Clear, predictable pad names make a PCB library usable at scale. They shorten part creation time, reduce ambiguity when selecting footprints, and allow automated checks and scripting. This article presents a concise, practical naming convention for common pad geometries in PCB layout libraries, with examples that are easy to parse by both humans and EDA tools.
Notation and General Rules
The examples below use a compact alphanumeric scheme designed to encode geometry directly in the pad name. The following conventions are used consistently:
- Units: dimensions are in millimeters.
- Decimal marker: the letter R is used as a decimal separator. For example, 1R60 means 1.60 mm, 2R00 means 2.00 mm.
- Separators:
- X separates length and width (L x W).
- - separates outer pad size from the hole size in through-hole pads, or outer size from inner size in thermal (flash) pads.
- Prefixes identify pad categories and geometries:
- SC, SR, SOB for surface-mount (SMD) pad shapes: circular, rectangular, and oblong.
- C, R, OB for through-hole pad shapes: circular, rectangular, and oblong.
- FLASH for thermal relief pads (flash pads).
- PAD-[package]-[pin] for irregular or package-specific pad shapes.
- Zero padding is used for clarity and sorting: 1R00 rather than 1R0.
- Consistency in case improves filtering and sorting. While some examples show lowercase r, using a consistent uppercase R throughout the library is recommended.
Surface-Mount Pad Naming
Circular SMD Pads
Format: SC + diameter.
Example: SC1R00 denotes a circular SMD pad with a diameter of 1.00 mm.
This format keeps the name compact while providing the essential dimension in millimeters.
Rectangular SMD Pads
Format: SR + length X width.
Example: SR1R00X1R00 denotes a rectangular SMD pad 1.00 mm long by 1.00 mm wide (a 1.00 mm square).
Using L x W avoids ambiguity when different solder fillets require asymmetric pads. The X separator ensures the dimension pair is easy to parse and sort.
Oblong (Rounded-Rectangle) SMD Pads
Format: SOB + length X width.
Example: SOB1R00X2R00 denotes an oblong SMD pad with dimensions 2.00 mm by 1.00 mm. The order is written as length X width.
Oblong pads are frequently used for chip resistors, capacitors, and other passive devices to improve solder wetting and reduce tombstoning. Encoding both axes supports quick differentiation between similar components with different aspect ratios.
Through-Hole Pad Naming
Through-hole pads include both the copper pad dimension and the drill size. The dash character separates the pad size from the hole size. This makes it easy to verify annular ring and manufacturability directly from the name.
Circular Through-Hole Pads
Format: C + pad diameter - hole diameter.
Example: C1R60-1R00 denotes a circular pad with a 1.60 mm pad diameter and a 1.00 mm hole diameter.
This format is helpful when selecting between otherwise similar drill sizes or assessing whether the annular ring meets design rules.
Rectangular Through-Hole Pads
Format: R + pad length X pad width - hole diameter.
Example: R1R60X1R60-1R00 denotes a rectangular pad 1.60 mm by 1.60 mm with a 1.00 mm hole.
When length equals width, the pad name can be abbreviated by omitting the X pair for brevity:
Example: R1R60-1R00 denotes a 1.60 mm square pad with a 1.00 mm hole.
Oblong Through-Hole Pads
Format: OB + pad length X pad width - hole diameter.
Example: OB1R60X1R60-1R00 denotes an oblong pad 1.60 mm by 1.60 mm with a 1.00 mm hole.
Oblong through-hole pads are useful where additional annular ring is required in one axis for mechanical strength or routing clearance.
Thermal Relief (Flash) Pad Naming
Thermal relief pads (often called flash pads) encode the outer and inner dimensions to distinguish copper annulus from the clearance or inner aperture. The dash separates these two sets of dimensions.
Circular Flash Pads
Format: FLASH + outer diameter - inner diameter.
Example: FLASH2r20-1r50. In this example, the inner diameter is 2.20 mm and the outer diameter is 1.50 mm as annotated. Use consistent case (e.g., FLASH2R20-1R50) in your library to avoid ambiguity.
These pads are typically used on power and ground planes to control heat flow during soldering while maintaining electrical connectivity.
Rectangular Flash Pads
Format: FLASH + outer length X outer width - inner length X inner width.
Example: FLASH3r20X2r50-2r20X1r50 denotes a flash pad with outer dimensions 3.20 mm by 2.50 mm and inner dimensions 2.20 mm by 1.50 mm. A consistent uppercase format (e.g., FLASH3R20X2R50-2R20X1R50) is recommended for standardization.
This representation makes it straightforward to verify copper annulus and inner opening clearance directly from the pad name, which is especially useful when creating or reviewing thermal relief patterns.
Irregular or Package-Specific Pads
Not all pads are simple circles, rectangles, or oblong shapes. Some packages require custom copper shapes for mechanical reasons, solder fillet tuning, or manufacturer recommendations. For such cases, reference the package and the pin number directly.
Format: PAD-[package]-[pin].
Example: PAD-SOT89-1 denotes the pad for pin 1 of a package identified as SOT89.
This form ensures traceability back to the package drawing and clarifies which pin the special pad corresponds to. It also prevents accidental reuse of a custom pad shape for an incompatible pin or device.
Why Consistent Pad Naming Matters
Consistent pad naming is more than aesthetics—it supports correct design, review, and manufacturing:
- Library search and reuse: Engineers can quickly filter pads by size and shape without opening properties, reducing footprint creation time and avoiding duplication.
- Automated checks: Scripts can match pads to design rules, check annular ring margins, and flag nonconforming geometries based on name patterns.
- Footprint auditability: During review, anyone can validate that selected pads match the intended dimensions at a glance.
- Manufacturability: Encoded hole and pad sizes help verify that drill sizes and annular rings meet fabrication constraints.
- Documentation: Clear names flow into BOM data, library catalogs, and drawing notes with less manual annotation.
Interpreting the Examples at a Glance
- SC1R00: SMD circular pad, 1.00 mm diameter.
- SR1R00X1R00: SMD rectangular pad, 1.00 mm x 1.00 mm.
- SOB1R00X2R00: SMD oblong pad, 2.00 mm x 1.00 mm.
- C1R60-1R00: Through-hole circular pad, 1.60 mm pad, 1.00 mm hole.
- R1R60X1R60-1R00 or R1R60-1R00: Through-hole square pad, 1.60 mm x 1.60 mm pad, 1.00 mm hole.
- OB1R60X1R60-1R00: Through-hole oblong pad, 1.60 mm x 1.60 mm pad, 1.00 mm hole.
- FLASH2R20-1R50: Circular thermal relief pad. Outer and inner diameters are encoded as outer-inner; verify values per your library convention.
- FLASH3R20X2R50-2R20X1R50: Rectangular thermal relief pad, outer 3.20 mm x 2.50 mm, inner 2.20 mm x 1.50 mm.
- PAD-SOT89-1: Custom pad for SOT89 package, pin 1.
Best Practices for Deploying This Convention
- Define units once: Document in the library guide that all dimensions are in millimeters and R denotes the decimal point. Avoid mixing mils and millimeters in pad names.
- Standardize case: Use uppercase consistently for prefixes and the decimal marker R to prevent duplicate entries differing only by case.
- Use leading zeros: Maintain fixed precision (e.g., two decimal places) so lexical sorting reflects numeric ordering and names align neatly.
- Keep separators consistent: Always use X for length-by-width and - for pad-to-hole or outer-to-inner separation.
- Tightly couple pads and footprints: Where a pad is designed specifically for a footprint, encode both pad and footprint dependencies (e.g., PAD-SOT89-1) and avoid reusing the pad in incompatible contexts.
- Add library notes: In each pad entry’s description or documentation field, restate dimensions, units, and any special fabrication or assembly considerations.
- Review before release: Incorporate a lightweight review process to catch typographic errors (e.g., 1R6 instead of 1R60) and inconsistencies in the outer/inner order for flash pads.
Common Pitfalls and How to Avoid Them
- Confusing R as radius: In this convention, R is a decimal separator, not a radius indicator. 1R60 means 1.60 mm.
- Mixing units: If your organization sometimes uses mils, ensure conversion is done before naming. Do not embed mixed units in names.
- Omitting hole size: For through-hole pads, the hole size must appear after the dash to prevent drill selection errors.
- Outer/inner reversal in flash pads: Maintain a consistent outer-inner order. If historical entries deviate, add a note and align new entries to the standard.
- Inconsistent precision: Stick to one precision (e.g., two decimal places) to avoid ambiguous interpretations when comparing similar pads.
- Case inconsistency: Decide on uppercase conventions and apply them consistently across the library to improve searchability and prevent duplicates.
Conclusion
A compact, readable pad naming convention dramatically improves the speed and correctness of PCB library work. By encoding geometry directly in the name—across SMD, through-hole, thermal relief, and package-specific pads—engineers can select, audit, and automate with confidence. Establish these rules early, document them, and enforce them via review and library management processes. The result is a cleaner, safer, and more maintainable PCB design flow.
