3D Diagram Analyzes The Internal Structure of The Multi-Layer PCB Board

When hardware engineers are new to multi-layer PCBs, it is easy to get dizzy. It’s ten or eight layers, like a spider’s web.

Today, I found several internal structure diagrams of multi-layer PCB circuit boards, and used three-dimensional graphics to show the internal architecture of various laminated structures.

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The core of the high-density interconnection board (HDI) is in the hole

The line processing of multi-layer PCB is no different from that of single layer and double layer, and the biggest difference is in the process of passing holes.

The lines are etched out, the holes are drilled and then copper plated out, these do hardware development everyone understands, there is no need to repeat.


Multilayer circuit boards, usually have through hole plate, first-level board, second-level plate, second-level laminated plate these several. Higher level such as three level board, arbitrary layer interconnection board is usually used very little, the price thief is expensive, first not to discuss.


Under normal circumstances, 8-bit single-chip microcomputer products with 2-layer through hole plate; 32-bit single-chip microcomputer level intelligent hardware, using 4-6-layer through hole plate; Smart hardware at Linux and Android levels, using 6-layer through-hole to 8-level first-level HDI boards; Compact products such as smart phones generally use 8-layer first-level to 10-layer second-level circuit boards.

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The most common through hole

There’s only one through-hole, from the first to the last. Whether it is an external line or an internal line, the hole is pierced, which is called a through-hole plate.

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Through the hole plate and the number of layers does not matter, usually we use 2 layers are through the hole plate, and many switches and military circuit boards, do 20 layers, or through the hole.

The circuit board is drilled through with a drill bit, then copper is plated in the holes to create a path.

It should be noted here that the inner diameter of the through hole is usually 0.2mm, 0.25mm and 0.3mm, but generally 0.2mm is much more expensive than 0.3mm. Because the drill bit is too thin and easy to break, the drill is slower. The extra time and the cost of the drill is reflected in the rise in the price of the circuit board.


Laser hole for high density board (HDI board)

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This diagram is a laminated structure diagram of a 6-layer, 1-order HDI board, with laser holes on both surface layers and 0.1mm bore diameter. The inner layer is a mechanical hole, equivalent to a 4-layer through hole plate, and the outside is covered with 2 layers.

The laser can only punch through the glass fiber plate, can not punch through the metal copper. So the outer surface punching will not affect the other lines inside.

After the laser is drilled, the copper is plated to form a laser through hole.


Two layers of laser holes on a 2-stage HDI board

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This diagram shows a 6-layer, 2-order staggered HDI board. Usually, we use 6 layers and 2 levels less, mostly 8 layers and 2 levels. There are more layers here, same thing as six.

The so-called second order is that there are two layers of laser holes.

The so-called wrong hole is that the two layers of laser holes are staggered.

Why stagger it? Because the copper plating is not satisfied, the hole is empty, so it can not directly punch holes on the above, to stagger a certain distance, and then play a layer of empty.

6 layers of second order =4 layers of first order plus 2 layers.

8 layers of second order =6 layers of first order plus 2 layers.



The process of laminated orifice plate is complicated and the price is higher

Multilayer PCB board5


The two layers of laser holes in the staggered plate overlap. The line will be tighter.

The inner laser hole needs to be electroplated and filled, and then the outer laser hole is made. The price is more expensive than the error hole.


Ultra-expensive arbitrary layer interconnect plate multi-layer laser hole stack

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That is, each layer is a laser hole, and each layer can be connected together. You can line the line any way you want, punch the hole any way you want.

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