Low stress die attach material challenges for critical Si node with Cu wire

Abstract

Low stress die attach material is of big interest for multi applications, for example, automotive, high voltage and thermal enhancement packages that require high package reliability performance; and sensitive output current applications for display driver, battery controller. The challenges of low stress die attach material started to occur when moving wire bonding technology from Au wire to Cu wire on specific Si nodes. Although it's well known that Cu wire bonding remains a challenge on bondpad with critical pad metallization or layout due to its harder wire property, however the fact that non-stick on bond pad tendency to occur on specific die attach materials with limited Si node combination became the challenge for moving forward the low stress package to low cost solutions. This paper includes the deep dive root causes investigation on the factors of die attach materials, Si nodes, and Cu wire bonding for the non-stick on pad failure. Design of experiment is carried considering materials, machines, methods include bond pad hillock, bond pad metallization thickness, wafer batch, die attach material batch, die attach material types, die attach outgas, die attach fillet height, bond line thickness, die tile, Cu wire bond jig...etc. The DOE results revealed the non-stick on pad root cause is a combination factors of die attach materials modulus at high bonding temperature, Si node under layer material types. Bond pad metallization thickness, die attach outgas, bond pad hillock... were not root cause of the bondability issue. Being the facts that Si node changed is high risk and also high cost, the solutions to overcome the non-stick on pad are mainly focus on die attach materials modulus and wire bonding technology enhancement. In this paper, we demonstrated the development of the reasonable modulus level for die attach materials to overcome the non-stick on pad issue for the sensitive Si nodes with Cu wire bonding. Besides, potential root causes are well studied via design of experiences. In the meantime, package reliability performance is well maintained post preconditioning, and stress treatment of temperature cycling per package requirement. With this study, we identify the solutions for the balance of Assembly manufacturability and package reliability.