Reflection by Embedded Copper Plane and Volumetric Heating in Laser Microvia Drilling

2008 ◽  
Vol 5 (3) ◽  
pp. 126-134
Author(s):  
Chong Zhang ◽  
Islam A. Salama ◽  
Yonggang Li ◽  
Nathaniel R. Quick ◽  
Aravinda Kar
Keyword(s):  
Laser Beam ◽  
Material Removal ◽  
Laser Energy ◽  
Polymer Layer ◽  
Drilling Process ◽  
Copper Sheet ◽  
Microelectronics Packaging ◽  
Volumetric Heating ◽  
Nanosecond Pulsed Laser ◽  
Thin Polymer

A finite difference thermal model is developed to analyze volumetric heating during laser drilling. The substrates of interest are multilayered polymeric sheets containing an embedded copper plane, which are generally used for high-density microelectronics packaging, and the laser of interest is a CO2 laser of wavelength 9.3 μm. Both the incident laser beam propagating toward the embedded copper plane and the beam reflected upward by the copper plane contribute to the volumetric heating of the substrate, which is the main mechanism for material removal. When the polymer layer above the copper sheet thins down as drilling progresses, the exit of the laser beam from the polymer layer after reflection by the copper sheet and the heat conduction within copper increase the energy loss significantly, making the process energetically inefficient. Consequently, the material-removal capability of the process diminishes, and a very thin polymer layer is left as residue on top of the copper sheet. The thickness of the residue depends mainly on the laser pulse width as predicted by the model. A nanosecond pulsed laser is found to effectively reduce the residue thickness to about 0.1 μm. The reflected laser energy, however, is found to contribute to the drilling process when the thickness of the polymer is higher than the absorption depth.

scholarly journals Effects of Beam Size and Pulse Duration on the Laser Drilling Process

2016 ◽  
Author(s):  
Nazia Afrin ◽  
Pengfei Ji ◽  
J. K. Chen ◽  
Yuwen Zhang
Keyword(s):  
Laser Beam ◽  
Pulse Duration ◽  
Material Removal ◽  
Convection Heat Transfer ◽  
Laser Drilling ◽  
Drilling Process ◽  
Beam Diameter ◽  
Beam Size ◽  
Laser Beam Diameter ◽  
Ablation Efficiency

A two-dimensional axisymmetric transient laser drilling model is used to analyze the effects of laser beam diameter and laser pulse duration on the laser drilling process. The model includes conduction and convection heat transfer, melting, solidification and vaporization, as well as material removal resulting from the vaporization and melt ejection. The validated model is applied to study the effects of laser beam size and pulse duration on the geometry of the drilled hole. It is found that the ablation effect decrease with the increasing beam diameter due to the effect of increased vaporization rate, and deeper hole is observed for the larger pulse width due to the higher thermal ablation efficiency.

scholarly journals Preliminary Laser Cleaning Studies of a Consolidated Prehistoric Basketry Coming from the Pile Building of Fiavè-Carera in the North-East of Italy

2006 ◽  
Vol 2006 ◽  
pp. 1-5 ◽  
Author(s):  
Romina Belli ◽  
Antonio Miotello ◽  
Paolo Mosaner ◽  
Laura Toniutti ◽  
Marta Bazzanella
Keyword(s):  
Energy Density ◽  
Material Removal ◽  
Laser Energy ◽  
Laser Cleaning ◽  
Original Surface ◽  
North East ◽  
The North ◽  
Cleaning Procedures ◽  
Krf Excimer Laser ◽  
Organic Deposits

In the archaeological field, some specific advantages are recognized to laser cleaning, like, for example, the absence of mechanical contacts with the sample. The cleaning procedures generally involve a multilayer structure (dust, dirty, organic deposits, and, in some cases, consolidant substances). In this work, prehistoric wood samples (found and consolidated in 1970s) have been laser irradiated (KrF excimer laser) in order to restore their original surface aspect. A certain amount of burned matter was also present. Samples came from a fragment of a prehistoric basketry found in the lake dwelling site of Fiavè-Carera, Trento, Italy (1500–1400 BC). It was observed that the laser cleaning effects are strictly dependent on the irradiation parameters (power density and number of pulses). Efficient material removal was possible by using appropriate energy density. Moreover, for lower laser energy density, special structures appeared on the surface of the consolidating substance that we attributed to heating-induced stresses on the consolidant surface.

Early Dynamics of a Laser-induced Underwater Shock Wave

2021 ◽  
Author(s):  
Guihua Lai ◽  
Siyuan Geng ◽  
Hanwen Zheng ◽  
Zhifeng Yao ◽  
Qiang Zhong ◽  
...  
Keyword(s):  
Shock Wave ◽  
Numerical Method ◽  
Cavitation Bubble ◽  
Laser Energy ◽  
Optical Breakdown ◽  
Pulsed Laser ◽  
Underwater Shock Wave ◽  
Time Resolved ◽  
High Attenuation ◽  
Nanosecond Pulsed Laser

Abstract The objective of this paper is to observe and investigate the early evolution of the shock wave, induced by a nanosecond pulsed laser in still water. A numerical method is performed to calculate the propagation of the shock wave within 1µs, after optical breakdown, based on the Gilmore model and the Kirkwood-Bethe hypothesis. The input parameters of the numerical method include the laser pulse duration, the size of the plasma and the maximally extended cavitation bubble, which are measured utilizing a high time-resolved shadowgraph system. The calculation results are verified by shock wave observation experiments at the cavitation bubble expansion stage. The relative errors of the radiuses and the velocity of the shock wave front, reach the maximum value of 45% at 5 ns after breakdown and decrease to less than 20% within 20 ns. The high attenuation characteristics of the shock wave after the optical breakdown, are predicted by the numerical method. The quick time and space evolution of the shock wave are carefully analyzed. The normalized shock wave width is found to be independent of the laser energy and duration, and the energy partitions ratio is around 2.0 using the nanosecond pulsed laser.

A Fractional-Diffusion Theory for Calculating Thermal Properties of Thin Films From Surface Transient Thermoreflectance Measurements

2001 ◽  
Vol 123 (6) ◽  
pp. 1133-1138 ◽  
Author(s):  
Vladimir V. Kulish ◽  
Jose´ L. Lage ◽  
Pavel L. Komarov ◽  
Peter E. Raad
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Analytical Solutions ◽  
Laser Energy ◽  
Diffusion Theory ◽  
Complete Solution ◽  
Diffusion Problem ◽  
Gaas Sample ◽  
Volumetric Heating ◽  
Pulsed Laser Heating

The transient thermoreflectance (TTR) method consists of measuring changes in the reflectivity of a material (thin film) under pulsed laser heating, and relating these changes to the corresponding surface temperature variations. Analytical solutions of the diffusion problem are then used to determine the thermal conductivity of the material following an iterative matching process between the solutions and the experimental results. Analytical solutions are attainable either when the material absorbs the laser energy volumetrically or when the material absorbs the laser energy at the surface. Either solution allows for the determination of only one thermal property (thermal conductivity or diffusivity), with the other one assumed to be known. A new, single, analytical solution to the transient diffusion equation with simultaneous surface and volumetric heating, found using fractional calculus, is presented in a semi-derivative form. This complete solution provides the means to determine the two thermal properties of the material (thermal conductivity and diffusivity) concomitantly. In this preliminary study, the solution component for surface heating is validated by comparison with experimental data for a gold sample using the classical thermoreflectance method. Further results, for surface and volumetric heating, are obtained and analyzed considering a GaAs sample.

Numerical Analysis of Temperature Field in Laser Cladding on Teeth Surfaces of Gear Shaft

2010 ◽  
Vol 29-32 ◽  
pp. 571-576
Author(s):  
Lie Chen ◽  
Pei Lin Xie
Keyword(s):  
Temperature Field ◽  
Laser Beam ◽  
Laser Cladding ◽  
Horizontal Plane ◽  
Laser Energy ◽  
The Other ◽  
Analysis Software ◽  
Element Analysis ◽  
Result Show ◽  
Two Sides

Temperature field of laser cladding on teeth surfaces of gear shaft was numerical simulated with finite element analysis software – ANSYS. The simulation result show that the heat caused by laser beam is concentrated inside the tooth mostly. An effect of preheating in the adjacent tooth is also brought about by injected laser energy. In order to make use of the effect of preheating and avoid the concentration of heat, all of the corresponding flanks of teeth should be cladded first and the other flanks of teeth be cladded secondly in the process of laser cladding. It is also shown that the problems of excessive melted down and collapsing of tooth-tip would be easily resulted in by the heat that concentrated in tooth-tip if the tooth-side and tooth-tip be cladded at the same time. The results of analysis and experiment show that at least two times of scanning should be executed in the process of laser cladding on teeth surfaces. At the first scanning, dimension of laser beam should be reduced properly. And the tooth-tip should not be irradiated directly by laser beam. After the first scanning, the gear should be circumrotated a certain angle. And the included angles between the two sides of tooth-tip and horizontal plane should be approximately equal. Then the second scanning could be prosecuted at the tooth-tip. Experiment results show that continuous and compact cladding coat could be gained by this craft. It is proved that this technological craft is reasonable and effective.

Effect of Temperature on the Evolved Microstructure During Laser Beam Forming of Sheet Steels

2017 ◽  
Author(s):  
Stephen Akinlabi ◽  
Madindwa Mashinini ◽  
Esther Akinlabi
Keyword(s):  
High Temperature ◽  
Energy Density ◽  
Laser Beam ◽  
Laser Energy ◽  
High Energy ◽  
Phase Changes ◽  
High Energy Density ◽  
Effect Of Temperature ◽  
Beam Forming ◽  
Heating And Cooling

Laser Beam Forming (LBF) being a novel technique and non-contact manufacturing process, employs laser beam as the tool of shaping and bending metal sheets into different shapes and curvatures for various applications. LBF is a high-temperature process, where rapid heating and cooling occurs causing microstructural changes like dynamic recrystallization and phase changes. The study becomes necessary to ensure that the structural integrity of the processed material is not compromised. Hence, the investigation focuses on the effect of temperature on the developed microstructure during the LBF process. The design of experiment was considered, using three levels and five factors. The experimentally measured curvatures were validated with the predicted measured curvatures, which were found to be in agreement. The result shows that the developed ferrite and pearlite grains were due to the heating and cooling. Furthermore, the average grain sizes at a low energy density of about 355°C and high energy density of about 747°C were found to be about 10 μm and 6 μm respectively. It is implied that the high temperature from the high laser energy aided the deformation of the grains significantly. However, such high temperature must be closely monitored so to avoid metallurgical notches in the processed component.

Experimental Investigation of Polymeric Material Removal by Low Diffraction Laser Beam

2002 ◽  
Vol 124 (2) ◽  
pp. 475-480
Author(s):  
Xuanhui Lu ◽  
Y. Lawrence Yao ◽  
Kai Chen
Keyword(s):  
Laser Beam ◽  
Polymeric Material ◽  
Material Removal ◽  
Beam Quality ◽  
Power Level ◽  
Average Power ◽  
Laser Material ◽  
Theoretical Predictions ◽  
Removal Processes

Effects of improved beam quality of a low diffraction laser beam on laser material removal processes are experimentally investigated in a polymeric material. The experimental results are in agreement with theoretical predictions. The results show that the low diffraction beam has marked advantages over the Gaussian beam in ablation-dominated material removal processes in terms of larger depth and smaller taper at the same average power level.

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