PURPOSE: To prevent a substrate from being deformed and ensure excellent soldering without requiring any jig by laminating frame-shaped or sheet-shaped thin plates, holding them between the substrates, the foregoing thin plate taking as a chief material a shape storing alloy which returns to a prestored flat plane state when a predetermined temperature is attained by heating.

CONSTITUTION: The outer periphery of a substrate 3 is surrounded by a rectangular frame 2, and is held between substrates 1, 4 and superimposed to form a laminate substrate A. Herein, the rectangular frame 2 employs a shape storing alloy as a chief material and is constructed to restore a flat plane stored therein by heating. The laminate substrate A is transferred into a soldering device for soldering of chip parts, and when it reaches the high temperature atmosphere around molten solder in a solder reservoir, the rectangular frame 2 restores its shape to a flat plane with the aid of its storage performance and passes through the solder reservoir parallely to a solder surface.