Fabrication and optimization of wafer level SAW filter package using laser via drilling

Wafer level surface acoustic wave (SAW) filter package, 0.8times0.6 mm², is drilled by laser via process. Via formation for interconnection is based on smaller package manufacture. LT (LiTaO₃) which is base material of SAW filter is difficult to drill a small via by RIE (Reactive Ion Etching) because the RIE gets a very small etch rate and has wafer broken issue by thermal heating. So, our previous review is focused on the sand blasting process for via formation. However, there is limitation on via size and via depth and makes a leakage path at interface of Cu and via side wall by roughness and micro crack after electroplating. So, study on the laser via technology for meeting a design rule requests below 30 um via hole size and over 110 um depth. That gives a good solution of via formation for our package. However, the laser via makes the secondary issues such as debris and via shape, which disturb the electroplating of via inside. Overcoming these troubles and removing debris of via inside by new cleaning method are applied to general etching steps. Finally, we make a 0.8times0.6 mm² SAW filter using laser via with etching steps compared with it using normal laser process. The result of electrical performance and laser process for wafer level SAW filter package is also discussed.