What’s the reason for Lifted components during wave soldering for PCB assembly?

Lifted components can occur during wave soldering for a number of reasons.

1.Generally components lift due to: Incorrect lead length causing the leads to hit the solder bath and lift during entry to the wave. 

2.Flexure of the board which is commonly seen on large connectors, IC sockets or large IC packages. Basically the board flexes and the component remains still. Light components are lifted by the turbulent wave used for surface mount applications.

3.Components with either different thermal demands or different lead solderability can also cause the lifting seen during wave contact. 

4.Although not associated with the wave, vacuum formed shrinkwrap may cause lifting during wave contact. The shrink wrap is some times used to hold components on the surface of the board for lead cutting. It can be pulled under the leads which causes components to lift during wave contact. 

5.If a lead is slow to wet due to the thermal demand of the component it can lift in the plated through hole and not sit back on to the surface of the board.

Figure 1-Lifted components

In the case of Figure 1, the part lifted due to the thermal demand on the leads.Simply by increasing the immersion time in the wave eliminated the problem.

Figure 2-Lifted components

In the case of Figure 2, the part was not inserted correctly prior to entering the soldering process.