Mold compound optimization and certification for Cu wire leaded package

Semiconductor industry is moving rapidly from gold (Au) wire to cooper (Cu) wire for several packages mainly due to gold price increase and remains volatile in recent years. The package encapsulation material (mold compound) needs to be studied to understand the interaction of it with Cu wire bond for package reliability and not to introduce new failure mechanism. Various studies shows that the mold compound pH and Chloride (Cl-) content are the primary factors affecting Cu wire package reliability performance [1, 2]. The purpose of this study is to certify our existing green mold compound and to have single mold compound for Au & Cu parts. In this work, we investigated the impact of mold compound properties for Cu wire reliability performance particularly Highly Accelerated Stress Test (HAST) 130 degree C/ 85% humidity and Temperature Cycle (TC) -65 degree C to 150 degree C. The test vehicle chosen for the evaluation is 80 lead LQFP 14 × 14mm package with 4N bare Cu wire and wire diameter of 25um. Two material properties of mold compound which are pH and Cl- level are the focus in this study. We evaluated compound lots with different pH and Cl- for our study and submitted for reliability test. Effects of mold compound pH and Cl- content on the reliability failure rate and how we define the specification range of pH and Cl-level for Cu wire package will be discussed. From result, we also understand Cu wire bond IMC coverage and device bias voltage are also major factor for Cu wire package reliability performance.