PCB News - The design process of high-end PCB boards

When hardware engineers are new to multilayer PCB, it is easy to get dizzy. There are ten and eight layers at every turn, and the lines are like spider webs.

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

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

The circuit processing of multilayer PCB is no different from single-layer and double-layer. The biggest difference lies in the process of vias.

The lines are all etched, and the vias are all drilled and then plated with copper. Everyone who does hardware development understands these, so I won't go into details.

Multilayer circuit boards usually include through-hole boards, first-level boards, second-level boards, and second-level stacked-hole boards. Higher-end boards, such as third-order boards and arbitrary-layer interconnect boards, are usually used very little and are expensive, so I won't discuss them first.

In general, 8-bit single-chip microcomputer products use 2-layer through-hole boards; 32-bit single-chip microcomputer-level smart hardware uses 4-layer-6-layer through-hole boards; Linux and Android-level smart hardware uses 6-layer through-hole to 8-level HDI board; compact products such as smart phones generally use 8-layer first-order to 10-layer 2-layer circuit boards.

8 layers 2 steps stacked holes, Qualcomm Snapdragon 624

Through hole

There is only one type of via hole, from the first layer to the last layer. Regardless of whether it is an external circuit or an internal circuit, the holes are punched through, which are called through-hole boards.

Through-hole boards have nothing to do with the number of layers. Everyone usually uses through-hole boards with 2 layers, but many switches and military circuit boards do 20 layers with through-holes.

Use a drill to drill through the circuit board, and then plate the hole with copper to form a via.

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 time spent and the cost of the drill bit are reflected in the increase in the price of the circuit board.

Laser hole of high density board (HDI board)

This picture is a laminated structure diagram of a 6-layer 1-stage HDI board. Both layers on the surface are laser holes, with an inner diameter of 0.1mm. The inner layer is a mechanical hole, which is equivalent to a 4-layer through-hole board, and the outer layer is covered with 2 layers.

The laser can only penetrate glass fiber sheets, not metal copper. Therefore, the outer surface punching will not affect other internal circuits.

After the laser has drilled the hole, go to copper plating again, and the laser via is formed.

2nd order HDI board, two layers of laser holes

This picture is a 6-layer, 2-step HDI board with wrong holes. Usually, people use 6 floors and 2 levels few, and most of them start with 8 floors and 2 levels. There are more layers here, the same as 6 layers.

The so-called 2nd order means that there are 2 layers of laser holes.

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

Why staggered? Because the copper plating is not full, the hole is empty, so you can't directly drill holes on it, you have to stagger a certain distance, and then make a layer of empty.

6 storeys second level = 4 storeys 1 level plus 2 layers outside.

8 storeys second level = 6 storeys 1 level plus 2 layers outside.

Stacked orifice plate, complex process, higher price

The two layers of laser holes of the wrong hole plate overlap each other. The line will be more compact.

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 wrong hole.

Super expensive any layer interconnection board Multilayer laser stacking hole

means that each layer is a laser hole, and each layer can be connected together. You can route the cables as you want, and punch as you want.

Layout engineer feels cool to think about it! Never worry about not being drawn anymore!

I want to cry when I think about purchasing it, more than 10 times more expensive than ordinary through-hole boards!

Therefore, only products like the iPhone are willing to use it. For other mobile phone brands, I have never heard of anyone who has used any layer of interconnection boards.

to sum up

Finally, put a picture, and compare it carefully.

Please pay attention to the size of the observation hole and whether the pad of the hole is closed or open.