Plated Through-Hole Via in PCB Manufacturing
What Is a Plated Through-Hole Via?
A plated through-hole via is a drilled hole with copper plated along the inner wall to connect copper features across the layers it penetrates. Unlike non-plated thru holes, a plated through hole is intentionally conductive, forming a vertical path through the stackup to tie surface pads to internal planes and route signals between layers. It is frequently used for ground stitching, power distribution, thermal conduction, and assembly of through-hole components.
IPC-2221 (Generic Requirements for Designing Printed Boards and Other Forms of Component Packaging) is an essential design standard for specifying via sizes, copper plating, and stackup construction, ensuring robust interlayer connections and manufacturability.
Plated through-hole vias provide both electrical and mechanical benefits. The continuous copper barrel offers low resistance and high current capability, while the cylindrical structure withstands assembly and operational stresses better than small microvias. In advanced designs, a plated through-hole complements blind, buried, and microvias to balance performance, cost, and reliability. It helps maintain return paths, reduce loop area for digital and RF signals, and move heat away from high-power components. In short, circuit board vias, especially through-hole vias, remain a dependable backbone for interlayer connectivity.
Structure and MaterialsA plated through-hole is comprised of a drilled hole, an annular ring on each connected layer, and a plated copper barrel along the hole wall. Common substrates include FR-4 and high-performance laminates. Manufacturing starts with mechanical drilling of via holes followed by desmear and hole preparation, then electroless copper deposition to create a conductive seed layer, and electroplating to build the barrel thickness. External circuitry is imaged and etched, and final solder mask and surface finish (such as ENIG, HASL, or immersion tin) are applied. Copper barrel thickness for standard boards typically ranges around 20–25 microns, selected based on current, thermal, and reliability requirements. Effective via plating is central to plated through hole technology, ensuring uniform copper distribution through high-aspect-ratio thru holes.
IPC-A-600 (Acceptability of Printed Boards) emphasizes the requirement for uniform copper plating in drilled holes, with specific guidelines on ensuring that the barrel thickness and finished hole sizes align with the manufacturer’s capabilities to maintain reliability over time.
Compared with other via types:
- Blind vias connect an outer layer to one or more inner layers without passing through the entire board.
- Buried vias connect only internal layers and are not visible on the outer surfaces.
- Microvias are laser-drilled, very small, and often stacked or staggered in HDI designs.
- Plated through holes pass through the full stackup, providing strong anchoring and higher current capacity, but occupy more land area and can create via stubs that affect high-speed signals.
Where PTH Vias Excel
Through-hole vias are widely used in industrial controls, automotive electronics, aerospace, medical devices, consumer hardware, and power systems. They are chosen when robust interlayer connection, dependable assembly, or higher current paths are required.
- Mechanical reliability: Reinforced barrels around connectors and through-hole parts withstand repeated mating cycles and vibrational stress.
- Thermal conduction: Arrays of plated through holes under heat sources move thermal energy into internal planes or heat spreaders to reduce junction temperatures.
- Ground stitching: Dense stitching patterns using circuit board vias lower EMI by providing low-impedance return paths and isolating analog and digital regions.
IPC-2226 (Design and Fabrication of High-Density Interconnects) recommends the use of plated through-holes in systems requiring high current capacity and thermal conduction, particularly where space and reliability constraints require robust, long-term performance.
Example applications include via holes under power MOSFETs in automotive ECUs to reduce thermal hotspots, backdrilled plated through-hole vias in high-speed networking cards to remove stubs and improve eye diagrams, and reinforced thru holes around high-cycle connectors in medical imaging interfaces to preserve signal integrity and mechanical robustness. In each case, the choice of plated through-hole technology and consistent via plating practices drives long-term reliability.
Effective via design balances electrical, mechanical, and fabrication constraints. Key practices include:
- Annular ring: Choose adequate width to account for drill tolerance and registration. Follow fabricator minimums to avoid breakout on circuit board vias.
- Finished hole size: Specify sizes for through hole vias that meet component lead and assembly needs, considering plating-in and drill tolerances.
- Barrel thickness: Set based on current, fatigue resistance, and reliability targets; avoid overplating that reduces hole diameter.
- Solder mask: Maintain proper clearances. Use solder mask-defined pads where needed to control solder fillet formation.
Signal integrity and thermal management are highly sensitive to via geometry:
- High-speed signals: Minimize via stubs that behave as unterminated transmission lines. Use backdrilling or blind vias where feasible to optimize plated through-hole performance.
- Plane clearances: Control anti-pad sizes to manage impedance and parasitic capacitance. Keep consistent anti-pad geometry for differential pairs.
- Differential routing: Maintain symmetrical via transitions, matched stub lengths, and identical anti-pad shapes for both lines.
- Power and ground: Use via farms to distribute current and reduce DC resistance. Place thermal through-hole vias beneath hot components to conduct heat into copper planes or heat sinks.
Placement and sizing should reflect board density, assembly, and reliability goals. Stitch ground pours near high-edge-rate devices and along enclosure seams. Cluster thermal plated through holes under regulators, LEDs, and power semiconductors, with spacing that avoids resin starvation during lamination. Typical finished hole sizes for signal circuit board vias range from 0.2–0.4 mm, with larger diameters for mechanical or power vias. For fine-pitch BGAs, consider via-in-pad with filled and capped plating to enable escape routing and prevent solder wicking. Align design rules with your fabricator’s capability table for minimum annular ring, aspect ratio, drill sizes, via plating thickness, and backdrill limits to improve yield and lead time.
IPC-7351 (Surface Mount Design and Land Pattern Standard) offers guidelines for pad design and via-in-pad solutions, particularly for small-pitch components like BGAs, which is crucial when working with complex, high-density designs.
Plated through-hole vias remain essential in modern PCB design for robust interconnects, high current capability, and mechanical strength. By specifying proper annular rings, finished hole sizes, copper barrel thickness, and solder mask clearances—and by managing stubs, anti-pads, and thermal via placement—you can achieve reliable performance and manufacturable layouts. Close alignment with fabrication capabilities and disciplined via plating ensures consistent yield, shorter lead times, and predictable assembly outcomes. Whether you are routing critical signals or reinforcing connectors, through-hole vias and other circuit board vias built with proven plated through hole technology deliver dependable, long-term results.
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Frequently Asked Questions
Do plated through-hole vias connect all layers by default?
No. A plated through-hole via connects only layers that have annular rings tied to the barrel. Layers without pads are isolated by anti-pads.
How does barrel thickness affect reliability?
Thicker barrels increase current capacity and fatigue resistance but can shrink finished hole size if overplated. Specify both finished hole size and minimum barrel thickness to meet electrical and assembly requirements for thru holes.
When should I backdrill?
Backdrill when high-speed signals would otherwise leave long stubs that degrade return loss and eye openings. Target only the layers necessary to remove the unused portion of the plated through hole.
What aspect ratio limits apply?
High aspect ratios are harder to plate uniformly and may reduce yield. Consult your fabricator for maximum board thickness-to-hole diameter ratios and adjust drill sizes for through-hole vias accordingly.
Are via-in-pad features viable for fine-pitch BGAs?
Yes, if the vias are filled and capped to prevent solder wicking and ensure coplanarity. Verify process compatibility with your assembly and fabrication partners, particularly around via plating and hole fill for via holes.