Exploring PCB Via Types: Choosing the Right Vias for Your Design Needs

Introduction

Vias are holes that allow conductivity to go through the board’s layers in printed circuit boards. Every hole serves as a conductive channel for the transfer of electrical signals between circuit layers. A printed circuit board has levels that vias go through. Depending on how the PCB is designed, the board may need a hole that passes through each layer from top to bottom. On the other hand, some vias go through an inner layer, while others only reach the top or bottom layer. Vias on a printed circuit board come in a variety of options. One of the most important components of a printed circuit board is the via. As a result, they bear a substantial portion of the expenses associated with the production of boards.  

Even though all of these via types have the same basic function, some PCB designs will fit one via type over another more than others. This article discusses the many via types used in printed circuit board design and how they can be used to help with electrical connections.

 

PCB Via Types  

On a PCB, there is a via that connects at least two layers, allowing power or signals to move between them. A copper-plated cylindrical barrel that serves as a conductive channel is present in every PCB via. In PCBs, a variety of via types are used:  

Through-hole
These  vias can connect to any layer and are available throughout the PCB stackup. Every layer of these PCB vias will feature a pad where a connection to a trace is made.  

Blind vias
These end at a landing pad and extend from an outside layer to an interior layer. Signals can then pass via an internal layer by connecting the pad to another trace.

Buried vias

These  do not reach the surface layers; instead, they extend between two interior layers. Like regular vias, buried vias can connect on any layer between their starting and terminating layers.  

Microvias
They are basically miniature blind or buried vias that span one layer at most, or two layers at most in cases of extremely thin dielectric (the latter being referred to as a skip via or skipped microvia).
stacked microvias.
Vertical stacks of blind and buried microvias, or stacks of several buried microvias, spanning multiple levels are known as stacked microvias.

Via -in-Pad
Using vias on ball grid array (BGA) pads—also referred to as via-in-pads—is one of the more widely used printed circuit board designs of today. The vias of the via-in-pad design are positioned on the PCB’s BGA pads. Because the design allows manufacturers to reduce the amount of space needed for vias, it has gained popularity. Because of this, via-in-pad enables producers to create printed circuit boards that are thinner and require less room for signal routing. For today’s small electronic and computing devices, which manufacturers have made to fit inside pockets and occasionally around wrists, via-in-pad technology is ideal.

 

When to Use Each Type of Via: Matching Application to Functionality

Through-hole:
This is the type of via that is used most often in a circuit board. The holes are drilled all the way through the board with a mechanical drill bit and can get down to 6 mils in size.

Buried via:
This via only connects internal layers of the board and is useful for PCBs with very dense routing. Blind via: This via starts on either the top or bottom of the board but doesn’t go all the way through it. 

Microvia:
For hole sizes smaller than 6 mils, a laser-drilled microvia is used. These vias connect only two adjacent layers of the board and can be on the surface or buried within the board layer stack up. Microvias are extremely versatile and can be stacked together, or on top of a buried via, but have a higher fabrication cost associated with them.

Via-in-pad (VIP):
These vias can either be standard thru-hole vias or microvias, but their position in a surface mount pad makes them unique. If a standard mechanical drill is used, the via will require extra fabrication steps to prevent solder on the pad from flowing down through the hole. Microvias on the other hand don’t have this problem, but they can be more difficult to fabricate due to the tighter trace and space tolerances in a high-density design.
A path that sends a signal from a source to a receiver is called a via. Effects of inductance on via design and low capacitance on signal integrity have been demonstrated. It will be demonstrated that this return path may be regulated with careful via environment design, allowing vias to be sorted out according to cable specifications within specific frequency ranges.
This indicates that the via stubs effect is addressed, as are ways to lessen it by moving undesired resources outside of the area of interest. This indicates that the via impedance can be adjusted to meet a certain goal in order to reduce reflections.

How to Choose Via’s for a PCB: 

Taking Design into Account
Assess the requirements of your PCBA project first. Evaluate factors including signal quality, heat control, power distribution, and required space. Controlled impedance vias may be required for high-speed signal traces in order to preserve signal integrity, and suitable ground and power via arrangement is essential for the best possible power distribution and heat dissipation.  

Via Size:
A device’s heat dissipation efficiency and current carrying capacity are determined by its size. Better heat dissipation and less resistance are provided by a bigger via. A densely packed PCB is better served by a smaller via. The precise design specifications determine how to strike a balance between utility and size.

Plating:
To guarantee electrical conductivity, vias are frequently plated with copper. Plating influences dependability and performance. To improve corrosion resistance, pick between through-hole copper plating and other methods like ENIG. 

Aspect Ratio:
The ratio of diameter to via depth is known as the aspect ratio, and it is important. Drilling difficulties, uneven plating, and decreased dependability might result from a high aspect ratio. When choosing the aspect ratio, consider the production capacity of the PCB manufacturer of your choice.  

Via and Layer Count:
Selection is influenced by the PCB board’s layer count. Blind and buried vias are frequently used in multilayer boards to maximize signal quality and space utilization. But producing these vias is difficult and can get expensive.

Testing and Simulation:
Analyze the effects of various vias on overall functionality, signal quality, and thermal performance by using simulation tools. Before any manufacturing happens, problems are found and the design is optimized through virtual testing.

Thermal Considerations and Heat Dissipation with VIAs

 PCB Using channels (through-holes) that pierce through the PCB, heat dissipation holes, also known as PCB thermal vias, are a technique used to dissipate heat to the backside of a PCB. They are positioned as close to or directly beneath the heat-producing element as feasible.  

By employing the PCB as a heat sink, heat dissipation holes help surface-mounted components dissipate heat more effectively. They entail drilling through holes in the PCB structurally.  Connecting the copper foil on both sides of the PCB increases the surface and volume accessible for heat dissipation, which lowers thermal resistance in single-layer and double-sided PCBs.  

The similar goal can be accomplished for multi-layer PCBs by joining the planes between layers or restraining connections to particular layers. 

Thermal Via Design  

In multi-layer boards, vias offer low heat resistance conduction channels between layers:  

 

Quantity
Increased via number minimizes lateral spreading before heat enters a via by reducing conduction channel lengths in the in-plane direction. But costs go up with additional vias.  

Arrangement Scheme
In comparison to peripheral distribution, gridded arrays provide superior heat dispersal from hot regions. It’s also possible to see mixed patterns.  

Density and Size
Although they take up more routing area, wider via diameters and higher via densities enhance vertical heat conduction. Laser micro-vias contribute to higher density.  

Depth
Compared to partial depth vias, full depth vias that span the entire board thickness transport heat to inner layers more effectively.

Barrel Plating Depth
Via barrels with thicker plating have less conduction loss via the via. A higher current rating is also permitted.

Size of Anti-pad
Better heat dispersal into plane layers is achieved with larger anti-pads or clearing spaces surrounding vias. However, it also shrinks the signal layers’ routing space.  

Pads for Thermal Relief
Heat from plated through-hole vias is kept out of the solder mask by exposed thermal pads. Temperatures are lowered by the enhanced heat transmission. 

Stuffing
Heat is transferred to interior layers more quickly in filled vias with conductive inserts than in hollow vias that solely rely on barrel plating.

Manufacturing Constraints and Cost Implications

Production Constraints:
It is important to consider the capabilities and constraints of the production process. Requirements for things like annular ring width, aspect ratio, minimum drill size, and pad size should match the capabilities of PCB production and assembly procedures. Respecting these limitations guarantees manufacturability and keeps possible production-related problems at bay.

Cost and Reliability:
Aspects of cost and reliability should be taken into account when optimizing the route design. While too many vias could raise production costs, improper via location or size could affect the PCB’s dependability and functionality. Achieving a dependable and affordable design requires striking a balance between these variables.

Advanced Via  Frameworks and Methodologies  

With recent developments in via fabrication, PCBs can be made denser and more complicated, enabling increased capabilities. Here are some cutting-edge technologies and via types: 

Back drilled Vias:
The stub portion of the via is removed by mechanically drilling off the via barrel after it has extended through the pad on the outer layers. This lowers stub resonance for high-speed signals considerably.  

Filled & Capped Vias:
Compared to just plated vias, completely filling a via’s hole reduces the possibility of contamination and increases heat transfer. Capped vias have protective epoxy covering only the end holes.

Tented Vias:
To completely isolate tented vias and keep solder and debris out of vias not used for component terminals, a layer of solder mask coating is applied.  

Via in Pad (VIP):
By positioning drill pads over function pad centers, VIP enables vias to be implanted straight into footprints, preventing routing channels from being blocked.  

Microvias Assisted by Lasers:
Lasers create tiny holes that are impossible to drill with mechanical tools, allowing for direct copper plating without the need for seeding.

 

PCB Vias Design Guidelines for Buried, Blind, and Through-Hole Vias

Every one of the aforementioned PCB kinds has unique design guidelines. The same is covered in this section.

Hole-through PCB Vias 

  • Every layer of the circuit board needs to have a drill pad for through-hole PCB vias. While it should be small, the drill pad should be big enough for the drill being used. 
  • Additionally, in order to prevent short circuits between adjacent holes, the through -hole via requires a conventional anti-pad on the board’s plane layers. 
  • Choosing the right via size is a crucial design guideline for through-hole PCB vias. 
  • The aspect ratio of the drilled hole in relation to the thickness of the board should be considered while selecting the via sizes.

The residual or unused via barrel in the multi-layer circuit board may function as an antenna if a through-hole via can connect high-speed signals between the first two layers. But this could lead to problems with signal integrity. OEMs use back drilling to get around this issue. Nevertheless, the overall cost of fabrication goes up with this procedure. To increase board performance, using blind and buried or micro vias is the ideal approach.
If necessary, through-hole vias can be covered or filled. The PCB designer gives the fabricator precise instructions for this.

 

PCBs buried via 

  • Buried vias, as previously mentioned, link the circuit boards’ inside layers, which are not in contact with the exterior layers. For a single connection, the hole needs to be defined as a distinct drill file.
  • Buried vias, as previously mentioned, link the circuit boards’ inside layers, which are not in contact with the exterior layers.  
  • For a single connection, the hole needs to be defined as a distinct drill file. 
  • Aspect ratios of at least 1:12 are required.  
  • The maximum distance and overall depth between the corresponding outer layers and inner layers are determined by the small hole.  
  • Mostly helpful for PCBs with thick routing are buried vias.

 

Blind PCB Vias 

  • Since blind vias are mechanically bored, their drill size restrictions are comparable to those of through-hole drilling. Through in-the-layer stack-up, they permit additional routing channels above or below. Blind vias have a benefit over through-holes because of this capability.  
  • Similar to buried, every hole in a blind route needs to be identified as a distinct drill line.  
  • Aspect ratios ought to be at least 1:1.  
  • The layers of the circuit board are drilled and plated before being fused together in this sort of via, which is constructed sequentially. PCB designers should therefore use them with caution and only when necessary.

 

How should a micro via for an advanced HDI PCB be designed? 

 

Hole Size:
Modify every component of a PCB that has been traditionally intended for microvia design. excessively large holes, or those that will produce a small PCB that is not functional or not ideal.  

Copper Thickness:
The circuit is connected throughout thanks to patterned plating. Conversely, wire bond plating might be chemical or electrical. Produce robust and stiff FR4 laminates with thin micro double-sided or single circuits for micro via design in order to ensure reliability. 

Security Marking:
For accurate PCB identification, very tiny individual barcodes can be imaged onto the solder mask.

Future of PCB vias 

The PCB industry’s automated assembly technology is a future trend.

SMT Vias 

With well-known PCBA manufacturers like JCLPCB and PCB Way embracing this technology, digital intelligence has clearly emerged as a prominent trend in the PCB market. A significant amount of PCBA boards are becoming more and more necessary as market demands change. As a result, Surface Mount Technology has taken the lead and now holds around 70% of the market. 

In order to finish PCB assembly, component leads are manually placed into drilled holes on the PCB and soldered to the copper traces on the other side of the board using the conventional Through-Hole Technology. By placing components directly on the PCB surface, the SMT method, on the other hand, avoids the requirement for drilling holes thanks to automated equipment. This comprises a variety of parts, including integrated circuits, resistors, and capacitors. 

Build up technology for vias 

A common method for creating HDI advanced PCBs is the build-up technique. The inner and outer layers of a multilayer PCB are typically made independently and then pressed together. Additionally, we start with the creation of the inner layers and work our way outward, adding layers on both sides. Laser lasers are typically used to drill blind or buried vias in order to expedite the production process. Furthermore, the build-up technique can result in circuits with finer trace and spacing up to 2 microns. However, plating micro-vias still requires more sophisticated equipment, making it more expensive and challenging.

Via Filling 

We may have problems with air bubbles remaining in the laser-drilled blind or buried vias, which impacts the thermal shock resilience of advanced PCBs. The traditional techniques involve using a resin or unique resist to fill the blind or hidden vias. These techniques are not very efficient, though, and they are challenging. Via filling is introduced to fill buried or blind vias by electroplating, which significantly boosts reliability, in order to improve processing. More sophisticated machinery, specialized plating solutions, and the necessary copper weight are required to achieve effective filling, which nevertheless entails difficulty and high expense. PS Electronics is happy to be involved in the development of other cutting-edge PCB technologies, such as Lo PCB, Rigid-flex PCB, and High-frequency PCB. 

Conclusion 

Vias are required to manufacture multilayer PCBs, which are the way of the future for PCB manufacturing. These PCBs are required to produce the highly functional and compact devices that are the mainstay of modern electronics.

The movement of heat and electrical current between the various layers of a board is facilitated by vias. These vias differ in size and type as well. The kind and dimensions of vias to be used depend on the needs of a circuit board. Vias also improve the signal integrity of circuit boards. Throughout the board, annular rings and multilayer lamination are crucial. Additionally, when creating vias, copper pad and surface components are essential. In PCBs, many vias and signal lines are frequently employed. The outer layers hold significance as well.

PCB Runner handles all type of Via’s categories including blind, buried, stacked & staggered via’s. Do submit your gerber files on https://www.pcbrunner.com/free-pcb-quote/ or do reach out to our team offline at engineering@pcbrunner.com or sales@pcbrunner.com for your current or upcoming projects needs.