Mold Void Improvement for Stack Die Overhanging Structure Inside Automotive Gate Driver Package

Vehicle electrification is driving advanced functional safety, control and protection features in automotive EV (electric vehicle) electronics. Many on-board systems such as EV traction inverters, DC/DC converters, and on-board chargers are powered by or connected to high voltage power sources. These require the use of gate driver components to control Si IGBTs (insulated-gate bipolar transistor) and SiC MOSFETs (silicon carbide metal oxide semiconductor field effect transistor) in these systems while maintaining communication to the other lower voltage vehicle circuits. The combination of functional, safety and HV (high voltage) isolation requirements of such gate drivers necessitated development of a novel package technology known as GICL (galvanically isolated communication linkage) [1] [2]. For safety and functional reasons, the package must maintain galvanic isolation between the LV and HV domains after both short duration voltage spikes (system irregularities) and after long term exposure to the working voltages. This applies to both the package external surface and internal volume. A 32 lead SOIC (small outline integrated circuit) package with leads on only two sides was selected to meet the creepage and clearance requirements. Internal isolation was achieved by placing a high voltage dielectric barrier between two stacked die which could communicate by inductive (magnetic) coupling. The package internal configuration and isolation strategy are shown in Fig. 1. Device functionality was partitioned into two die, one for each domain. The stacked structure permitted communication elements on each die to directly transfer data using inductive coupling across the galvanic isolation barrier. The overhanging isolation barrier is designed for sufficient isolation distance between HV die and LV die. But its existence also brings challenges to mold process development on mold void. Mold void can be found at the corner between the isolation barrier overhang and HV die in Fig. 2. Several optimization of design and process had been tried to improve mold void. It is very difficult to 100% eliminate the mold void. As mold compound reaction proceeds, the spiral flow decreases and the viscosity becomes lager. Air is easy to be trapped and form mold void under isolation barrier overhang in Fig. 2. Vacuum mold is as one promising solution to decrease the air-content in the mold cavity were evaluated and confirmed that it can eliminate the mold void under isolation barrier area. This paper will show the vacuum mold process for SOIC package with stack die, overhang structure, Then it summarized evaluation results including vacuum mold parameter development and its process responsibility, reliability evaluation results.