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Differ in size and the application is mandated by current conduction capability, dimensions to fit in a location, capability of the printed circuit manufacturer to make them, reliability redundance, and your choice to have many small or a big single as to spread conductivity and ground planes
Usually PCB manufacturers provide informations about their standard capabilities.
There is a wide range
* of application requirements
* a wide range of PCB manufacturers regarding techniques, materials, precision ...
* a wide range of cost
The close you go to the high end technology, the higher the cost, the lss manufacturers you will find, the higher error rate you may expect.
I try to go a conservative way, when possible.
And a have a couple of PCB manufacturer for:
* low / high volume,
* delivery time
* low cost / high end
A Microvia is basically a very small via. Most PCBs now days are multi-layer boards. Vias are used to make connections between each layer of the printed circuit board. Microvias, as the name suggests have a smaller diameter and thus take up less board real estate and leave more space for routing. They also have a lower parasitic capacitance which is important for high-speed circuits.
Most PCB companies classify vias with a diameter less than 150 microns to be microvias. These vias lower the possibility of any type of manufacturing defect since they are drilled using lasers which mitigates the chances of any residue left after the proces
Microvias are used to connect one layer of the board to its adjacent layer and have a very small diameter in comparison to the mechanically drilled vias such as PTH.
When copper is plated on the holes, holes are made through the PCB to route electrical connections between layers. These holes are known as vias (plated through-holes). The hole can be classified as a microvia, depending on its diameter.
According to the Institute of Printed Circuit Boards, a microvia is any hole drilled in a PCB with a 1:1 aspect ratio and not exceeding 0.010 inches. The IPC used to consider microvias according to their size if they were smaller than 0.006 inches. With the advancement of technology, lasers can drill these small holes more often.
The IPC adopted the microvia definition of the 1:1 aspect ratio to prevent meanings from changing. Microvias, also known as uVias or microwires, can be used to connect layers within a PCB. They are usually limited to connecting two layers at a time.