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INTERCONNECT STRATEGIES
PCB densities are increasing in support of highly integrated VLSI IC packages that boast improved I/O performance. As a result, conductor feature sizes must be scaled down to support finer-- pitch package lands and higher signal counts. Thin dielectric layers are part of the solution to address this increase in circuit density, and they can also be used to enhance PCB power delivery But performance, cost and reliability tradeoffs must be carefully weighed when considering their use.
Dielectrics come in copper-clad or unclad pre-impregnated sheets in thicknesses down to ~50 (mu)m (~0.002"). Each core or prepreg dielectric will have a glass cloth style, resin content, dielectric constant, loss dissipation factor, glass transition temperature, coefficient of thermal expansion, dielectric insulation strength, surface finish and flammability rating.
Dielectric materials are laminated in symmetrical combinations at a nominal thickness and dimensional tolerance per layer to form the board's final construction. Maximum metal layer counts offering the greatest circuit routing area are...