7. Process control & metrics: monitoring
Relying solely on final end-of-line yield metrics is a lagging indicator; by the time the reported yield drops, the scrap has accumulated and the financial impact is already realized. To thrive in high-reliability manufacturing, we must monitor and react to leading indicators in real-time using Statistical Process Control.
In this chapter, we detail the daily application of formal control charts (X-bar/R, p-charts) to relentlessly monitor all defined Critical-to-Quality parameters. By clearly differentiating between inherent common cause variation and assignable special cause variation, Engineering and Production teams are empowered to safely intervene and correct the equipment before a drifting process shifts out of its required specification limits.
- 7.1 Statistical process control: cₚ & cₚₖ
SPC represents the fundamental shift from merely inspecting quality in at the end of the line (reactive waste) and actively building quality in at each step (proactive engineering). Inspection only determines that a bad part was made; SPC indicates t...
- 7.2 Operational metrics: FPY, RTY, CoQ & review cadence
In high-volume, high-reliability manufacturing, standard end-of-line "Yield" is a lagging metric. A production line reporting a 99% Output Yield can still be financially unviable if 40% of those units required expensive rework loops just to finally p...
- 7.3 Test process quality: ICT/FCT & retest limits
Testing is an appraisal process designed to verify the hardware. It's important to understand that a test station does not fix poor quality; its role is to identify functional units and segregate failures. In high-reliability Electronics Manufacturin...
- 7.4 Layered process audits
End-of-line inspection checks the physical product; LPAs check the underlying process. A seemingly perfect product built by an undocumented process introduces significant risk in the field. Layered Process Audits (LPA) act as the immune system of the...