The accurate installation of surface assembly components to the fixed position of the PCB is the main purpose of SMT patch processing, in the process of patch processing will inevitably appear some process problems that affect the quality of the patch, such as the displacement of components.
In general, if in the process of patch processing, if there is a shift of the components, it is a problem that needs attention, and its appearance may mean that there are several other problems in the welding process. So what is the reason for the displacement of components in chip processing?
Common causes of different package shifting 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.
Address 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.
(1) When designing, the gap between the structural parts and it should be enlarged appropriately.
The above is the factor that causes the displacement of components in the patch processing, and I hope to provide you with some reference ~
Post time: Nov-24-2023