Analysis of laser typing spots at gold-plated kovar alloy cavity

Based on the phenomenon that a large number of spots appear in the type area on the surface of the gold-plated kovar alloy cavity, combined with scanning electron microscope (SEM) and energy disperse spectroscopy (EDS) analysis method, this paper analyzed the causes of spots and promoted effective encapsulation of electronic components. The result shows that uneven laser typing edge affect the smoothness of gold plating, increasing the coating porosity and specific surface area, which provides high probability for water and Cl-attachment, even reach to kovar alloy layer through pore. What´s more, the strong penetrating power of Cl-through the atoms gap contributes to react with metal layer and form chloride. The reaction products, such as NiCl2, FeCl2, FeCl3 become electrolyte layer of the electrochemical corrosion. Anode is iron and nickel corrosion, while cathode is oxygen corrosion. As the reaction, the chemical environment tends to alkaline. Fe2+ and Fe3+ easy to combine with OH-to produce Fe(OH)2 and Fe(OH)3, and the further evolution products, oxide Fe2O3, characterized by a large number of spots in macroscopic. Internal stress of the electrochemical corrosion gradually turns gold layer gap to crack, exposing internal kovar alloy layer. The formation of the electrochemical corrosion aggravates coating damage.