CONTROLLING PHOTOIMAGING OF EPOXIES BY BLENDING TO A SPECIFIC MOLECULAR-WEIGHT

An epoxy formulation developed for a photoimaging application was found to exhibit poor clean‐out in the developing solvent depending on the lot of one of the base resins. Size exclusion chromatographic (SEC) analysis of the residual material showed it to be a high molecular weight (Mw) fraction of the base resin EpiRez SU‐8. The resin was fractionated, and it was demonstrated that removing the high Mw fraction from the formulation enhanced its developability. Lower Mw versions of this resin were evaluated and found to be unsuitable. However, blending one of these resins (EpiRez SU‐6) with the SU‐8 resulted in a formulation that exhibited excellent developability. Mathematical relationships were calculated that enabled blends to be made, resulting in a defined molecular weight regardless of the lots of resins used. Copyright © 1990 John Wiley & Sons, Inc.