Wafer based processes are more recent and have more in common with front end semiconductor fabrication than the three circuit technologies described above. Feature dimensions are typically in the 5-50um range, in between semiconductors at <0.1um and "2nd level" circuit interconnects at 50-250um.
DuPont is focusing its efforts in a few areas:
Bumping of wafers for eventual use (after wafer dicing and subsequent assembly) in flip chip in package or chip on board applications Passivation and redistribution of interconnect layers on the wafer for flip chip and wafer level packages 3-D structuring for MEMS applications (e.g., ink jet heads)
For wafer bumping applications we have taken our photopolymer expertise and developed thick (50-100um), negative acting dry film photoresists for both stencil and electroplating bump processes. Dry film has less wastage compared to spin on liquids and further gives better thickness uniformity (hence better utilization), especially for larger 300mm wafers. To improve the quality and yields of wafer bumping processes, we are currently developing resist removers based on technology within our EKC division.
We have the broadest portfolio of liquid polyimides in the industry. Our liquid polyimides are the proven standard for stress buffers (between die and overmold) in wire bonded packages because of their excellent thermal, mechanical and electrical properties. For newer C-4 and redistribution flip chip packages, our negative working HD-4000 photosensitive polyimide is gaining increasing end-user acceptance because of its superior mechanical properties, especially higher elongation to break. Our HD-7000 material has low modulus, can be cast in thick layers (20-70um) and has good gap filling characteristics, making it ideal for system-in-package applications. For applications like memory packaging where low temperature curing is desirable, we have recently introduced HD-8800. This is aqueous processable, positive working and can be cured at 225C.
MEMS applications are very varied and the technology is not yet standardized. Our MX series of dry film photoresists can be used for specialty etching. We also have permanent dry films and DuPont™ Green Tape™ Systems for applications like ink jet heads and microfluidics where small channels and cavities need to be created.