We have developed a new thermosetting polyimide build-up material for high performance build-up PWBs, which can mount high speed CPUs with high I/O numbers. These PWBs meet the following requirements; good processability for the fine-pitched circuits, the low dielectric characteristics, and the excellent mechanical properties. Our proposed polyimide build-up material shows a dielectric constant (Dk) of 3.1 and a dielectric loss (Df) of 0.01 (at 1GHz). Moreover the material shows following mechanical properties; a low coefficient of thermal expansion (CTE) of 45ppm and a tensile strength of 100MPa. Even though the material has a low surface roughness Ra of less than 200n meters, we have successfully deposited an electro-less plated copper layer with very high peel strength. This means that the material is suitable for fabricating fine-pitched circuits, even when using a conventional semi-additive process. Actually, we could make a fine-pitched circuit of less than 10micron L/S (Line and Space).
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