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BLIND & BURIED VIAS

With the industry moving towards finer pitch devices, the problem of fanning out connections from BGA’s and SMT devices increases. When the limits have been reached on track widths and sizes the next step it to use buried VIAS.

These holes connect the outer layers to inner layers but do not go through to the other side of the PCB.

Construction techniques

Controlled depth drilling
This is both cost efficient and has the added technical advantage in that there is only one set up on the drill machine giving excellent positional accuracy. Our LENZ drill machine will stop at a pre determined depth into the board on the via holes selected for this process.

LENZ Drill Machine

Cross section of a depth controlled VIA

Because of plating limitations caused by air entrapment it is important to limit the depth of the hole equal to the diameter of the drill. (Smallest drill size 0.1mm)

Sequential build
This method involves producing separate bonded cores which are drilled and plated first like a normal multilayer board. The cores are then bonded together before the final drill and plate operations. The through holes of the cores then become blind VIAS.

Sometimes the design requires the VIAS to be totally embedded in the board to form the buried VIAS.

VIAS Sequential builds are the least cost effective way to produce blind VIAS, but do offer greater flexibility to overcome design constraints.