RU2582849C1 - Method for laser punching through-hole in non-metal plate - Google Patents

Abstract

FIELD: optics; physics.

SUBSTANCE: invention relates to laser punching of through hole in non-metal plate and can be used in producing plates from semiconductor, ceramic and glass-like materials with holes. Plate surface is exposed to pulsed laser radiation. Pulsed radiation wavelength is selected from condition: 1.2<_Xh<3.1, where _X is plate material absorption at wavelength of laser radiation; h is thickness of plate. Initial laser beam is divided into two beams and coaxially to act on both surfaces of plate with energy density defined by relationship:

where e is base of natural logarithm; Q is specific energy of sublimation material; R is coefficient of reflection of material. Surface of plate pre-polished.

EFFECT: reduced power consumption in laser punching of through holes in plates of non-metallic materials having volumetric absorption of laser radiation.

2 cl, 2 dwg

Description

The invention relates to the field of technological processes and can be used for laser penetration of holes in plates of semiconductor, ceramic and glassy materials.

A known method of processing non-metallic materials [1], in which the processing of the plates is carried out by irradiating the surface with a laser pulse. The temporal shape of the pulse is described by a certain ratio, depending on the density of the laser radiation energy flux, the constants b ₁ and b ₂ characterizing the front and decay of the laser pulse, the duration of the laser pulse, the current time from the onset of exposure, the energy density and the maximum value of the laser radiation flux in momentum. The effect is achieved by forming a laser pulse, the temporary shape of which is described by the relation

where q (t) is the energy density of the laser radiation, W / m ² ;

τ is the laser pulse duration, s;

b ₁ and b ₂ - constants characterizing the front and the decline of the laser pulse;

t is the current time from the onset of exposure, s.

The specified method allows to minimize thermoelastic stresses in the absorbing layer of the plate material, but it does not allow scribing of plates of non-metallic materials and penetration of through holes in them with minimal energy costs.

A known method of laser processing [2], in particular, used to create holes in the plates, in which the energy density required for the evaporation of a layer of material of thickness x is equal to

where W is the energy density of the laser radiation;

x is the coordinate measured from the surface into the interior of the material;

ρ is the density of the material;

L _u - latent heat of evaporation of a unit mass of material.

Equation (1) characterizes the stationary process of material evaporation under the action of laser radiation when it is absorbed in a very thin surface layer of the material (much less than the thickness of the evaporated layer). Equation (1) cannot be used when the absorption of laser radiation occurs in the volume of the material, for example, in a layer of material several millimeters thick.

The disadvantage of this method is the inability to determine the optimal value of the energy density of the laser radiation when processing materials having volumetric absorption of radiation with a wavelength at which the material is processed.

There is also known a method of laser processing of non-metallic materials [3], which consists in irradiating their surface with laser pulses with energy density per pulse, determined by the ratio

where e is the base of the natural logarithm (e≈2.7183);

Q - specific sublimation energy of the material, J / m ³ ;

χ is the absorption coefficient of the plate material at a wavelength of laser radiation, m ^-1 ;

R is the reflection coefficient of the material.

At such an energy density of the acting laser radiation, the absorption layer of the material 1 / χ thick is sublimated, and the maximum specific (per unit of energy input) ablation of the material mass will be

For through penetration of holes in the plate, it is necessary that the thickness of the plate is 1 / χ. These conditions provide the optimal processing mode for unilateral exposure to laser radiation on non-metallic materials with volumetric absorption of laser radiation. This method is selected as a prototype.

The disadvantage of this method is that it does not allow the penetration of through holes in non-metallic plates with volumetric absorption of laser radiation, with minimal energy costs.

The technical result of the invention is to reduce energy costs when laser penetrating through holes in plates of non-metallic materials having volumetric absorption of laser radiation, such as semiconductor, ceramic and glassy materials.

The technical result is achieved by the fact that in the method of laser processing of non-metallic plates, which consists in irradiating their surface with laser radiation, the wavelength of the pulsed laser is selected from the condition:

where χ is the absorption coefficient of the plate material at a wavelength of laser radiation; h is the thickness of the plate,

the initial laser beam is divided into two beams and simultaneously coaxially act on both surfaces of the plate with an energy density determined by the ratio:

where W ₂ is the energy density on each surface of the plate.

e is the base of the natural logarithm;

Q is the specific energy of sublimation of the material;

R is the reflection coefficient of the material.

The surface of the plate is pre-polished.

In FIG. 1 shows a diagram of a laser installation for implementing the proposed processing method.

The installation contains a pulsed laser (1), a telescopic beam diameter transducer, consisting of a collecting lens (2) and a scattering lens (3), a dielectric mirror (4) with a reflection coefficient of 0.5 at a laser wavelength, which is divided into two beams of equal density energy of the original laser beam, and two dielectric mirrors (5, 6) with a reflection coefficient of ~ 0.99, directing laser radiation to both surfaces of the processed plate (7). Using a telescopic converter, the original laser beam is converted into a beam of the desired diameter with the smallest possible divergence.

If

where a is the coefficient of thermal diffusivity of the plate material;

R _{p the} radius of the laser beam after the scattering lens,

then we can consider the problem of the evaporation of the material in a one-dimensional formulation and neglect the energy transfer in the material due to thermal conductivity during the duration of the laser pulse.

The specific energy release over the thickness of the plate during two-sided irradiation with its laser radiation will have the form

where x is the coordinate measured from the surface into the plate (0≤x≤h);

h is the thickness of the plate.

To break through the through hole in the plate, it is necessary that the minimum specific energy release occurring at χh = 0.5 be no less than the specific sublimation energy of the plate material Q.

From (6) we have

From (7) we obtain

The mass (per unit area) of the evaporated material will be

The specific gravity (per unit of energy input) of the evaporated material will be

From (10) we obtain

Research on the extremum of equation (10) shows that m _UD has a maximum at χh = 2, and at the maximum point it is constant for a specific type of material and is

, $${(m_{\mathrm{At}D})}_{max}\approx 0,736\frac{\rho }{Q}$$

,

which is two times higher than in the prototype.

от безразмерного параметра χh. In FIG. 2 shows the relationship $$m_{\mathrm{At}D}\frac{Q}{\rho }$$

from the dimensionless parameter χh.

It can be seen that for the range of values

находится вблизи максимума и уменьшается не более чем на 12%. value $$m_{\mathrm{At}D}\frac{Q}{\rho }$$

It is near the maximum and decreases by no more than 12%.

Since the wavelengths of technological lasers have certain values, and the plate thicknesses can be arbitrary, it is difficult to ensure the optimal processing mode for χh = 2. The rational mode of penetration of through holes in the plates is the action of a laser pulse on the plate with a wavelength that ensures the fulfillment of condition (12), while the energy density on each surface of the plate is calculated by the relation (8). Thus, a positive effect is achieved during laser penetration of through holes in non-metallic plates with volumetric absorption at a wavelength of laser radiation.

Prevention of laser radiation scattering requires preliminary polishing of the plate surfaces.

Literature

1. Atamanyuk V.M., Kovalenko A.F. Levun I.V., Fedichev A.V. A method of processing non-metallic materials. Patent RU 2211753 C2. Publ. 09/10/2003. Bull. Number 25.

2. Laser equipment and technology. In 7 kn. Prince 4. Laser processing of non-metallic materials: Textbook for universities / A.G. Grigoryants, A.A. Sokolov. Ed. A.G. Gregorianets. - M.: Higher School 1998. - 191 p. ISBN 5-06-001453-3.

3. Sakharov M.V., Kovalenko A.F., Vorobyov A.A., Konyukhov M.V., Astrauskas Y.I., Nikitin I.V., Zaponov A.E., Udintsev R.D., Chupyatov A.S. A method of processing non-metallic materials. Patent RU 2486628. Publ. 06/27/2013. Bull. Number 18.

Claims (2)

1. The method of laser punching a through hole in a non-metallic plate, including processing the surface of the plate using a pulsed laser, characterized in that the plate is affected by a laser pulse with a wavelength that ensures the following conditions:
1,2 <χh <3,1,
where χ is the absorption coefficient of the plate material at a wavelength of laser radiation; h is the thickness of the plate, while the initial laser beam is divided into two beams and simultaneously coaxially act on both surfaces of the plate with an equal energy density, determined by the ratio:

where e is the base of the natural logarithm;
Q is the specific energy of sublimation of the material;
R is the reflection coefficient of the material. 2. The method according to p. 1, characterized in that the surface of the plate is pre-polished.

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