Availability is the percentage of time equipment is in a ready-to-run state, excluding periods when it is down for failures or planned service - it reflects mechanical and operational readiness independent of upstream wafer supply.

What Is Availability?

• Definition: Uptime divided by uptime plus downtime over a defined measurement window.
• Downtime Scope: Includes both scheduled and unscheduled outages depending on reporting convention.
• Distinction: Availability measures readiness, not whether wafers are actually present.
• Use Context: Fundamental KPI in maintenance management and OEE frameworks.

Why Availability Matters

• Reliability Signal: Declining availability indicates worsening equipment health or maintenance control.
• Capacity Planning Input: Accurate availability assumptions are required for realistic throughput forecasts.
• Benchmarking Value: Enables objective comparison across tools, fleets, and sites.
• Financial Impact: Low availability forces overtime, additional tools, or missed output targets.
• Improvement Prioritization: Guides focus on MTBF and MTTR programs.

How It Is Used in Practice

• Calculation Standard: Define consistent uptime and downtime event boundaries across operations.
• Trend Surveillance: Monitor rolling availability with drill-down by downtime category.
• Action Coupling: Tie availability losses to corrective maintenance and reliability engineering plans.

Availability is a primary readiness metric for manufacturing assets - sustained high availability is required for predictable output and efficient capital utilization.