# Prediction of Curing Time/Shear Strength of Non-Conductive Adhesives Using a Neural Network Model
## 1 Introduction  
Electronic packaging technology has been developed with the semiconductor industry to offer the functional capability to apply high density and performance [1, 2, 3]. Due to the requirement of high resolution and fine interconnection pitch (less than 25 um), the flip-chip bonding process using adhesives has been also emerged and developed in electronic packaging industries to replace underfill materials, which are widely used in electronic packaging but prone to cause void defects after gap-filling [4]. Adhesives for the flip-chip bonding process are classified as an isotropic conductive adhesive (ICA), an anisotropic conductive adhesive (ACA), and a non-conductive adhesive (NCA) [1]. NCA does not contain conductive fillers and reduces the probability of electric short-circuiting between the fine-pitch or the bump (chip) and the pad (substrate) caused by trapped conductive fillers that are included in ICA and ACA [5]. In addition, a chip and a substrate can directly contact electrically using NCA, therefore the contact area is increased, and then the contact resistance is also reduced [6]. The application of NCA increases as the number of I/O pads and the fine-pitch density of the interconnections increase. Many researchers have formulated NCA by combining epoxy resin, hardener, catalyst, etc. Epoxy resins are widely used as polymeric adhesives with versatility, good wetting ability, chemical resistance, and high tensile strength. However, epoxy resins have low toughness and weak peeling/impact strength [7, 8]. Therefore, epoxy resins are formulated with a hardener and a catalyst to compensate for their disadvantages. [PERSON] et al. [4] showed the reliability of fine-pitch chip-on-film (COF) flip-chip packages using NCA. They evaluated 4 types of curing agents and suggested 2E4 MZ-CN as a suitable curing agent for the formulation of NCA in terms of the curing rate and pot life. [PERSON] et al. [9] studied theeffects of hardeners and catalysts on the reliability of copper-to-copper adhesive joints. They evaluated 4 types of hardeners and 2 types of catalysts to formulate 6 types of NCAs. Curing behaviors and shear strengths of NCAs were compared, and the optimum formulation with high initial joint strength and reliability was suggested. Recently, [PERSON] et al. [10] investigated epoxy/silane pre-synthesis, which improved thermal properties and adhesion strength. The modified NCA showed 1.45 times higher shear strength than the neat NCA. Inherently, the properties of NCAs depended on the components and their compositions and components [11; 12; 13; 14; 15], and formulation of NCA is extremely sophisticated because various kinds of materials are employed as components. Snap curing time and shear strength are important properties of NCAs to determine productivity in mass production and the reliability of the electronic packages. Snap curing time of NCA should be considered to improve productivity in the flip-chip bonding process, which is to bond between Si chip and substrate one by one [16; 17]. Additionally, high-temperature thermo-compression is accompanied by the bonding process, which causes substrate softening and the joint deterioration [18; 19]. Therefore, the shear strength for interconnection between a chip and a substrate affects the reliability of the package. Curing time and shear strength have been experimentally and analytically examined for various NCAs according to their composition. [PERSON] et al. [17] reported an evaluation method for snap curing behavior on NCA for flip-chip bonding. They proposed the DEA (dielectric analysis) method for quantitatively investigating snap curing behavior of NCA and verified the DEA method as compared with the results using the isothermal DSC method. [PERSON] et al. [20] proposed the effects of four types of catalysts on the curing time of NCA. The curing time was decreased with an increase in the content of catalysts. [PERSON] et al. [21] studied an analytical approach to evaluate shear stress in flip-chip interconnection using NCA.