Advanced packaging (3D and chiplets)
In a glass core substrate, what is the main reason cracks tend to form around copper-filled through-glass vias (TGVs)?
- AGlass conducts electricity, so discharges occur between neighboring TGVs
- BThe thermal expansion coefficients of copper and glass differ greatly, so stress builds around the TGVs with each temperature change
- CGlass is softer than organic materials, so the area around the holes deforms greatly
Show answer and explanation
Answer: B. The thermal expansion coefficients of copper and glass differ greatly, so stress builds around the TGVs with each temperature change
A glass core substrate replaces the organic core of a package substrate with a glass panel; because it is flat and dimensionally stable, it is expected to allow fine wiring even on large substrates. Glass is brittle, however, and around copper-filled TGVs each rise and fall in temperature repeatedly applies stress from the expansion mismatch between copper and glass, which can start microcracks. Stress-relieving structures and materials, strengthened glass and long-term reliability verification are challenges for practical use.
- A. Glass is an insulator; discharges between TGVs are not the issue.
- B. Correct. Stress from the expansion mismatch starts the cracks.
- C. Glass is hard and brittle; it cracks rather than deforms.
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