Terminology

/Terminology
Terminology 2017-11-07T07:07:34+00:00

Blind Via

A via that starts on a surface layer, but does not continue all the way through the board. Typically a blind via descends 1 layer, down to the next copper layer.

Buried Via

A via that starts on one internal layer and ends on another internal layer, but does not reach a surface copper layer.

Core

A rigid laminate (often FR-4) with copper foil on both sides.

Double-Sided Board

A board that has 2 copper layers, one on either side of an insulating core. All holes are through holes, that is they pass all the way from one side of the board to the other.

Fine Line Features and Clearances

Tracks/clearances down to 100µm (0.1mm or 4mil) are considered standard for PCB fabrication today, the current technology limit available in component packaging is around 10µm.

High Density Interconnect (HDI)

High Density Interconnect technology, a PCB that has a higher wiring density per unit area than a conventional PCB. This is achieved using fine line features and clearances, microvias, buried vias, and sequential lamination technologies. This name is also used as an alternative to Sequential layer Build-Up (SBU).

Microvia

Defined as a via that has a hole diameter smaller than 6 mils (150µm). Microvias can be photo imaged, mechanically drilled, or laser drilled. Laser drilled microvias are an essential High Density Interconnect (HDI) technology, as they allow vias to be placed within a component pad, and when used as part of a build-up fabrication process, allow signal layer transitions without the need for short tracks (referred to as via stubs), greatly reducing via-induced signal integrity issues.

Multilayer Board

A board that has multiple copper layers, ranging from 4 to over 30. A multilayer board can be fabricated in different ways:

  • As a set of thin, double-sided boards that are stacked (separated by prepreg) and laminated into a single structure under heat and pressure. In this type of multilayer board the holes can be all the way through the board (through-hole), blind, or buried. Note that only specific layers can be mechanically drilled to create the buried vias, as they are simply through holes drilled in the thin double-sided boards before the lamination process.
  • Alternatively, a multilayer board is fabricated as just described, and then additional layers are laminated onto either side. This approach is used when the design demands the use of microvias, embedded components, or rigid-flex technology.

Prepreg

A glass-fiber cloth, impregnated with thermosetting epoxy (resin+hardener) which is only partially cured.

Sequential Lamination

The name given to the technique of creating a multilayer PCB which includes mechanically drilled buried vias (drilled in the thin, double-sided boards prior to final lamination).

Sequential layer Build-Up (SBU)

Starts as a core (double-sided, or an insulator), with conductive and dielectric layers formed one after the other (using multiple pressure passes), on both sides of the board. This technology also allows blind vias to be created during the build-up process, and discrete or formed components to be embedded. Also referred to as High Density Interconnect (HDI) technology.

Surface Laminar Circuit (SLC)

Starts as a multilayer core, with build-up layers added on either side (typically 1 to 4). The common notation used to describe the finished board is Build-up copper layers + Core copper layers + Build-up copper layers. For example, 2+4+2 describes a board with a 4 layer core, with 2 layers laminated on either side (also written as 2-4-2). This technology allows blind vias to be created during the build-up process, and discrete or formed components to be embedded.