• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.4
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• pp.69-74
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• 2010

A new package substrate for dynamic random access memory(DRAM) devices has been developed using selective aluminum anodization. Unlike the conventional substrate structure commonly made by laminating epoxy-based core and copper clad, this substrate consists of bottom aluminum, middle anodic aluminum oxide and top copper. Anodization process on the aluminum substrate provides thick aluminum oxide used as a dielectric layer in the package substrate. Placing copper traces on the anodic aluminum oxide layer, the resulting two-layer metal structure is completed in the package substrate. Selective anodization process makes it possible to construct a fully filled via structure. Also, putting vias directly in the bonding pads and the ball pads in the substrate design, via in pad structure is applied in this work. These arrangement of via in pad and two-layer metal structure make routing easier and thus provide more design flexibility. In a substrate design, all signal lines are routed based on the transmission line scheme of finite-width coplanar waveguide or microstrip with a characteristic impedance of about $50{\Omega}$ for better signal transmission. The property and performance of anodic alumina based package substrate such as layer structure, design method, fabrication process and measurement characteristics are investigated in detail.