4, Monument
(1) Uneven printing or too much deviation, thick tin on one side, high tensile force, thin tin on the other side, small tensile force, causing one end of the component to be pulled to one side to form an empty solder, and one end to be pulled up to form a tombstone.
(2) The patch is offset, causing uneven force on both sides.
(3) One end of the electrode is oxidized, or the size of the electrode is too different, and the tinning performance is poor, causing uneven force on both ends.
(4) The width of the pads at both ends is different, resulting in different affinity.
(5) If the solder paste is left for too long after printing, FLUX volatilizes too much and the activity decreases.
(6) REFLOW preheating is insufficient or uneven. The temperature is high in places with few components, and the temperature in places with many components is low. The high temperature places melt first. The tensile force formed by the solder is greater than the adhesive force of the solder paste to the components. The uneven force causes tombstones.
5, Empty welding
(1) The temperature of the board surface is uneven, the top is high and the bottom is low. The bottom of the solder paste melts to disperse the tin, and the temperature below can be appropriately reduced.
(2) There are test holes around the PAD, and the solder paste flows into the test holes during reflow.
(3) The uneven heating makes the component feet too hot, causing the solder paste to be led to the pins, and the PAD is less tin.
(4) The amount of solder paste is insufficient.
(5) Poor component coplanarity.
(6) The pins are tin sucked or there are wiring holes nearby.
(7) The tin is not wet enough.
(8) Too thin solder paste causes tin loss.