Flux and solder paste

A solder paste comprising:

• a solder alloy powder and a flux,
• wherein the flux comprising:
• a resin component;
• an activator;
• and
• a solvent,
• wherein the resin component contains
• a copolymer (A) having an alkene-derived repeating unit (a1), and an acrylic acid-derived repeating unit (a2) in which a hydrogen atom bonded to a carbon atom at an α-position may be substituted with a substituent, and
• a rosin (B),
• a mixing ratio of the copolymer (A) and the rosin (B) is 2 or more as a mass ratio represented by copolymer (A)/rosin (B),
• regarding the solder paste, an evaluation of temperature cycle reliability is A, and
• regarding the solder paste, an evaluation of solder paste separation prevention ability is A or B,
• wherein the evaluation of the temperature cycle reliability is determined by preparing a printed circuit board,
• regarding the printed circuit board, thickness is 1.0 mm, land dimension is 1.5 mm×0.25 mm, pitch is 0.5 mm, width between lands is 0.25 mm, number of the lands is 64,
• printing the solder paste on the printed circuit board using a metal mask having a thickness of 150 μm,
• obtaining a test board by performing reflow soldering to the printed circuit board after printing the solder paste,
• in the reflow profile, the pre-heating is performed at 150° C. to 180° C. for 90 seconds, the peak temperature is 240° C., and the solder melting time is 40 seconds,
• the reflow is performed in a nitrogen atmosphere, and the oxygen concentration is 1,000 ppm or less,
• putting the obtained test board in a heat cycle tester and subjecting the obtained test board to 3,000 cycles with standing at a low temperature of −40° C. and at a high temperature of 125° C. as one cycle,
• the standing times at the low temperature and the high temperature are both 30 minutes, and the time for one cycle is set to 70 minutes,
• observing cracking of the flux residue after performing 3,000 cycles, and
• evaluating the temperature cycle reliability as A when no cracks are confirmed at any point,
• wherein the evaluation of the solder paste separation prevention ability is determined by putting 500 g of the solder paste in a container and left to stand in a constant-temperature tank at 40° C. for 3 days,
• after a lapse of the following predetermined time, visually observing the solder paste to determine whether or not the solder paste is separated according to the following criteria,
• evaluating the solder paste separation prevention ability as A when the solder paste is not separated after a lapse of 72 hours, and
• evaluating the solder paste separation prevention ability as B when the solder paste is not separated after a lapse of 48 hours and the solder paste is separated after a lapse of longer than 48 hours and shorter than 72 hours.