Polymer filling of medium density through silicon via for 3D-packaging

In this paper, we present some process developments and polymer material evaluations done to achieve the complete filling of 3D-WLP via. The test wafers used for these studies were either blankets with several via sizes specifically designed to determine via filling process window, or wafers with patterns and stacking which result from a real set-top box demonstrator. Initially, the 3D-WLP integration scheme of the demonstrator which required complete via filling is presented. Then the different test structures and patterns needed to characterize via filling behavior are described. Two methods for via filling are exposed and discussed: spin-on process of liquid polymers and vacuum assisted lamination of dry film resists. Some results concerning filling morphology with dedicated polymers are presented for both methods. After that, the defined set of chemical, mechanical and electrical properties chosen to select the polymers is given and explained. Finally, some materials which fulfill previously defined requirements are evaluated and characterized.