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Photo Sensitive PI/PBO for Low Temperature Cure
Keywords: Photosensitive Polyimide, Low temperature cure, High reliability
Photo-definable polyimides (PI) and polybenzoxazoles (PBO) have been widely used as dielectrics for re-distribution layers in wafer level packages (WLP). These materials can simplify the manufacturing process and ensure high reliability owing to their excellent mechanical properties and high thermal stability. For next generation electronic components fabricated by utilizing advanced packaging technologies, the most important requirements for dielectric materials are low temperature curability, high lithographic performance, high adhesion to Cu RDL after reliability test, and high chemical resistance. In this paper, we will report the latest evaluation results of our novel PI and PBO. Usually conventional photosensitive PIs and PBOs need high cure temperatures greater than 300ºC to complete cyclization as well as generating interactions between polymers. As a result, strong interaction brings about the high film properties of PI/PBO. On the other hand, for low temperature curable materials, we re-designed the design concept in order to achieve high film properties even though the curing temperature is low. Firstly polymer backbone was changed in order to achieve smooth cyclization at low curing temperature. Then, cross-linker was changed to form a strong network structure even when cured <200⁰C. Based on our new design concept for low temperature cure, we developed both photosensitive PI and PBO. A novel solvent negative tone PI was developed by incorporating a new cross-linker to accelerate low temperature curability as well as a high pressure cooker resistance (PCT resistance) from the viewpoint of moisture treatment resistance. In addition, unique photo-initiator was selected to improve lithographic properties. As a result, the novel PI when cured at 175⁰C for 1hr showed high Cu adhesion after 168hr PCT, high film properties and excellent lithographic properties with a resolution of 4μm (via). A novel alkaline positive tone PBO was also developed by re-designing our concept and the new PBO material showed higher lithographic performance than conventional PBOs due to its high dissolution contrast and which resulted in a resolution of 2μm (L/S) with a 7μm cured thickness and 3μm (L/S) with a 15μm cured thickness, respectively. This material also produced strong Cu adhesion and high chemical resistance at curing temperatures <200⁰C with no delamination from the Cu RDL being observed after a 168hr PCT. Furthermore, the new PI and PBO materials were evaluated from the viewpoint of bias HAST resistance. As a result, we found that both new materials showed high bias HAST resistance and kept high insulating properties even though the curing temperature was 200 oC.
Daisaku Matsukawa,
Hitachi Chemical DuPont MicroSystems, Ltd.
Hitachi-shi, Ibaraki
Japan


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