Nowadays, the trend of increasingly compact electronic products requires three-dimensional design of multilayer printed circuit boards. However, layer stacking raises new problems related to this design viewpoint. One of the problems is to obtain high-quality stack construction for the project.
With the production of more and more complex printed circuits composed of multiple layers, the stacking of PCB is becoming particularly important.
Good PCB laminate design is very important to reduce the radiation of PCB circuits and related circuits. On the contrary, poor accumulation may significantly increase radiation, which is harmful from the safety point of view.
What is PCB laminate?
Before the final layout design is completed, the insulation and copper of the PCB are layered by PCB laminate. Developing an effective stack is a complicated process. PCB connects power supply and signal between physical devices, and the correct layering of PCB materials directly affects its function.
Why do you want to laminate PCB?
Developing PCB laminate is very important for designing efficient circuit boards. PCB laminate design has many advantages, because multilayer structure can improve energy distribution ability, prevent electromagnetic interference, limit cross interference and support high-speed signal transmission.
Although the main purpose of stacking is to place multiple electronic circuits on one board through multiple layers, the structure of PCB stack also provides other important advantages. These measures include minimizing the vulnerability of circuit boards to external noise, and reducing crosstalk and impedance problems in high-speed systems.
A good PCB laminate can also help ensure a lower final production cost. By maximizing the efficiency and improving the electromagnetic compatibility of the whole project, PCB lamination can effectively save time and money.
Precautions and Rules for PCB Lamination Design
● Number of layers
A simple stack may include four layers of PCB, while a more complex board requires professional sequential lamination. Although it is more complicated, the higher number of floors allows designers to have more layout space without increasing the risk of encountering impossible solutions.
Generally, eight or more layers are required to obtain the optimal layer arrangement and spacing to maximize functions. Using mass plane and power plane on multilayer board can also reduce radiation.
● Layer arrangement
The arrangement of the copper layer and the insulating layer constituting the circuit constitutes the PCB overlapping operation. To prevent PCB warpage, the cross-section of the board should be symmetrical and balanced when the layers are arranged. For example, in an eight-layer board, the thickness of the second layer and the seventh layer should be similar to achieve the best balance.
The signal layer should always be adjacent to the plane, while the power plane and the quality plane are strictly coupled together. It is best to use multiple ground planes, because they can usually reduce radiation and ground impedance.
● Layer material type
The thermal, mechanical and electrical characteristics of each substrate and how they interact with each other are crucial to the selection of PCB laminate materials.
The circuit board is usually composed of a strong glass fiber substrate core, which can provide the thickness and rigidity of the PCB. Some flexible PCBs may be made of flexible high-temperature plastics.
The surface is a thin foil made of copper foil attached to the board. Copper exists on both sides of double-sided PCB, and the thickness of copper varies according to the number of layers of PCB laminate.
Cover the top of the copper foil with a solder resist layer to make the copper traces contact with other metals. This material is essential to help users avoid welding the correct position of jumpers.
A screen printing layer is applied to the solder mask to add symbols, numbers and letters for easy assembly and better understanding of the circuit board.
● determine wiring and vias
Designers should wire high-speed signals in the middle layer between layers.This allows the ground plane to provide a shield that contains radiation emitted at high speed from the orbit.
The placement of the signal level close to the plane level enables the return current to flow on the adjacent planes, thus minimizing the return path inductance.There is not enough capacitance between the adjacent power supply and the ground plane to provide decoupling below 500 MHz using standard construction techniques.
● spacing between layers
As the capacitance decreases, the tight coupling between the signal and the current return plane is crucial. The power supply and ground plane should also be closely coupled together.
The layers should always be close to each other even if they are located in adjacent planes. Tight coupling and spacing between layers is essential for uninterrupted signal and overall function.
summary
There are many different multilayer PCB designs in PCB lamination technology. When multi-layer is involved, it is necessary to combine the three-dimensional method considering internal structure and surface layout. With the high running speed of modern circuits, careful PCB lamination design is necessary to improve distribution capacity and limit interference. A poorly designed PCB may reduce signal transmission, productivity, power transmission and long-term reliability.
