An experimental and numerical investigation into the effects of the chip‐on‐film (COF) processing parameters on the Au‐Sn bonding temperature

Abstract

Purpose -The reliability of chip-on-film (COF) packages is fundamentally dependent upon the quality of the eutectic Au-Sn joint formed between the Au bumps on the integrated circuit (IC) device and the Sn-plated Cu inner leads. Therefore, it is essential that an appropriate bonding temperature is achieved during the inner lead bonding (ILB) process. The purpose of this paper is to identify the optimal processing conditions which maximize the reliability of the Au-Sn joints. Design/methodology/approach -The paper commences by performing an experimental investigation to establish the temperature at three specific locations within the COF/ILB system in a typical gang-bonding process. The relationship between the setting temperature of the bonding tool and the temperature of the tool surface is then calibrated using an off-line experimental system. An ANSYS finite element (FE) model is then constructed to simulate the temperature distribution within the COF/ILB system under representative temperature conditions. The validity of the numerical model is confirmed by comparing the simulation results with the experimental temperature measurements. The FE model is then used in a 2 3 factorial design process to evaluate the effect of the principal COF/ILB processing parameters, namely the contact area, the tool temperature and the stage temperature, on the temperature induced at the interface between the Au bumps on the IC chip and the Sn-coated Cu leads on the polyimide film. Findings -The results reveal that the interfacial bonding temperature is determined primarily by the stage temperature. Originality/value -A regression analysis model is applied to the factorial design results to construct a COF/ILB design chart which enables the rapid identification of the stage and tool temperatures required to achieve the minimum feasible eutectic bonding temperature.

Intermetallic Compound Formation and Mechanical Property of Inner Lead Bonding Joints

“…Tung et al [6] performed failure analysis of the ILB joint subjected to stress and found that one major failure was the lead fracture owing to the formation of intermetallic compound at the interface between the Cu lead and its Sn plating layer. Relevant investigations were also conducted, including understanding of the effects of process parameters on the ILB performance by using numerical simulation [7]- [10], development of novel ILB bonding without any Au bump [11], optimization of the bonding conditions to avoid degradation of the adhesive [12], and understanding of the eutectic AuSn microstructure and the Cu/Sn interfacial reactions [13]- [16]. Because of increasing demands on multifunctionality and variety of panel dimension, the packaging technology of LCD needs to move toward high-density input/output (I/O) connections and smaller size.…”

Characteristics and properties of Bi‐11Ag solder

“…The eutectic Au‐20Sn solder is suitable from the viewpoint of its melting point, good thermal and electric conductivity and it also has good wettability (Yoon et al , 2007; Liu et al , 2010). Its natural disadvantage is its high price.…”