UBM FOR MEMS, OEMS AND CMOSAuthor: Donald Gudeczauskas
Company: Uyemura International Corporation
Date Published: 11/3/2005 Conference: IWLPC (Wafer-Level Packaging)
Wafer manufacturers are continuously searching for various methods to increase throughput and decrease wafer processing costs. Of note, the final layer of many integrated circuit bond pads consists of aluminum or copper. Aluminum can serve as an acceptable surface for standard wire bonding since the wire bonding techniques form an acceptable wire bond through the tenacious oxide layer normally present on the aluminum surface, but this surface is not acceptable for soldering or conductivity. As a result, UBM methods are used in order to form a good bond to the aluminum pad and also help prevent diffusion of metals into the IC itself.
Traditionally, dry methods are used to form the UBM (sputtering or vacuum deposition), but these methods require large capital cost for equipment and result in relatively low productivity. These methods are, however, industry accepted and dry metallization techniques are still used for the majority of wafers. Wet chemical methods such as ENIG have been investigated to serve as both a solderable surface for the bumps themselves and as a wire bondable surface while also increasing productivity. The standard processing sequence for ENIG as a UBM process for aluminum pads is shown in Figure 1.
Members download articles for free:
Not a member yet?
What else do you get when you join SMTA? Read about all of the benefits that go along with membership.
Notice: Sharing of articles is restricted to just your immediate work group. Downloaded papers should not be stored on an external network or shared on the internet.