Dispensing Process of Silver Adhesive to Minimize the Joint Surface Area-to-Volume Ratio for Premature Dried Adhesives Prevention

The market value of flexible hybrid electronics is USD 95 million in 2019 and is predicted to reach USD 231.12 million by 2025 [1]. One of the FHE assembly processes is printing silver adhesive paste to form electrical joints between the rigid components and the flexible substrate. The fine-pitch printed adhesive circuitries have a low aspect ratio and a large surface area-to-volume ratio. These phenomena have been observed in the fine-pitch screen-printed silver, which often leads to premature dried joints. Fortunately, the dispensing process could prevent the issue associated with the large surface-area-to-volume ratio because the dispensing method can control the thickness of the deposited adhesives. However, the dispensing of the silver adhesive has a relatively long lead-time. Therefore, this paper will study the dispensing process parameters of electrically conductive silver adhesive to optimize the lead-time and control the aspect ratio of the fine-pitch adhesive joints. In this study, a design of experiment of 3-parameters 2-levels full-factorial was conducted. The investigated parameters included dispensing velocity, dispensing pressure, and gap. The experimental run outcome is the deposit aspect ratio. The test vehicles were 10mm-length silver patterns for the empirical study and the assembly of resistors for mechanical-shearing and electrical tests. The adhesive joints of the assembled resistors were dispensed using the optimized parameters found in the experimental research. The study results indicated that the significance of the investigated parameters in order from the strongest to the weakest included speed, pressure, and gap.