| 摘要 |
PCT No. PCT/JP92/01611 Sec. 371 Date Aug. 9, 1994 Sec. 102(e) Date Aug. 9, 1994 PCT Filed Dec. 9, 1992 PCT Pub. No. WO94/13595 PCT Pub. Date Jun. 23, 1994A fluxless soldering process for soldering a pressure sensor unit having a sensor chip incorporating a semiconductor circuit of a large scale integration, for example, to a metal stem without scratching the surface of the chip. For the soldering, a nickel layer and an oxidation-preventing layer are formed on the surface of the glass substrate of the sensor unit. The oxidation-preventing layer acts to prevent the nickel layer from oxidizing. The substrate undergoes a thermal hysteresis before soldering. The thickness of the oxidation-preventing layer is so set that after the thermal hysteresis, movement of nickel atoms of the nickel layer to the top surface of the substrate is suppressed in relation to the thermal hysteresis. The substrate and the stem are heated in a reducing atmosphere to melt a solder foil placed between the substrate and the stem. Thus, the sensor unit is soldered to the stem. The solder-wettability of the soldered surface of the substrate is not deteriorated. Good solder-wettability can be imparted to the soldered surface without the need to increase the load applied to the joint portion during the soldering. Furthermore, since the soldering is effected by heating in a reducing atmosphere, the two surfaces can be soldered together with a high degree of gastightness without using a flux.
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