JPH0985473A - Laser heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a large area to be heated uniformly by driving a semiconductor laser through a continuously changed driving current and thereby emitting a laser beam. SOLUTION: The laser heating device is constituted of a high output semiconductor laser 4 and a modulation circuit for modulating a current to drive the semiconductor laser 4. The semiconductor laser 4 is a gain waveguide type semiconductor laser having a quantum well structure or a DH(double heterostructure) structure, and is a semiconductor laser (broad stripe laser) with a wide stripe width. As a result, uniform heating is possible for a large area at one time using a linear beam characteristic. In addition, in a semiconductor laser with a large distribution of NFP(noise figure power) unsuitable for linear heating, NFP can be improved so that the laser is used as a light source for a laser heating device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser heating device used in, for example, a laser soldering device.

[0002]

2. Description of the Related Art In response to recent technological advances in integrated circuits and the like, the range in which laser heating devices are used is expanding as electronic parts are mounted on printed circuit boards with higher densities and hybrids.

Actually, there is an increasing tendency for surface mounting of electronic components on a substrate, automation of component mounting is demanded, there are cases where components having heat resistance problems coexist, or Due to the progress of miniaturization, the usefulness of this type of laser heating device is drawing attention.

On the other hand, as a completely different method of use, the field of application of the laser heating device is expanding to the field of selective film growth by local heating and surface modification such as phase control of crystals.

As a laser heating device used in such a field, a YAG (Yttrium Alminium Garnet) has hitherto been used.
) Lasers are mainly used. Then, as a method of heating an object using such a laser heating device, some optical methods are adopted. The main ones are a spot moving method, a linear beam irradiation method, and a scanning method.

Among these methods, the spot moving method is
This method has been used since ancient times and is the most general method. In this method, for example, when heating and joining the objects, the output lens unit of the optical fiber is gripped by the robot arm, and the laser spot is moved by this to heat the joining portion to be heated. is there. This method has a simple structure and can be said to be an inexpensive method compared to other methods.

The linear beam irradiation method is a method in which a circular spot-shaped laser beam is converted into a linear laser beam by using a cylindrical lens to widely heat the joint portion to be heated.

The scanning method is a method in which a linear beam having a uniform temperature distribution is supplied to a joint portion to be heated by reciprocally scanning a laser beam with a galvanometer. This system is characterized in that the length and temperature distribution of the linear beam can be changed by controlling the scanner motor (see "Laser Processing" edited by the Laser Society of 1990).

[0009]

However, among the heating methods using such a laser heating device, in the linear beam irradiation method, a circular spot laser beam is formed into a linear beam by a cylindrical lens. ing. Therefore, since the circular laser beam is optically crushed into a linear shape, the energy density at the central portion of the linear beam becomes higher than the energy density at both ends, and the light intensity in the length direction is not uniform. Occurs. This is a very important problem when performing laser heating.

To give a concrete example, FPIC (Flat Plat
In ackage ICs), the uniformity of heating characteristics at each joint is reflected in the quality as the number of pins increases and the pin pitch becomes narrower. Therefore, the uniformity of the light intensity in this length direction is important.

By the way, recently, due to the development of a high-power semiconductor laser, its output power has been dramatically increased.
The output of one element is about 1 to 3 W, and a laser of several 10 to 100 W or more has been developed by forming an array or stacking, and it has been used as a substitute for the YAG laser.

As such a high-power semiconductor laser,
At present, a semiconductor laser with a wide stripe width (hereinafter referred to as "broad stripe laser") is most often used among the gain waveguide type semiconductor lasers of the quantum well structure or the DH (double hetero) structure. This broad-stripe laser has a linear beam profile of several hundred microns due to its electrode structure. Therefore, it is not necessary to use a cylindrical lens or the like, and it is attracting attention because it can be used as a device that replaces the laser heating device of the linear beam irradiation method using the YAG laser described above.

In heating using a high-power semiconductor laser, a laser beam is irradiated through a lens to a portion that needs to be heated. At this time, the light intensity of the irradiated portion is the light intensity distribution ( Hereinafter, this is referred to as a "near field image" or "NFP: Near Field Pattern". Therefore, to provide uniform heating, the NFP is required to be uniform over the entire stripe.

However, in general, the NFP of a broad-stripe laser becomes non-uniform due to mode competition during oscillation when trying to obtain a high output, and it is difficult to use it as it is in the above laser heating device.

Since the NFP changes with time, it may become unsuitable for the laser heating device before the life of the semiconductor laser is reached, due to long-term driving. This leads to an increase in cost because the laser replacement time is shortened.

The present invention has been made in consideration of such circumstances, and a uniform NFP is obtained over all stripes by driving a semiconductor laser with a current that is continuously changed. A laser heating device capable of uniformly heating an area is provided.

[0017]

In a high-power semiconductor laser having a general structure, an inherent transverse mode (distribution of electric field of light parallel to the junction surface) is determined according to changes in drive current and light output. Utilizing this, in the present invention, the NFP is made uniform by continuously changing the drive current.

That is, according to the present invention, a modulation circuit that continuously changes and outputs a drive current for continuous oscillation required to obtain a desired light output, and a drive current output from the modulation circuit are received. It is a laser heating device including a semiconductor laser that emits light.

In the present invention, the modulation circuit may be of any type as long as it can continuously change and output the drive current for continuous oscillation required to obtain a desired light output, and it is the simplest. Various modulation circuits can be used, such as a combination of a resistance circuit and a switching element for switching the resistance circuit, or a structure satisfying a functional expression represented by y = f (x). .

The above-mentioned continuous oscillation drive current required to obtain a desired optical output is a threshold value or more and a continuous value at which a desired optical output can be obtained by continuously oscillating a semiconductor laser. The drive current may have any value as long as it is a direct current equal to or lower than the limit current at which oscillation is possible.

By modulating the drive current by the modulation circuit, the drive current is continuously changed. For example,
As the continuously changed drive current, various currents such as an analogly modulated current and a pulse driven current can be applied. That is, as the drive current, those having various waveforms such as a sine wave, a triangular wave, and a rectangular wave can be applied.

As the semiconductor laser which receives the drive current output from the modulation circuit and generates light, any high-output type semiconductor laser capable of laser heating can be used. As such a high-power semiconductor laser, a broad-stripe laser having a wide stripe width is most often used among the gain-guided semiconductor lasers having a quantum well structure and a DH (double hetero) structure.

According to the present invention, the modulator circuit continuously changes the drive current for continuous oscillation required to obtain a desired optical output, and the semiconductor laser is driven by the continuously changed drive current. It is driven and laser light is output.

Therefore, the transverse mode of the semiconductor laser is continuously changed by modulating and continuously changing the drive current, so that the time-average (average of one cycle) NF is obtained.
P is averaged compared to CW drive (continuous oscillation drive),
Linear heating with a uniform temperature distribution is possible.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. The present invention is not limited to this.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the laser heating apparatus of the present invention. In this figure, 1 is a DC power source, 2 is a high frequency generator, 3 is a coaxial cable, R is a resistor, C is a capacitor, L is a coil, D is a diode, and 4
Is a high power semiconductor laser.

The coaxial cable 3 is for 50 Ω,
The resistance R is 47 Ω. The high-power semiconductor laser 4 is a gain waveguide type semiconductor laser having a quantum well structure or a DH (double hetero) structure, and a semiconductor laser having a wide stripe width (broad stripe laser) is used. As this broad stripe laser, a conventionally known one can be used.

As shown in this figure, the laser heating apparatus of the present invention comprises a high power semiconductor laser 4 and a modulation circuit for modulating the current for driving the high power semiconductor laser 4.

FIGS. 2A and 2B are explanatory views showing an example of the structure of a high-power semiconductor laser. (A) is a plan view and (b) is a side view. In these figures, 11 is a stripe, 12 is a P-side electrode, 13 is a high-reflection coating, 14 is a low-reflection coating, 15 is an n-side electrode, 16 is a substrate crystal made of n-GaAs (gallium arsenide),
Reference numeral 17 is a clad layer made of n-AlGaAs (aluminum gallium arsenide), 18 is an n-type or P-type active layer, 19 is a p-AlGaAs clad layer, 2
0 is a cap layer made of p-GaAs, 21 is Al ₂ O
_A current confinement layer made of ₃ or n-GaAs, and 22 is a light emitting region.

The laser light emitting region 22 is a current injection region corresponding to the portion of the stripe 11 in the central portion of the active layer 18, and the laser light is irradiated in the direction of the arrow shown in FIG. In this way, a laser gain is generated in the current injection region of the active layer 18 and laser oscillation occurs, so that the light intensity distribution at almost this portion is the light intensity distribution (N
FP).

FIG. 3 is a timing chart showing the waveform of the modulated drive current. In this figure, the solid line is CW
The current waveform when driving (continuous oscillation driving) to obtain a desired optical output is shown. The broken line shows the current waveform when the current during CW driving is modulated into a rectangular wave. The modulation current is a current that is continuously changed from the bias current to the peak current, and the high-power semiconductor laser 4 is pulse-driven by the current of the modulated pulse wave.

In this modulation, modulation is performed so that the average value of the modulation current for pulse driving becomes the same value as the current value for CW driving. By pulse-driving the high-power semiconductor laser 4 with the modulation current having such an average value, the same optical output as that in CW driving can be obtained by pulse driving.

The frequency, duty ratio, amplitude, etc. of this modulation current can be set arbitrarily. However, with respect to the frequency of the drive current, when the frequency is set to 500 kHz or less, the NFP changes to the same extent as during CW drive, and no improvement is seen. Also, 3MHz
Even if the frequency is set to the above, the degree of improvement of NFP is the same as the case of 3 MHz or less. Moreover, if the frequency is set to 3 MHz or higher, a complicated circuit is required, driving is difficult, and transmission loss increases. Therefore, the frequency of pulse driving may be 500 kHz to 3 MHz, and preferably 1 MHz to 3 MHz.

In this modulation, the average value is CW.
The amplitude and the duty ratio can be set to arbitrary values as long as the modulation has the same current value as during driving.
However, as a matter of course, it is necessary that the bias current is equal to or higher than the threshold value capable of emitting light and the peak current is equal to or lower than the application limit current value.

FIG. 4 is a comparative example of the present invention and is a graph showing NFP when a high power semiconductor laser is driven by CW. (A) shows NFP in a direction parallel to the joint surface,
(B) shows NFP in a direction perpendicular to the joint surface. These figures show the NFP when a semiconductor laser is CW-driven with a drive current of 1.6 A and an optical output of about 0.8 to 1 W is obtained.
Is shown.

Although it depends on the structure of the semiconductor laser, when it is driven at a current slightly higher than the threshold value, the laser light normally emits in a lateral mode in the form of a fine filament.
The NFP is relatively uniform over the entire light emitting region 22. However, as the light output is further increased, several peaks become prominent due to mode integration and competition.

When the semiconductor laser is used as the light source of the laser heating device, the light output must be large. However, when the optical output is increased and CW driving is performed,
As shown in (a), the groove between peaks and NF
It often happens that the shoulder of P is depressed to about 50% of the maximum strength. The same thing occurs when the output is increased up to about 3W. This is a fatal problem when used as a light source of a laser heating device. On the other hand, in the case of pulse driving as in the present invention, even if the light output is increased, the NFP does not have a groove or a depression.

FIG. 5 is a graph showing NFP when a high-power semiconductor laser is pulse-driven, (a) showing NFP in a direction parallel to the joint surface, and (b) showing NFP in a direction perpendicular to the joint surface. Is shown. In these figures, the semiconductor laser is pulse-driven to the same 0.8-1 W as the above CW driving.
It shows NFP when a light output of a certain degree is obtained.

The drive current is a peak current of 2.6 A and a bias current of 0.6 A. The pulse width is 200 ns.
The duty ratio is 50%. Therefore, the average drive current is 1.6 A, which is the same value as the current value during the CW drive.

In this way, the NFP can be improved by switching the drive current from CW drive to pulse drive. In this figure, the fluctuation of NFP is improved to 70 to 80% or more, which is a level that can be used as a light source of a laser heating device.

Such a laser heating device can be used as a laser soldering device, for heating a bonding portion of an FPIC (Flat Package IC), for heating for surface modification of crystal phase control, and the like.

In this embodiment, the pulse waveform of the drive current is rectangular, but the same effect can be obtained by replacing it with a sine wave or a triangular wave instead of a rectangle. Also, by changing the frequency, duty ratio, amplitude, etc., N
It is possible to improve FP.

[0043]

According to the present invention, the semiconductor laser is driven to emit the laser beam by the continuously changed drive current. Therefore, if the linear beam characteristic is utilized, Uniform heating of a large area is possible. Further, even for a semiconductor laser having a large NFP distribution which is not suitable for linear heating, it is possible to improve the NFP, so that it can be used as a light source of a laser heating device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a laser heating device of the present invention.

FIG. 2 is an explanatory diagram showing an example of the configuration of the high-power semiconductor laser of the present invention.

FIG. 3 is a timing chart showing a waveform of a modulated drive current according to the present invention.

FIG. 4 is an NF when a high power semiconductor laser is driven by CW.
It is a graph which shows P.

FIG. 5 shows N when a high power semiconductor laser is pulse-driven.
It is a graph which shows FP.

[Explanation of symbols]

 1 DC power supply 2 High frequency generator 3 Coaxial cable 4 High power semiconductor laser C capacitor D diode L coil R resistance

Claims (1)

[Claims] 1. A modulation circuit for continuously changing and outputting a drive current for continuous oscillation required for obtaining a desired light output, and generating a light by receiving a drive current output from the modulation circuit. A laser heating device consisting of a semiconductor laser.