Ultra-high density, thin core and low loss organic system-on-package (SOP) substrate technology for mobile applications

In this paper we present an ultra-high wiring density build-up substrate targeted at 30 mum IC-to-substrate interconnect pitch, using a new low loss thin core laminate (RXP-1) and low dielectric constant and low loss thin build up dielectric (RXP-4). The RXP-1 core is a glass fiber reinforced organic laminate with a thickness in the range of 50-110 mum. The RXP-1 core has a stable dielectric constant of 3.25 and loss tangent of 0.004 at 1-40 GHz. The RXP-4 build-up film has a stable dielectric constant Lt3, a loss tangent of 0.004 at 1-40 GHz [1] and a film thickness of 10-25 mum. A process test vehicle having a 4-metal layers structure (1+2+1) was designed for process development and reliability characterization. The total thickness of the completed 4-metal layer substrate demonstrated was 160 mum. The substrate design rules include a minimum copper line width and space of 15 mum, blind microvia diameter of 25 mum and through hole diameter of 50 mum. Line width and space of 10 mum and through hole diameter of 30 mum was also designed for testing the process limits. Preconditioning test, 3X lead-free reflow and thermal shock (-55~+125degC, air-to-air) test up to 1,400 cycles showed that the new low loss thin dielectric film and thin core organic system is reliable. This substrate can be used for high speed systems, low profile thin packages, portable devices, mobile applications, system-in-package (SiP) and system-on-package (SOP).