Types of PCB Holes: Functions and Applications

A hole on a printed circuit board may look simple, but it can perform many different functions. It may carry a signal, connect ground planes, transfer heat, hold a component, secure the PCB inside an enclosure, locate the panel during production or provide access for testing.

Some PCB holes look similar on the finished board, but their design and manufacturing requirements can be very different. Whether the hole wall is plated, which copper layers it connects, its finished diameter, positional tolerance and annular ring all depend on its intended purpose.

Misunderstanding that purpose may increase cost or create problems during plating, soldering, assembly, testing and long-term use.

This guide explains the major types of PCB holes according to their functions. It also introduces structural classifications such as through vias, blind vias, buried vias and microvias. Via tenting, plugging, resin filling and copper capping are separate treatment methods and will be discussed in another article.

How Are PCB Holes Classified?

There is no single classification system that describes every characteristic of a PCB hole. In practice, holes can be classified from at least three perspectives:

1. By function: signal vias, ground vias, thermal vias, stitching vias, component holes, mounting holes, tooling holes and test holes.
2. By structure: through vias, blind vias, buried vias and microvias.
3. By treatment: open, tented, solder-mask plugged, resin filled, or resin filled and copper capped.

These classifications can apply to the same hole at the same time.

For example, a hole placed inside a BGA pad may be:

• A signal via by function
• A laser-drilled blind via by structure
• A via-in-pad by location
• Resin filled and copper capped by treatment

Therefore, Signal Via, Blind Via and Via-in-Pad are not competing names for the same category. They describe different characteristics of the hole. Understanding these separate layers of classification is the first step toward choosing the correct PCB hole design.

Types of PCB Holes

Eight Common Types of PCB Holes by Function

1. Signal Via

A signal via carries an electrical signal from one copper layer to another. It is one of the most common types of plated holes in double-sided and multilayer PCBs.

The signal travels through the copper deposited on the wall of the hole. Depending on the layer connection and routing density, the signal via may be a through via, blind via, buried via or laser-drilled microvia.

Important design considerations include:

• Finished hole diameter and drill diameter
• Pad size and annular ring
• PCB thickness-to-hole aspect ratio
• Trace density and layer transitions
• Current-carrying requirement
• Parasitic inductance and capacitance
• Via stub effects in high-speed designs
• Drilling, copper deposition and plating capability

For ordinary low-speed circuits, a standard plated through via is often sufficient. Fine-pitch BGAs, dense routing and high-speed signals may require blind vias, microvias, back drilling or via-in-pad technology.

However, a more complex via structure normally means additional manufacturing processes, higher cost and tighter reliability control. It should be selected because the design requires it—not simply because it appears more advanced.

2. Ground Via

A ground via connects ground copper on different PCB layers, such as a top-layer ground area, an internal ground plane and bottom-layer ground copper.

Its purpose can extend beyond basic electrical continuity. Ground vias may:

• Shorten current return paths
• Reduce ground impedance
• Improve electromagnetic compatibility
• Maintain a return path near a high-speed signal transition
• Connect shielding areas to a ground plane
• Assist heat transfer between copper layers

Ground-via position and quantity can affect performance around connectors, crystal oscillators, RF circuits, high-speed layer transitions and power components.

Using several ground vias in parallel can generally reduce connection impedance. Nevertheless, “more vias” is not automatically the best answer. Layout space, return-current path, frequency, manufacturability and cost still need to be considered.

3. Thermal Via

A thermal via transfers heat from a component or copper area to other copper layers or to the opposite side of the PCB. Thermal-via arrays are commonly used below LEDs, MOSFETs, power modules, QFNs and other heat-generating components.

Thermal performance depends on more than the number of holes. Important factors include:

• Via diameter, pitch and quantity
• Copper thickness on the hole wall
• Connected copper area and number of copper layers
• PCB thickness and dielectric material
• Whether the holes are open, plugged, filled or capped
• Component thermal-pad and solder-paste design
• The cooling arrangement of the complete product

In an ordinary plated thermal via, heat is mainly conducted through the copper on the hole wall, not through the air inside the hole.

If open thermal vias are placed directly inside a component pad, solder may wick into the holes during reflow. This can cause insufficient solder, excessive voiding or an uneven component position. Whether plugging, resin filling or copper capping is required should be decided according to the pad structure, assembly process and reliability requirements.

4. Via Stitching

Via stitching refers to arranging multiple vias at suitable intervals to connect copper areas on different layers. It describes a layout method rather than a unique drilling process.

Common applications include:

• Connecting ground pours on the top and bottom layers
• Creating a grounded via fence around the PCB edge
• Improving shielding around RF and high-speed circuits
• Reducing impedance between ground planes
• Providing parallel current paths in high-current areas
• Helping heat spread between copper layers

Via stitching may overlap with other functional classifications. A row of vias that connects ground areas is both ground vias and via stitching. If those vias also conduct heat, they can simultaneously perform a thermal function.

This is why the names in a PCB-hole classification do not always describe mutually exclusive physical holes.

5. Component Hole

A component hole is used to install and solder the lead of a through-hole component, such as a connector, pin header, capacitor, resistor, transformer, relay or terminal block.

Most through-hole component leads require both an electrical connection and mechanical support. Therefore, component holes are generally plated through holes.

The designer should consider:

• Maximum lead size and lead shape
• Finished hole diameter
• Reduction in hole diameter after copper plating
• Required insertion clearance
• Pad and annular-ring dimensions
• Solder-fillet and barrel-fill requirements
• Component weight, insertion force and mechanical stress

A hole that is too small may prevent insertion. A hole that is too large can reduce solder filling and mechanical stability. For square or rectangular leads, hole selection should consider the diagonal dimension, component tolerance and assembly method—not only the width of one side.

Some connectors include both electrical pin holes and purely mechanical support holes. Although they may look similar, their plating, net connection and tolerance requirements can be different. These properties should be clearly distinguished in the drill data and fabrication drawing.

6. Mechanical Mounting Hole

A mechanical mounting hole is used with screws, standoffs, rivets, clips or other hardware to secure the PCB. It may be a non-plated through hole, or it may be plated when grounding, shielding or another electrical connection is required.

Mounting-hole design should consider:

• Screw, washer and standoff dimensions
• Hole-diameter and positional tolerances
• Distance from the hole to the board edge
• Clearance from copper and nearby components
• Grounding or insulation requirements
• Metal enclosures, washers and fastening hardware
• Mechanical stress created during tightening
• Whether solder mask should cover or expose the surrounding copper

If a mounting hole must connect to chassis ground, the electrical net and exposed-copper requirements should be clearly defined. If it must remain electrically isolated, sufficient copper clearance is necessary.

A PCB manufacturer should not have to guess these requirements from the words “mounting hole” alone.

7. Tooling Hole

A tooling hole is used to locate a PCB or panel during fabrication, solder-paste printing, component placement, testing or final assembly. It normally has no electrical function and is often designed as a non-plated through hole.

Tooling holes may be placed directly on the individual PCB or on the breakaway rails of a production panel. They work with locating pins on machines and fixtures. Their diameter, position and quantity depend on the equipment and process.

An asymmetric tooling-hole arrangement is often used to prevent a panel from being loaded in the wrong orientation.

The design team should confirm whether the hole is required for:

• PCB fabrication
• Solder-paste printing or SMT placement
• Electrical-test fixtures
• Final product assembly

Different operations may require different positional tolerances. If a tooling hole is placed only on a breakaway rail, the panel drawing should also confirm that it will be removed during depanelization.

8. Test Hole

A test hole provides access for electrical inspection, functional testing or debugging. A probe may contact its plated wall, annular ring or an associated test pad to measure continuity, voltage, signals or other parameters.

Not every test point needs to be a drilled hole. Flat test pads are often easier to access during flying-probe, in-circuit and functional testing, while avoiding unnecessary drilling cost.

A dedicated test hole may be useful when a probe needs to enter the hole, a temporary connector must be installed, a signal needs to be brought out, or a special fixture requires it.

Test-hole design should consider:

• Test method and probe type
• Whether hole-wall plating is required
• Surface finish on the contact area
• Probe accessibility and test-point spacing
• Possible effects on high-speed signals
• Whether the hole will have another function after testing

For volume production, confirming test access with the test and assembly teams early in the design stage is more reliable and economical than adding test points after the PCB layout has been completed.

PCB Hole Types by Structure

Customers also commonly describe holes according to which PCB layers they connect.

Through Via

A through via extends from one side of the PCB to the other. It is a mature and relatively economical structure used extensively in double-sided and multilayer PCBs.

Its main limitation is that it occupies routing space on every layer it passes through. In high-speed applications, the unused section of the plated barrel may also form a via stub.

For early design validation, standard through-hole structures are often the most practical option for a PCB prototype when routing density permits.

Blind Via

A blind via connects an outer layer to one or more inner layers without passing through the entire PCB. It preserves routing space on the opposite side and is frequently used for HDI and fine-pitch BGA designs.

Blind vias require tighter control of lamination, drilling, registration and plating than ordinary through vias.

Buried Via

A buried via connects two or more internal copper layers and is not visible from either outer surface of the finished PCB.

The relevant inner-layer subassembly must normally be drilled and plated before final multilayer lamination. This adds manufacturing steps and cost, so buried vias should be used only when their routing benefit justifies the additional process.

Microvia

A microvia is normally produced by laser drilling and is widely used in HDI PCBs. It frequently connects adjacent layers, although staggered or stacked structures can provide connections across additional layers.

Microvias support fine-pitch devices and high routing density. However, the via diameter, dielectric thickness, copper filling and stacked construction must match the PCB manufacturer’s stable process capability.

Again, these structural terms explain which layers a hole connects. Signal Via, Ground Via and Thermal Via explain what it does. A laser-drilled blind microvia can carry a signal, connect ground or transfer heat.

PTH vs. NPTH: What Is the Difference?

Plated Through Hole (PTH)

A PTH has copper deposited and electroplated on the hole wall, allowing it to form an electrical connection between copper layers.

Signal vias, ground vias, thermal vias and most through-hole component holes are PTHs.

The finished diameter of a PTH is affected by drilling, electroless copper deposition and electroplating. Design and purchasing documents should therefore distinguish between Finished Hole Size and Drill Size.

Stable hole-wall copper, a suitable aspect ratio and adequate annular rings are especially important in a high-reliability PCB, where thermal cycling and long-term service may place repeated stress on the plated barrel.

Non-Plated Through Hole (NPTH)

An NPTH has no copper plating on its wall. It is commonly used for mechanical mounting, tooling, alignment or electrical isolation.

NPTH properties should be clearly marked in the drill file or fabrication drawing. Adequate clearance from nearby copper is also necessary.

PTH and NPTH holes often appear on the same PCB. If drill-layer names are unclear or the mechanical drawing conflicts with the Gerber data, engineering clarification is necessary before production.

Six Common PCB Hole Design Problems

1. Not Specifying Finished Hole Size or Drill Size

Copper deposition and plating reduce the diameter of a PTH. Component assembly is normally concerned with the finished hole, while the PCB manufacturer needs to select a larger drill diameter to achieve it.

The drawing should clearly state which dimension is being specified.

2. Insufficient Annular Ring

Both drilling and imaging have manufacturing tolerances. An annular ring that is too small increases the risk of breakout, tangency or an insufficient local connection, especially on thick, small-hole and high-layer-count PCBs.

3. An Unsuitable Aspect Ratio

The smaller the hole and the thicker the PCB, the more difficult it becomes to deposit and electroplate copper uniformly through the barrel.

The correct question is not only, “Can this hole be drilled?” It is also, “Can sufficient and uniform hole-wall copper be produced reliably?”

4. Using an Open Via Inside a Soldering Pad

An open via-in-pad can draw solder away from a BGA, QFN or thermal pad during reflow. An appropriate filling and capping method should be selected according to soldering and reliability requirements.

5. Unclear PTH and NPTH Definitions

Whether a mounting hole should be plated and connected to ground cannot be determined by its name alone. The drill properties, electrical net and mechanical requirements should agree across all design files.

6. Ignoring Assembly, Testing and the Service Environment

A PCB hole must do more than pass fabrication inspection. Component insertion, screw pressure, probe access, soldering conditions and plated-barrel reliability after thermal cycling can all affect the finished product.

How to Select the Right PCB Hole Type

Before finalizing a hole, answer the following questions:

1. Is its main purpose signal transmission, grounding, heat transfer, component installation, mounting, tooling or testing?
2. Which copper layers must it connect?
3. Does the hole wall require copper plating?
4. Is it located inside or close to a soldering pad?
5. What electrical, thermal, signal-integrity or mechanical requirements apply?
6. Can a standard through hole meet the need, or is a blind, buried or laser-drilled microvia genuinely necessary?
7. Are the diameter, annular ring, aspect ratio and tolerance within a stable production capability?
8. Are there special soldering, testing, depaneling or assembly requirements?

SQPCB reviews Gerber data, drill files, stack-ups and assembly requirements before production. For small holes, thick boards, HDI structures, via-in-pad and unusual mounting holes, early DFM communication makes it easier to balance manufacturability, cost and reliability.

When delivery time is also critical, confirming the hole structure before ordering helps avoid engineering delays in quick-turn PCB manufacturing.

Conclusion

PCB holes should not be understood by appearance alone.

Signal vias, ground vias, thermal vias, stitching vias, component holes, mounting holes, tooling holes and test holes are classified by function. Through vias, blind vias, buried vias and microvias are classified by layer connection. Tenting, plugging, filling and copper capping describe how a hole is treated.

One physical hole can belong to several of these categories simultaneously.

The most important questions are not simply what the hole is called, but what it must do, which layers it connects, whether it requires plating, how it will be soldered or assembled, and what reliability level it must achieve.

If a design includes unusual hole structures, discussing them with the PCB manufacturer early is worthwhile. One small hole can affect drilling, plating, lamination, soldering, testing and cost throughout the manufacturing process.

Frequently Asked Questions

1. Do All PCB Holes Need Copper Plating?

No. Vias and most through-hole component holes normally require copper plating for electrical connection. Purely mechanical mounting holes and some tooling holes are commonly non-plated. The correct choice depends on the intended function.

2. What Is the Difference Between a Via and a Through Hole?

A via normally provides an electrical connection between PCB copper layers and does not receive a component lead. Through hole is a broader structural term and may also describe a component hole or a mechanical hole passing through the complete PCB. The hole’s function and plating requirement should be specified clearly.

3. Do More Thermal Vias Always Provide Better Cooling?

Not necessarily. A suitable increase in thermal vias can help, but performance also depends on hole-wall copper, connected copper area, layer count, board thickness, dielectric material, soldering and the complete cooling system. Excessive vias may also occupy routing space or add manufacturing difficulty.

4. Can a Tooling Hole and Mounting Hole Be Shared?

Sometimes, but the same hole must meet the dimensional, positional and functional requirements of both production tooling and final assembly. The PCB, SMT and mechanical-assembly teams should confirm this before volume production.

5. Why Should Component Holes Be Specified by Finished Hole Size?

A plated hole becomes smaller after copper deposition and electroplating. Component insertion depends on the final diameter, so fabrication data should clearly specify the finished hole size and its tolerance.

6. Does Every BGA Require Via-in-Pad?

No. The need for via-in-pad depends on BGA pitch, pad size, fan-out space, layer count and signal requirements. If conventional fan-out routing meets the design needs, there is normally no reason to add via-in-pad and its associated filling cost.