Fabrication method of plastic-packaged semiconductor device

Abstract

A fabrication method of a plastic-packaged semiconductor device is provided, which prevents the high-frequency characteristics of a semiconductor element chip from degrading without complicating a package configuration. In the first step, a wax with a property of being solid at room temperature (e.g. paraffin wax) is melted due to heat and coated to cover bonding terminals of a semiconductor element chip, thereby forming a wax layer at a location where a cavity is formed. In the second step, the wax layer and the chip are covered with a liquid-like thermosetting packaging resin produced by dissolution in a solvent. In the third step, the packaging resin covering the wax layer and the chip is cured to form a plastic package and at the same time, the wax layer is melted to penetrate into the package due to application of heat at a first temperature, thereby forming the cavity inside the package at the location where the wax layer has been formed. The melted wax layer is discharged from the cavity through micro pores produced in the package, and almost all the pores are closed by the wax. In the fourth step, a residue of the wax layer left in the cavity is vaporized due to application of heat at a second temperature, thereby removing the residue of the wax layer from the cavity. The remaining unclosed pores of the package are closed by the residue of the wax layer.