“VIAS IN PCB”
VIA plays an important role in PCB. Let’s discuss about via, its types and applications.
What is via?
Vias are the small conductive paths that establish electrical connections between layers of a PCB. They are formed by drilling holes in the PCB which are then filled with copper. Vias can vary in size, pad shape and hole diameter(diameter range: 0.15mm to 0.8mm). The depth of via can vary based on number of layers (Eg: 2-layer: 1mm, 12-layer: 6–8mm).
COMPONENTS OF VIA:
- BARREL: is a conductive tube that fills the drilled hole.
- PAD/ ANNULAR RING: It connects the each end of barrel to the plane.
- ANTIPAD: It is a clearance hole between the barrel and non contact metal layer.
Different types of vias:
- THROUGH HOLE VIA: It passes through the entire board, from the top layer to the bottom layer of the PCB. It can be plated through hole(PTH) or a non-plated through hole(NPTH). It is well suited for low-speed designs.
PTH: With PTH, there is a conductive path from one side of the board to the other. After drilling the holes, a thin layer of copper is plated onto the walls.
NPTH: With this, there is no copper plated onto the walls of the holes. So, there is no electrical path. It is used for mounting the mechanical parts.
- MICROVIA: Via length is less than 0.25 mm and depth is not more than 2 layers. Their small size and aspect ratio enable to used in HDI design. The process of copper plating is tedious for microvias.
Microvia features -> Capture land: is where microvia originates.
Target land: This is where the microvia ends.
Aspect ratio: This is the ratio between the depth and diameter of the hole.
- STACKED VIA: This consists of multiple vias layered directly on top of each other.
- STAGGERED VIA: This connects different layers of the board but does not come in direct contact. Their positions are on adjacent layers.
- SKIPPED VIA: This connects multiple layer but does not have an electrical connection with specific layers.
- BLIND VIA: These connect from an outer layer(either top or bottom) and end in at least one interior layer, without passing through the entire PCB. They are hidden from one side, used for reducing the size of PCB and helps to maintain the Signal Integrity.
- BURIED VIA: These do not have connections with any outer layers but connect one or more interior layers. They are hidden from both sides and enhance Power integrity by providing low impedance path for power distribution within layers.
Via in pad/VIP technology:
VIP is a kind of placing the via in the copper landing pad (footprint) of a component. It helps to reduce inductance and improve routing.
Stitching vias: They are often used to provide the low impedance path for signals. It is to ensure proper grounding and minimize the signal interference, thereby improving the signal integrity of the circuit.
Thermal vias: They are designed to help dissipate heat from the surface of a PCB in high power applications such as in power transistors.
Via covering means that the vias are covered by solder mask. This is done to prevent the solder paste from getting into the vias, which would cause a short circuit.
Via Tenting: This is the process of covering the via with a solder mask, leaving the via open on one side.
Via Plugging : This is the process of filling the via partially, leaving upper/bottom portion of via open.
Via Filling: This is the process of completely filling the via with a non-conductive material such as epoxy or resin. This is done to avoid the penetration of solder paste.
Overall, the choice of via type depends on the specific requirements of the PCB design such as size, density and thermal management.
Thank you,
Sathya Priya N.
