JPS6325501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an aluminum package that is lightweight and has excellent hermetic sealing properties, on which a semiconductor circuit such as a microwave GaAsFET can be mounted.

(2) Conventional technology and problems Conventional microwave packages are manufactured from iron-based materials, mainly stainless steel, in order to mount the microwave GaAsFETs and the like mentioned above. However, when such a package is mounted on an aircraft, problems arise in terms of both weight and thermal conductivity. First, stainless steel is heavy, so it cannot meet the recent demands for weight reduction in such packages, and its poor thermal conductivity makes it difficult for high-power amplifiers to generate heat inside the package. often damage circuit elements.

Attempts have also been made to use aluminum instead of stainless steel for package cages. In this case, the thermal conductivity is good, so the heat dissipation is also good.
Although the advantages of aluminum, such as light weight and excellent workability, can be taken advantage of, new problems arise in terms of hermetic sealability. The conclusion is that cracks occur in the weld bead between the case and cover of the aluminum package, making it impossible to make the package completely airtight.

It is well known that when sealing a circuit board or a package on which elements are mounted, care must be taken to avoid thermal deterioration of the elements. for that,
Sealing methods such as brazing, which require exposing the entire aluminum package to high temperatures, cannot be used here. Although it is possible to employ a welding method that locally heats the package, ordinary welding methods cannot be used. This is because aluminum, which has very good thermal conductivity, is selected as the package material, and therefore heat dissipation is too great to carry out welding. In the end, the current situation is that we have to rely on welding methods using pulsed lasers. However, even if the package is sealed by this method, the good thermal conductivity of aluminum causes the weld to cool down extremely quickly, causing cracks to form in the weld bead.
It becomes impossible to keep the package airtight. It has been found that such cracks occur not only when pure aluminum is used as the package material, but also when aluminum alloys with excellent corrosion resistance, such as Al-Mg, are used. There is.

(3) Object of the Invention As is clear from the above description, a drawback inherent to the conventional aluminum package is poor airtight sealability. An object of the present invention is to dramatically improve the hermetic sealability of an aluminum package without changing the basic idea of performing hermetic sealing welding of an aluminum package using a pulsed laser.

(4) Structure of the Invention The present inventors have recently discovered that when an aluminum package is hermetically sealed by laser welding, at least one of the case and the cover of the package is made of a casting aluminum alloy containing Si (silicon). It has been found that by doing so, it is possible to avoid the occurrence of cracks in the weld bead.

According to a preferred embodiment of the present invention, only the case is made of aluminum alloy for casting, particularly Al-Si.
It is advantageous to use a casting aluminum alloy (for example, JIS 4047). This is because, for example, when casting is performed using a die-casting method, the advantages of the casting, that is, the aluminum alloy for casting, can be further utilized by manufacturing the case by casting, which has a more complicated shape than the cover.

When one of the case and its cover is made of cast aluminum alloy, the other member is made of pure aluminum (e.g. 1100 specified by JIS) or corrosion-resistant aluminum alloy (e.g. 5052 specified by JIS). be able to. Such combinations will depend on various factors such as the desired hermetic seal, the intended use of the package, etc.

Casting aluminum alloys containing Si that are useful in the present invention include, in addition to the above-mentioned Al-Si alloys, Al-Cu-Si alloys, Al-Si-Mg alloys,
Al-Si-Cu alloy, Al-Si-Mg-Cu alloy,
Al-Si-Cu-Ni-Mg alloy, Al-Si-Cu-Mg
Examples include alloys. All of these alloys are compatible with other Si-free casting aluminum alloys (e.g. Al-Cu alloys, Al-Cu-Ni-
On the other hand, the eutectic structure of Al-Si can be crystallized by the rapid cooling effect during welding. It is possible to perform laser welding because the welded part can be strengthened.

(5) Embodiments of the Invention The aluminum package of the present invention will be described with reference to the attached drawings.

FIG. 1 shows the case and cover of an aluminum package according to the invention before hermetic welding. In the illustrated case, the cover 1 is made of pure aluminum 1100, and the case 2 is made of Al-Si cast aluminum alloy 4047. The case 2 further has input/output terminals 3, and is also equipped with a circuit board and elements, although not shown. If the case 2 is manufactured by casting as shown in the figure, the manufacturing cost will be approximately one-third of that of manufacturing it by machining it from a block of corrosion-resistant aluminum alloy 5052 or the like.
It can be suppressed up to. Furthermore, aluminum alloys for casting such as 4047 have good melt flow and high strength at high temperatures, so they do not cause any cracks even when cooled quickly.

FIG. 2 is a conceptual diagram showing a state in which the aluminum package of the present invention is hermetically sealed by laser welding. As shown in the figure, a laser beam from a laser oscillator 4 is focused by a lens system 5 and irradiated onto a sealing portion 6 of an aluminum package.
This laser beam irradiation is preferably carried out in an atmosphere of an inert gas such as nitrogen or argon. Here, the average output is 200W, the pulse width is 4m・sec, the pulse rate is 15pps, and the welding speed is 4.
Laser welding was performed using the conditions of mm/sec and beam diameter of 0.1 mm. When welding is performed by irradiating the sealing part 6 with a laser beam as shown in the figure, the case 2 and the cover 1 are locally heated and melted, but the flow and wettability of the casting alloy 4047, which is the material of the case, is Since the weld bead had a good temperature and was not easily affected by the cooling rate, stable hermetic sealing was possible without any cracks occurring at the weld bead. When the hermetically sealed aluminum package according to the present invention was examined using a helium leak detector, it was found that it had a high airtightness of 10 ^-10 atm.cc/s or more, which was no problem for practical use.

(6) Effects of the Invention According to the present invention, a lightweight, stable, and highly hermetically sealed microwave aluminum package can be provided at low cost. Furthermore, this package can be equipped with high-power devices because the material that makes up the package has excellent heat dissipation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an aluminum package according to the present invention in a state before hermetic sealing welding, and FIG. 2 is a conceptual diagram showing a state in which the aluminum package according to the present invention is hermetically sealed by laser welding. It is. In the figure, 1 represents a cover, 2 a case, 3 an input/output terminal, 4 a laser oscillator, 5 a lens system, and 6 a sealing part.

Claims (1)

[Claims] 1. An aluminum package characterized in that at least one of the case and its cover is made of a cast aluminum alloy containing silicon, and these members are hermetically sealed by laser welding.