The Impact of Environment Humidity on WS Paste Characteristics

This present study focused on the impact of the environment humidity on the rheology change of water soluble paste over stencil life test. In parallel, this research work also studied the impact of the environment humidity on the solder ability change of the paste after experiencing some periods of exposure to the different environment humidity. The influence of the environment humidity on paste solder ability was evaluated and characterized by the results of reflowing solder paste at small open pad (008004) and small components (01005) on both OSP and ENIG finish. For a further and deeper understanding about the effect of the environment on the paste solderability, additional test was conducted under N2 atmosphere as a contrast to verify the mechanism proposed. It was found that, the environment humidity and the time exposed and the presence of oxygen in the environment and the substrate finish factors all are crucial to affect the resulting performance of the paste solder ability. Lastly, the mechanism of how these factors working together to impact the paste performance was proposed.