Reasons for BGA insufficient solder & short
There are cases of insufficient solder and solder short in BGA soldering, but it is also possible. Because the PCB BGA board has too much gap due to heat shrinkage (CTE), the edge of the BGA board is upturned. The smile curve is formed, and the circuit board is too long due to TAL (Time Above Liquidus), and the temperature difference between the upper and lower furnaces of the reflow furnace is too large, and the two-phase interaction forms a circuit board to bend down，Caused the so-called cry curve. If the cry curve, smile curve is severely deformed, short-circuit and air-welding of the BGA will be formed at the same time, which is usually the case when both occur at the same time. The picture shows that the BGA smile curve and the cry curve on the printed circuit board strongly squeeze the BGA solder balls, causing several short circuits. In general, consider reducing the slope of the reflow oven, either by preheating the BGA to eliminate thermal stress, or by requir...