R. J. von Gutfeld

20‐MHz acoustic waves from pulsed thermoelastic expansions of constrained surfaces

Repetitive pulses from lasers with pulse widths 5–10 nsec or a current generator with 10–25‐nsec widths have been used to launch acoustic waves by thermoelastic expansions. For the laser case, when transparent media such as quartz plates are used to acoustically constrain the energy absorbing surface, an increase of up to 46 dB at 20 MHz was observed over that generated from a free surface. An experiment using a scannable laser to generate elastic waves for flaw detection in a metallic sample is described.

Laser enhanced electroplating and maskless pattern generation

Maskless plating has been achieved through a new technique that utilizes a cw or pulsed laser, focused onto an electrode in an electroplating bath. In the region of optical absorption on the cathode, plating enhancement rates on the order of 103 occur for optical power densities on the order of 104 W/cm2. Laser scanning produces a plating pattern along the scanning path. A qualitative theory based on convective mass transport is used to explain the results.

Laser enhanced etching in KOH

We have used a focused laser beam to perform localized etching on 〈111〉 Si and several ceramic materials submerged in an aqueous potassium hydroxide solution. The etching process is accompanied by localized melting of the material whenever high material removal rates are observed. Mil sized blind holes, through holes, and slots have been fabricated. Instantaneous etch rates as high as 200 μm/s have been observed in alumina/TiC ceramic for 1‐W of incident laser power (∼106 W/cm2). An average rate of a 15 μm/s has been observed in the etching of through holes in 10‐mil silicon with 15 W of incident laser power (∼107 W/cm2).

Electronic probe measurements of pulsed copper ablation at 248 nm

We have used a single wire probe to measure time of flight velocities for copper photoablated with a 248 nm pulsed excimer laser. For the range of fluences, 1.6–12 J/cm2, we find copper ion velocities in the range of 1–2×106 cm/s. We have used Langmuir probe theory to determine ion densities and electron temperatures as a function of fluence and target‐probe separation. Results are consistent with recent kinetic and photoablated plasma theories.

Jet and Laser‐Jet Electrochemical Micromachining of Nickel and Steel

Experimental results on jet and laser-jet electrochemical micromachining of nickel and steel in neutral solutions of sodium chloride and sodium nitrate are reported

Laser‐generated MHz elastic waves from metallic‐liquid interfaces

The thermoelastic generation of MHz waves from a three‐layer structure consisting of a transparent substrate with an evaporated metallic film in contact with a liquid is described. Results with laser excitation indicate the magnitude of the strain wave to be strongly dependent on the expansion coefficient of the liquid and thickness of the metal film. The data are compared to a three‐medium one‐dimensional theory. Some practical applications such as nondestructive evaluation are discussed using this structure.

Electrostatic collection of debris resulting from 193 nm laser etching of polyimide

Ablated debris produced by 193 nm laser irradiation of polyimide can be preferentially collected on charged wire or plate electrodes placed on the polymer surface. Scanning micrographs indicate several types of debris structure depending on laser fluence and applied potential. The fragment morphology and possible charging mechanisms are discussed. The collected debris is believed to consist of pure carbon.

Laser‐enhanced jet plating: A method of high‐speed maskless patterning

We describe a metal deposition technique that combines free‐standing jet plating with an intense laser beam, directed collinearly along the jet. Experiments were made to deposit gold areas on nick‐plated beryllium‐copper substrates. The deposits are found to be crack‐free and dense, possessing excellent adhesion to the substrate. Deposition rates for 0.05‐cm‐diam gold spots are on the order of 10 μm/s, faster than any previously reported rate for gold plating.

Connections and disconnections on integrated circuits using nanosecond laser pulses

Nanosecond pulses from a focused nitrogen pumped dye laser have been used to connect and disconnect conductors on FET chips. Experiments on connections between n+ diffusion layers and aluminum, separated by an insulating layer of SiO2, show promise for high yield and reliability. The connections have Ohmic characteristics. Sectioned laser connections were examined with an electron microprobe and microscope in order to examine physical details of the connection process.

Thermoelastic generation of elastic waves for non-destructive testing and medical diagnostics

The generation of MHz elastic waves by means of thermoelastic expansions is described. Several multilayered structures are described which use constrained boundary conditions at the energy absorbing surface. Elastic waves of sufficient amplitude can be generated to be useful for non-destructive testing applications. Biomedical ultrasonics using thermoelastically generated MHz waves will also be discussed.