Application of the SUSS Angular Exposure System to Fabricate True-Chip-Size Packages for SAW Devices

SAW components require low cost, small size, high reliability and good electrical performance. These requirements do not only relate to the SAW component itself but also to its packaging. True chip size packaging as DSSP meets these reqirements but poses a challenge to the photo- lithographical process due to its packaging caused topography. For high topography structures like true-chip- size packaged SAW devices 3D-lithography is required. Conformal coating of such high topography wafers is solved by spray coating of positive tone resist. For the exposure of the interconnect structures on the vertical sidewalls of the package, SUSS MicroTec and EPCOS developed a solution for this challenge with the angular exposure system. The inclination angle gap exposure causes a shift in the print that can be corrected by the mask layout or by the offset parameters of the alignment software to achieve accurate alignment. As the shift depends on the exposure gap, the correction factor needs to be calculated by geometrical considerations. For exposure of all sidewalls of the structures, up to 4 exposures are necessary. Realization of the metal connects for high topography structures on the wafers is done successfully with SUSS lithography equipment. Simulations and experimental resuslts proofed the fulfillment of the requirements of the DSSP and the processing technology successfully.