> Best suited for small components and micro bgas.
> Copper plate closed for small drill vias (for conductive finish).
> Non-conductive epoxy matches CTE of laminates better.
Component design today is being driven by consumer demand for ever-smaller devices. This process allows the PCB designer to route the device, and have the via hole filled solid (either by plating closed with copper or epoxy fill). The process also offers stability for CTE, and keeps out plating bath solution – which can compromise the PCB.
Conductive epoxy-filled is the best practice for the vias to have a finished diameter between .008” and .018”. This allows the epoxy – conductive or non-conductive – to be pushed through the hole completely, but not to run out it. The associated aspect ratio is best if the depth-to-diameter is less than 10:1.
A plate-shut process provides greater reliability for micro via, as opposed to filling with non-conductive ink and then plating over. Filling vias creates a solid core. This allows for a flat surface to be plated, and also keeps the solder at the assembly level from leaking through and compromising the solder joint. This provides for the most reliable finished assembly.