PCB Technical - How to determine the number of PCB copy board layers?

Why do PCB copy boards need to confirm the number of layers

The number of board layers has a lot to do with the time and difficulty of PCB copying. After getting the customer's circuit board, the number of board layers needs to be estimated, and then a more accurate delivery date and quotation can be provided to the customer.

How to determine the number of PCB layers?

The circuit connection of the multilayer board is through buried via and blind via technology. Most motherboards and display cards use 4-layer PCB boards, and some use 6, 8-layer, or even 10-layer PCB boards. If you want to see how many layers the PCB has,

you can identify it by observing the via holes, because the 4-layer boards used on the motherboard and display card are traces on the first and fourth layers, and the other layers have other uses (ground wires). And power supply). Therefore, like the double-layer board, the via hole will penetrate the PCB board. If some vias appear on the front of the PCB but cannot be found on the reverse, then it must be a 6/8-layer board. If the same via holes can be found on both sides of the PCB, it will naturally be a 4-layer board.

Tips: Point the motherboard or display card to the light source. If the position of the guide hole can transmit light, it means that it is a 6/8-layer board; otherwise, it is a 4-layer board.

Single-sided PCB determination

On the bottom PCB board, the parts will be gathered on one side, and the wires will be gathered on the other side. Since the wires only appear on one side in between, we call this kind of PCB a single-sided (Single-sided).

Single-sided PCB copy board

Because single-sided circuit boards have many serious bindings on the planned circuit (because only one side is needed, the wiring room cannot be crossed* and it is necessary to go around a separate path), so only the previous circuit is used to use this type of board.

How to determine the double-sided circuit board

This kind of circuit board has wiring on both sides. However, to use double-sided wires, it is necessary to have a proper circuit connection between the two sides.

Double-sided PCB copy board

This kind of "bridge" between circuits is called a via. Guide holes are small holes on the PCB that are covered or coated with metal, which can be connected with double-sided wires. Since the area of the double-sided board is twice as large as that of the single-sided board, and because the wiring can be interwoven (can be wound to the other side), it is more suitable for use in circuits that are more messy than the single-sided board.

How to determine the multi-layer PCB board

Multi-layer circuit board: In the case of more messy application requirements, the circuit can be arranged into a multi-layer plan and pressed together, and through-hole circuits are arranged between layers to connect the circuits of each layer.

Multilayer PCB copy board

The inner circuit copper foil substrate is first cut into specifications suitable for processing and production. Before laminating the substrate, it is usually necessary to properly roughen the copper foil on the surface of the board by brushing, microetching, etc., and then attach the dry film photoresist tightly to it at the appropriate temperature and pressure. The substrate with dry film photoresist is sent to the UV exposure machine for exposure. The photoresist will undergo polymerization reaction after being irradiated by ultraviolet rays in the light-transmitting area of the negative (the dry film in this area will be affected by the later development and copper etching process). Save it as an etching resist), and transfer the circuit image on the negative to the dry film photoresist on the board. After tearing off the maintenance film on the membrane surface, first use sodium carbonate aqueous solution to develop and remove the unlit area on the membrane surface, and then use a mixed solution of yansuan and hydrogen peroxide to corrode the exposed copper foil to form a circuit. At the end, use an aqueous solution to wash away the dry film photoresist that has been exhausted.

PCB layers

In fact, a more general and simple way of distinguishing is to pick it up against the light. The inner core is opaque, that is, it is all black, which is a multilayer board, otherwise it is a single and double panel. Single-sided board, only one layer of wiring, no copper in the hole. The double-sided board has lines on the front and back, and there is copper in the lead-through hole.

With regard to the inner PCB circuit board of six layers (inclusive), the riveting reference hole for the alignment of the line between the layers is punched out by the active positioning punching machine. In order to increase the wiring area of the four-layer circuit board, the multilayer board uses more single or double-sided wiring boards. The multi-layer board uses several double-sided boards, and a layer of insulating layer is placed between each board and then glued (compressed) firmly. The number of layers of the board means that there are several independent wiring layers. Usually the number of layers is even and includes the two outer layers. Most motherboards are planned with 4 to 8 layers, but technically it can achieve nearly 100 layers.