Layer Stackup

February 2, 2021

Why stack-up?

The irreversible development of modern electronics has been increasingly pushing PCBs towards such demands as miniaturization, light weight, high speed, better functionality and reliability, and longer lifetime, which results in the popularity of Multilayer PCBs. Combined by a type of semi-solid adhesive which is called "prepreg", two or more single and/or double-sided PCBs are stacked together to generate multilayer PCBs through reliable predefined mutual connection between them. There are three or more conductive layers in one multilayer PCB with two layers outside and one layer synthesized in the insulation board. With the increase of PCB complexities and densities, it's possible for some issues to take place such as noise, stray capacitance and cross talk when layer arrangement gets inefficient design.

 

Planning optimal multilayer stack-up is one of the most important elements in determining the Electromagnetic Compatibility (EMC) performance of a product. A well-designed layer stack-up can both minimize the radiation and can stop circuit from being interfered by external noise sources. Well-stacked PCB substrates can also reduce signal cross talk and impedance mismatch issues. However, an inferior stack-up may get EMI (Electromagnetic Interference) radiation rising, because reflections and ringing in the system as a result of impedance mismatch can dramatically lower products' performance and reliability. This article then focuses on layer stack up definition, its designing rules and essential considerations.

What Is Stack-up?

Stack-up refers to the arrangement of copper layers and insulating layers that make up a PCB prior to board layout design. While a layer stack-up allows you to get more circuitry on a single board through the various PCB board layers, the structure of PCB stack-up design confers many other advantages:
• A PCB layer stack can help you minimize your circuit's vulnerability to external noise as well as minimize radiation and reduce impedance and crosstalk concerns on high-speed PCB layouts.
• A good layer PCB stack-up can also help you balance your need for low-cost, efficient manufacturing methods with concerns about signal integrity issues
• The right PCB layer stack can enhance the Electromagnetic Compatibility of your design as well.

 

It will very often be to your benefit to pursue a stacked PCB configuration for your printed circuit board-based applications.

 

For multilayer PCBs, general layers include ground plane (GND plane), power plane (PWR plane), and inner signal layers. Here's a sample stack-up of an 8-layer PCB.