Via in Pad & Designing PCBs: Guidelines & Options

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Jun 24, 2020|Product Innovations and Design

Via in pad is the practice in design where a person places the via in a copper landing pad instead of putting it on top. A person creates via in pad by drilling a hole into the pad, placing the via, and then capping it.

What Does Via Stand For?

Vertical interconnect access (via) is the electrical connection in a circuit that runs between layers. Without the via there is no conductivity of the power within the printed circuit board (PCB) from layer to layer.

You can have different types of vias. You may wonder what is a blind via? It is one that connects layers in a PCB. You can see a blind via.

What Is a Pad in PCB?

A pad is a small area of copper. It is copper so that you can solder components to the board and so it will provide proper conductivity for the via.

Pros and Cons of Via in Pad

When deciding whether to use via in pad or not, you have to think about the pros and cons this method offers. Only then can you accurately assess your project to know if it is the right method.

Benefits of Using Via in Pad

There are a few key reasons why via in pad is becoming more popular with engineers. It has some significant advantages over traditional methods that make it a superior choice in certain situations.

Size Reduction

Size in electronics a concern. Nobody wants huge items anymore, so engineers have to find a way to get all the components into a unit in a compact way. That is not an easy task without using methods like via in pad. When you look at the traditional via and the via in pad, it is easy to see how you save space, which means you have more room for other components. You also can use smaller components with via in pad. Both things add up to an excellent reduction in the overall size of the PCB.

Simplified Routing

Via in pad allows you to minimize the use of components and reduces the space between elements. It can help to minimize inductance. It also lets you run a shorter path to the ground and the power on the PCB with a benefit of reductions in EMF emissions.

Better Heat Management

Being able to place components close and other elements of the board close together gives you better management over heat. As anyone who uses or works with circuit boards knows, being able to reduce heat build-up is a huge benefit and can extend the life of the board and components.

Disadvantages of Using Via in Pad

Nothing is perfect, and that is true of via in pad. Not every application or situation will be a good one for using this method. Looking over the disadvantages can help you to pinpoint when via in pad may not be the best choice.

Increased Complexity

Because you will need to cap off your vias in pad, you may have a bumpy surface. You can’t solder on a surface that isn’t smooth and expect it to take. So, you have to take extra steps to fix any bumps.

Takes Longer to Manufacture

The process of creating via in pad takes longer because there are more steps in the process. Not only do you have to drill into the pad and place the via, but you usually will not want to leave the hole open. You must fill it in with an epoxy. So, you’ve added a few additional steps to the process overall, which means manufacturing will take a little longer.

More Expensive

Via in pad is more complex and takes more time, so it is no surprise that it also costs more. The additional expense is one of the most significant issues with this method.

How to Design PCBs for Via in Pad

Since via in pad is much different than the traditional method, it goes without saying that you will need to use different designs for PCBs using via in pad. The recommendation is only to use via in pad in specific situations with surface mounted devices (SMD) where you really need them because of the disadvantages.

Some guidelines you can follow when designing your PCB include:

* Set the vias in between the pads

* Cap the vias

* Stick with a small diameter

* Use vias that are only on one layer

You should generally follow the manufacturer’s guidelines. In most cases, you won’t use via in pad unless the manufacturer recommends it. So, it should provide you with instructions for the Printed circuit board design.

Ensure that you design the pads to meet the minimal annular ring requirement when looking at the guidelines. You may have specific situations that you will need to do additional research to figure out how to incorporate via in pad. For example, you may ask what is VIPPO? VIPPO is a design structure that you may need to incorporate with via in pad.  

Sizing

One of the essential aspects you want to think about when designing for via in pad is sizing. You will more likely have to use this method with component packages that have small pitch. Small would be anything under 0.5mm.

Via Options

If you use this method, then you should have some idea of the via options:

* Tenting

* Capping

* Plugging and filling

These are all options you have to cover a via on your PBC. Leaving it uncovered can create issues with SMD soldering as the solder gets into the via. It also can lead to energy problems and shorts.

If you ask, what is via tenting? It is covering it in a solder mask. It helps with the prevention of accidental contact with other components of the board. When tenting vias, you do not need to cover the via completely. You only need to cover the area of concern. Tenting can also offer extra protection for the via from damage and short circuits.

Via capping is closing off a via in pad. Typically, you will do this with copper. It creates a smooth surface that lets you attach other components with solder.

Plugging and filling a via is when you use solder to close the via hole. You actually can use any material for via plugging that you want as long as it is not conductive. The second step in the process is to cover it with an LPI mask. It is similar to tenting but ensures the complete via has covering over it.

You can always leave the via open if you want. It may work in a circuit board without solder pads when you use other methods to attach your components.

Via in Pad Guidelines

There’s a lot to think about when using via in pad. The bottom line seems to be that it is potentially the future of the industry since it allows for smaller devices. So, while you may not be using it a lot now, it is a good idea to become familiar with it as you may start to use it more often in time.