How much do you really know about roads, one of the basic components of PCB design?
Vias are a basic element of PCB design. But before you can decide whether to use buried, blind or through vas, you must understand what they really are and what they do for your board.
This article will serve as a guide through basic information.
What is a va?
The Vias are used to electrically and thermally join traces, pads and polygons in different layers of a PCB. Vias are copper cylinders that are placed or formed in holes that have been drilled in a PCB.
What is a Via Pad?
The Vias require a minimum amount of copper in a layer for proper connection, so that, in most cases, a pad (copper circle called an annular ring) is placed at the end of narrow traces to increase the available material for a connection.
What is an antipad?
Around the pad goes there is a copper-free area known as "antipad," which roams the pad of the surrounding copper.
Two traces (left) that belong to the same network are in adjacent layers of a PCB. The traces expand in the connection area with the va pads and join with a va (right).
How are the roads made?
Unless you are at home with a DIY through a rivet gun on a 2-layer board, the vases are created during the PCB manufacturing process.
Briefly, the holes are drilled through copper pads on the PCB, a chemical is placed in the hole to dissolve the epoxy in the inner layers to further expose the copper pads of the inner layer. Finally, a little copper is placed in the hole with electroplating.
To see an animation of how the tables are made (including valas), watch this video:
Most PCB manufacturers will place slaughter vessels on their PCBs in a section of the production board. Then the vas are cut and the sections are examined to determine the effectiveness of the electroplating process.
A cross section of a va. Image used courtesy of Data Respons
When should I use Vias?
Vias provides a path for electrical and thermal energy to move from one layer to another on its board. In general, the more energy dissipates an IC, the more you must have to connect your thermal pad to the underlying copper layers that can distribute the thermal energy.
A thermal pad for the QFN IC has 64 vas! Image used courtesy of Bittele Electronics Inc.
For parts of your circuit that carry energy, or fast signals, use several vas to connect layer by layer. In general, it is better to have several smaller ones than one large one. The design option reduces the inductance and provides additional routes for the current in case one of the vas fails.
There are three basic types of vas:
- You go blind: connect an outer layer to an inner layer
- Buried roads: connect two inner layers
- Through the vas: connect two outer layers
A basic visual representation of a blind, a buried and a va. The orange here represents PCB layers and the yellow bars represent the vas, since they connect the layers differently. Image created by Mark Hughes.
For a simple two-layer board, your only option is through. For boards with more than two layers, you can also specify going blind or buried in your design (at a higher cost).
Often, it is necessary for one to form an electrical connection between an inner layer and an outer layer. The use of a through hole through such situations places an unused hole (and possibly an unused pad) in other layers, and this consumes the actual state of PCB and interferes with routing. A blind person through this problem solves this problem, but the speed of the blind person is high due to costs, reliability concerns and the difficulty of solving problems.
Through a through hole for a 6-layer stack, with non-functional pads present (left) and removed (right)
What type should I use?
In general, the vas are the most economical to include in your design. The hidden and hidden vessels should be discussed with their manufacturer before designing the plate to determine their capabilities.
How do I use blind and buried roads in my design?
It is important to remember that when PCBs are manufactured, each layer consists of two copper sheets separated by a dielectric core.
The image shows a stack of PCBs through assorted copper traces and traces. Image used courtesy of RayMing Technology.
These layers can be assembled in various ways during manufacturing, which allows a combination of blind buried vases. It is likely that your computer software allows you to specify which layers you want to connect, but most will not prevent you from making decisions that cannot be manufactured. If you cannot recreate your stackup with cardboard and a stapler, without folding or tearing the cardboard, your PCB manufacturer cannot make your board.
What size should Vias have?
Verify with your manufacturer the minimum drill size and the minimum ring ring for the manufacturing process they will use. Typical mechanical drills do not have a much smaller diameter than 12 milsimas without frequent breakage, so the manufacturer will increase the cost of broken drills. Ring rings usually do not go below 6 thousand for standard processing. Therefore, the smallest va that you will create has a 12 mm diameter hole and a 24 mm diameter pad.
What other information about roads would you like to see added to this guide? Let us know in the comments below.