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Keywords
Flip chip, Assembly, Yield, Reliability, Adhesives
Abstract
A reliable packaging process for flip chip on ceramic substrate using gold bumps and adhesive was successfully developed. The bonding parameters and flip chip assemblies using four adhesive materials were investigated by means of design of experiments and yield runs. The packaging yield was 100 per cent. All the packages assembled during the yield runs passed various reliability tests. The packages attained 100 per cent reliability required for an industrial application.
Introduction
Adhesive and solder alloys can be used for die attachment for flip chip assemblies. Flip chip attachment either using gold bumps with adhesive or using eutectic solder bumps with underfill epoxy is a promising low-cost flip chip mounting process.
A packaging process for flip chip on ceramic substrate using gold bumps with adhesive was developed. Design of experiments (DOE) was performed using the fractional factorial techniques and reliability tests were carried out. The reliability performance of the flip chip packages assembled using four adhesive materials was compared.
The packaging process
The adhesive materials studied are non-conductive adhesive (NCA), anisotropic conductive film (ACF) and anisotropic conductive paste (ACP). Flip chip attachment using gold bumps with adhesive is an assembly process at a low temperature. For the industrial application targeted in this study, the flip chips cannot undergo reflow of a solder alloy that has a time-temperature profile with a peak temperature of above 200 deg C. Therefore, a flip chip assembly process using gold bumps with ACP, ACF or NCA was considered.
Also, flip chip attachment with ACP, ACF or NCA is a simple assembly process. It has fewer process steps compared with other flip chip processes, although its reliability may need to be improved compared to that of flip chip attachment using solder bumps with underfill epoxy in order to meet stringent reliability requirements for many applications (Zhong, 1999).
The packaging process investigated in this study involved five or six process steps:
1ACF, NCA or ACP placement;
2 pre-bonding if ACF was used;
3 IC (integrated circuit) placement and final bonding;
4 encapsulation;
5 curing of encapsulant; and
6 dicing.
Process Step 2 was needed only when ACF was used. Thus, when NCA or ACP was used, the packaging process involved only...