Due to the increasing complexity of design structures blind vias and buried vias are increasingly used in high-density circuit boards (HDI).

A blind Via connects exactly one outer layer with one or more inner layers.

A buried via is a via between at least two inner layers, which is not visible from the outer layers. This technology allows more functionality in less board space (packing density).

For cost reasons, we recommend avoiding an overlap of blind and buried vias in the layer build-up! For example, avoid blind vias from L1 - L3 and simultaneously buried vias from L2 - L4.

Blind Via

Microsection of a blind via

Blind vias are used to connect one outer layer with at least one inner layer.

The holes for each connection level must be defined as a separate drill file.

The ratio of hole depth to drill diameter (aspect ratio) must be ≤ 1.

The smallest hole determines the depth and thus the max. distance between the
outer layer and the corresponding inner layers.

 
Design parameters for printed circuit board blind vias.

 

 

Design Parameters

  Ø min. Ø max Via Pad Restring* Aspect Ratio
Blind Via (mecanical) 100µm 0,4mm 400µm 150µm 1:1 (a.A. 1:1,2)
Blind Via (laser) 75µm 0,4mm 225µm 75µm 1:1

* circular

Your advantage: Whether laser or mechanically drilled, we always use the best / cheapest technology suitable for the job!

Optional: Via-in-Pad

Copper filled via

You can also place your blind vias within pads (via-in-pad).

The following applies:

  • Ø ≤ 100µm - copper filled (galvanic)
  • Ø ≤ 400µm - filled with non-conductive paste and overplated
  • Production according to IPC 4761 Type VII
  • Aspect Ratio 1:1

See also Via-in Pad (Via Filling).

 
  Ø min. Pad size min. SS-clearance min. SS-bridge min.
Via-in-Pad (standard) 200µm 400µm 50µm 100µm
Via-in-Pad (extreme)* 100µm 300µm 50µm 100µm

 

* Note: Most economical are via-in-pad solutions with Ø ≥ 200 microns!

Buried Via

Microsection of a circuit board buried via.

Buried vias are used to create connections of the inner layers, which have no contact with the outer layers.

The holes for each connection level must be defined as a separate drill file.

The ratio of hole depth to drill diameter (aspect ratio) must be ≤ 12.

The smallest hole determines the depth and thus the max. distance between the respective inner layers.

 
Design parameters for printed circuit board buried vias.

 

 

Design Parameters

  Ø min. Ø max Via Pad Restring* Aspect Ratio
Buried Via 100µm 0,4mm 300µm 150µm 1:10
Buried Via (extreme**) 75µm 0,4mm 225µm 75µm 1:12

* circular, ** attention: higher costs

Generally: The larger you choose the annular rings on the inner layers, the more stable the connection.