The benefits of a flux-free atmosphere for wafer bump reflow

Abstract

There is constant pressure in semiconductor packaging to reduce costs while maintaining process yields. Wafer Level Packaging has increased in response to this pressure so that for the first time the packaging cost can remain constant despite the increasing number of die per wafer. The combination of shrinking pitch sizes and environmental regulations, causing materials changes, will make this even harder in the coming years. To keep costs down many wafer bump reflow processes use flux to reduce solder oxidation. However, the cost benefits of flux may not hold up when the total costs of the process are examined. We will examine using flux for wafer bump reflow including the impact on manufacturing and environmental considerations. The increased need for process cleanliness as it relates to flux and flux contamination will also be discussed. We will discuss alternatives to flux for oxide reduction. Specifically, Hydrogen atmosphere reflow will be examined including mechanism for oxide reduction and safety considerations. We will discuss the convergence of the needs for technology and cost reduction and form a conclusion on the best solutions to meet the needs of wafer bump reflow for leading technologists in the coming years.