4 layer PCB

What is 4 layer PCB? Yes, you guessed right, PCB is stacked layer by layer like a hamburger A PCB with four layers is a 4 layer PCB board.

What is the difference between 4 layer PCB vs 2 layer PCB?

The most important layer in PCB is the copper foil signal layer, which is the PCB circuit. Although 2 layer PCB has two circuit layers, 4 layer PCB has four circuit layers. These circuit layers are used to connect to other electronic components in the device. Between these circuit layers is an insulating layer or Core, which is added to the circuit layer to prevent short-circuit between the circuit layers. In 2 layers or 4 layers PCB boards, they also have resistance layers, which are used at the top of the circuit layer. This prevents the copper circuit from interfering with other metal components on the PCB. They also have a screen printing layer that adds numbers and text to different components to make them easier to layout.

A common 4 layer PCB stackup is designed, the top layer and bottom layer are the signal layers, and the middle 2 layer and 3 layer are the power layer and the GND layer (ground plane layer). The power layer and the GND layer can act as isolation and reduce interference in the middle. For larger sizes, PCB boards with loose components can also be completed with 2 layer PCB. If the 2 layers PCB board is difficult to layout, can not be wired, or can easily cause interference, you can use a 4-layer PCB board to solve the space overcrowding problem.

4 layer PCB is the most basic laminated structure in multilayer PCB board, and it's a cheap PCB 4 layer board one in multilayer PCB.

4 Layer PCB stack up

4 layer PCB stackup structure

Scheme 1: the first layer is the signal layer, the second layer is the layer, the third layer is the power layer, and the fourth layer is the signal layer. The setting of scheme 1 is the main scheme for setting four layers of boards, the ground plane is below the components, and the key signals are arranged on the top layer.

Scheme 2: the first layer is the stratum, the second layer is the signal layer, the third layer is the signal layer, and the fourth layer is the power layer. Scheme 2 is applicable to the whole board with no power plane and only GND plane. The wiring of the whole board is simple, but the radiation area for the wiring of the interface filter board must be paid attention to. There are few patch components on the board, and most of them are plug-ins.

Scheme 3: the first layer is the signal layer, the second layer is the power layer, the third layer is the layer, and the fourth layer is the signal layer. Scheme 3 is similar to scheme 1 and is applicable to the bottom layout of main devices or the bottom wiring of key signals. Generally, this scheme is not used

Four-layer PCB has a larger surface copper area than 2 layer PCB, which increases the possibility of more wiring. Therefore, a 4 layer PCB is ideal for more complex devices. Due to the complexity of the 4 layer circuit, the production cost of the 4 layer PCB will be higher and the development will be slower. 4 layer PCB circuit is also more likely to have propagation delays or interaction, so a reasonable 4 layer PCB design is important.

How to design a 4 layer PCB? Let's take a look at the 4 layer PCB layout rules.

1. 4 layer PCB during the design of connecting lines above 3 points, regular yield lines shall pass through each point in turn to facilitate later test, and the line length shall be shortened as far as possible.

2. Avoid wiring around pins, and pay special attention to reducing wiring design between and around IC pins.

3. Four layer PCB is better not to route the adjacent layers in parallel. Theoretically, there will be interference as long as the lines are parallel.

4. Minimize bending wiring to avoid electromagnetic radiation.

5. The design of ground wire and power line of the multi logic circuit shall be at least 10-15mil.

6. Try to connect the ground-laying polylines to increase the grounding area. Line to line shall be kept neat.

7. At the initial stage of wiring, a space for uniform discharge of components in the later stage shall be reserved for the installation, plug-in, and welding of components in the later stage. The text is arranged in the current character layer, and the position is reasonable to avoid being blocked.

8. The placement and installation of components shall be considered from the sense of space, and the positive and negative poles of SMT components shall be marked at the end of packaging and.

9. At present, 4 layer PCB printed circuit boards can be used for 4-5mil wiring, but usually 6mil line width, 8mil line spacing, and 12 / 20MIL pad. The influence of multiple factors such as pouring current shall be considered during wiring.

10. Function block elements shall be placed together as far as possible to facilitate later inspection. Special reminder: components near LCD such as Zebra bar shall not be too close.

11. The through-hole shall be painted with green oil.

12. 4 layer PCB is better not to place pads, vias, etc. under the battery base to ensure the firmness of repeated use.

13. After wiring, carefully check whether each connection is really connected (lighting method can be used).

14. The oscillation circuit elements shall be as close to the IC chip as possible and as far away from the antenna and other vulnerable areas. The grounding pad shall be placed under the crystal oscillator.

15. Consider reinforcement, hollowing out elements, and other methods to avoid too many radiation sources.

4 layer PCB

The layout of each layer of 4 layer PCB prototype

1. The first layer in the middle has multiple GNDS laid separately, and a small number of lines can be taken, but do not divide each copper laying; The second layer of VCC copper in the middle is laid separately with multiple power supplies. A small number of wires can be laid, but do not divide each layer.

2. There are four wiring layers, generally the top layer, the bottom layer of the button layer, VCC, and GND. Generally, through-holes, buried holes, and blind holes are used to connect the layers of each other. There are more buried holes and blind holes than double-layer PCB boards. In addition, the VCC and GND layers should not take signal lines as far as possible.

The difference between 2 layer PCB vs 4 layer PCB manufacturing is that 4 layer PCB increases the work of inner circuit fabrication and lamination. The manufacturing process of 4 layer PCB is as follows:

1 cutting - 2 inner circuit fabrication - 3 inner AOI detection - 4 laminations - 5 drilling - 6 copper plating in holes - 7 outer circuit fabrication - 8 outer AOI detection - 9 solders resist printing - 10 silkscreen characters - 11 tin spraying - 12 surface treatment - 13 appearance processing - 14 electronic test - 15fqc - 16 packagings and shipment.

The 4 layer PCB manufacturing process of the inner circuit is 1 press dry film - 2 exposure - 3 development - 4 etching - 5 film removal. The dry film used here is an etching-resistant dry film, that is, the exposed dry film will not be corroded by the etching solution, so as to protect the circuit layer.

The core process of making a laminated 4 layer circuit board is that the semi-cured sheet is cooled by high temperature and high pressure, and then the circuit layers are bonded together to form a 4 layer PCB prototype. The lamination process has very strict requirements on temperature and pressure. The L2 and L3 layers in the middle belong to the inner circuit layer, which is called the core board. Before lamination, the plates shall be arranged in order, riveted with rivets, and then sent to the lamination equipment. The laminating equipment will provide temperature and pressure according to the set temperature-time curve and pressure-time curve. The maximum temperature during lamination can reach 200 degree Celsius, and the maximum pressure can be 250N / C ㎡. The thickness of H/Hoz copper foil is about 17um.

IPCB company is a professional 4 layer PCB manufacturer. We provide mass production of cheap PCB 4 layer, which has the advantage of 2 layer vs 4 layer PCB cost. If you want the best PCB price, please send the PCB Gerber file to the email of the IPCB company, and we will reply to your PCB quotation soon.