Fine Copper Lines with High Adhesion on High Rigidity Dielectrics

Fine line and space of 10 micrometer widths were demonstrated on a smooth surface prepreg by semi-additive process (SAP) assisted by ultraviolet (UV) irradiation. The flipchip ball grid array (FC-BGA) packages were fabricated using substrates made of prepreg with glass cloth or insulation film without glass cloth. The warpage of the package at 260 degree Celsius using prepreg was 45% of that using insulation film. The reason would be the high rigidity of prepreg. Highly Accelerated Stress Test (HAST) reliability of the comb copper pattern for the 10 micrometer line and space was also confirmed for 200 h. The SAP technology assisted by UV irradiation would be a solution not only for high-frequency application due to the smooth surface but for warpage reduction of FC-BGA package and for fine-pitch solder joint of flip-chip chip scale package (FC-CSP).