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Elimination of Surface Defects For Printable High Density Gold Conductor Pastes
Keywords: thick film, gold conductor paste, surface defect
Screen printable high density gold conductor pastes have many important applications in high reliability applications such as medical devices and military circuits. The basic requirements are dense and fine lines / patterns as well as excellent electrical properties with high bonding strength. In high volume automotive applications, surface defects on the fine lines and patterns can cause the need for wirebond rework and more frequent bonder setup. Surface defects such as domes are of great challenge for gold pastes because of the high density of the fired film compared to silver. It is necessary to investigate the root causes of surface defects to be able to develop gold conductors which are defect free. Surface defects for gold conductors include regular round-like shapes and irregular shapes of dots on the lines or patterns. The dots could be further classified as hollow dots and solid dots. The most frequently seen surface defects for gold conductors are regular round-like shapes of hollow dots, called domes or blisters. Their size ranges from over 3 mils to less than 1 mil. In this paper, we investigated several mechanisms to explain the root causes of different kinds of surface defects, including domes or blisters. We designed several experiments to prove the mechanisms. Using these principles, we established several methods to make gold conductor pastes with the changes to the formulation or manufacturing process to prevent surface defects after printing, drying, and firing. We applied the new methodology to several gold conductor products and have achieved improved pastes with defect free surfaces and lower cost to use.
Dong Zhang, Research Scientist
Heraeus Incorporated - Thick Film Materials Division
W. Conshohocken, PA

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