A multilayer PCB has more than two layers in its stack-up. Stack-up is one of the most important aspects of your design. It describes how layers are arranged in a multilayer board. An accurately stacked board will reduce electromagnetic emissions and crosstalk and improve signal integrity.
Stack-up describes the construction of a multilayer board in sequential order. It provides vital information like material thickness and copper weights required to fabricate a PCB. Stack-ups are also referred to as build-ups.
A stack-up also gives the details of trace width for different controlled impedance traces, such as 50 ohms or 100 ohms differential. The above image shows an example of a 6-layer stack-up.
A stack-up primarily consists of metal foil, prepreg, and copper-clad laminate (core).
Metal foil: Copper is the most commonly used metal foil in PCB construction.
Prepreg:It is an interwoven glass cloth impregnated in epoxy resin. The resin is left semi-cured.
Copper-clad laminate: Single or multiple plies of prepreg bonded together along with the top and bottom copper foil makes a copper-clad laminate. This is also known as the core.
The power plane is a copper layer connected to the power supply. It is often designated as VCC in PCB design. The main function of the power plane is to provide a steady voltage supply to the PCB.
In multi-layered boards, if a component needs to draw power, then it is simply connected to the via that makes contact with the power plane. Similarly, the ground plane is a plane of flat copper connected to the common ground point in the PCB.
The lamination is the process of placing the stack-up under extreme temperature and pressure to bond prepreg and copper foil to the base PCB inner layers. The temperature and pressure values are mentioned in the datasheets of the chosen PCB materials.
The thickness of a PCB mainly depends on factors such as copper thickness, materials used, number of layers, and the operating environment.
The standard thickness of a conventional board is around 62 mils (1.57mm).Today, PCBs have become more complex as the copper layer weight and the layer count have increased for various applications.
Due to this, the PCBs tend to become thicker. Manufacturers, based on the customer’s request, are now fabricating PCBs with two new standard thicknesses, 93 mils (2.36mm) and 125 mils (3.17mm) (150% and 200% of the old standard thickness).
Electronic devices are becoming more complex and consist of a higher number of components and circuits. It becomes tedious to accommodate complex circuits in a single-layered PCB. This problem can be solved by adding layers to the stack-up.
Let us have a look at a few advantages of multilayer boards:
Step 1: Inner layer core selection
