Types of vias on the PCB board and precautions for punching

2021-03-01 11:51:26 Edward Qin 139

Vias are part of the printed circuit board (PCB) design. The function of vias is to electrically connect, fix and locate components. A via is composed of three parts: the hole, the pad area around the hole, and the POWER layer isolation area. Production of via holes: a layer of metal is plated on the cylindrical surface of the hole wall of the via hole, which is used to connect the copper foil of the middle layers. The upper and lower sides of the via hole are made into pads, and the lines are directly connected (or not connected).

Vias are generally divided into three categories: blind holes, buried holes and through holes. Blind holes-located on the top and bottom surfaces of the printed circuit board, have a certain depth (aperture and hole depth are in a certain ratio), and are used to connect the surface circuit and the inner circuit. Buried holes-connection holes in the inner layer of the circuit board (not visible on the surface of the circuit board). Through hole-through the entire circuit board, generally used for positioning and installation of components.

In the general PCB design, because the parasitic capacitance and parasitic inductance of the via have little effect on it, the via design of the 1 to 4 layer PCB is usually 0.36mm (aperture)/0.61mm (pad)/1.02 mm (POWER isolation area) via. For signal wires with special requirements, such as power wires, ground wires, etc., through holes of 0.41mm/0.81mm/1.32mm are generally used.

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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 the mechanical holes of 0.2mm and 0.25mm are used, the fine drilling speed of the drill bit is slow and the bit is easy to break, and the price will be more expensive. Not all PCB manufacturers can make such small mechanical holes. The drill bit penetrates the circuit board at once, so mechanical holes are also called through holes.

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)