Round vs. Square Via Pads in PCB: Design and Manufacturing

When reviewing flexible PCB Gerber files, sometimes we can find round and square pads used for vias on the same board. Both connect copper layers through plated holes, but their shapes create different copper shapes around the holes.

Why do designers use both shapes? Does the difference matter during manufacturing?

The choice often comes from design conventions or specific layout needs. However, pad shape also affects the minimum copper width around a drilled hole. This is worth checking, especially when working with small vias and tight drilling tolerances.

Round and Square Via Pad Shape

First, most PCB vias choose round pads. Because their shape matches the circular drilling process and provides a uniform annular ring when the hole is centered.

Second, Square pads are also used in PCB layout. Designers may use them to distinguish specific connections, follow existing design library settings, or meet specific customer requirements. Square pads do not have a unified electrical function. Their shape alone does not indicate different signal types or higher current capacity.

The main shape difference is the distribution of copper around the hole.

• Round pad maintains a consistent distance between the hole edge and pad boundary.

• Square pad has less copper width near the middle of each side and more toward its corners.

This difference becomes clearer when we compare the minimum annular ring rather than the total pad area.

Annular Ring and Drill Offset

The annular ring is the copper remaining between the drilled hole and the outer edge of the pad. Its minimum width is important because drilling deviations can reduce the available copper on one side.

Imagine a hole with a diameter of 0.3mm and a hole plate with a specification of 0.6mm. What is the difference between a square and a circular shape?

When the hole is in the center, both have a minimum annular ring width of 0.15 mm. The round pad has the same width in every direction, while the square pad has wider copper areas toward its corners.

If the drilling offset of 0.05 mm. When the hole moves horizontally, the minimum annular ring on the affected side decreases to 0.10 mm for both shapes.The result is different when the hole moves diagonally.

For a square pad with sides parallel to the coordinate axes, a diagonal offset of 0.05 mm in both directions reduces the minimum edge clearance by 0.05 mm.

For the round pad, the reduction is about 0.071 mm, because the diagonal displacement is greater than the offset along either individual axis.

Above example shows that pad shape affects how much copper remains under different offset directions. It doesn't mean square pads are always better. The actual result depends on pad dimensions, hole size, and the direction and magnitude of the drilling deviation.

For flexible circuit factories, the important value is the minimum remaining annular ring after accounting for the relevant process tolerances.

Manufacturing Considerations for Flexible PCB

If you are not sure which shape is good for your board, Flex Plus can evaluate via structures based on your Gerber files and manufacturing requirements. Pad shape is only one part of this evaluation. For flexible PCB, we pay attention to three main areas.

1. Drilling and copper registration

Small vias leave less room for drilling deviations. We check the relationship between finished hole and pad dimensions, and expected positioning tolerances to identify potential breakout risks.

2. Via placement in bending areas

A plated through-hole creates a locally constrained structure in a flexible circuit. Repeated bending can place stress on the hole wall and surrounding copper. We therefore pay attention to via locations, particularly in areas designed for repeated movement.

3. Copper and substrate structure

Copper and PI thickness, layer count, and stack-up all influence fabrication and mechanical reliability. We consider these details together rather than evaluating the pad shape in isolation.

A square pad does not automatically require a different drilling process from a round pad. Both can be manufactured using conventional PCB processes, provided their sizes and clearances meet the applicable manufacturing needs.

Conclusion

Round and square via pads serve the same basic electrical purpose, but their shapes affect the distribution of copper around drilled holes.

Round pads provide a uniform annular ring when centered. Square pads have wider copper areas toward the corners, which can change their response to drilling offsets.

Neither shape is universally better. We focus on the minimum annular ring, hole positioning, and surrounding copper clearance when evaluating flexible PCB designs. These details help decision whether the supplied design can be manufactured consistently and reliably.