stackups

A stackup is the arrangement and thickness of the material layers in a multi-layer assembly, most commonly a printed circuit board (PCB). It defines the order of copper, dielectric layers, and protective finishes, as well as the overall thickness and tolerances. The stackup influences mechanical strength, thermal performance, and electrical behavior, including signal integrity and impedance control.

A typical PCB stackup includes copper foil layers for signals and planes, dielectric core materials such as FR-4 or polyimide, prepregs that bond layers, adhesives, and outer finishes like soldermask. Inner layers often serve as grounding or power planes, while outer layers carry signals. In flexible or rigid-flex boards, materials and adhesives are chosen for bendability and durability. For high-frequency applications, specialized laminates with stable dielectric properties may be used.

Designers specify the layer sequence, thicknesses, and copper weights to meet electrical goals such as controlled impedance, minimal crosstalk, and effective thermal pathways. Impedance calculations and simulations guide trace width, spacing, and the placement of planes. Via placement and the use of blind or buried vias interact with the stackup, affecting signal delay and integrity. Manufacturing tolerances, laminate warpage, and resin cures are also factored into the design.

Stackups are defined in fabrication drawings and guided by standards and company practices. Common references include IPC guidelines for PCB design and fabrication, which cover material specifications, tolerances, and test methods. Variants include metal-core PCBs for enhanced heat dissipation, and flex or rigid-flex constructions for bendable or curved applications.