Functional Yield Loss is yield loss from die that fail functional/structural testing — the die has one or more circuits that do not function correctly, typically due to killer defects (shorts, opens), process errors, or design bugs that prevent the chip from performing its intended function.

Functional Test Types

• Structural Test: ATPG (Automatic Test Pattern Generation) scan patterns — test individual gates and flip-flops for stuck-at faults.
• Functional Test: Apply actual operational patterns — test the chip performing its intended function.
• Memory BIST: Built-In Self-Test for SRAM and other memories — detect single-bit and multi-bit failures.
• I/O Test: Test all input/output interfaces — verify signal integrity, timing, and protocol compliance.

Why It Matters

• Primary Filter: Functional test is the primary screen for shipping quality — only passing die are shipped to customers.
• Kill Ratio: Functional yield loss is driven by killer defects — particles, shorts, opens, and via failures.
• Redundancy: Memory redundancy (repair) can recover functionally failing die — spare rows/columns replace defective ones.

Functional Yield Loss is dead on arrival — die that fail to function due to physical defects or circuit errors, caught by electrical testing.