IPC-4121 provides industry-approved guidelines for selecting core constructions for multilayer printed wiring boards (PWBs). The specification sheets in the document categorize the different core constructions by laminate type and nominal thickness. The constructions are rated for characteristics such as dielectric constant (DK), dimensional stability (DS), flatness, smoothness and drillability. This document is a "must have" for those responsible for purchasing laminate materials for their company. Supersedes IPC-CC-110A. 12 pages. January 2000.