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.
Blind & Buried Vias
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
Your advantage: Whether laser or mechanically drilled, we always use the best / cheapest technology suitable for the job!
Design Parameters
| Type (A, B, C) | Ø min. | Ø max | Via Pad | Annular ring* | Aspect Ratio | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Type (A, B, C) | Blind Via (mecanical) | Ø min. | 100µm | Ø max | 0,4mm | Via Pad | 400µm | Annular ring* | 150µm | Aspect Ratio | 1:1 (rfq 1:1,2) |
| Type (A, B, C) | Blind Via (laser) | Ø min. | 75µm | Ø max | 0,4mm | Via Pad | 225µm | Annular ring* | 75µm | Aspect Ratio | 1:1 |
* circular
Optional: Via-in-Pad
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 pasteand overplated
- Production according to IPC 4761 Type VII
- Aspect Ratio 1:1
See also Via-in Pad: Via Filling.
Most economical are via-in-pad solutions with Ø ≥ 200 microns!
| Type | Ø min. | Pad size min. | SS-clearance min. | SS-bridge min. | |||||
|---|---|---|---|---|---|---|---|---|---|
| Type | Via-in-Pad (standard) | Ø min. | 200µm | Pad size min. | 400µm | SS-clearance min. | 50µm | SS-bridge min. | 100µm |
| Type | Via-in-Pad (special) | Ø min. | 100µm | Pad size min. | 300µm | SS-clearance min. | 50µm | SS-bridge min. | 100µm |
SS = solder-stop
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.
Generally: The larger you choose the annular rings on the inner layers, the more stable the connection.
Design Parameters
| Type (A, B, C) | Ø min. | Ø max | Via Pad | Annular ring* | Aspect Ratio | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Type (A, B, C) | Buried Via (standard) | Ø min. | 100µm | Ø max | 0,4mm | Via Pad | 300µm | Annular ring* | 150µm | Aspect Ratio | 1:10 |
| Type (A, B, C) | Buried Via (special) | Ø min. | 75µm | Ø max | 0,4mm | Via Pad | 225µm | Annular ring* | 75µm | Aspect Ratio | 1:12 |
* circular
