Inner-Layer Copper Pattern Density Influence on Thin Core Dielectric Squeeze-Out
Unbalanced inner-layer copper density drives uneven resin flow during lamination, thinning dielectric over dense areas and altering impedance tolerances.
106 Glass Prepreg
Material Composition
Thin bonding ply uses a lightweight woven glass reinforcement saturated with partially cured epoxy resin. Manufacturers select 106 glass prepreg when building high layer count boards requiring very thin dielectric separations. This specific glass style features a very open weave pattern compared to heavier cloths.
Layer Thickness
Finished dielectric height typically reaches approximately 1.5 to 2.0 mils after the lamination cycle completes and resin flows into the surrounding copper features. Achieving this target relies on precise control of the resin content and the starting weight of the glass fabric. Fabricators calculate the final pressed thickness based on the copper percentage of the adjacent signal or plane layers.
Resin Content
High resin percentages usually exceeding seventy percent by weight characterize this material. This abundance of resin allows 106 glass prepreg to fill the voids between dense copper traces and provide a smooth surface for subsequent plating. Because the glass fibers are sparse, the resulting layer remains prone to resin recession if the lamination pressure is not managed correctly.
During the heating phase of lamination, the epoxy transitions through a liquid state before hardening into a solid thermoset matrix. If the press cycle fails to maintain uniform temperature, the resin may escape the edges of the panel and leave internal voids.