Impact of chip-package parameters on the thermomechanical reliability of high thermal die attach materials in RF, power, and automotive applications

The utilization of silver (Ag) sintering die attach materials has witnessed a rapid surge in demand, particularly in applications that demand superior thermal performance, such as RF, Power, and Automotive, including their potential use in Cu clip and heat spreader attachment. Ag sintering materials offer a solution for high thermal performance packaging with thermal conductivity ranging from 50 to 200 W/mK, and even higher with pressure-assisted sintering, surpassing traditional die attach materials significantly.The paper highlights the complexity of selecting Ag sintering materials and designing thermally challenging semiconductor packages. It emphasizes the need to consider multiple assembly parameters simultaneously, such as die size, thickness, metallization, surface finish, material composition, and process-related factors. The intricacies of these parameters make it impractical to establish a universal guideline for selecting materials for new package development, given the diversity in production package configurations. The study also presents a practical case demonstrating the improvement in thermal resistance when transitioning from conventional silver-epoxy die attach adhesives to Ag sintering materials using experimental study and thermal simulation. This improvement in thermal performance helped achieve the desired reliability levels for an RF product utilized in wireless base stations.A comprehensive dataset obtained was from an extensive Design of Experiments (DOE) study. It covers two types of wafers (MOSFET and GaAs), four die sizes, two backside metallization options, and two lead-frame finishes. Three popular Ag sintering materials were compared in an apple-to-apple manner across two different Outsourced Semiconductor Assembly and Test (OSAT) providers. The study includes an assessment of die attach process quality and package reliability. It identifies the significance of leadframe surface roughness such as for roughened PPF leadframe in improving die attach adhesion. The findings from this holistic study provide insights into failure mechanisms and offer guidance for selecting appropriate die attach adhesives in thermally demanding product-package applications.