Known Good Die (Kgd)

A Known Good Die (KGD) is a bare semiconductor die that has been fully tested and verified to meet all functional and reliability specifications before being placed into a package or integrated into a multi-chip module. The concept is critical in advanced packaging scenarios like 2.5D/3D integration, chiplets, and system-in-package (SiP) designs.

Why KGD Matters

• Multi-Die Economics: When combining multiple dies into one package, a single bad die renders the entire expensive assembly defective. Each die must be proven good beforehand.
• Cost Avoidance: Packaging and assembly costs can be significant — catching defects at the bare die stage avoids wasting downstream resources.
• Yield Compounding: If you assemble 4 dies each with 95% yield, compound yield drops to ~81%. KGD testing pushes individual die yield as close to 100% as possible.

KGD Testing Challenges

• Probe Testing at Speed: Bare dies lack package parasitics, making high-speed testing tricky. Specialized probe cards and temporary carriers are used.
• Burn-In Without Package: Some KGD flows use wafer-level burn-in (WLBI) to screen early-life failures before assembly.
• Standardization: The JEDEC KGD standard defines quality levels and test coverage expectations for bare die shipments.

KGD has become increasingly important as the semiconductor industry moves toward heterogeneous integration and chiplet-based architectures where dies from different fabs and process nodes are assembled together.