Method for cap lamination for tighter impedance control

Method for cap lamination for tighter impedance control

Disclosed is a method for cap lamination for tighter impedance control. Benefits include improved performance and improved design flexibility.

Background

        � � � � � Variations in dielectric constant (Dk) and impedance (Zo) are caused by glass/resin variations in the woven glass fabric used as material reinforcement, limiting the range of impedance control that a board can maintain.

        � � � � � Conventional methods of reducing Dk variation in glass woven reinforced printed circuit board (PCB) laminate materials are to use multiple layers of woven glass fabric in the dielectric and wider traces for the bus design.

� � � � � The conventional method of building a PCB uses layers of woven glass fibers embedded in an epoxy resin to provide a dielectric separation between circuit layers (see Figure 1).

� � � � � A double thickness of glass fibers at the cross over points in a material weave results in variations of the epoxy/glass ratio between points along an external circuit and the internal reference plane below it.

Description

        � � � � � The disclosed method is PCB fabrication that reduces the range of impedance and dielectric constant variation. The key elements of the method include:

•        � � � � Cap lamination, which is typically used for laser-drilled microvias, can be applied to conventional PCBs for tighter impedance control.

•        � � � � Eliminating the irregular thickness of glass fibers results in a more homogenous diel...