Metallization options for optimum chip-on-board assembly

摘要

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 back-end. Driven by cost pressures, alternative metallic systems have come under scrutiny, the options refined and made viable. This paper examines and explains to the SMT professional the strengths, limitations, pros and cons and science behind the gold-gold, gold-aluminum, gold-copper, gold-silver, aluminum-aluminum, aluminum-nickel and copper-aluminum systems and examines how each produces different metallurgical interactions with the various die pad and substrate metallizations and how the resulting intermetallic structures and growth impact reliability & cost.