JPH02247076A - Laser beam soldering device - Google Patents

Abstract

PURPOSE:To solder joining parts of electronic parts on the surface to be stuck at a time and to efficiently perform welding in a short time by forming a laser beam to be projected into a prescribed shape where the energy density is almost uniform and the joining parts of the electronic parts are almost covered. CONSTITUTION:A hole 18a having a square cross section through which the laser beam is passed is formed on the center of a calite scope 18 and the laser beam made incident from one end of the hole 18a is reflected multiply by the inner wall surface 18b. The emitted laser beam has an almost uniform energy distribution and its cross section is made to the same square shape as the hole 18a. A substrate 2 is irradiated via a mask 22 with the laser beam having the uniform energy which is emitted from the calite scope 18 and condensed by combined lenses 20. Soldering paste under each lead terminal 6 is molten and all of the lead terminal 6 are soldered and joined on the substrate 2 at the almost same time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a laser soldering device that heats the bonded portion of an electronic component by irradiating it with laser light and solders it to a mounting surface.

2. Description of the Related Art In recent years, as electronic components have become smaller and mounted on substrates with higher density, electronic components are increasingly being mounted using a surface mounting method. The surface mounting method is a method in which electronic components are mounted on solder paste printed on a board in advance and then reflowed all at once to mount the electronic components.

In this way, the surface mount method is a mounting method suitable for high-density mounting of miniaturized electronic components on a board, but when mounting on both sides of the board, it can only be used for mounting on one side; For mounting on this surface, it is necessary to use a local heating method to avoid damaging the joints of the mounted electronic components. Furthermore, there are some electronic components that absolutely need to be mounted after reflow, and such electronic components also need to be mounted using a local heating method.

There are several local heating methods, but the method of local heating by irradiating laser light with a laser soldering device is easy to automate as it can heat without contact, and can heat the board and mounting board sufficiently in a short time. This is an extremely effective method as there is little effect of heat on the finished electronic components.

[Prior Art] A soldering method using a conventional laser soldering device will be described with reference to FIG.

First, solder paste 52 is printed on the board 50 in advance.
A lead terminal 56, which is a joint portion of the electronic component 54, is arranged above. Laser light emitted from a laser light source 62 in a laser soldering device 60 is focused by a condensing lens 64 and irradiated onto a lead terminal 56 to be soldered. Then, the solder paste 52 is melted by the laser beam, and the lead terminals 56 are soldered to the substrate.

[Problems to be Solved by the Invention] As described above, in the conventional laser soldering device 60, the laser beam that irradiates the joint is focused and locally heated, and the lead terminals 56 are soldered one by one. Ta. In order to increase the efficiency of soldering, it is possible to increase the diameter of the laser beam and heat the multiple lead terminals 56, but the energy distribution of the laser beam is uneven, and the center is strong and the periphery is weak, so it is difficult to bond. It was not possible to apply sufficient energy to a plurality of lead terminals 56 at the same time, and the only way to do so was to condense laser light and locally heat the lead terminals 56 one by one to solder them, which was inefficient.

For this reason, optical fibers have been used to separate the laser beams, but the use of four to five optical fibers is the limit. Furthermore, since the energy of the laser beam irradiated by the optical fiber is attenuated, it takes time to perform each soldering joint, and the efficiency has not increased dramatically. Another problem was that a large and expensive device was required to separate the laser beams.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a laser soldering device that can efficiently solder electronic components in a short time using laser light.

[Means for Solving the Problems] The above object is to provide a laser soldering device that heats the bonded part of an electronic component by irradiating it with a laser beam and solders it to a surface to be mounted. A laser beam shaping means is provided for forming a laser beam into a predetermined shape that is substantially uniform and substantially covers the bonded portion of the electronic component, and the bonded portion of the electronic component is soldered to the surface to be bonded by the laser beam. This is achieved by a laser soldering device characterized by the following.

[Function] According to the present invention, the laser beam to be irradiated is shaped into a predetermined shape that has a substantially uniform energy density and almost covers the joints of the electronic components, so that it does not cover the joints of the electronic components at once. Can be soldered to the adhesive surface.

[Embodiment] FIG. 1 shows a laser soldering apparatus according to an embodiment of the present invention.

The laser soldering device 10 performs soldering by irradiating a laser beam onto a lead terminal 6, which is a joint portion of an electronic component 4 placed on a substrate 2.

Laser light is emitted from the laser light source 12. The laser light source 12 of this embodiment is a pulsed Nd-YAG laser.

The laser beam is processed by an optical system housed within the lens barrel 13. This optical system includes a combination lens 14, 16, a kaleidoscope 18, a combination lens 20, and a mask 22.

The combination lens 14 diffuses the laser light from the laser light source 12 and makes it incident on the next combination lens 16 . The combination lens 16 condenses the incident laser light and makes it enter the kaleidoscope 18 .

FIG. 2 shows a kaleidoscope 18 as a laser beam shaping means, which is a characteristic structure of this embodiment. Figure 2 (a
) is a front view of the kaleidoscope 18, and (b) is a plan view. As shown in FIG.
is formed, and the inner wall surface 18b of this hole 18a is made into a mirror surface by, for example, gold plating. Laser light incident from one end of the hole 18a is multiple-reflected by the inner wall surface 18b. When a laser beam having an energy distribution is multiple reflected within the kaleidoscope 18, the energy distribution is averaged,
As shown in FIG. 3, the emitted laser beam has a generally uniform energy distribution, although there are minute irregularities, and has a square cross section similar to the hole 18a.

Note that in order to prevent the kaleidoscope 18 from overheating, cooling water is circulated within the cooling pipe 19 to cool it.

A uniform energy laser beam emitted from the kaleidoscope 18 is focused by a combination lens 20 and irradiated onto the substrate 2 through a mask 22 .

The mask 22 is used to irradiate the laser beam only to the lead terminals 6, which are the bonding portions of the electronic components 4 to be bonded, and to block other areas. In this example, it was made of Kovar.

When the electronic component 4 is a flat package with lead terminals 6 on four sides as shown in FIG. 1(b),
The mask 22 may have a hole 22a corresponding to each lead terminal 6 as shown in FIG. 4(a), or may have a shape that covers a plurality of lead terminals 6 as shown in FIG. 4(b). A hole 22b may be formed.

Note that a gas inlet 13a is provided at the bottom of the lens barrel 13, and an inert gas such as Ar is applied to the joint portion to prevent the lead terminals 6 and the substrate 2 from deteriorating due to heating.

Next, a soldering method using the laser soldering apparatus of this embodiment will be explained.

First, solder paste is printed on the board 2 in advance. Lead terminals 56, which are the joints of electronic components 54, are placed on the printed solder paste.

Next, while introducing Ar gas into the lens barrel 13 through the gas inlet 13a, the laser light source 12 irradiates the joint with a laser beam.

By irradiating the laser beam, the solder paste under each lead terminal 6 melts, and all the lead terminals 6 are attached to the board 2 almost simultaneously.
It is joined by soldering.

In this embodiment, flux-cored 5n-Pb eutectic solder paste is used as the solder paste, and the laser light source 12
The laser irradiation conditions were: pulse width 1mS, average output 400
W, pulse ray) 140 pps, irradiation time 0.5 seconds, Ar gas introduction conditions were gas pressure 1.5 kg/cm2,
Assuming a gas flow rate of 30j/min, the number of 10mm square terminals is 6.
An electronic component 4, which is a 4-pin flat package LSI element, was bonded to a glass epoxy substrate 2.

After laser soldering, the solder joints were observed under a microscope and it was confirmed that all the joints were well bonded. In addition, when measuring the electrical characteristics of the LSI element, no change in characteristics was observed before and after bonding, and
It was found that the solder joints were electrically connected reliably.

The present invention is not limited to the above-mentioned embodiments, and various modifications are possible.

For example, the cross-sectional shape of the kaleidoscope hole in the above example was square, but if it is to be shaped into a laser beam with almost uniform energy density, it can be shaped into a rectangle, triangle, polygon, or even circle or ellipse. It can be of any shape.

Furthermore, in the above embodiment, the area other than the joint of the electronic component was shielded by the mask, but if the electronic component is a package that does not deform due to heat, such as a ceramic package, the laser beam can be transmitted without being shielded by the mask. It may be irradiated as is.

Furthermore, the laser soldering apparatus of the present invention can be used for soldering and joining electronic components without lead terminals, such as chip carriers.

The beam was shaped into a predetermined shape that had a nearly uniform energy density and almost covered the joints of the electronic components.
- The joint part of the electronic component can be soldered to the surface to be bonded in one step, and the electronic component can be soldered efficiently and in a short time.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a laser soldering device according to an embodiment of the present invention, Fig. 2 is a diagram showing a kaleidoscope in the same laser soldering device, and Fig. 3 is a diagram showing the energy of a laser beam in the same laser soldering device. A graph showing the distribution, FIG. 4 is a diagram showing a mask of the same laser soldering apparatus, and FIG. 5 is a diagram showing a conventional laser soldering apparatus. [Effects of the Invention] As described above, according to the present invention, in the irradiating laser diagram, 2... Board 4... Electronic component 6... Lead terminal 10... Laser soldering device 12... Laser Light source 13... Lens barrel, 13a... Gas inlet 14.16.20... Combination lens 18... Kaleidoscope 19... Cooling pipe 22... Mask 50... Substrate 52. ... Solder paste 54 ... Electronic component 56 ... Lead terminal 60 ... Laser soldering device 62 ... Laser light source 64 ... Condenser lens

Claims (2)

[Claims] 1. In a laser soldering device that heats the bonded portion of an electronic component by irradiating it with a laser beam and solders it to the surface to be mounted, the laser beam is applied to the bonded portion of the electronic component with a substantially uniform energy density. 1. A laser soldering apparatus, comprising: a laser beam shaping means for shaping a laser beam into a predetermined shape that substantially covers the soldering surface; 2. 2. The laser soldering apparatus according to claim 1, further comprising a mask means for shielding a region other than a joint portion of the electronic component from the laser beam shaped by the beam shaping means.