RU2405229C2 - Solid-state device package - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: proposed package comprises ceramic base with refractory metal layer deposited in vacuum thereon, 1.5-2.0 mcm-thick nickel layer and 1.5-2.0 mcm-thick gold layer: device output terminals and flange being soldered on said layers, while 3-4 mcm-thick load coat is applied on soldered package in one layer without interlayer.

EFFECT: lower heat resistance and higher reliability of high-power transistors.

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Description

The invention relates to the field of semiconductor electronics and is intended for the production of housings of powerful bipolar and field RF and microwave transistors.

One of the main requirements for high-power transistor housings operating in extreme heat conditions is to ensure the minimum value of the transition-case thermal resistance.

A typical housing design for a high-power RF and microwave transistor includes a metallized ceramic crystal holder (base), a heat sink (flange), and strip leads. As the ceramic base, ceramics based on beryllium oxide are used, which has one of the highest thermal conductivity values in a number of known insulating materials. On ceramics there are metallized platforms for planting a semiconductor crystal and soldering strip terminals. The reverse side of the ceramic is also coated with metallization for soldering to the heat sink [1].

In the production of microwave transistors, the crystal is mounted on a ceramic base by contact reactive soldering with the formation of a gold-silicon eutectic alloy, therefore high quality requirements are imposed on the quality of the metallized coating with respect to the surface cleanliness class. A metallized surface is created either by vacuum deposition of refractory metals with the subsequent formation of a precision photolithographic pattern [1], or a metallized pattern is created by the silk-screen printing method [1, 2].

The technology for manufacturing a ceramic base using the vacuum deposition of refractory metals (niobium, titanium, tungsten, molybdenum) is more preferable, since it is possible to create a high surface quality with a smaller thickness of the metal layer, which reduces the thermal resistance of crystal-case transistors by 20-30%. However, subsequent housing assembly processes can minimize the benefits achieved by using the vacuum deposition of metals on ceramics. Therefore, improving the design of the housings and the technology of their manufacture, providing a reduction in the thermal resistance of high-power RF and microwave transistors, is an urgent technical solution.

Known methods of assembly of the case, in which metallization of refractory metals deposited on a ceramic base, is coated with a layer of nickel to improve the further spreading of silver or solder based on it, as a rule PSR-72 [2]. PSr-72 solder or pure silver is applied by high-temperature treatment (approximately 900-1000 ° C) in a hydrogen medium to the entire metallization surface, and then the leads and flange are soldered also in a hydrogen medium. Maintenance (silvering) of the metallization surface is carried out either before soldering, or in the same process with soldering, depending on the design of the housing. This technological technique is used in order to obtain a high-quality gold coating in the future - without peeling and swelling, since after soldering the body it is layered: nickel 1 μm, gold 0.5 μm, palladium 0.5 μm, gold 3 μm ( H.1. Evil. 0.5 Pd. 0.5 Evil. 3) [1].

However, the above manufacturing technology of the case cannot guarantee high quality soldering of silicon crystals on the ceramic base by the thermosetting method with the formation of the Au-Si eutectic alloy, since diffusion-oxidation processes occur in the metal layers at a temperature of soldering 420-430 ° С, which lead to the formation of intermetallic compounds [1]. Intermetallic compounds significantly degrade the quality of the crystal-to-case connection, thereby increasing the thermal resistance of transistors. Intermetallic compounds are formed not only due to the multilayer coating, but also due to the presence of silver, copper and nickel in the eutectic layer. Copper is a component of PSr-72 solder. In addition, when coating by the galvanic method, there is a tendency to reduce its thickness from the periphery to the center, in connection with which it is necessary to increase the total thickness of the gold coating or use a gold gasket so that there is an amount of gold in functionally important areas, namely, at the crystal landing sites. sufficient to form a eutectic alloy. A significant drawback of the standard technology is the lack of reproducibility of the quality of the metallized surface of the ceramic base due to the uncontrollability of the crystallization process of PSR-72 solder during cooling of the ceramic assembly after the brazing process. Therefore, the formation of the crystallographic structure of the solder layer and, accordingly, its properties cannot be technologically controlled.

The best results can be obtained by using a housing design in which layers of titanium and molybdenum are successively applied to a ceramic base [3]. However, in this case, during the subsequent technological process of assembling the housings, which does not differ from the above, the same negative processes occur during the installation of crystals on a eutectic.

The technical effect of the present invention is to reduce the thermal resistance of high-power RF and microwave transistors, increase their reliability during operation, and also increase the percentage of output during their production.

The technical effect is achieved due to the fact that a layer of gold with a thickness of at least 1 μm is deposited on a ceramic base with successive layers of refractory metals and nickel. After applying a gold coating to the ceramic base, the terminals and flange are soldered to it in a hydrogen medium, and then the gold-plated brazed body is coated to the required thickness, and gold is applied without preliminary undercoats.

Preliminary gilding of the ceramic base before high-temperature soldering of the case allows you to fully realize the advantages of the method of deposition of metals by condensation in vacuum and thereby significantly reduce the thermal resistance of transistors, and therefore increase their reliability. This is done, firstly, by eliminating the multilayer coating that is applied after soldering the housing; secondly, due to the exclusion of the conditions for the formation of intermetallic compounds, both due to the absence of silver and copper on the metallization surface, and because gold is burned during soldering of the case and forms a reliable barrier layer for nickel diffusion.

The proposed housing design and its manufacturing technology provide high quality installation of crystals in the housing. In addition, the complexity of the production of cases decreases, the consumption of gold for non-functional sections of the case decreases, the percentage of output increases due to the reproducibility of the quality of the metallized surface.

An example of a specific implementation of the invention

The design and assembly technology described above are carried out as follows. Layers of refractory metals are successively applied to the ceramic base by vacuum deposition, then nickel 1.5–2 μm thick is applied, and then a gold layer 1.5–2.0 μm thick is applied. Then the leads and flange are soldered to the gold-plated metallized sections of the ceramic base with PSr-72 solder in a hydrogen medium. Further, depending on the technological requirements and the thickness of the preliminary gold coating of the ceramic base, gilding of the soldered case to a thickness of 3–4 μm is performed (Zl. 3; Zl. 4).

For comparison, the table shows the results of a study of thermal resistance for the first ten samples of transistors made according to standard technology and transistors made in a new structural and technological solution of the housing.

No. p / p The values of thermal resistance, ° C / W Typical design, standard technology Suggested design and technology one 1.19 0.91 2 1.19 0.91 3 1,0 0.91 four 0.94 0.88 5 0.97 0.88 6 1,0 0.91 7 1.19 0.88 8 0.94 0.91 9 1.19 0.88 10 1,0 0.88 Absolute value spread 26% 3%

From the experimental data presented, it can be seen that the proposed design of the ceramic base and the corresponding manufacturing technology of the housing can reduce the thermal resistance of transistors by an average of more than 15%. At the same time, the variation in the values of thermal resistance is significantly reduced from 26% for the standard case design to 3% with the new design and technological option. The proposed design of the case and, accordingly, the technology of its manufacture not only significantly increase the operational reliability of products, but also due to the reproducibility of the process, increase the percentage of suitable products in production.

Literature

1. Sidorov V.A. Features of the design and manufacturing technology of microwave enclosures of semiconductor devices. Electronic equipment. Series 2. Semiconductor devices, 2005, issue 1-2, pp. 117-124.

2. Gladkov A.S. and others. Soldering parts of vacuum equipment. M .: Energy, 1967, p. 213-214.

3. A.S. USSR No. 758972. The body of a semiconductor device. Onuprienko F.G., Sidorov V.A., Pospelov A.N., Mitin BC, Dikovsky V.I., MKI ⁵ H01L 23/02, 04/28/1980.

Claims (1)

The case of a semiconductor device containing a ceramic base with layers of refractory materials, a nickel layer 1.5–2.0 μm thick and a gold layer 1.5–2.0 μm thick, successively applied to it and a flange, and on a soldered case in one layer without a sublayer a gold coating 3-4 microns thick is applied.