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● Signal routing: This type of vias routes signals between different board layers.
● Escape routing: it also connects the pinout of surface mount components to the inner layers of the board.
● High-Density PCBs: Buried vias are used in high-density PCBs to connect inner layers while keeping the surface layers free for component placement.
● Connecting surface mount components to inner layers of the board: These vias are used to connect the pinout of surface mount components to the board's inner without going through the top or lower layer.
● Miniaturization: Microvias are small vias with diameters less than 0.15 mm (150 microns). They are used in densely populated boards and enable the miniaturization of electronic devices.
Design Considerations for Via-in-Pad
● Preventing Contamination: Uncovered vias have a high chance of being contaminated by moisture dust and other environmental parameters, which can cause corrosion, electrical shorts, or decreased performance.
● Improving Solderability: Covered vias provide good solderability, making assembling components onto the board simple during production. The vias are consistently covered with solder due to accurate covering.
● Enhancing Signal Integrity: With the covering of via, designers and engineers can control the dielectric constant of the via, which affects signal quality. That maintains the quality of high-frequency signals flowing in the board.
It is the simplest and most common technique, where a layer of solder mask covers the via. This saves solder paste from flowing into the via, resulting in a short circuit. It is used for vias that are less than 0.3 mm in diameter.
This process partially fills the via with a non-conductive material, like epoxy or resin. It is mainly used for vias larger than 0.3 mm in diameter or existing in areas with a high risk of solder bridging.
It involves filling the via with a non-conductive material. It is costly but offers the best protection against solder bridging and other environmental conditions. It is also used for vias in critical components of the board, like power supply circuits and high-speed signal paths.
Here is a comparison of the three methods:
After placing the via, there is a need to define its properties. Here are the main properties explained:
● Via Type: Confirm which vias types you need based on your project need
● Via Size: Define the value of the diameter of the via. Based on software settings, that can be defined as either mils or millimeters.
● Via Drill Size: Also define the drill diameter for through-hole vias. Buried and Blind vias can have different drill sizes for different layers.
● Via Layers: It should be confirmed which layers the via connect. In the case of a through-hole, usually, all layers are connected. For other vias like blind and buried, you'll specify the related external and internal layers.
● Annular Ring: Define the annular ring width, the copper pad about the via. It is essential for ensuring accurate soldering and electrical connectivity.
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