| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 107 === The purpose of this research is to recover the silver paste waste with hydrometallurgical methods, and then use the retrieved silver to prepare a remade silver conducting paste and find the right recipe with low sheet resistances.
The silver paste waste is not uncommon in the processes related to thick film technology. Our study tries to recover the noble metal of silver. The study involves retrieval of silver particles with tetrahydrofuran, dissolution of impure silver with nitric acid, conversion of silver nitrate into silver particles of high purity, and then preparation of a conducting silver paste with low sheet resistance. The emphasis is placed on reduction time and the reducing agent for silver particle conversion, then the recipe for preparing the conductive silver paste, and the sheet resistances on different substrates.
Our results indicate that the reaction time and the reducing agent effect the average particle size of silver particles, and proper measures control the particle size. The silver particles of 700 - 800 nm in size is optimal for sheet resistance since this particle size grants the opportunity for particle contact and reduce the contact resistance between particles.
With a proper recipe, the silver paste of recovered silver can be applied to a soft substrate, such as photocopying paper. When the paste is written by dip pen can perform smoothly on the paper with good wettability. The results show that can quickly dry and form conductive path with low resistance. In addition, the state of silver paste can be settled after two hours and allowing a new steady state, which is good for paste use.
It can also apply to rigid oxide substrates such as ceramics, but the difference in thermal expansion between silver paste and ceramics may cause the silver film to peel off. Therefore, zinc oxide is added to the silver paste in order to help the silver film to grip on its foothold when heated up to 800 degree. In addition to adhesive strength improvement, the sheet resistance after calcination is as low as 0.0241 ·sq-1. The reported two recipes in this study show good performance whether the conducting paste is either applied to low temperatures or high temperature applications.
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