1. Same process
It can be manufactured in PCB factory. Under normal circumstances, a copper foil is pressed on both sides of the four-layer core, and a copper foil is pressed on one side of the three-layer core. As far as the process flow is concerned, stamping is necessary.
2. Same price
The difference in the cost of the two processes is that the four-layer board has an extra layer of copper foil and an adhesive layer, and the cost difference is not large. When the sheet metal factory quotes, the quotation of 3-4 layers is generally used as a level, and the quotation is defined by an even number (of course, more than multiple layers). For example, if you design a five-layer board, the other party will quote according to the price of the six-layer board, that is, the price of the three-layer board you designed is the same as the price of the four-layer board you designed.
3. Process stability
In the PCB process, four-layer boards are easier to control than three-layer boards. Mainly in terms of symmetry, the warpage of the four-layer board can be controlled below 0.7% (ipc600 standard). However, when the size of the three-layer board is large, the warpage will exceed this standard, which will affect the reliability of the SMT patch and the entire product. Therefore, ordinary designers do not design odd-numbered layers, even if the odd-numbered layers realize the function, they will design as pseudo-even layers, that is, 5 layers are designed as 6 layers, and 7 layers are designed as 8 layers.
This is why there is no three-layer board in pcb! I hope it can provide you with some references!
