High performance photo-sensitive insulating materials for MCM-L

The sequential build-up process with photo-sensitive dielectric is a most significant candidate for achieving high density multilayer wiring substrates for low cost multichip modules. A high performance dielectric material is essential in order to obtain high reliability on the wiring substrate. Two types of photo-imageable dielectric have been developed: an aqueous alkaline developable type and a semi-aqueous developable type. The results of the performance evaluation of the dielectric materials and sequential build-up wiring substrates are described here. Both dielectric types deliver high resolution in fabricating photo-formed micro-via holes. The maximum aspect ratio of the micro-via has reached 1.0 for both materials. The aqueous developable type photodielectric showed excellent electrical and mechanical properties for surface mount wiring boards with a panel electroplate subtractive process. The semi-aqueous type high performance photo-dielectric, designed for MCM-L, showed outstanding mechanical properties especially in a high temperature region. Excellent insulating properties and adhesion were proven even after pressure cooker test (PCT) conditions. Sufficient adhesion for full-build electroless copper metallization was also achieved. These features offer a great advantage in achieving higher interconnect reliability in direct chip attachment on low cost multichip modules using sequential build-up substrates.