Mechanical Shift
Displacement of a component from its intended position on a circuit board during the soldering process. Surface tension of the molten solder often causes post-reflow offset as the part floats on the pads. This phenomenon is a common challenge in the assembly of small surface mount devices.
Surface Tension
Uneven wetting of the solder paste can pull the component toward one side of the footprint. The post-reflow offset is more pronounced when the pads are not symmetrical or if the paste is applied unevenly. Designers must account for these forces when creating the land patterns for high-precision sensors.
Alignment Error
Automatic optical inspection systems detect the deviation between the actual position and the design coordinates. A large post-reflow offset can result in short circuits or open connections if the leads no longer touch the pads. Re-centering of the component requires manual rework which increases the cost of production.
Calibration Compensation
Software algorithms can sometimes correct for the electrical errors caused by a slight physical misalignment. If the post-reflow offset is repeatable, the manufacturing team can adjust the pick and place machine to compensate for the drift. This corrective loop improves the yield of the assembly line over time.
Accurate measurement of the displacement is necessary to ensure that the finished product meets its performance targets.
