When hardware engineers first come into contact with multi-layer PCBs, it is easy to get confused. There are often ten or eight floors, and the lines are like spider webs.
Today I drew several internal structure diagrams of multi-layer PCB circuit boards, using three-dimensional graphics to show the internal structure of PCB diagrams with various stacked structures.
The circuit processing of multi-layer PCB is no different from that of single-layer and double-layer. The biggest difference lies in the through-hole process.
The circuits are all etched, and the vias are drilled and then plated with copper. Everyone who develops hardware knows these, so I won’t go into details.
Multilayer circuit boards usually include through-hole boards, 1-stage board,2-stage board, and 2-stage stacked hole boards. Higher-end boards such as 3-stage boards and arbitrary-layer interconnection boards are rarely used and are very expensive, so we won’t discuss them further now.
Generally speaking, 8-bit microcontroller products use 2-layer through-hole boards; 32-bit microcontroller-level smart hardware uses 4-6-layer through-hole boards; Linux and Android-level smart hardware uses 6-layer through-hole to 8-layer through-hole boards. HDI board; Compact products such as smartphones generally use 8-layer first-level to 10-layer 2-level circuit boards.
There is only one kind of via hole, which is drilled 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 and are called through-hole boards.
The through-hole board has nothing to do with the number of layers. Usually the 2-layer boards used by everyone are through-hole boards, but many switches and military circuit boards have 20 layers and are still through-hole boards.
Use a drill to drill through the circuit board and then plate copper in the holes to create vias.
It should be noted here that the inner diameters of through holes are 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, it drills slower. The extra time spent and the cost of drill bits are reflected in the increase in the price of circuit boards.
This picture is a laminated structure diagram of a 6-layer 1st-order HDI board. Both surface layers 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 plate, and the outer layer is covered with 2 layers.
The laser can only penetrate fiberglass plates, not metal copper. Therefore, drilling holes on the outer surface will not affect other internal circuits.
After laser drilling, copper plating is performed to form laser vias.
This picture is a 6-layer 2-stage staggered hole HDI board. Usually, few people use 6 layers and 2 levels, but most people use 8 layers and 2 levels. There are more layers here, which is the same as 6 layers.
The so-called 2nd level means that there are 2 layers of laser holes.
The so-called staggered holes mean that the two layers of laser holes are staggered.
Why stagger it? Because the copper plating is not full and the holes are empty, you cannot drill holes directly on them. You have to stagger them by a certain distance and add a layer of holes.
6 floors and 2 floors = 4 floors and 1 floor plus 2 floors outside.
8 floors and 2 floors = 6 floors and 1 floor plus 2 floors outside.
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.
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.
Layout engineers think about it! No longer afraid of not painting!
Think about purchasing want to cry, more than 10 times more expensive than ordinary through hole plate!
Put a picture at the end and compare it more closely.
Note the size of the hole and whether the pad for the hole is closed or open
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