There is a lot of rosin in the PIN pin fixed after SMT of the connector, and it is virtual welded (OK after repair welding). After various verifications, the flatness, tin staining and monomer film thickness of the product are all fine. As you said: after SMT, there is a lot of rosin on the pins.

There is something wrong with the setting of solder paste or the temperature curve of reflow oven for welding.

If the solder paste is authentic and has not expired,

When setting the furnace temperature curve, it is necessary to pay attention to the setting of activation time and welding time. You can refer to the curve recommended by solder paste and monitor whether the curve setting is qualified with a temperature tester.