Development of core-less substrate for multi wiring layers

A chip size package (CSP) and fine pitch ball grid array (FBGA) are increasing by becoming the focal point of attention in semiconductor field. A reel-to-reel consecutive manufacturing process has been developed by the authors for a tape-based substrate consisting of multi conductive wiring layers (minimum four layers) with ball grid array connections. This substrate, compared to those presently in use, is (a) thin (150∼200um for four layers) and low weight; (b) applicable to many pin counts; (c) makes possible fine conductive wiring and insulating layers with high accuracy in layer thickness and (d) facilitates the control of characteristic impedance. Interlayer connection technology is key to multi-conductive wiring layer structures, which may have effect primarily on substrate reliability. In the present study, a copper deposited plating process was used in conjunction with UV-laser drilling so as to produce very small via-holes in diameter 40-50um as interlayer connections. The reliability of interconnections was confirmed for via-holes with diameter 40-50um under the condition of 1000cycle thermal shocks of -65C/+150C a gaseous phase. Filled via-hole formation without interior voids was found to take place in the plating process. Minute stacked via-hole formation was noted to provide a substrate with high density pin counts. The substrate structure was designed with consideration electromagnetic transmission characteristics by computer simulation. The present substrate meets recent requirements for GHz order signal transmission.