When hardware engineers are just exposed to multi-layer PCB, it is easy to see dizzy. Ten or eight layers at a time, the wiring is like a spider web.

Draw several internal structure diagram of multi-layer PCB circuit board, and display the internal structure of various laminated PCB diagram with three-dimensional graphics.

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 PCB, but the biggest difference is in the process of through-hole.

Lines are etched out, holes are drilled and copper plated out, these do hardware development, we all know, do not belabor.

Multilayer circuit board, usually through the hole board, the first order board, the second order board, the second order laminated hole board. Higher order such as the third board, any layer of interconnection board usually used very little, the price thief expensive, not much discussion first.

In general, 8-bit single-chip products with 2 layer through the hole plate; 32-bit microcontroller level intelligent hardware, using 4-6 layer through hole board; Linux and Android grade smart hardware, using 6-layer through-hole to 8 first-order HDI board; Compact products, such as smartphones, typically use eight layers of first-order to 10 layers of second-order circuit boards.

The most common through hole

There is only one type of perforation, from the first layer to the last layer. No matter the external circuit or the internal circuit, the hole is punched through, called through hole plate.


The circuit board is drilled through with a drill and copper plated in the hole to create a pathway.

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 slow. The extra time and cost of the drill is reflected in the higher price of the circuit board.

Laser holes for high-density board (HDI board)

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

The laser can only hit through the glass fiber plate, not through the metal copper. So drilling the outer surface will not affect the other wiring inside.

After the laser punched the hole, the copper was removed to form the laser through hole.

The second order HDI plate has two layers of laser holes

The picture above is of a 6-layer, 2-step split-hole HDI plate. At ordinary times we use 6 layers of 2 less, mostly 8 layers of 2. More layers here, same thing as 6.

By order 2, there are two layers of laser holes.

The so-called wrong hole, is two layers of laser hole is staggered.

Why stagger them? Because the copper plating is not satisfied, the hole is empty, so it can not be directly drilled on the top, to stagger a certain distance, and then hit a layer of empty.

6 levels of 2nd order =4 levels of 1st order plus 2 levels.

8 second floors =6 first floors plus 2 floors.

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

The two layers of laser holes in the staggered hole plate are overlapped. The lines will be more compact.

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

Super expensive multi-layer laser hole stacking of any layer interconnected plate

Is that each layer is a laser hole, and each layer can be connected together. Thread as you like, and punch as you like.

Layout engineer think feel good! I'm not afraid I can't draw it anymore!

Purchasing just want to cry, more than 10 times more expensive than the ordinary through plate!

So, only products like the iPhone are willing to use. Other phone brands. I don't know anyone who's used any laminated boards.



Let's put a picture at the end and compare it a little bit more.

Note the size of the holes and whether the pads for the holes are closed or open.

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