1. Field of the Invention
The present invention relates to a plate type member consisting of a copper-tungsten and/or molybdenum alloy which is applied to a package for a semiconductor device, a method of manufacturing the same, and a package for a semiconductor device employing the plate type member.
2. Description of the Background Art
As integrated circuits and high frequency/high output transistors are implemented with higher density of integration and higher outputs, power consumption is increased year by year, while the sizes and heating values of semiconductor devices employed therefor are also increased in response. Following such circumstances, packages for housing the semiconductor devices are increased in size, while members such as substrates for mounting the semiconductor devices and radiating plates having excellent heat radiation properties are required for the packages.
In general, a copper-tungsten, copper-molybdenum or copper-tungsten-molybdenum alloy (hereinafter referred to as a copper-tungsten and/or molybdenum alloy) having an excellent heat radiation property is employed as the material for a substrate serving as a member for a semiconductor device package for improving its heat radiation property and the thermal expansion coefficient of the substrate is matched with those of a ceramic member and a semiconductor chip, thereby obtaining a highly reliable package, as described in Japanese Patent Laying-Open No. 59-21032 (1984) (corresponding to U.S. Pat. No. 4,680,618) or 59-46050 (1984).
Such a copper-tungsten and/or molybdenum alloy is prepared by an infiltration method of adding copper powder to tungsten powder and/or molybdenum powder as needed, sintering the mixture and infiltrating copper in the obtained skeleton, or a sintering method of sintering a compact of copper powder and tungsten powder and/or molybdenum powder. In order to suppress structural defects such as blowholes, an iron family metal may be added by 0.02 to 2 percent by weight in the infiltration method or within 8 percent by weight in the sintering method.
In case of integrating a plate type member consisting of the aforementioned copper-tungsten and/or molybdenum alloy into a package for a semiconductor device, brazing is generally performed for bonding the member to a ceramic member serving as a counterpart. In advance of this brazing, nickel plating such as electrolytic nickel plating and/or electroless nickel-phosphorus plating, electroless nickel-boron plating or the like is performed on the plate type member for improving the brazing property and corrosion resistance and forming an underlayer for gold plating etc. which may be performed in a later step. The electrolytic nickel plating may be performed with addition of a metal such as cobalt.
As a pretreatment for this nickel plating, the plate type member is heated to 780 to 900.degree. C. under a general temperature condition in a non-oxidizing or reducing atmosphere, for the purpose of activating its surface and/or improving adhesion after the plating and adjusting brazing flowability. However, the plate type member of the copper-tungsten and/or molybdenum alloy is disadvantageously warped due to this heat treatment.
Such a warp of the plate type member of the copper-tungsten and/or molybdenum alloy causes the formation of a clearance between the bonding surfaces of the same and the ceramic member, i.e., between the brazing layers, and deteriorates the airtightness of the package. The degree of warp is increased as the diameter (in case of a circular plate) or the diagonal length (in case of a rectangular plate) of the plate type member consisting of a copper-tungsten and/or molybdenum alloy, which has been about 15 mm in general, is increased to 30, 40, 50 or 60 mm due to size increase of the package, to result in a serious problem in assembling of the plate type member and the ceramic member by brazing.
Due to requirements of improveming the yield and reducing of the cost of brazing filler metals in package manufacturers, the requirement for further reduction of the warp is increased also in relation to a plate type member of a copper-tungsten and/or molybdenum alloy having smaller sizes than heretofore provided.
In order to prevent the plate type member of the copper-tungsten and/or molybdenum alloy from suffering such a warp before assembling, it is important to uniformly and sufficiently remove a lubricant of an organic compound in order to easily compact the material so that no carbon remains and/or segregates in the alloy, and to uniformalize the compacting density distribution. Even if carbon is sufficiently removed and the density distribution of a compacted body is uniformalized, however, the occurrence of a warp caused by heating in a plating step cannot be completely prevented.