How Do Filleted Vias Affect the Overall Size of PCBs?

Filleted Vias Affect the Overall Size of PCBs

Vias are crucial to circuit board design, allowing power and signals to pass between layers. They can both be underused and overused, and designers must find a balance. Following a set of PCB via size guidelines can help.

Vias can be either filled or plugged, and there are advantages to both options. Conductive via fills are better at transferring electric current between layers and also provide greater thermal conductivity. This allows them to deviate heat from under components, reducing temperature and extending the lifespan of the board. However, conductive via fills are expensive, and require more time and effort to fabricate.

On the other hand, plugged vias are cheaper and easier to produce, and they are better at preventing impurities from being trapped in the holes. They can also improve mechanical strength, reduce solder wicking and silkscreen printing issues, and prevent voids in the hole walls. They are also less prone to damage from etching, and can be used for high-speed designs with high levels of current flow.

The first step in creating a filled vias is drilling the hole with either a mechanical drill or laser. It is important to use a drill with the right aspect ratio and depth to ensure that the hole is large enough for the desired function of the via. This is important as a mechanical drill is limited to how deep it can reliably go, while a laser is only limited by the amount of light that it can penetrate the board.

How Do Filleted Vias Affect the Overall Size of PCBs?

After the via hole is drilled, it must be metalized with an electroless copper seed layer and imaged. A tin plate is then deposited over the copper, and any areas that are not to be used as vias are masked off with a solder mask. The tin plate is then etched to reveal the copper, which is then plated with the desired thickness and diameter. It is important to ensure that the plating process is done properly, as if there are any voids in the via it will not be able to conduct electricity or handle high voltages.

Another method of via filling is the injection of a conductive resin into the via. This can be a copper epoxy or silver epoxy, which provides higher thermal conductivity than non-conductive epoxy, and can also improve the mechanical strength of the via. It can also be made more resistant to chemicals like acid and flux, which makes it a good option for harsh environments.

When a PCB is in production, it is important to ensure that all vias are properly filled. This will help to avoid voids, which can cause problems with the electrical and thermal conductivity of the board. This is particularly important for a board that will be in harsh environments, such as those that will need to operate at high temperatures or with high levels of current. It is also important to make sure that the CTE of the via fill and the dielectric material are the same, as this will help to avoid stress fractures due to unequal expansion.

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