During smt circuit board assembly, what are the common reasons for component shifting?

During smt circuit board assembly, the common reasons for different package shifts are as flowing:

(1) The smt circuit board assembly reflow soldering furnace has too high wind speed (mainly occurs on the BTU furnace, and small and high components are prone to shift).

(2) Transmission rail vibration and SMT machine transmission (heavy components)

(3) The smt circuit board assembly welding pad design is asymmetrical.

(4) Large size welding pad lift (SOT143).

(5) Smt circuit board assembly components with small pins and large spans are easily tilted by the surface tension of the solder. For such components, such as SIM cards, the width of the pad or stencil window must be less than the component lead width plus 0.3mm.

(6) The size of the components at both ends is different.

(7) The smt circuit board assembly components are unevenly stressed, such as the package's anti-wetting thrust, positioning holes or installation slot card position.

(8) There are components that are prone to venting, such as tantalum capacitors.

(9) Smt circuit board assembly solder pastes with high activity are not easily displaced.

(10) Any factor that can cause a Tombstone will cause a shift.

Handle for specific reasons.

The components show a floating state due to reflow soldering. If you need accurate positioning, you should do the following:

(1) Solder paste printing must be accurate and the stencil opening size should not be more than 0.1mm wider than the component leads.

(2) Properly design the smt circuit board assembly welding pads and mounting locations so that the components can be automatically calibrated.

(3) When designing, the matching gap of the structural device is appropriately enlarged.