Method for improving one-time first pass yield of QFN device welding

The invention discloses a method for improving the one-time first pass yield of QFN device welding, which comprises a PCB, pins arranged on the PCB, a steel mesh and a scraper installed on a solder paste printer, the steel mesh is provided with steel mesh holes corresponding to the pins, and the method further comprises the following steps: S1, the steel mesh is attached to the PCB or flatly laid on the PCB in a gap-reserved manner, the steel mesh holes correspond to the pins, the reserved gap is-1 to-0.5 mm, and the surface of the steel mesh is coated with solder paste through a solder paste screen printing machine. According to the method for improving the one-time first pass yield of QFN device welding, the optimal printing parameters, explored through tests, of the QFN device are as follows: the scraper pressure is 9-10 kgs, the scraper speed is 23-26 mm/s, the demolding speed is -0.5 mm/s to -1 mm/s, the pre-printing gap is -1 mm to -0.5 mm, the delay time is 200-300 ms, and the number of qualified weldi