JP2001350117A - Laser beam intensity distribution flattening mask, and device and method for laser plating using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser plating method which makes the light intensity distribution of a laser beam constant and improves the flatness of a plating deposit surface. SOLUTION: The output beam from a laser oscillator 1 is passed through a condenser lens 4 and a mask 3 having a prescribed amplitude transmittivity and a prescribed phase shift to make the light intensity distribution on a light convergence surface 5 constant in a specific figure. ON the light convergence surface 5, a plated surface which is brought into contact with electroless planting liquid liquid is arranged to improve the flatness of the planting deposit surface. Laser plating wherein the output beam from the laser oscillator 1 is expanded through a beam expander and guided in the mentioned device is adaptive to cases wherein a large-output laser is needed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a mask for flattening the intensity distribution of laser light, a laser plating apparatus and a laser plating method using the same.

[0002]

2. Description of the Related Art In recent years, studies have been made on irradiating a laser beam in electroless plating and plating metal only on necessary portions. However, if laser light is focused on a small spot of about several tens of microns and plating is performed, the central part of the spot is excessively heated because the intensity distribution of the laser light is large near the center, and the central part of the plating surface is Problems such as denting and roughening have been pointed out.

This is an important problem that must be overcome when laser plating is applied to the manufacture of printed circuit boards for small and light electronic devices such as mobile phones and mobile terminals.

As a recent known example of this technical field, "electroless plating of copper by laser irradiation" (lecture number 19A-08 of the 13th Annual Meeting of the Japan Institute of Electronics Packaging, Heisei 1)
March of the year). In this case, the argon laser light is simply condensed by the lens, and a depression is formed at the center of the copper spot plated on the nickel surface.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned drawbacks of the prior art, and has a mask disposed near a lens for condensing an output beam from a laser. By doing so, it is an object to make the light intensity distribution on the condensing surface constant and improve the flatness of the laser plating deposition surface.

[0006] Further, the diameter of the output beam from the laser is enlarged by a beam expander and condensed through a mask and a lens, so that the light intensity level on the mask surface is reduced, and a laser using a higher output laser is used. The purpose is to enable plating.

[0007]

Means for Solving the Problems The present inventor has conducted various studies in consideration of the current state of the art as described above, and as a result, has determined that a predetermined transmittance distribution and a phase shift distribution can be obtained in the vicinity of a converging lens. It has been found that by giving light, the light intensity distribution produces a constant spot shape on the condensing surface.

That is, the present invention provides a mask capable of converting a laser beam into a spot having a constant light intensity, and it is possible to improve the flatness of a plating surface by a laser plating method using the mask.

[0009]

According to the present invention, a mask for giving a predetermined amplitude transmittance and a phase shift is arranged in the vicinity of a lens for collecting an output beam from a laser, and a mask is provided within a predetermined range on a light collecting surface. It is characterized in that the light intensity distribution is kept constant.

If the spot size of the laser beam of the basic Gaussian beam incident on the mask and the condenser lens is w, the radius of curvature of the wavefront is R, the wavelength is λ, and the focal length of the lens is f, then d = On the (1 / f-1 / R) ^-1 light-converging surface, for example, in order to obtain a constant light intensity within a circle having a radius a, the diffraction formula calculates the amplitude transmittance T of the mask as T = exp [(r / w) ² ] │J ₁ (2πar / λd) │λd / (πar) (Equation 1) Here, r is the radius from the center on the light-converging surface, J ₁ is a first-order Bessel function, and | │ indicates an absolute value. Further, the amount of phase shift of the mask is 0 when the value of the Bessel function is positive and π radian when the value is negative.

In general, the pattern of the amplitude transmittance and the phase of the mask may be any pattern obtained by dividing the Fourier transform of the target plating spot shape by the light intensity distribution function of the output laser beam. The number of masks giving the amplitude transmittance and the phase shift as described above is not limited to one, but may be plural.

Further, the laser plating method using the mask is characterized in that the flatness of a plating deposition surface can be improved and the performance of drawing a fine plating pattern can be improved.

As a laser used for laser plating, there have been many reports using a water-cooled argon laser in the past. A small solid-state laser pumped by a semiconductor laser or its second harmonic can be used depending on the material of the object to be plated. This has been confirmed by experiments.

Embodiment 1 FIG. 1 shows an embodiment of the present invention, wherein 1 is a laser oscillator, 2 is a laser beam, 3 is a mask, 4 is a condenser lens, and 5 is a condenser surface. is there. When laser plating is performed, a surface to be plated that is brought into contact with the electroless plating solution is disposed on the light-collecting surface 5. The mask 3 is arranged immediately before or immediately after the condenser lens 4.

The laser beam 2 having the light intensity distribution of the basic Gaussian beam shown in FIG.
As shown in FIG. 3, a constant light intensity is obtained within a circle having a predetermined radius on the light-converging surface by the mask 3 that provides a predetermined amplitude transmittance and a phase shift. As described above, the amplitude transmittance provided by the mask 3 to obtain the light intensity distribution shown in FIG. FIG. 4 shows the amplitude transmittance and the phase shift. FIG. 4 shows changes in the amplitude transmittance and the phase shift of the mask 3 in the radial direction.

Using such a mask 3, a light-collecting surface 5
If the laser beam 2 is subjected to laser plating with the light intensity distribution shown in FIG. 3, the central portion of the laser beam spot is not excessively heated, and problems such as dents and roughness of the plating surface are improved. The flatness is improved.

Embodiment 2 FIG. 5 shows a second embodiment of the present invention.
1 is a high-power laser oscillator, 2 is a laser beam, 3 is a mask, 4 is a condenser lens, 5 is a condenser surface, and 6 is a beam expander. When laser plating is performed, a surface to be plated that is brought into contact with the electroless plating solution is disposed on the light-collecting surface 5.

With the configuration shown in FIG. 5, the laser beam 2 from the high-power laser oscillator 1
The spot size is enlarged, and the light is incident on the mask 3 at a light intensity level lower than that of the first embodiment. As shown in FIG. 3, the inside of a circle having a predetermined radius on the light collecting surface has a constant light intensity. According to the second embodiment, the mask 3 by the laser beam 2
Temperature rise is alleviated, and a high-power laser can be used. Laser plating of a metal surface requires a laser with a higher output than plating of a polymer surface because of good heat conduction, and the application of this embodiment is useful.

[0019]

According to the mask of the present invention, an output beam from a laser having a larger light intensity distribution toward the center can be converted into a constant light intensity within a predetermined plating spot pattern on the light-collecting surface. Therefore, the central portion of the plating spot is not excessively heated.

In the laser plating method using the mask of the present invention, the conventional problems such as the depression or roughening of the center of the plating deposition surface are improved, the flatness is improved, and a finer pattern can be plated. .

The laser plating method using the beam expander and the mask of the present invention can cope with plating requiring a high-output laser.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a laser plating method using a laser beam light intensity distribution flattening mask of the present invention.

FIG. 2 is a diagram showing a light intensity distribution of an output beam from a laser.

FIG. 3 is a diagram showing that a light intensity distribution on a condensing surface becomes constant within a circle by using a mask.

FIG. 4 is a diagram showing changes in the amplitude transmittance and the phase shift of a mask in the radial direction.

FIG. 5 is a diagram showing a configuration of a second embodiment of a laser plating method using a laser beam light intensity distribution flattening mask according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Laser beam 3 Mask 4 Focusing lens 5 Focusing surface or laser plating surface 6 Beam expander

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C23C 18/16 B23K 101: 42 // B23K 101: 42 G02B 27/00 E

Claims (7)

[Claims] 1. A method according to claim 1, wherein the laser beam is arranged in the vicinity of a focusing lens for focusing the laser beam and on the optical axis of the laser beam so as to give the laser beam a predetermined change in amplitude and phase.
Using the radius of curvature R of the wavefront of the laser beam and the focal length f of the condensing lens, the condensing light is located away from the condensing lens by a distance d represented by d = (1 / f−1 / R) ^−1. A laser light intensity distribution flattening mask for making the intensity distribution of the laser beam on the surface constant. 2. In order to maintain a constant beam intensity distribution in a circular area having a radius a on a converging surface whose distance from the converging lens is d, a spot size radius w of an incident beam and an incident beam T = exp [(r / w) ² ] │J ₁ (2πar / λd) │λd / (πar) with respect to the wavelength λ of the light-condensing surface and the distance r from the center of the light-collecting surface within the circular region. has a transmittance T, and the laser light intensity distribution flattened mask according to claim 1, wherein the value of the first-order Bessel function J ₁ gives a relative phase shift of π radians in the range of the negative r. 3. A laser plating apparatus for performing plating by condensing an output beam from a laser oscillator with a condensing lens and projecting the converged output beam onto a surface to be plated. Or a laser that is disposed immediately after the output beam to give a predetermined amplitude and phase change so that the intensity distribution of the output beam projected on the surface to be plated is kept constant within the projection range on the surface to be plated. Light intensity distribution flattening mask. 4. The surface to be plated is d = (1 / f−1 / R) ⁻¹ using the focal length f of the condenser lens and the radius of curvature R of the wavefront at the position of the condenser lens of the output beam. 4. The laser light intensity distribution flattening mask according to claim 3, wherein the laser light intensity distribution flattening mask is disposed at a position apart from the focusing lens by a distance d represented by the distance. 5. The laser beam by changing the diameter of an output beam from a laser oscillator with a beam expander and causing the beam to enter a laser beam intensity distribution flattening mask and a condenser lens according to claim 3 or 4. By changing the intensity of the output beam on the surface of the intensity distribution flattening mask to make the intensity distribution of the output beam projected on the surface to be plated constant, and changing the intensity of the output beam projected on the surface to be plated Laser plating equipment. 6. An output beam from a laser oscillator is focused on a metal or polymer surface brought into contact with an electroless plating solution by using the laser light intensity distribution flattening mask according to claim 3 or 4, A laser plating method for improving the flatness of a formed plating layer. 7. Using a laser plating apparatus according to claim 5, an output beam from a laser oscillator is focused on a metal or polymer surface brought into contact with an electroless plating solution to flatten a plating layer to be formed. Laser plating method to improve the degree.