Low-temperature soldering flux of photovoltaic soldering strip for HIT heterojunction and preparation method

The invention relates to a low-temperature soldering flux of a photovoltaic soldering strip for a HIT heterojunction and a preparation method. The low-temperature soldering flux is prepared from the following raw materials including, by mass, 35% - 40% of bismuth, 1.5%-2.5% of silver powder, 0.01% - 0.02% of copper and the balance tin. The low-temperature soldering flux adopts spherical silver powder and other conductive materials which are identical with conductive materials of battery piece grid line silver paste, the ingredients and the form particle size levels are within the same specification range, even under a low-temperature soldering condition, the materials are promoted to undergo eutectic transformation, so that a formed electrode interference metal intermediate compound is more uniform and denser, conductive phase network contact is more complete, and therefore the conductivity, the adhesion force (namely soldering tension force) and reliability (namely TC200 and DH1000) of the silver electrode a