Vias provide electrical connections between layers in a printed circuit board. There are three main types of vias: through vias connect outer layers, blind vias connect an internal layer to one outer layer, and buried vias connect internal layers without connecting to outer layers. Stub vias have portions that originate on one layer and terminate on another layer, with a stub portion continuing to another layer. Back drilled vias remove stub portions through post-fabrication drilling. Microvias use lasers to generate connections between layers in multilayer boards. Via filling techniques include direct filling without a stencil or indirect filling using screen printing or roller coating with a stencil.

1. 2 0 1 3 / B / 0 6
2 0 1 3 / B / 2 3
Overview Of Vias

2. Via
A Via is an electrical connection between layers in a
physical electronic circuit that goes through the
plane of one or more adjacent layers. They can carry
signal and power between layers.

3. Types Of Vias
Basically Via are classified into mainly three section
• Through Via
• Blind Via
• Buried Via
Through Blind
Buried

4. Through Via
These types of vias originated and terminated from
the outer layers of printed circuit board. This
technique is too expensive practically.

5. Blind Via
A blind via connect one or more internal layers to
only one external layer of printed circuit board.

6. Buried Via
A buried via, a plated hole which is completely
buried with in the board. It connects one or more
internal layers and doesn’t connect any external
layer. Using buried via technology is costly because
the inner layer being interconnected need to be fully
fabricated plated before final lamination of the
printed circuit board.

7. Stub Via
The stub via is most common via configuration found in
the PCB today. They are two types of stub via:- A and B.
Stub A-: The portion originating form top layer and
terminating at same internal signal layer. The stun
portion is the remaining portion continuing from the
inner layer to the bottom layer.
Stub B-: The portion originating from one internal signal
layer and terminating on another internal signal layer.
The first stub is the from first internal layer to the top
layer; second stub from the second inner layer to the
bottom layer.

8. Stub Via

9. Back Drilled Via
Back drilling is the
process to remove the
stub portion of PTH via.
Its is post fabrication
drilling process where
back drill hole is of large
diameter than the origin
PTH. This technology is
often used instead of
blind via to remove the
stub of connector via in a
very high thick back
plane settings.

10. Micro Via
Microvias are minute drilled hole by a laser to
generate the electrical connection between the layers
in a multi layer circuit board. It is a sub part of
through via.

11. Via Aspect Ratio
Via aspect ratio is defined as the ratio of the circuit
board thickness to the smallest unplanted drilled
hole diameter. It is an important parameter to
specifying the via hole size for your design, and
designing your stack up.

12. Other types of Via
 Tented Via-: Dry film solder mask is stretched over
the hole. No other material added.
 Tented and Covered-: An additional dry film or
liquid solder mask layer covers the tenting type of a
tented via.
 Plugged-: A non conducting material penetrate
partially into the hole but does not go all the way.
 Plugged and Covered-: An additional dry film and
solder mask layer cover the plugging of a type
plugged via.

13. Other Types of Via
 Filled-: A conductive and non conductive material
penetrates completely into the hole; filling the hole
all the way through.
 Filled and Covered-: An additional dry film and
solder mask layer covers the filled material of a type
filled via.
 Filled Capped-: A metalized coating covers the filled
material of a type filled via.

14. Via Filling
Essentially there are two types of via fill material-:
o Conductive Material (Mixture of epoxy resin with Cu
and Ag particle)
o Non Conductive Material (Epoxy material filled with
inorganic material)
For both types of via fill material few prosperity are
there
o No solvent (100% solid content)
o Copper can be reliably placed across the surface of
the cured hole plugging material.

15. Via Filling Method
For filling vias there are two technique
Direct Filling (No Stencil Required)
Indirect Filling (Stencil Required)
o Screen or Stencil Print
o Roller Coating
o Through Automatic Hole Filled System