How to Use VIAs in PCB Design
A VIA, or vertical interconnection access, in the printed circuit board (PCB) refers to holes that serve a specific function. Including VIAs is essential in almost every type of PCBs.
Here you will learn what exactly are VIAs and how do you use them when designing PCBs.
What are VIAs?
VIAs are created by drilling holes through the copper pads on the circuit board. A chemical is put in the hole that dissolves epoxy inside thereby exposing the interior layer pads. Lastly, a small amount of copper is put inside the hole through electroplating.
But what exactly is the purpose of creating VIAs in circuit board?
VIAs are created to provide a conductive path by means of a plated hole wall through which electrical signals can pass from one layer of the circuit to another.
A circular copper ring known as the VIA pad is attached to the end of the traces. The ring is attached to the end of the traces which increase the material required for proper connection. The area around the VIA pad is known as anti pad that insulates the pad from copper.
Different Types of VIAs
PCB designers can use different types of VIAs and different configurations on the circuit board. While the purpose of the different types of VIAs is the same, the way they connect the layers is different.
Buried VIAs — Connect interior layers
Blind VIAs — Connect interior and exterior layers
Through VIAs — Connect two exterior layers.
You can use buried and blind VIAs for boards with more than two layers. Through VIA, is the only option for simple two-layer boards. It consists of a hole that is drilled from the top to the bottom layer. The hole is open at both sides that allows a solution to flow through and make it conductive. Buried VIAs are also drilled from top to bottom, but they are closed at one end.
Using VIAs in Designing Circuit Boards
Each layer on a PCB consists of two copper sheets that are separated by a dielectric core. You can assemble the layers differently when manufacturing the board. For boards with more than two layers, you can use either both buried and blind VIAs or just one type. The computer app can also determine the best VIA type for a PCB.
Every PCB has specific requirements regarding VIA size. Every manufacturer has a minimum drill size and VIA pads that must be used for the circuit board.
Generally, a standard drill size is above 12 mm in diameter. Lower drill size is prone to frequent breakage. On the other hand, the standard annular ring size is typically above 6 mm. However, some manufacturing process may require an even smaller size of rings. The smallest VIA that you can create has a 24 mm diameter VIA pad and 12 mm hole.
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