Flip-Chip on Organic Carrier Assembly Evaluation

ABSTRACT Flip-chip integrated circuits on organic ball grid array (BGA) substrates are often the package of choice for new applications. Electrical performance advantages, board real estate savings, ease of assembly, and superior reliability account for the increasing popularity of flip-chip plastic BGAs. Leading edge packages have larger die and higher bump counts than have historically been assembled in this type of package. This paper describes ongoing assembly feasibility studies for application-specific integrated circuits (ASICs) customers who use a fluoropolymer-based organic substrate. Organic BGA manufacturing concerns include underfill, solderability, finished package coplanarity, and reliability. In this paper, the substrate technology will be discussed, as well as assembly techniques to ensure reliable flip-chip joints and minimum package warp. Known failure modes will be reviewed. 3M's test vehicle contains a 10.6 by 12.0 mm die with five testable daisy-chain nets contained within 898 flip-chip bumps on a 240-micron pitch. The die were assembled onto 40 x 40mm substrates having 1521 BGA pads on a 1mm pitch. Assembled packages were tested in air-air thermal cycling. Various underfill filler loadings and underfill seal fillet versus no fillet were tested. Construction analyses from C-mode scanning acoustic microscopy (CSAM) and cross-sectioning will be shared.