The concept of manufacturing PCB Vias resembles contortion games since the aim is to maximize the available space. However, unlike a contortionist who enjoys the freedom of using any means available to suit in the box, you must follow specific rules in designing your PCB vias. Adhering to these rules and guidelines is vital to the success of your circuit board design project.
It is indisputable that vias play an integral role in the PCB design and production process, but to what extent do you know about them? What are the various types of vias, and how do they vary from each other? Why do you need vias when designing a PCB? This article presents all the basics- not forgetting the via-production process, the primary types, and PCB design tips for vias.
1. What is a PCB Via?
A via is a plated-through hole in a PCB that you can use to route a trace from your board's surface layer to the inner and other layers. It is essential to realize that you can drill PCB vias mechanically, and you can plate them to create electrical connections.
Vias are vital in multi-layered boards, which are challenging to design and produce. They create routes for the sufficient flow of electrical and thermal current between the board's different layers. In a layman language, vias are basically "channels" that vary in size and type.
2. PCB Via Types
Through-hole via- It goes through the printed circuit board from the upper to the lower side, and you can use it to connect any layer of your board. A through-hole via is the commonest and easiest via you can make.
Blind via- You can use a blind via to connect the surface layer of your board to the next layer. We call it a blind via because you cannot see it on the other part of the PCB.
Buried via- You can use it to link the inner layer of your board. We call it a buried via since you cannot see it on the surface of a PCB.
3. Components of a Via
Barrel- This is a conductive tube that fills the percolated hole.
Pad- It links all barrel ends to the components or traces.
Antipad- It is a clearance hole that separates the barrel and the non-connective layer.
4. PCB Via: Micro vias & Stacked
Microvias have smaller diameters than through-hole vias, and you can drill them using lasers. It is also good to note that you can use Microvias in High-Density Interconnection (HDI) boards.
Microvias have depths of less than two layers because it is difficult to plate copper inside. Therefore, the smaller the via diameter, the higher the coating bath's throwing capacity to establish electroless copper coating.
We can classify Microvias into stacked and staggered vias, depending on their position in the board layers.
Stacked vias- You can create Stacked vias by piling them on top of each other in distinct layers.
Staggered vias- You scatter them in various layers, and they are a bit expensive.
Skip vias- You pass them through a layer and ensure there is no electrical contact with that layer. This means that the skipped layer will fail to create an electrical link with the via.
5. PCB Via: Via-In-Pad
High signal speed, PCB component density, and thickness spurred the invention of the via-in-pad technique. You can use VIPPO and standard via structures to create rout ability and signal integrity features.
5.1 What is Via-In-Pad?
In standard vias, manufacturers route the signal trace from the pad to the vias. They do this to prevent leakage of the solder coat into the vias. In a Via-in-pad, you should place your vias in the pad of the external mount component.
The first thing you should do is filling the via with a non-conductive epoxy based on your PCB manufacturer's requirements. Then, it would be best if you capped the via and coat to reclaim the land space. For this reason, the signal path stretches, eliminating the opportunistic inductance and capacitance impact.
It is also good to note that the via-in-pad hosts small pitch sizes and minimizes your board's general size. This technique is best suited for BGA footprint parts.
You should implement the back-drilling process with your via-in-pad to achieve better results. You carry out back-drilling to remove any signal echoes in the remaining parts of your via.
6. The Importance of Vias When Designing a PCB
If you have a simple circuit board, you may not need vias. But you need vias when you are dealing with a multi-layered board, as mentioned earlier.
- Vias will help you to establish an excellent component density in multi-layered boards.
- Besides, they also raise trace density in multi-layered boards as you can run them over and beneath each other in different directions. Vias allow the various traces to link with each other. In this case, they act as vertical connection factors.
- If you fail to incorporate vias into a multi-layered PCB routing process, you will end up placing your components densely.
- Lastly, you need vias to facilitate the transmission of signals and power between layers. If you do not want to use vias, you should route your PCB components on a single plane. Remember, surface mounted parts in a multi-layered PCB make it impossible to route components on a single plane.
7. How to Make a Via in PCB
It would be best to make vias during the circuit board design process unless you have a DIY Via Rivet gun.
First, drill holes through copper pads on your board.
Secondly, apply a chemical in the drilled holes to liquefy epoxy on the inner PCB layers. Additionally, this will uncover the inner copper pad layers further.
Lastly, apply some copper in the holes with electro-coating.
Most circuit board manufacturers place sacrificial vias on parts of the design board. They then slice them and scan the cross-sections to determine the efficiency of the electro-coating process.
You can watch out this video to gain a better visual understanding of how to make vias in PCB.
8. Genius PCB Design Tips for Vias
Below are some genius tips you should consider while using vias in your circuit board design project.
- It would help if you employed maximum via structures in your PCB design.
- In case you are stack between stacked and staggered vias, go for staggered vias because you may need to fill and planar the stacked vias.
- Minimize the aspect ratio as much as you can to achieve excellent electrical performance and signal efficiency. Also, reduce noise, crosstalk, and EMI.
Use smaller vias.
- This will enable you to create a quality HDI board by minimizing the stray capacitance and inductance.
- Always fill via-in-pads, unless they exist within thermal pads.
- Remember that the pad matrix where you will fix a BGA may consist of through-hole and blind vias. With this in mind, fill and planar them to avoid compromising the solder joints.
- Include vias in QFN thermal pads to enable the solder to move to the transmission planes quickly.
- Remember, vias facilitate secure solder joints of thermal pads and bar solder from clogging the set during PCB design. This may hinder the creation of quality solder joints within the QFN joints.
- You can use an assembly shop instead of a through-hole via in case of thermal pads. It would help if you introduced windowpane-designed openings within the solder coat stencil on top of the pad to achieve this. By doing this, you will get rid of solder merging and outgassing effects during assembly.
- It would be best if you looked for the least trace and via clearance from the routed parts.
- Check via the location of your BGA packages.
- Always remember to fill your via-in-pad assembly.
- For dog-bone assembly, isolate every via from its pad using a pre-determined short trace.
- Your PCB documentation should have a drill template with feature codes and X-Y points for each hole.
- You Gerber templates should contain via plugging holes if necessary.
8.1 Via Requirements for Type and Treatment
To avoid circuit board problems with your manufacturer, you should define your via requirements accordingly to obtain what you need. Besides, you can also create a separate document for every via set you use in the design.
8.2 What Size Should Vias Be?
Always confirm the least drill size and annular ring that your manufacturer uses. Standard mechanical drills are usually more than 12 miles in diameter. Therefore, the manufacturer can add expenses to cater for any broken drill.
Besides, annular rings are generally above six mils in diameter for regular manufacturing. Hence, the least via you make should have a 12 mil diameter hole, and the pad should be twice the size of the hole.
8.3 What Kind of Via Should You Use?
Your PCB's size and role should determine the kind of vias you select for circuit board design. If you plan to use your PCB for an older, big computer, you will most likely require a circuit board design that aligns well with the older versions. A newer standard may be unable to get along with the gadget in question.
Through-hole vias are the most cost-effective via to use. You should contact your manufacturer to deliberate on blind and buried vias before PCB design to decide their capacities.
8.4 When Should I Use a Via?
Vias act as paths for conducting signals and thermal energy from one layer to another. Basically, the more your IC dissipates energy, the more vias it requires to link its thermal pad to the surface layers, distributing the heat.
For board components bearing power, or quick signals, you should apply several vias to link the layers. Moreover, it is good to have numerous vias instead of a single large via. This technique minimizes inductance and provides extra current pathways if one of the vias fails.
As seen in the discussion, there is a wide variety of vias you can select when it comes to PCB design. For the modern miniaturized boards, Micro vias are the most suitable for use in machines with several features.
PCB vias are very important, especially in multi-layered circuit boards. Without vias, you will find it quite hard to make reliable and quality-layered boards. It is crucial to have a team of professionals that can consider you via requirements for type and treatment to avoid getting the wrong final products. Reach out to us today for a quote on circuit board products and services.