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Understand the design rules of PCB vias in one article!
2021-09-11
View:24
Author:Frank

Vias (VIA), holes on the circuit board, connect the lines between different layers, changing the circuit boardfrom a planar structure to a three-dimensional structure.

It is too difficult for single-layer lines to not cross, and double-layer or more layers of lines must be connected through vias. Through the copper on the hole wall, the circuit copper wires of the upper and lower layers are connected.

Single-layer PCB, sometimes cannot be routed, you must change layers through vias

Large and small vias to connect circuits of different layers

What types of vias are there?

There are mainly two types of via holes on the circuit board: mechanical holes and laser holes.

Mechanical hole: A hole drilled with a mechanical drill bit. The inner diameter of the hole is above 0.2mm. The holes drilled with a thicker drill bit will be larger.

Consumer electronic products are usually designed with an inner diameter of 0.3mm. Ordinary circuit board factories can make 0.3mm mechanical holes.

If you use the mechanical holes of 0.2mm and 0.25mm, the drill bit will be broken at a slower speed and the bit will be more expensive. Not all PCB manufacturers can make such a small mechanical hole.

The drill bit penetrates the circuit board at once, so mechanical holes are also called through holes.

pcb board

Laser hole: A hole made with a laser. The inner diameter is generally 0.1mm. There are few laser holes with other specifications.

Because the power of the laser is limited, it cannot directly penetrate the multilayer PCB board, and it is usually used to make the blind hole on the surface.

Precautions for PCB board via design

The aperture should be as large as possible: As mentioned above, small drills should be used for small holes. Small drills are expensive and have high requirements for the board factory. If the circuit board area is large, even 0.5mm inner diameter mechanical holes can be used.

Try not to use laser holes: that is, try not to use laser holes. Circuit boards with a layer of laser holes are 30% more expensive than those without laser holes (first-order boards). The one with two layers of laser holes is 30% more expensive than the one with one layer of laser holes (second-order board).

Other more expensive designs: the more complex the via process, the higher the price of the circuit board, and the difference between the cheapest and the most expensive is more than a few times. For example, a 0.2mm mechanical hole is about 20% more expensive than a 0.3mm mechanical hole circuit board; a laminated hole board with two layers of laser holes is more than 20% more expensive than a staggered hole board with two layers of laser holes; any layer of interconnection that Apple phones like to use The board is more than 10 times more expensive than the ordinary circuit board with only mechanical holes (the whole board is overlapped with laser holes).

Dense perforation, regular arrangement or random arrangement?

The inner surface area of each via hole is limited, and the current passing through is also limited.

For PCB lines that need to pass large currents such as power lines and ground lines, many vias need to be punched.

Random punching and regular punching

These vias can be arranged regularly in a matrix or randomly. Is there any difference between the two?

The regular arrangement is better than the random arrangement. The drawing speed of random arrangement is fast. Most companies do not have mandatory requirements, and PCB engineers with "obsessive-compulsive disorder" like to use rules.

A matrix of regularly arranged vias may have a stronger ability to block signals in some directions. If you don’t deliberately chase to look good, random punching will be more secure.

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