4 Layer PCB Layout Tutorial, Stack-up design, and Cost of manufacturing

4-layer PCB refers to the PCB board comprising 4 substrate or glass fiber layers. There are 4 primary wiring layers, such as the top. Bottom, VCC, and GND layers. Generally, buried holes, through holes, and blind holes are used for connecting the layers of the 4-layer PCB. There are many more blind and buried holes than the double-side boards. Additionally, do not run the signal tracks on the 2-layer of the GND and VCC. The 4-layer PCB comes with many more benefits than the double-sided boards. They are made more compact, provide reduced PCB cost, improve noise immunity, and are easier to lay out.

Capability Of The 4-layer PCB Design

The 4-layer PCB Design offers free DFM checking. The recommended option for the 4-layer PCB is as follows:

• Copper Thickness: Maximum of 6 oz inner copper to 12 oz external copper. 
• Min Hole: 0.15mm by the mechanical drilling of about 0.1mm by laser.
• PCB Thickness: 0.4mm-6.5mm
• Surface Process: HASL-LF, Immersion gold, Hard Gold, Immersion Tin.
• Solder Mask: Green, Yellow, White, Black, or any other customized color.
• Silkscreen: Black, yellow, white, or custom.
• Accept 4-layer PCB with buried and blind holes. 

How To Design The 4-layer PCB?

4-layer PCB Layer-out guidance

The 4-layer PCB design includes a top layer, two middle layers, bottom layer. The bottom and top layers are laid out with the signal lines. The middle layer uses the command LAYER/DESIGN STACK MANAGER for adding INTERAN PLANE1 and the INTERNAL PLANE 2 as the most used powering layers in the 4-layer PCB such as the VCC and the ground layering like the GND that is to connect the corresponding networking labels. Remember that you should not add a layer since it will increase the MIDPLAYER, primarily used for multi-layering signal line placement.

PLANE 2 and PLANE 1 are the two copper layers connecting the power supply ground of the GND and the VCC. If there are several power sources, such as the GND2 and VCC2, initially, use the wire that is thicker in the PLANE1 or PLANE2, or FILL. During this, the corresponding copper or wire is not visible, and the filling or the wiring is seen when exposed to light. 

To delimit the ground place or power for the 4-layer PCB, it is necessary to choose the SPLIT/PLACE PLANE for delimiting the area in the areas of the INTERNAL PLANE1 and INTERNAL PLANE2. The GND2 Copper and VCC2 copper should not be in the plane as the VCC. Remember that the network’s different surface layers in the same plane must not overlap. 

Suppose SPLIT 1 and 2 overlap in the same PLANE. The 2-pieces have separated automatically according to the SPLIT2 Border. You should pay attention to the vias or pads of the SPLIT1 when overlapping and not connect the SPLIT1 in the 4-layer PCB to the SPLIT area of the 4-layer PCB. The via holes near the area are connected to the copper within the same layering. The DIP footprint plug-ins and footprint components parts pass through the bottom and top boards, which will automatically get away from the PLANE.

The Layering Setting

There are two electrical layer types in the 4-layer PCB. You should open the 4-layer PCB prototype or the file and press the shortcut key L, and the layering setting window will open. The signal on the left is positive layering, including the bottom, top, and mid layers. The internal plane acts as the negative layer, called the 4-layer PCB prototype. 

These two coatings come with different properties and usage methods. The positive layer is usually used for pure tracking and inner and outer lines. The negative film coating is generally used as the power and ground layer. In the multi-layer and the 4-layer PCB, the power and ground layers use the whole piece or many large copper partitions of the circuit.

You must lay the copper to use the MID LAYER, the positive layer. Paving the copper will make the whole design data volume very large. It is not conducive to data transmission and communication and affects the design. With the negative film, you only have to create the THERMAL PAD junction with the inner and outer layers. It can be highly beneficial for data transmission and design.

Delete and Add the Inner Layer

In the 4-layer PCB, there are many instances where you can delete or add the layers. For instance, the double-sided board will be changed to the 4-layer PCB or the 4-layer board with higher signal needs which is upgraded to the six-layer board. If you want to add the electrical layer, follow the steps 4-layer board given below:

In the DESIGNING-LAYER STACK MANAGER, the schematic diagram of the current stack structure is on the left side. You should click on the upper layer of the 4-layer board, where you can add a new layer, such as the TOP, and then click on the ADD LAYER or ADD PLANE on the right side to complete the additional new layering. If the additional layer is the PLANE, you should assign the corresponding network to a new layer by clicking the layer’s name.

There will only be one assigned network in the 4-layer board. Generally, the GND will be efficient for ground layering. If you wish to add the network to the layer, such as the power coating, it can be achieved through internal segmentation to the subsequent operations of the 4-layer board. Hence, you must allocate the network with many connections on your 4-layer PCB.

If you tap or click on ADD LAYER or the MID LAYER, you can add the positive film, and the application method for the 4-layer PCB will be similar to the outer circuit. If you wish to add mixed electrical layering with a large copper surface and wiring surface for the power, you should use the layer generated by the ADD LAYER to the design.

Slip Of The Internal Electrical Layer

If multiple groups of power suppliers are within the design of the 4-layer PCB, you can then use the internal coating division in the powering layer for distributing the power network. You can use the command “PLACE-SPLIT PLANE. And then, set the 4-layer board in the dialog box, which pops up and specifies the network which should be allocated at the CONNECT TO NET split and insert the split according to the paving method of the copper.

Once the placement is set, the holes with the network will generate the flowering hole pads in the 4-layer board to complete the electrical connection of the powder coating. You can repeat this step until you have allocated all the power. When the internal layer of the 4-layer board needs to allocate more networks, it can be daunting to divide the inner layer and needs proper expertise.

Why Design 4-layer PCB?

The PCB cost is associated with the actual specific needs and area. If there are no specific needs, the PCB cost is almost two times that of the 2-layer PCB. However, it is not a linear relationship. In case the 4-layer PCB has impedance or blind, buried holes, the PCB cost difference will be greater.

Conclusion

After reading this article, you will learn how to design the 4-layer PCB and reduce the PCB cost. Choosing to design the PCB board by yourself will save you time and money since you can make it according to your needs and preferences.