There are many different techniques that we employ when building circuit boards. Vital to all these constructions are vias – copper-lined connection ports that connect each layer of the board in one cohesive electrical flow.
Vias are necessary for constructing multi-layered or double-sided PCBs, as they allow for electrical current to pass between each layer or between various components. The copper-lined boreholes allow the current passed through the copper paths on the outer layer of the board to feed through its surface.
(nanoslavic / pixabay)
PCB designers need to use via switching to tie together larger copper areas on varying surfaces. This can be a low-cost and effective way to help maintain short return loops and low impedance.
What is Via Stitching?
Via stitching is used to create strong vertical connections through boards by using a network of vias. The basic concept is that via stitching will allow for a larger amount of current to be fed through the board in a steadier flow. These networks of vias are installed over a large area, helping spread the current and reducing the risk of damage to the board and its components.
Vias are drilled through boards using extremely thin drills or lasers. There are three different types:
- Through-hole is bored through every board layer, connecting the top to the bottom.
- Blind vias connect the surface to a layer inside the board without going all the way through.
- Buried is a hole in the inner layer of the board and only connects the undersides of the outer layers.
The outer parts of each layer and the inner bore of the vias connect through a thin copper layer, which allows for the conduction of heat and current. This wider area of connected copper between each layer makes the vias “stitched.”
Types of Via Stitching
There are three methods of via stitching currently in use, each with its specific uses and benefits:
1. Constant ground via stitching
This is the most common form of via stitching used in PCB construction. It entails creating a wide ground plane, which creates a strong ground return path. Numerous vias are created to follow the path of the circuit. They connect either the top to the bottom of all layers within the board. It offers a wide disbursement of voltage with minimum resistance, greatly reducing the chances of power surges and drawing all excess power away from vital components. It also produces a lower heat dissipation, as the copper pour covers a larger area and connects all PCB layers.
2. Thermal via stitching
Thermal via stitching allows you to create or improve an inbuilt heat sink by giving the heat another location to disperse through. Typically, heat in a PCB is distributed sideways along the copper plane in which a heat source is seated. With thermal via stitching, heat is also dispersed down through the board and spread across both sides of the board, reducing buildup and potential damage. This allows PCBs with high-power components to run much more efficiently without overheating.
3. Shielding via stitching
High-frequency RF or Mixed-Signal circuits are a very common part of modern PCBs. Wi-Fi, Bluetooth, and other HF Band elements are used in most modern phones, TVs, and computers. All these devices can be easily damaged by Electromagnetic Interference (EMI). For this reason, Shielding via stitching is being used to help protect these fragile components. This works by drilling vias on the ground plane around the component. One or more rows of stitched vias are laid around the component, effectively building a fence and creating a shield against incoming EMI. They are typically spaced at 1/10th the targeted wavelength, though some people use distances of 1/8th.
Benefits of Via Stitching
As you have seen, via stitching offers many benefits for PCB construction. From it, you can look to gain the following benefits:
- Better grounding – ground via stitching will give your circuit a much wider and more direct route from component to ground. This will decrease any resistance in the board’s construction and allow energy buildup to dissipate quickly and efficiently.
- Better thermal management – the wider spread of energy and heat amongst the copper layers of your board through vias will protect components on each layer from overheating. It spreads the heat out and down from them, keeping the heat level lower and less concentrated.
- Ease of multi-layer connections – stitched vias will give your circuit a greater array of lines to follow for creating circuits that cover more than one layer of your board. This gives you more space, preventing you from having to limit your component layout to a single layer or even side of the board.
- Increase shielding for electronic components – layers of vias can help form barriers to protect components from electromagnetic interference. This will help prevent damage to those components and increase their functionality.
- Better copper balancing – the increased use of copper in creating stitched vias means that more copper will be used in the PCB construction. This continuous copper helps strengthen the board and helps prevent warping during reflow.
Considerations for Using Via Stitching
Given the many benefits of using via stitching in your PCB assembly, including them in your future designs makes sense. As with any PCB design, including stitched vias requires a few considerations to accommodate their placement.
The Thickness of the Board
It stands to reason that the thickness of the board you are building – and the number of layers it will use – will determine how many and what kinds of vias you will need. Single-layer boards will have no use for blind or buried vias, while thicker boards will require you to decide which of these you need to use. It will also determine the amount of copper you will need, as the routing you desire will add to it.
Component Placement
You will need to ensure that your components are laid out with enough space for your vias. Larger components will lead to a larger board, particularly if you use stitched vias for grounding or heat dispersal. Also, you will need to bear in mind that vias bored too close together can lead to crosstalk between the copper.
PCB Function
If your PCB is used for high-intensity machines, you will need to consider the amount of heat and power they will produce. This will affect the need for ground and thermal stitching and the number of vias to aid the board appropriately.