Akiomi Kohno

Ultra-hydrophobic fluorine polymer by Ar-ion bombardment.

A study has been made of the improvement of the hydrophobicity of a fluorine-polymer (polytetra-fluorinethylene, PTFE) by Ar-ion bombardment. Ar-ion bombardment to PTFE) by Ar-ion bombardment. Ar-ion bombardment to PTFE sheets was carried out at the fluences ranging from 3.1x10(20) to 18.3x10(20) ions/m(2). The beam current densities were ranged from 1.25 to 7.5 A/m(2). The hydrophobicity of modified materials has been investigated by means of a sessile drop method of water. The roughness, morphology and structure of bombarded specimens have been estimated as a function of beam current density and acceleration energy. It was found that Ar-bombardment causes the contact angle of water to increase from the original value 103 to 170 degrees. The results indicate that Ar-bombardment at an optional condition results in the formation of ultrahydrdophobic surfaces. The effects of Ar-bombardment to hydrophobicity of PTFE are discussed with the relationship among roughness, morphology and chemical bonding states of the surfaces.

Effect of residual stress on the strength of alumina-steel joint with Al-Si interlayer

The effect of residual stress on the strength of an alumina-steel joint with the Al-Si interlayer was studied. Alumina rods, 32 mm in diameter and 9 mm in length and steel pipes were diffusion bonded at 873 K and at a contact pressure of about 5 M Pa for 30 min in a vacuum of 2∼4×10−2Pa. The interlayer of aluminium sheet clad with Al-10% Si alloy on both sides was used. The tensile strength of the joints is influenced by the thickness of the interlayer or the intermetallic compound formed between the interlayer and the steel. The strength increases with increasing interlayer thickness and with decreasing intermetallic compound thickness. It is found that the residual stress measured by Sachs method is much lower than that by the elastic calculation. The stress decreases with increasing interlayer thickness. Increase in thickness of the aluminium core of the interlayer is effective in improving the joint strength. This improvement can be explained by considering the stress of the joint.

Residual stress estimation of a silicon carbide-Kovar joint

Residual stress of silicon carbide and Kovar is calculated using the elasto-plastic method and its validity is checked by the four-point bending test. Silicon carbide and Kovar (Fe-27% Ni-7% Co) are diffusion bonded using Al-10% Si alloy clad on a pure aluminium sheet at 883 K and 4.9 MPa under a vacuum condition. The non-linear structure analysis program (ADINA) is used for the stress estimation. It is found by the calculation that the maximum tensile stress, about 170 MPa, is generated in the silicon carbide close to the interlayer. In the bending test, the fracture of the joint is found to occur from the point where the maximum calculated tensile stress is generated, and the bending strength of the joint is 113 MPa. It becomes clear that the calculated stress and the measured strength of the joint is nearly equal to the strength of the silicon carbide itself (280 MPa). Therefore, it can be concluded that the stress estimation in this method indicates a good approximation of the practical residual stress of the joint.

Bonding of IC bare chips for microsystems using Ar atom bombardment

This paper describes integrated circuit (IC) bare chip bonding to micromechanical devices and discusses factors affecting bond and IC qualities. Test element group (TEG) with protective diode and TEG with transistors, small-scale circuits and junctions were used here as the IC chips. Some of the TEG dies were thinned into films. In the bonding process, an Ar atom beam is used to sputter clean the surface to be bonded. After contaminants on the surfaces to be bonded are removed by the Ar atomic beam irradiation, the IC chip, a die or a film is bonded to a silicon substrate. The IC dies and the films can be bonded at low temperature and under low pressure. The strengths of the joints are good enough for use in microsystems. There is no difference in current-voltage properties of the IC films before and after the irradiation. The shapes of the ring osillator waves of the bonded IC films are not distorted by the thermal tests. This suggests that the thermal tests do not cause electrical damage to the IC chips. Although the joints of IC film/Si substrate have a few fine voids at the interface, the thermal conductivities of the joints are compared to those of IC films before bonding. The results given show the feasibility of mounting bare IC chips onto substrates of microsystems.

Low-temperature bonding technology on piezoelectric ceramics and metals

The authors studied methods of bonding piezoelectric ceramics and metals using technology of low-temperature bonding. Effects of compositions of interlayers, bonding temperatures, and surface treatment of piezoelectric ceramics on bonding strength were investigated.