Meaning
Post-assembly quality evaluation sits between primary surface mount inspection and final product boxing to quantify successful circuit repair rates. Calculating rework yield measures the percentage of repaired printed circuit board assemblies that pass subsequent electrical verification without further defect. The metric applies to surface mount touch-up operations and component replacement routines inside electronic manufacturing plants.
It stops applying to first-pass assembly lines where no secondary touch-up or manual soldering occurs.
Metric Calculation
Reworked unit tracking divides successfully re-tested circuit assemblies by the total number of boards submitted to repair stations. Tracking rework yield identifies secondary defect rates caused by operator handling or excessive thermal cycles. Low conversion percentages highlight inadequate soldering tools or uncontrolled heating profiles.
Quality control logs document daily yield variations.
Thermal Impact
Multiple heat applications during component replacement induce localized mechanical stress and substrate darkening. Sub-optimal rework yield values correlate directly with solder pad damage and internal micro-cracking around ball grid array lands. Process engineering limits component touch-up attempts to two reflow cycles per board location.
Unrecoverable board scrap increases when limits are exceeded.
Qualification Threshold
Process capability acceptance requires sustained repair success rates exceeding ninety-five percent on production lots. Production lines failing this metric trigger immediate process audits.
