Development of two-metal layer flexible substrate for high density IC packaging

A two-metal layer (2-ML) flex with Cu fully filled blind vias has been developed by Compass to meet market demands, by using our developed direct Cu build-up process for high density interconnection (HDI). Unlike the conventional Cu metallization process, the direct Cu build-up processes have several advantages such as more reliable blind vias, fewer problems in blind via filling of solder masks, fine blind vias with reduced aspect ratio and better via-on-pad structure in flip chip applications. Reliability tests such as thermal shock, pressure cooker (PCT) and moisture sensitivity tests (MST) at tape level have been conducted and the results showed that the 2-ML flex passes all of these tests without any failures. The design rules for the two-metal layer flex for roll-to-roll mass production at Compass has been finalized, and prototype samples have been produced for customers for IC packaging in applications including TBGA, μBGA, FC BGA, MCM, etc