The present invention relates to a single plate capacitor, or a so-called chip capacitor, and more particularly, to the capacitor used in a semiconductor device for an impedance matching or other functions.
In a high power amplifier device for a microwave frequency signal, an impedance matching circuit is used for signal input and/or signal output. Such circuit is formed by a lumped constant network consisting of a lumped constant capacitor and a wire inductor. As the capacitor and the inductor, are used a single plate capacitor employing a substrate of high dielectric constant and a Au bonding wire having a diameter of 20 to 30 .mu.m in order to fully exploit the performance of each circuit element.
The above-mentioned single plate capacitor is equipped with electrodes having Au films on uppermost and lowermost surfaces. The single plate capacitor is first mounted on a stem in a package by soldering the lowermost Au film with the use of an eutectic solder such as AuSn or AuSi, together with a semiconductor chip, and then the uppermost Au film is connected by the Au bonding wire to the semiconductor chip.
However, adhesion strength of the conventional single plate capacitor to the package stem has greatly depended on a processing period of the soldering step and was inversely lowered as the processing period became longer. Particularly, when a plurality of single plate capacitors were mounted into one package, the Au of the electrode was consumed by reacting with the solder in the subsequent mounting work of other single plate capacitors, so that the first-mounted single plate capacitor lost the Au from the electrode to be peeled off easily from the solder. Furthermore, when the area of the electrode of the capacitor became smaller than 1 mm.sup.2, the adhesion strength was lowered a great deal. In particular, if tensile strength were applied to the capacitor through the Au bonding wire in the wire-bonding process, the electrode peeled off easily from the package stem.