As the development of different electronic products continues as well as applications of the finer pitch devices, the vias plays a significant role in interconnection between the layers present in a printed circuit board. In addition, vias can be found in virtually all PCB designs.
There are some designers that see them as a straightforward, simple aspect of the printed circuit board. Moreover, vias might look innocuous, which makes PCB fabrication a complex process even of the process of PCB assembly in some circumstances.
What Does Tenting Vias Mean and Why is it Usually Done?
Vias helps in connecting the layers of a printed circuit board, regardless of the size. A tented vias means that you are creating a shape like a tent over the hole in order to cover the vias. Tenting is majorly done to help in limiting the conductive exposed pads that are present on the printed circuit board.
When tenting a via, the manufacturer uses a solder mask in enclosing the opening. This tenting of a via comes with both negative and positive effects on the printed circuit board. Now, if you are confused if you should go ahead and have a tented via on your circuit board, it all depends on the board’s design as well as manufacturing requirements.
What are the Benefits of Tented Vias PCB?
Tented vias offer lots of benefits for PCBs. The first has to do with the protection provided by the solder mask to the vias. Similar to the way the copper traces are prevented by the solder mask from corroding and oxidizing, thus the solder mask offers the same benefit to the via. The tenting via forms a specific barrier which helps in preventing damages to the layer of the PCB.
Also, making use of tenting methods helps in reducing the conductive components, which get exposed to the external elements. Whenever it is left exposed, these elements can reduce the components’ integrity and result in corrosion. This also reduces the probability of shorts happening as a result of solder bridging.
In addition, tented vias serve as a very cost-effective way for offering protection to your via as well as the copper surrounding it.
What are the Cons of Tented Vias PCB?
To cover the via, tented vias isn’t the best method. One of the disadvantages of tented vias is that the LPI can break and small holes are created inside the tent since the solder mask you’ll be using is in liquid form. This small hole may lead to the passage of chemicals and moisture, which could cause damage and corrosion to the tenting PCB.
Whenever the printed circuit board is in the prototyping stage of manufacturing, leaving your vias exposed aids in finding possible problems with the traces. This allows you to correct and then reroute them. Also, covering the vias may limit your chances of finding the problems and then fixing them immediately.
When Should You Use Tented Vias
The idea surrounding the tented vias is very simple. If you take a close look at the PCB layout, you will spot the tented vias easily. Below are cases when you can use tented vias.
Prevent solder wicking
The vias that are placed near the SMD components might offer a solder wicking path onto the board’s back side. Below are possible ways of solving this.
- Move the vias far away from the SMD pads, making sure that there is solder mask dam present between the pads as well as the connecting via
- Reduce the opening of the paste masks to ensure the application of less solder paste to that SMD pad
- Tent every vias close to the SMD pads without having to modify the paste mask
To provide environmental protection for the small vias
The use of tenting is best on small vias having a hole diameter below 12 mil. This diameter limit is dependent on your solder mask solution. Your fabricator must have the ability to recommend the maximum diameter for the via to achieve reliable tenting.
When there is a very large diameter, this could cause the solder resist to break, leaving a small hole. This can allow the entrance of contaminants in the via barrel. Now, this is where concerns related to reliability arise, most especially when there is a need for environmental protection.
Assembly Concerns
In some cases, tented vias could create assembly concerns. The potential problems for assembly depends on if you have to assemble the fine-pitch component. It also depends on if you will be working at very high densities that will bring you to a point where the use of via in pad is inevitable. Tenting vias during PCB assembly has to be viewed from two different perspectives.
- Will too much flux residue lead to issues with contamination as well as possible shorting? If this is the case, then you should un-tent the vias close to as well as underneath the component footprint.
- Will the solder wick to the board’s back during the assembly? If this is the case, then you should tent your vias close to the component footprint.
When the Vias Should be Exposed
At times, tenting vias causes more harm rather than good. This LPI solder mask is usually in liquid form, therefore it must serve as a bridge over a via hole. Sadly, this could cause incomplete skinning or tenting of the solder mask over the via. This leaves a very small hole (most especially when there is a large hole).
Furthermore, this small hole could be the main avenue for moisture, corrosive flux, other unwanted chemicals to become trapped inside the via. This can cause via failure because the corrosion is eating up the copper via. For cases like this, just leave the via exposed and unintended.
Conclusion
Tenting the via entails using the solder paste to cover the via hole and annular ring. This is mainly done to prevent exposing sensitive components of the printed circuit board. These include the environmental elements and conductive pads, which could cause damage from oxidation and corrosion.
