METALLIZATION OPTIONS FOR OPTIMUM CHIP-ON-BOARD ASSEMBLYAuthor: Mukul Luthra
Company: Waterfall Technologies
Date Published: 10/11/2007 Conference: SMTA International
This paper examines many of the options of Metallization and Bonding for applications involving organic based substrates. In particular when COB is merged within mainstream SMT the choice of metallization has to serve both the SMT process and bonding – that choice can be a make or break factor. In the initial migration of die bonding onto organic substrates the Au/Au and Au/AlSi system was more or less defacto – ‘inherited’ from the packaging backend. Alternative metallic systems have been known since long, but with maturity and driven by cost pressures have come under scrutiny, the options refined and made viable. The paper examines and explains in straight forward terms to the SMT professional, the strengths, limitation, pros and cons and science behind the Gold – Gold, Gold-Aluminum (AlSi & AlMg), Gold – Copper, Gold – Silver, Aluminum – Aluminum, Aluminum – Nickel and Copper – Aluminum systems. It also examines how each produces different metallurgical interactions with the various die pad and substrate metallizations, the resulting intermetallic structures and growth and how they impact reliability & cost and hence must be understood and evaluated carefully for the targeted application.
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