Buried and Blind Vias

Buried and blind via’s are advanced design and manufacturing process’s when space restrictions or design parameters dictate that you can’t have drilling passing through the entire length of the board, from the top to the bottom layer.

Buried via’s connect two or more layers within a multilayer without having direct connection to either the top or bottom surface layer. These via’s are usually on thin core laminate inner layers allowing micro via hole size to be used. Finished hole sizes of 0.10mm can be accomplished.

Blind via’s connect either the top or bottom surface layers to the inner layers but do not penetrate the entire printed circuit board. The copper surface z-axis feature on our Schmoll drill machine allows close tolerance z-axis controls. Due to the advanced plating process specialist drills are used with diameters of 0.12mm and 0.40mm. The maximum drill depth has to be controlled to allow the correct plating parameters. If the hole is too deep then the copper can’t plate the entire length of the hole, resulting in opens. The depth of the hole is a 1 to 1 ratio of drill width to hole depth. If a deeper depth is required blind via’s can be stacked.

As with any advanced process, buried and blind via holes will increase the cost of your PCB. If they can be avoided, by rerouting the tracks etc, then this is recommended.

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cross section of Blind via's in a printed circuit board