Abstract: Soldering paste obtained by mixing solder material with photosetting flux, which hardens by the irradiation of ultraviolet light, is used for reflow soldering. The photosetting flux contains flux base material, flux base material solvent, a photopolymerization initiator and photosetting prepolymer. The soldering paste obtained by mixing this photosetting flux is printed and bonded on the surface of soldered portion of a printed substrate, and is brought into tight contact with the pad portion of a lead of an electronic part to be soldered. The surface of soldering paste exposed is irradiated with ultraviolet light to cause the surface to gel. Thereafter, soldering is effected by means of preliminary heating and solder melting and heating (reflow heating). Since the surface of the soldering paste is thereby hardened by the irradiation of ultraviolet light, no sags occur during preliminary heating, thus making it possible to prevent any defective bridge caused by sags.

Abstract: Soldering paste obtained by mixing solder material with photosetting flux, which hardens by the irradiation of ultraviolet light, is used for reflow soldering. The photosetting flux contains flux base material, flux base material solvent, a photopolymerization initiator and photosetting prepolymer. The soldering paste obtained by mixing this photosetting flux is printed and bonded on the surface of soldered portion of a printed substrate, and is brought into tight contact with the pad portion of a lead of an electronic part to be soldered. The surface of soldering paste exposed is irradiated with ultraviolet light to cause the surface to gel. Thereafter, soldering is effected by means of preliminary heating and solder melting and heating(reflow heating). Since the surface of the soldering paste is thereby hardened by the irradiation of ultraviolet light, no sags occur during preliminary heating, thus making it possible to prevent any defective bridge caused by sags.

Abstract: Two DC motors are driven by switching pulse drive circuits, and the switching on times of drive pulses are made to be out of phase with each other at the two switching pulse drive circuits. One of the two DC motors rotates rotary video heads, and the other drives a capstan of a video tape recording and/or reproducing apparatus. The drive pulses are preferably synchronized with horizontal synchronizing pulses of a video signal to be handled by the video tape recording and/or reproducing apparatus in order to avoid pulse noises.