High temperature die attach material on ENEPIG surface for high temperature (250DegC/500hour) and temperature cycle (−65 to +150DegC) applications

There are five types of die attach materials with high melting point (>250°C) are evaluated in this study, these materials are high lead (Pb95.5Sn2Ag2.5) solder paste, Gold Tin (Au80Sn20) solder paste, pressure-less Silver (Ag) sintered paste, pressure type silver (P-Ag) sintered paste and Gold Germanium (Au88Ge12) perform solder. The reliability tests included high temperature storage (HTS) at 250°C/500hours with N2 purge and temperature cycling for 500cycles at −65°C to 150°C. Majorities of the test vehicles have good shear mode (Silicon die crack) after reliability tests. Only mix modes failure on the pressure-less Ag sintered die attach materials is observed at HTS 250°C, after 500hours with shear strength of 17.9Mpa. It is crucial to understand the conditions of the interfaces between these high temperature die attach materials to the devices and substrate after reliability tests. The cross sections samples are further studied on the interface between the die attach material and substrate (ENEPIG surface) with SEM and EDX analysis. It is interesting to found out that the pressure type Ag sintered has denser bulk materials compare to pressure type Ag sintered materials, and this provides an excellent heat transfer and low electrical resistance at the interface. After HTS for 500hours, the Sn rich phase of AuSn solder has the tendency to form at the ENEPIG site. High lead solder form a layer of Ni/Pb/Sn at the ENEPIG surface and where AuGe solder form a layer of Ni/Ge at the interface to ENEPIG substrate. A details study on the materials interface to the die and ENEPIG substrate surface are carried out; and out of these high temperature die attach materials, which will be more preferable in term of process ability and price is discussed.