Wednesday, April 1st, 2009

Asahi Glass is promoting a family of new photosensitive spin-on-dielectric (SOD) films for fan-out WLP and 3D packages, as well as for FPD and MEMS applications. The Chemicals Fluoroproducts Division of Asahi Glass has successfully developed the AL-X polymer series, primarily targeting the redistribution/rewiring layers in fan-out WLP packages. The company will begin production of the AL-X fluoropolymer dielectric precursor at its Chiba Plant (Japan), with marketing operations of the product already started in January 2009.

Mechanical properties of the final film include elongation of 20% and Young’s modulus of 1.3GPa, so this is a relatively soft and “rubbery” dielectric. The dielectric constant (k) is 2.6-2.7 (@1MHz-1GHz). The precursor is formulated in different viscosity blends so that three different final film thickness ranges can be achieved: 1.5-3.5µm, 3.5-10µm, and 8-30µm. Using the thickest viscosity spun to 15µm film thickness, 9 µm lines and spaces have been patterned with decent sidewall angles (see figure).

The precursor reportedly planarizes quite well over micron-scale topography. The basic process flow after spin coating the polymer is as follows:
• Soft bake for 90s at 80C,
• Expose with i-line using negative mask,
• Develop and rinse in solvent, and
• Hard bake at 180-250C.

Integration work on WLP using this material will be done by Asahi Glass in cooperation with RTI International in Research Triangle Park, North Carolina (U.S.) which has successfully developed processing guidelines for the new dielectric film. The material may also see use as a wafer bonding material for MEMS, and there is also a high transparency version for application as the interlayer dielectric for flat panel displays (FPD). More on spin-on dielectrics in the next BetaSights Newsletter. –E.K.

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