Contents
- What is a PCB Via?
- How Can You Maximize Space with PCB Vias While Following Design Rules and Guidelines?
- What are the types of PCB Via?
- Through-hole via
- Blind via
- Buried via
- What are the Components of a Via?
- What is a Microvia?
- Classification of Microvias: Stacked and Staggered Vias
- What is Via-In-Pad?
- The Importance of Vias When Designing a PCB
- How to Make a Via in PCB
- PCB Design Tips for Vias
- FAQs About Vias
- What Size Should Vias Be?
- What Kind of Via Should You Use?
- When Should I Use a Via?
What is a PCB Via?
A PCB via is a plated-through hole that allows for the routing of traces from the surface layer to inner and other layers of a PCB. PCB vias are typically drilled mechanically and plated to establish robust electrical connections. Vias are crucial for multi-layered boards, providing paths for the flow of electrical and thermal currents between layers. Vias act as "channels" that vary in size and type.
How Can You Maximize Space with PCB Vias While Following Design Rules and Guidelines?
Maximizing space with PCB vias requires careful planning within set rules and guidelines. The goal is to use all available space efficiently, but vias must be designed according to strict requirements. Vias are important in PCB design and production, differing in type and size based on the needs of the board. Knowing the different types and uses of vias helps optimize space while following design rules.
What are the types of PCB Via?
Through-hole via
A through-hole via runs through the entire PCB, connecting the upper and lower layers, and is the most common and easiest to make.
Blind via
A blind via connects the surface layer to the next layer but is not visible on the opposite side of the PCB, hence the name.
Buried via
A buried via links inner layers and remains hidden from both the top and bottom surfaces of the PCB.
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What is a Microvia?
Microvias have smaller diameters than through-hole vias and are drilled using lasers. They are commonly used in High-Density Interconnection (HDI) boards. Due to the difficulty in plating copper inside microvias, their depth is typically limited to less than two layers. Smaller via diameters require higher throwing capacity in the coating bath to ensure proper electroless copper plating.
Classification of Microvias: Stacked and Staggered Vias
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.
What is Via-In-Pad?
Via-In-Pad is a technique developed to accommodate high signal speed, PCB component density, and board thickness. It involves placing vias directly in the pad of a surface-mount component, unlike standard vias where the signal trace is routed from the pad to the via. This method helps improve signal integrity and routing efficiency. To prevent solder leakage, manufacturers often use VIPPO (Via-In-Pad Plated Over) to seal the via.
The first thing you should do is filling the via with a non-conductive epoxy based on your PCB manufacturing 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.
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.
How to Make a Via in PCB
Creating PCB via holes is a precise process carried out during the PCB design phase.
- Drilling Holes: Initially, drill through the copper pads at designated points on your PCB to create via holes.
- Chemical Application: Apply a chemical to these holes to dissolve the epoxy on the inner layers, exposing the copper pads necessary for effective via connections.
- Electroplating: Subsequently, fill these holes with copper using an electroplating technique to establish a solid via connection.
To validate the quality of vias in PCB, manufacturers often employ sacrificial vias that are tested for their electroplating efficacy by analyzing their cross-sections.
You can watch out this video to gain a better visual understanding of how to make vias in PCB.
PCB Design Tips for Vias
Here are essential tips for using vias in your PCB design project:
- Use More Vias: Incorporate as many vias as possible for better circuit performance.
- Prefer Staggered Vias: Choose staggered vias over stacked vias to avoid the need for filling and planarization.
- Minimize Aspect Ratio: Lower the aspect ratio to enhance electrical performance, signal efficiency, and reduce noise, crosstalk, and EMI.
- Opt for Smaller Vias: Smaller vias help create high-density interconnect (HDI) boards by minimizing stray capacitance and inductance.
- Fill Via-in-Pads: Always fill vias in pads, except those within thermal pads. This ensures strong solder joints and prevents solder clogging.
- Manage BGA Pad Matrix: Fill and planar vias in the pad matrix of BGA packages to avoid compromising solder joints.
- Include Vias in QFN Pads: Add vias in QFN thermal pads to facilitate better solder flow to the transmission planes.
- Avoid Solder Issues: Use windowpane-designed openings in solder masks for thermal pads to prevent solder merging and outgassing effects.
- Minimize Clearance: Ensure minimal trace and via clearance from routed parts.
- Check BGA Via Locations: Verify via locations relative to BGA packages for optimal performance.
- Fill Via-in-Pad Assemblies: Always fill via-in-pad assemblies to ensure reliable connections.
- Use Short Traces for Dog-Bone Assembly: Isolate vias with predetermined short traces in dog-bone assemblies.
- Provide Drill Templates: Include a drill template with feature codes and X-Y coordinates in your PCB documentation.
- Update Gerber Templates: Ensure Gerber templates include via plugging holes if needed.
These tips will help you design more reliable and efficient PCBs.
FAQs About Vias
What Size Should Vias Be?
Most manufacturers can handle standard drill sizes for vias, but using the same size for all vias on the board improves efficiency. This simplifies the drilling process, reduces time, and lowers production costs. Vias typically start at 0.15mm with a 0.3mm solder pad, though they can be drilled larger as needed. However, different sizes may require manual drilling, which increases costs. Vias smaller than 0.15mm must be laser drilled. The most common via size is a 0.6mm hole with a 1mm solder pad, found on most PCBs.
What Kind of Via Should You Use?
The choice of via type depends on the specific requirements of your PCB. For instance, if you are designing for older, larger computers, you'll likely need a through-hole via to ensure compatibility with older hardware configurations. Blind and buried vias might be necessary for newer, more compact devices. It's essential to discuss with your manufacturer the capabilities and costs associated with each type of via before finalizing your PCB design. Through-hole vias are typically the most cost-effective option.
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.
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