森田 昇

This paper describes the fracture mechanism and the prevention of crack propagation in laser-processing of the hot-pressed silicon nitride ceramics using the pulsed YAG laser. The crack formation mechanism is successfully explained by the thermal stress and fracture strength distribution. The laser pulses controlled at below the critical duration and frequency are effective for the purpose of crack-free processing because the thermal stress is localized only in the laser-heated shallow region. ? 1992, The Japan Society for Precision Engineering. All rights reserved.

Aluminum nitride (AIN) ceramics decomposes into aluminum vapor and nitrogen gas at about 2790 K. Peculiarly, The aluminum metallic phase is formed in laser processing of AIN ceramics. This is probably caused by the existence of high [ressure Aluminum vapor at high temperature. This paper describes the vapor pressure measurement for the purpose of explanation of the metallic phase formation mechanisms.

This paper describes the effect of crack-free laser processing of hot-pressed silicon nitride ceramics on the fracture strength and residual stress. The fracture strength was determined by three-point bending tests. The residual stress in the processed surface was characterized by X-ray diffraction measurement. The strength of the laser-processed test pieces is reduced to 90-80% compared with that of the ground test pieces because of surface layer damages, which are the recast layer and the residual stress layer. In particular, the latter greatly affects the fracture strength because the higher compressive residual stress layer generated during grinding is removed by laser machining. ? 1991, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the dynamic behavior of the vapor pressure and plasma potential to investigate the metallic phase formation mechanism in laser-processing of the covalent bond-ceramics. The vapor pressure was measured with a high sensitivity acceleration sensor. The plasma potential was detected with electrical probes, which have been newly developed. The vapor pressure increases linearly with the peak power to about 39.2 MPa. The plasma propagation speed is higher than the velocity of sound nearby the target. ? 1991, The Japan Society for Precision Engineering. All rights reserved.

Thermal-stress-induced cracks are generated during the laser-processing of ceramics. This paper describes the temperature profile and thermal stress propagation for silicon nitride ceramics heated by Gaussian heat flux. The thermal stress distribution is calculated with consideration of the temperature dependence on material properties, the influence of laser pulse duration and its repetition rate using FEM. The tensile stress in circumferential, radial and axial directions induces the radial, lateral and median cracks, respectively. The use of short laser pulses below 20 μs with a repetition frequency under 10 kHz is experimentally recommended to reduce thermal stress and to avoid crack formation. ? 1991, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the effects of laser heating on the electroless plating process. In the experiment, a focused YAG laser beam and a copper electroless plating solution were used. In the analysis, the temperature distribution was calculated by the solution of the heat conduction equation. In the first stage on the laser-induced plating, the rapid heating effect induces the nucleation reaction. In the second stage, the partially heating effect enhances the reduction reaction based on the micro-convection, which depends on the sharp temperature profile. ? 1991, The Japan Society for Precision Engineering. All rights reserved.

It is difficult to eliminate recast layers and cracks in laser-machining caramics. These defects significantly detract from the excellent properties of ceramics. This paper describes the feasibility of a crack-free processing method for hot-pressed silicon nitride (Si3N4) ceramics using a yttrium aluminum garnet (YAG) laser. The Q-switched YAG laser pulses controlled at below 500 ns in duration and 10 kHz in repetition rate are effective for the purpose of crack-free machining of Si3N4ceramics because the thermal stress is most likely localized only in the laser-heated shallow area. The integrity of the crack-free surface is evaluated by the fracture strength and residual stress. The strength of laser-processed test pieces is reduced by 10 to 20% compared with diamond-ground ones because the high residual compression layer generated during grinding is removed.

In the laser machining of ceramics, it is difficult to avoid the formation of a recast layers and cracks. These deffects significantly spoil some excellent properties of ceramics. This paper describes the feasibility of a crack-free processing method for hot-pressed silicon nitride(Si3N4) ceramics with an yttrium aluminum garnet(YAG) laser. It is found that, in order to attain the defect-free machining, it is necessary to process the ceramics using a laser beam pulsed below 500 ns in duration and 10 kHz in repetition rate. ? 1990, The Japan Society of Mechanical Engineers. All rights reserved.

A new method for direct formation of conductor lines onto ceramic substrates is presented. This method involves the selective forming of aluminum thin films by decomposing aluminum nitride (AlN) ceramics in argon (Ar) gas atmosphere with a Q-switched yttrium aluminum garnet (YAG) laser. The aluminum films can also be employed as a catalyst in electroless plating. With nickel (Ni) electroless plating solution, Ni conductor lines with a specific resistance about 1×10-7Ω m were directly and selectively formed on the aluminum layer.

This paper describes the feasibility of selective area deposition of metal thin films onto ceramic substrates by using a laser-induced plating technique. In experiments, a focused YAG laser beam and a copper electroless plating solution including CuSO4were used. For the ceramic workpieces, aluminum nitride (A1N) substrate without activation was used. As a result, a copperdeposit was produced on the ceramic surface only in regions where the laser beam was irradiated. A very high plating rate of about.2μm/s was achieved. This plating enhancement rate is about lxl03times the usual plating rate. The specific resistance of the copper film was about 3x 10-8Ωm. As an application, the direct drawing of copper lines was demonstrated with a writing speed of 0.2 mm/s. ? 1989, The Japan Society of Mechanical Engineers. All rights reserved.