Laser Machining Of Ceramics Research Articles

Local optimization of low power laser machining of MgO at the green state enables cost- and energy-efficient benchtop fabrication

Laser machining of ceramics at the green state offers a low-cost route to the near-net fabrication of ceramics. A matrix of laser machining (i.e., laser cutting and scanning) parameters were tested on 5 mm-thick green bodies of magnesium oxide (MgO) using a CO2 laser with a maximum power capacity of 130 W. The input parameters were feed rate and power; we scanned the feed rate of 3–14 mm/s and power of 23–31 W for laser cutting, and 10–60 mm/s and 16–27 W for laser scanning. The quality of the laser-cut and -scanned surfaces was tracked through SEM. Thermal damage along the laser path was assessed to optimize laser cutting. High laser power and/or long dwell time resulted in partial sintering. At both cutting and scanning operations, low feed rates induced thermal damage, while high feed rates provided better edge retention and surface smoothness. However, very high feed rates failed to generate complete cuts and through-holes due to insufficient transfer of the excitation energy. Various combinations of the feed rate and power produced completely cut 5 mm cubes with smooth surfaces via laser cutting in a single pass. The most energy-efficient combination of 12 mm/s and 28 W rendered the highest surface quality with minimum thermal damage. This parameterization set provides a practical roadmap for choosing process parameters for the laser machining of MgO at the green state.

Minimization of elastic thermal stresses during laser machining of ceramics using a dual-beam arrangement

Lasers are emerging as a valuable tool for shaping and cutting hard and brittle ceramics. Unfortunately, the large, concentrated heat flux rates that allow the laser to efficiently cut and shape the ceramic also result in large localized thermal stresses in a small heat-affected zone. These notable thermal stresses can lead to microcracks, a decrease in strength and fatigue life, and possibly catastrophic failure. In order to assess where, when, and what stresses occur during laser scribing, an elastic stress model has been incorporated into a two-dimensional drilling as well as a three-dimensional scribing and cutting code. The results of the analysis for a single Gaussian laser source show that substantial tensile stresses develop over a thick layer below and parallel to the surface, which may be the cause of experimentally observed subsurface cracks. In this work the effect of splitting the beam into two parts is discussed: a highly focused beam that does the actual drilling or scribing, and a partially defocused beam, used to heat the material ahead of, around, or behind the laser beam. Different secondary beam scenarios are investigated, and their effect on reducing the damaging tensile stresses is evaluated.

Excimer laser machining and metallization of vias in aluminum nitride

Laser machining of ceramics is used extensively in the microelectronics industry for scribing and via hole drilling. Scribing involves laser ablation of a groove or row of holes that form perforation lines to separate a large substrate into individual circuits. Via machining is generally followed by a metallization step to create three-dimensional (3-D) interconnections in a multilayer circuit board. Aluminum nitride (AlN) is a desirable substrate material for high power, high frequency applications because of its high thermal conductivity and low thermal expansion coefficient than Al/sub 2/O/sub 3/. In this paper, an excimer laser is used to machine high aspect ratio, straight walled via holes in aluminum nitride with or without a metallization layer deposited on the via walls. Via diameters range between 60 and 300 /spl mu/m through substrates 635 /spl mu/m thick. Through hole machining can cause damage to the back surface of the substrate, however, attachment of a second substrate or metal sheet will prevent damage. Ablation of the attached metal backing with subsequent redeposition on the via walls produces a metallized via with a resistance of less than 1 /spl Omega/ per via. Single and multilayer via structures are described. Substrate damage at through hole exits results from shock wave propagation and reflection in the substrate. The attached backing material reduces reflection of the shock wave at the back surface of the substrate to prevent damage. Shock wave analysis, via cross sections, and resistance measurements are discussed.

Laser machining of Si3N4 ceramics

Laser machining of ceramics is a promising alternative to diamond-based techniques. Technological problems and influencing factors are exemplified for the structural shaping of silicon nitride ceramics using Nd:YAG pulses of several hundred microseconds. Ablation rate and ablation geometry are discussed in relation to irradiation conditions and microstructure.

Crack-free processing of hot-pressed silicon nitride ceramics using pulsed YAG laser.

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.