Effect of Organic/Inorganic Coating on Moisture Diffusion in a Chip-on-Board Package with Globtop

摘要

The moisture diffusion in globtop material for a chip-on-board(COB)package coated with SiN-x and silicone,respectively,or coated with SiN_x plus silicone were measured by embedding a humidity sensor in the globtop and recording the capacitive change in three different temperature/humidity environments.The experimental results were simulated by Fick's diffusion law with finite-element method modeling.The moisture diffusion coefficients and activation energies were calculated to quantitatively compare the moisture-resistance effects of different coatings.For example,at 85 deg C/85% RH,the moisture diffusion coefficients for the uncoated reference,SiN_x-coated,silicone-coated,and silicone/SiN_x double-layered coated samples are 1E-5,0.8E-5,0.7E-5,and 0.2E-5 mm~2/s,respectively.The experimental and simulation results show that double-layered coating with silicone/SiN_x has excellent moisture-resistance properties because it not only smoothes the steps on a printed circuit board(PCB)but also keeps the good moisture resistance of the inorganic films.