PCB Slot: Complete Design Guide for Plated & Non-Plated Slots

If you’ve ever worked with blade-style connectors or components with rectangular leads, you know that standard round holes just don’t cut it. That’s where PCB slots come in — and getting them right can make the difference between a board that works perfectly and one that ends up in the reject pile.

I’ve seen plenty of designs come back from fabrication with slot issues, usually because the designer didn’t specify them correctly in the Gerber files or mixed up plated and non-plated requirements. This guide covers everything you need to know about PCB slot design, from basic concepts to advanced pcb manufacturing considerations.

What is a PCB Slot?

A PCB slot is a non-circular hole in a circuit board that’s too large or irregularly shaped to be created using standard drilling methods. Unlike round holes that can be punched through with a drill bit, slots require a routing bit to cut them out during PCB fabrication.

Think of it this way: if a standard via is like punching a hole with a paper punch, a slot is more like cutting with scissors — you’re removing material along a path rather than at a single point.

PCB slots serve several critical functions in modern circuit board design:

• Accommodating components with rectangular or blade-style leads
• Providing electrical isolation between high-voltage traces
• Creating mechanical mounting points
• Improving thermal management through airflow channels
• Enabling custom board profiles and cutouts

The key distinction is that slots can be either plated (with copper coating for electrical connection) or non-plated (bare FR4 for mechanical or isolation purposes). Choosing the wrong type will cause problems — I’ve seen boards where mounting slots were accidentally plated, creating unintended short circuits.

Types of PCB Slots: Plated vs. Non-Plated

Understanding when to use each type is fundamental to good PCB slot design. Here’s what separates them:

Plated Through Slots (PTS)

Plated slots have copper plating on the inner walls, connecting the top and bottom copper layers — essentially functioning like elongated plated through-holes. They’re the go-to choice when you need electrical connectivity.

When to use plated slots:

• Through-hole components with rectangular pins
• Large blade-style connectors (USB, HDMI, card-edge)
• Components where round holes would waste board space
• Multilayer PCBs requiring layer-to-layer connection through the slot

The plating process is identical to standard PTH: the manufacturer mills the slot, performs electroless copper deposition, then electroplates to achieve the required thickness.

Non-Plated Through Slots (NPTH)

Non-plated slots have no copper on the interior walls. They’re purely mechanical features used for isolation or structural purposes.

When to use non-plated slots:

• Voltage isolation between high-voltage traces (preventing arc-over)
• Thermal management slots for heat dissipation
• Mechanical mounting points
• Board cutouts and irregular profiles
• Cable routing channels

One important note: non-plated slots should have copper pulled back from the slot edge by at least 6 mils (0.15mm) to prevent accidental plating during manufacturing.

Quick Comparison Table: Plated vs Non-Plated PCB Slots

Feature	Plated Slot (PTS)	Non-Plated Slot (NPTH)
Copper plating	Yes, on all interior walls	No copper
Primary purpose	Electrical connection	Mechanical/isolation
Typical applications	Blade connectors, rectangular leads	Mounting, thermal, voltage isolation
Minimum width	0.5mm (most manufacturers)	0.8mm (most manufacturers)
Manufacturing process	Mill → Copper sink → Surface finish	Mill only (after copper process)
Cost impact	Standard	Standard
DRC clearance	Copper-to-edge per design rules	Minimum 6 mil copper pullback

Read more: A Step-by-Step Introduction of PCB Manufacturing :

PCB Slot Dimensions and Size Guidelines

Getting your slot dimensions right is critical — too small and you’ll get manufacturing rejects; too large and you’re wasting board space. Here are the industry-standard specifications:

Minimum PCB Slot Sizes

Parameter	Plated Slots	Non-Plated Slots
Minimum width	0.5mm	0.8mm
Minimum length	1.0mm (or 2× width)	1.6mm (or 2× width)
Inside corner radius	0.5mm minimum	0.5mm minimum
Standard milling tool	2.0mm diameter	2.0mm diameter
Special milling tool	0.8mm – 2.0mm range	0.8mm – 2.0mm range

The 2:1 Length-to-Width Rule

Here’s a rule that trips up a lot of designers: the minimum slot length must be at least 2× the slot width. This isn’t arbitrary — it’s a manufacturing constraint based on how NC milling cutters operate.

For example:

• 0.5mm wide slot → minimum 1.0mm length
• 0.6mm wide slot → minimum 1.2mm length
• 0.8mm wide slot → minimum 1.6mm length

If you specify a slot that violates this rule, expect either a rejection or a conversation with your fab house about what they can actually produce.

Inside Corner Considerations

Because slots are cut with round milling tools, inside corners will always have a radius equal to half the tool diameter. The standard 2.0mm milling tool produces 1.0mm inside corner radii, while the smallest common tool (0.8mm) produces 0.4mm radii.

This matters for enclosure designs — if your slot needs to fit a square-cornered component or mechanical feature, you’ll need to account for these rounded corners in your design or specify a smaller milling tool (which may add cost).

Flex and Rigid-Flex Considerations

For flex and rigid-flex PCBs, the rules change slightly. The thinner material allows for smaller slots, and laser cutting becomes an option:

• Rigid/Rigid-flex: NC milling, minimum 0.5mm width
• Flex circuits: Laser cutting possible, smaller slots achievable

Always confirm capabilities with your manufacturer, as these vary significantly between fab houses.

How to Design PCB Slots in Your CAD Software

The biggest cause of slot-related manufacturing issues? Improper definition in the design files. Here’s how to get it right:

Defining Slots in Gerber Files

The safest, clearest method is to define slots in the Gerber mechanical layer. This layer shows the PCB profile along with all slots and cutouts, leaving no ambiguity for the manufacturer.

Two approaches work well:

1. Draw with appropriate line width: Use a 0.5mm line to trace the slot outline. The line center defines the slot edge, and this method makes it easy to visually verify copper clearance to the board edge.
2. Use flashes or draws: Specify the exact slot dimensions using aperture flashes or draws matching the required slot size.

Critical rules:

• Always combine slot definitions with the PCB outline (contour) in the Gerber file
• Ensure the mechanical layer aligns with copper layers
• Include the PCB outline in the copper layer as well for redundancy
• Never define slots only in copper or legend layers — they’re easily overlooked

Using Drill Files for Slot Definition

Some CAD systems allow slots to be defined in the NC drill file using X and Y dimensions (width and length respectively). This can work, but:

• Not all systems support this method consistently
• Overlapping holes to create slots can cause issues
• Some manufacturers prefer separate mechanical layer definition

When using drill file definition, specify the finished slot size — the manufacturer will compensate for plating thickness on plated slots.

The README File Backup

Whenever there’s any potential ambiguity, document your slot requirements in a README file included with your Gerber package. Specifically note:

• Which slots are plated vs. non-plated
• Any non-standard tolerances required
• References to which layer contains slot definitions
• Special instructions for complex slot patterns

This 30-second step has saved countless boards from manufacturing errors.

Step-by-Step: Creating PCB Slots in Popular CAD Tools

Altium Designer

1. Open your PCB layout in Altium
2. For plated slots: Create a pad with slot hole definition using Pad Properties
3. For non-plated slots: Use the mechanical layer or board cutout features
4. Define slot dimensions in the Properties panel (X and Y for width and length)
5. Verify slots appear correctly in your Gerber preview before export

Most versions of Altium support native slot definitions. Non-circular plated holes export as board cutouts on Mechanical Layer 1 — ensure you include this layer in your manufacturing output.

KiCad

1. Open your design in Pcbnew
2. For slots in component footprints: Define slot shapes on the Edge.Cuts layer
3. For board cutouts: Draw closed shapes on Edge.Cuts layer
4. Use View → Drawing Mode → Sketch Pads to verify slot shapes

Note: KiCad handles slots as cutout outlines. While not native “slots” per se, board manufacturers interpret Edge.Cuts geometry correctly in Gerber files.

Eagle (Autodesk Fusion 360)

1. Open your board layout
2. For through-hole slots: Use an oblong pad definition matching your slot dimensions
3. Draw slot outlines using the dimension layer
4. Note that Eagle’s autorouter won’t route inside pad areas — verify connectivity manually

Limitation: Eagle’s dimension layer approach can cause dimension errors with complex slot matrices. Consider using milling layer definitions for complex designs.

Design Verification Checklist

Before sending files to manufacturing, verify:

• Slots appear on mechanical/outline layer
• Plated slots have copper pads on top and bottom layers
• Non-plated slots have copper pulled back from edges
• Slot dimensions meet minimum requirements (width, length, 2:1 ratio)
• Inside corners have appropriate radii for milling tools
• README file documents any ambiguous slots
• Gerber preview shows slots correctly positioned

PCB Slot Manufacturing Process

Understanding how slots are manufactured helps you design better boards. Here’s what happens at the fab house:

Milling Process

Most PCB slots are created through NC (Numeric Controlled) milling, similar to CNC machining. The process uses a rotating grooving cutter bit to remove material along the slot path.

Key manufacturing parameters:

• Standard milling tool diameter: 2.0mm
• Minimum milling tool diameter: 0.8mm
• Milling creates slightly rounded inside corners (radius = tool radius)
• Feed rate and spindle speed affect edge quality

For rigid boards (FR4, FR-5, PTFE), milling is the only option. The material thickness requires mechanical cutting.

Laser Cutting (Flex PCBs Only)

Flexible circuits are thin enough that laser cutting becomes viable. Benefits include:

• Tighter tolerances
• Sharper corners possible
• Smaller minimum slot widths
• Cleaner edges

However, laser cutting is generally limited to flex and thin rigid-flex constructions.

Plating Process for PTS

Plated through slots follow the same process as plated through holes:

1. Milling: Slots are cut to required dimensions
2. Electroless copper deposition: Thin copper layer applied to slot walls
3. Electrolytic plating: Builds up copper thickness
4. Surface finish: HASL, ENIG, or other finish applied

The manufacturer accounts for plating thickness when milling — your specified finished size is what you’ll receive.

Cost and Lead Time Considerations

Good news: most manufacturers don’t charge extra for slots. Standard milling is included in the base fabrication price. However, be aware that:

• Very small slots (requiring special tooling) may add cost
• High slot counts can extend lead time slightly
• Complex slot patterns may require DFM review

Common PCB Slot Design Mistakes (And How to Avoid Them)

After reviewing hundreds of designs, these are the errors I see most frequently:

Mistake 1: Defining Slots Only in Copper or Legend Layers

Problem: Slots defined only in copper or silkscreen layers are easily overlooked or misinterpreted by manufacturers.

Solution: Always define slots in the mechanical/outline layer. Use copper and legend layers only as supplementary references, not primary definitions.

Mistake 2: Forgetting the 2:1 Length-to-Width Ratio

Problem: Specifying slots that are too short relative to their width results in manufacturing rejections or distorted slots.

Solution: Ensure minimum length is always ≥2× the slot width. When in doubt, go longer.

Mistake 3: Not Distinguishing Plated from Non-Plated

Problem: Manufacturing receives ambiguous files and makes assumptions — often wrong ones.

Solution: Clearly mark plated vs. non-plated in:

• Layer naming conventions
• README documentation
• Separate drill files if your CAD supports it

Mistake 4: Ignoring Inside Corner Radius

Problem: Design assumes sharp corners; manufacturing produces rounded corners; component doesn’t fit.

Solution: Design with the expected corner radius in mind. For standard 2.0mm tools, that’s a 1.0mm inside corner radius. If sharper corners are required, specify smaller tooling (and expect potential cost increase).

Mistake 5: Copper Too Close to Non-Plated Slot Edges

Problem: Copper positioned too close to NPTH slot edges may accidentally plate during manufacturing, creating shorts or isolation failures.

Solution: Pull copper back at least 6 mils (0.15mm) from non-plated slot edges — more if your design rules require greater clearance.

Mistake 6: Missing Slot Definitions When Exporting Gerber

Problem: Slots are visible in your CAD tool but don’t make it into the exported Gerber package.

Solution: Always preview Gerber output in a standalone viewer (Gerbv, Altium 365 Viewer, etc.) before submitting. Verify every slot appears correctly.

Applications of PCB Slots in Real Designs

PCB slots aren’t just theoretical — they solve real design challenges across industries:

Connector Mounting

Large blade-style connectors (USB Type-A, HDMI, card-edge connectors) use plated slots to accommodate their rectangular pins. Round holes would waste significant board space and create weaker solder joints.

High-Voltage Isolation

In power electronics, non-plated slots create physical air gaps between high-voltage traces. This prevents electrical arcing that could cause PCB carbonation and eventual short circuits.

Thermal Management

Slots can create airflow channels across the board, improving heat dissipation in thermally challenging designs. This is common in power supply and LED driver PCBs.

RF and High-Speed Design

PCB slots help minimize impedance mismatches and improve signal integrity in RF circuits. Strategic slot placement can reduce crosstalk and enhance isolation between sensitive signal paths.

Consumer Electronics

Gaming consoles, networking equipment, and IoT devices use slots for both electrical connections (blade connectors) and mechanical mounting (securing boards to enclosures).

Automotive and Industrial Applications

Modern vehicles contain hundreds of PCBs, many requiring slots for robust connector mounting. Blade-style connectors in automotive applications must withstand vibration, temperature cycling, and mechanical stress — plated slots provide the secure mechanical and electrical connection needed for these demanding environments.

Medical Devices

Medical electronics often require precise component placement and reliable electrical connections. PCB slots enable compact designs while maintaining the connection integrity critical for patient safety and device reliability.

Plated Slot vs Round Hole: When to Choose Each

A common question from designers is whether to use a plated slot or simply drill a larger round hole. Here’s how to decide:

Choose plated slots when:

• Component leads are rectangular or blade-shaped
• Board space is limited and round holes would waste area
• You need a tight fit between lead and hole (minimizing solder volume)
• The connector datasheet specifies slot mounting

Choose round holes when:

• Component leads are circular or square
• Standard through-hole components are being used
• No specific space constraints exist
• Manufacturing simplicity is a priority

The solder joint quality is often better with properly sized slots because there’s less excess space between the lead and hole wall. This means less solder is required and the risk of solder voids decreases.

Useful Resources for PCB Slot Design

Design Tools and Viewers

Tool	Purpose	Link
Gerbv	Free open-source Gerber viewer	gerbv.geda-project.org
Altium 365 Viewer	Online PCB file viewer	altium.com/viewer
KiCad	Free PCB design software	kicad.org
Autodesk Fusion 360 (Eagle)	Professional PCB design	autodesk.com/products/fusion-360

Manufacturer Resources

Most PCB manufacturers provide detailed design guidelines. Check these resources before finalizing your design:

• PCBWay Design Guidelines: pcbway.com/pcb_prototype
• JLCPCB Capabilities: jlcpcb.com/capabilities
• PCBGogo Knowledge Center: pcbgogo.com/knowledge-center
• Sierra Circuits Design Guide: protoexpress.com/kb

Industry Standards

• IPC-2221: Generic Standard on Printed Board Design
• IPC-6012: Qualification and Performance Specification for Rigid PCBs
• Gerber RS-274X: Standard Gerber format specification

Frequently Asked Questions About PCB Slots

What is the minimum size for a PCB slot?

The minimum slot width is typically 0.5mm for plated slots and 0.8mm for non-plated slots. The minimum length must be at least 2× the width — so a 0.5mm wide slot needs to be at least 1.0mm long. These minimums vary slightly between manufacturers, so always verify with your specific fab house before finalizing designs.

Do PCB slots increase manufacturing cost?

Generally, no. Standard slots are included in base fabrication pricing at most manufacturers. However, very small slots requiring special tooling, extremely high slot counts, or complex patterns may incur additional charges. The bigger risk is incorrectly specified slots causing DFM rejections and delays.

How do I indicate plated vs. non-plated slots in my design files?

Define plated slots with copper pads on top and bottom layers connecting to the slot. For non-plated slots, pull copper back from the slot edge by at least 6 mils. Use clear layer naming, document in a README file, and consider using separate drill files for PTH and NPTH if your CAD software supports it.

Can I create slots in KiCad?

Yes, though KiCad handles slots differently than some other tools. Slots are typically represented on the Edge.Cuts layer as cutout outlines. Use View → Drawing Mode → Sketch Pads to see the actual slot shapes. While not “native” slot definitions, board manufacturers correctly interpret these cutouts from your Gerber files.

Why won’t my manufacturer produce my slot design?

Common reasons include: slot width below minimum (0.5mm plated, 0.8mm non-plated), length-to-width ratio less than 2:1, slots defined only in copper/legend layers (not mechanical layer), missing documentation for plated/non-plated distinction, or copper too close to non-plated slot edges. Review the common mistakes section and verify your design meets all requirements before resubmitting.

Conclusion

PCB slots are one of those features that seem simple until you get them wrong. The key takeaways:

1. Choose the right type: Plated for electrical connections, non-plated for mechanical and isolation purposes
2. Follow size rules: Minimum widths (0.5mm/0.8mm), 2:1 length-to-width ratio, account for corner radii
3. Define clearly: Use mechanical layer, document in README, verify in Gerber viewer before submission
4. Communicate with your fab house: When in doubt, ask — it’s cheaper than respins

Get these fundamentals right, and your slots will manufacture correctly the first time. Miss them, and you’ll be explaining to your project manager why the boards need another revision.

Got a specific slot design challenge? Most PCB manufacturers offer free DFM reviews — take advantage of them before committing to production.