Precise and accurate installation of surface-assembled components to the fixed position of the PCB is the main purpose of SMT patch processing. However, in the process of processing, there will be some problems, which will affect the quality of the patch, among which the more common is the problem of component displacement.
Different packaging shifting causes differ from common causes
(1) The reflow welding furnace wind speed is too large (mainly occurs on the BTU furnace, small and high components are easy to shift).
(2) Vibration of the transmission guide rail, and transmission action of the mounter (heavier components)
(3) The pad design is asymmetrical.
(4) Large-size pad lift (SOT143).
(5) Components with fewer pins and larger spans are easy to be pulled sideways by the solder surface tension. The tolerance for such components, such as SIM cards, pads or steel mesh Windows must be less than the pin width of the component plus 0.3mm.
(6) The dimensions of both ends of the components are different.
(7) Uneven force on components, such as package anti-wetting thrust, positioning hole or installation slot card.
(8) Next to components that are prone to exhaust, such as tantalum capacitors.
(9) Generally, the solder paste with strong activity is not easy to shift.
(10) Any factor that can cause the standing card will cause the displacement.
For specific reasons:
Due to reflow welding, the component displays a floating state. If accurate positioning is required, the following work should be done:
(1) The solder paste printing must be accurate and the steel mesh window size should not be more than 0.1mm wider than the component pin.
(2) Reasonably design the pad and installation position so that the components can be automatically calibrated.
(3) When designing, the gap between the structural parts and it should be enlarged appropriately.
Post time: Mar-08-2024