Microvia Stress Mechanics under Reflow Temperature Profiles
Substrate Z-axis thermal expansion above Tg drives low-cycle fatigue and target pad separation in HDI microvias during SAC305 lead-free reflow profiles.
HDI Laminate Selection
Resin Matrix
Dielectric material selection during high density interconnect fabrication dictates the structural performance of a multilayer printed circuit board assembly through controlled glass transition temperatures and thermal decomposition points. Thermosetting epoxy systems govern dimensional stability during sequential lamination cycles while preventing excessive z axis expansion during subsequent surface mount soldering operations. Selecting an incompatible resin system introduces delamination risks when coefficient of thermal expansion mismatches generate interfacial shear stress under thermal shock loading conditions.
High performance applications require advanced formulations possessing high modulus values to withstand multiple reflow passes without resin degradation.
Copper Foil
Foil profile characteristics determine impedance control accuracy and high frequency signal integrity across fine line outer layers. Etching tolerances depend directly upon treatment roughness at the bonding interface because excessive tooth depth increases insertion loss at gigahertz frequencies. Low profile reverse treated foils prevent signal scatter while maintaining sufficient peel strength to survive mechanical stress during component placement and depanelization.
Prepreg Thickness
Glass style selection dictates dielectric spacing between conductive layers to ensure capacitive stability and controlled impedance targets. Resin content percentages govern flow characteristics required for void free filling of microvia cavities during high pressure lamination presses. Insufficient resin volume leaves dry spots near copper features, whereas excessive resin bleed causes thickness variations that invalidate design rules for subsequent laser drilling operations.