Preventing conductive anodic filament (CAF) formation by sealing discontinuities in glass fiber bundles

摘要

An enhanced substrate for making a printed circuit board (PCB) includes a silane applied to the ends of glass fibers in via holes. In one embodiment, during a plated through-hole (PTH) via fabrication process, glass fiber bundles exposed in a drilled through-hole are selectively sealed. For example, after the through-hole is drilled in a substrate, the substrate may be subjected to an aqueous silane bath (e.g., an organo trialkoxysilane in an aqueous solution of an acid that acts as a catalyst) to deposit a layer of silane on the exposed glass fiber bundle ends. For example, trialkoxy groups of the silane may react with exposed silanols on the glass to form a siloxane, which is further polymerized to form a silane polymer barrier layer on the exposed glass fiber ends. The barrier layer effectively seals the glass fiber bundles and eliminates the conductive anodic filament (CAF) pathway between PTH vias.

主权项

1. An apparatus, comprising:
a substrate having a plurality of insulator layers and one or more conductive traces, wherein each of the insulator layers comprises a glass fiber substrate impregnated with a varnish coating, wherein a plurality of through-holes each of which extends completely through the substrate from a first surface of the substrate to a second surface of the substrate and passes through the glass fiber substrate of each of the insulator layers, and wherein the glass fiber substrate of one of the insulator layers includes one or more glass fibers extending from a first one of the through-holes to a second one of the through-holes; a silane polymer barrier layer formed over a first end of each of the one or more glass fibers in the first one of the through-holes; a silane polymer barrier layer formed over a second end of each of the one or more glass fibers in the second one of the through-holes.