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Copper Wrap Plating in Multilayer PCBs

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • The types of vias in multilayer boards are through-hole vias, blind vias, and buried vias.

  • Copper wrap plating can be described as electrolytic hole plating, extending from a plated via structure to the surface of a PCB.

  • Copper wrap plating is continuous; it wraps the plated through-hole shoulders and connects the top and bottom PCB layers electrically.

Vias in multilayer PCBs

Copper wrap plating is an important part of the construction of vias in multilayer PCBs

Multilayer PCBs are vital in electronics system design due to merits such as their light weight, high circuit assembly density, and compact sizing. Multilayer PCBs accommodate separate PCBs onto one board and thereby meet the weight and space constraints of modern electronic product development.

In the fabrication of multilayer PCBs, the via structure is critical, as it joins the traces, pads, and polygon on different layers of the PCB. Copper wrap plating is also an important part of the construction of vias in multilayer PCBs, as it improves the reliability of via-in-pads. In this article, we will discuss multilayer PCBs, via structures, and copper wrap plating.  

Multilayer PCBs 

Compact sizing with advanced features is a new trend in the electronics industry. To build compact electronic circuits, multilayer PCBs are best. Circuit compactness is enhanced by fabricating multilayer PCBs, as they offer higher capacity in a smaller footprint. Multilayer PCBs stack up circuits vertically rather than spread them out horizontally. The verticality increases the assembly density and decreases the number of separate PCBs and connectors required in a system design.

The energy distribution within a board is improved with multilayer PCB layouts. A multilayer board design diminishes the effect of electromagnetic interferences, cross-interferences, and noise. The inherit electromagnetic compatibility seen in multilayer PCBs makes them suitable for high-speed or high-frequency circuits. Multilayer PCBs are commonly used in data storage systems, industrial controls, satellite systems, space equipment, mobile communications, and signal transmission applications. Due to their reliability, flexibility, high heat, and pressure withstanding capabilities, multilayer PCBs can be used in harsh environments.

In the construction of multilayer PCBs, multiple layers of materials are laminated together to form a single board. The layers of copper and insulators are arranged vertically to incorporate multiple electronic circuits to form a single PCB. In this vertical arrangement, via structures are used to make connections between circuits or components in different layers. 

Via Structures in Multilayer PCBs

Vias are copper cylinders placed or formed in the drilled holes in a PCB. Vias are structures that join traces, pads, and polygons on different layers of a multilayer PCB, both electrically and thermally. In multilayer PCBs, vias are staples—they aid in achieving a decent density of components. With the help of vias, it is possible to connect traces and components on one layer of the multilayer board to another. It is the via structures in multilayer PCBs that permit the sharing of power and signals between layers. The inclusion of a via makes the routing process easier as well. 

Types of Via Structures

The types of vias in multilayer boards can be categorized as::

  1. Through-hole via - These vias connect the exterior layers and go through the entire board. When a through-hole via is plated with a conductive material such as copper, it forms a plated through-hole via. When non plated, it is called a non-plated through-hole via. 
  2. Blind via - The vias that connect an exterior layer to an interior layer are called blind vias.
  3. Buried via - The vias that connect the interior layers but never the exterior layers are called buried vias.

Irrespective of the via structure type, a copper wrap is needed to form a reliable via.

Copper Wrap Plating

Copper is a material that is of great importance in PCB manufacturing. A good amount of copper is utilized on PCB layer planes and over the edge of via holes. The copper used in a via can be on the surface layer in the case of through-hole vias. However, when it comes to buried vias, the copper is used at the end of the via. The copper is plated onto the via structure.

In general, copper wrap plating can be described as electrolytic hole plating, extending from a plated via structure to the surface of a PCB. In the PCB fabrication process, after plated through-holes are drilled, the inside of the through-hole is plated with copper. It covers the copper foil annular ring on the top and bottom surfaces of the PCB. Copper wrap plating is continuous; it wraps the plated through-hole shoulders and connects the top and bottom PCB layers electrically.

In IPC standard revisions such as IPC 6012B and 6012E, the requirements of copper wrap plating and wrap plating thickness are specified for all filled plated through-holes. The standard classifies electronics designs as class 1 for general electronic products, class 2 for dedicated service electronic products, and class 3 for high-reliability electronic products.

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