MonolithTM package-a novel FBGA using 3-D transfer laminate circuit process

In this paper, we propose a novel fine pitch BGA (FBGA) called the “Monolith” package that uses the 3D transfer laminate circuit (3D TLC) process. This package uses a circuit board with cavity down structure, with no via holes and no through holes to keep the packaging cost down. However, for FBGA applications, the circuit board must have a structure that lowers the wire-bonding plane to the ball-bonding plane and 60 μm pitch level microcircuit technology. In the 3D TLC process, fine pitch wiring patterns are formed on a carrier foil that consists of a thin barrier layer and a copper foil. At the next step, circuit pattern transfer to the substrate is carried out by pressing the foil on glass fabric resin prepregs using a heat vacuum press. As pressure is applied, the cavity is formed due to the metal mold. At the final process, the carrier foil and the barrier layer are selectively etched out. In this paper, we report not only a study of the 3D TLC process, but also the optimum assembly process to prepare the frame shape and the results of reliability tests