reaction with Cu. All the IMCs formed in the joints have remelting temperatures above 300°C according to the Cu-In, Cu-Sn, and Au-In phase diagrams. Therefore, the joint is able to sustain high service temperatures due to the presence of these IMCs.

Low Melting Temperature Solder Materials for Use in Flexible Microelectronic Packaging Applications

“…The microstructure reflects the mechanical properties of a solder [15][16][17][18][19][20][21]. Based on the microstructural analysis of low melting point solders, specific phases and their distribution in the microstructure can be observed, and these characteristics can be used to describe intended properties [15][16][17][18][19][20][21].…”

“…Based on the microstructural analysis of low melting point solders, specific phases and their distribution in the microstructure can be observed, and these characteristics can be used to describe intended properties [15][16][17][18][19][20][21]. In this section, we show how the microstructure of low melting point solders is altered by the incorporation of an additive, especially with regard to grain size and solid solution.…”

“…The reflow at 180°C for 20 min selected was the optimal condition due to the high bonding strength of 6.5 MPa and the interfacial layer with less microvoids or mechanical cracks [20]. Especially, the reflow temperature of 180°C was high enough for the active diffusion of the low melting temperature solders, although they were dissolved in the Cu substrates and formed IMCs such as Cu 6 (Sn, In) 5 and Cu 11 (In, Sn) 9 [20]. Therefore, the joint can sustain high service temperatures because it is formed completely from these IMCs.…”

Low Temperature Bonding of Pd/Ni Assembly for Hydrogen Purifier

“…Since solid liquid interdiffusion bonding has the merits of a low bonding temperature process and high temperature application, it has been applied in the past few decades to the manufacturing of microwave packages, high power devices, thick-film resistors, GaAs/Si wafer packages, and even gold jewelry. Recently, diffusion soldering has also been employed for ceramic multichip modules [2,3], MEMS packaging [4], semiconductor packaging [5], hybrid joining [6], and hermetic package sealing [7].…”

Characterization and reliability study of low temperature hermetic wafer level bonding using In/Sn interlayer and Cu/Ni/Au metallization

“…For example, image sensor module requires a relative low process temperature (below 200 • C) because it contains polymer structures like micro-lens which is sensitive to the temperature [8]. Various low temperature wafer bonding technologies have been investigated and they are categorized as two main approaches, i.e., direct bonding using special surface treatment techniques (such as plasma surface activated bonding [9], atom beam irradiation [10]) and intermediate layer bonding using polymers [11] and low temperature solders based on diffusion soldering method [12][13][14][15][16][17][18][19][20][21][22][23].…”