Wire Sag

Wire Sag is a wire bonding defect where the wire loop droops below its intended trajectory, risking contact with the die surface or other wires.

## What Is Wire Sag?

• Cause: Excessive loop height, inadequate wire tension, thermal softening
• Risk: Short circuits if wire touches die surface or adjacent wires
• Detection: Optical inspection, X-ray for encapsulated packages
• Specification: Minimum clearance typically 50-100μm above die

## Why Wire Sag Matters

Modern packages stack multiple die layers with minimal vertical clearance. Sagging wires can cause catastrophic shorts or intermittent failures under thermal cycling.

Prevention Methods:
- Optimize loop profile parameters
- Control bonding temperature precisely
- Use appropriate wire diameter for span length
- Verify wire tensioner settings daily