Common mistakes in drilling design

1. Incorrect Hole Attributes (Via vs. Pad)

In the 3D drawing below, the designer intended for two specific pads to remain exposed (uncovered by solder mask). However, these holes were defined with "Via" attributes in the EDA software, and the order was placed with the "via tented/covered with solder mask" option. Consequently, the manufacturer will cover these pads with solder resist ink. To ensure pads remain exposed for soldering or testing, always define them using "Pad" (component) attributes rather than "Via" attributes to avoid manufacturing discrepancies.

2. Spacing for Castellated Holes (Half-Holes)

For standard castellated hole (half-hole) designs, both the hole diameter and the spacing between holes should be at least 0.5mm. In the example below, the spacing is only 0.45mm, which significantly increases the risk of short circuits during assembly. Always verify this clearance during your design phase to prevent unnecessary yield loss.

3. Vias Lacking Sufficient Pads (Annular Rings)

In PCB design, if a through-hole has a large inner diameter without a proportionately large outer pad, it increases the risk of missing copper in the hole wall during plating. For example, if a design features a via with a 0.6mm inner diameter but lacks a proper pad, it is recommended to reduce the drill size to 0.3mm (while keeping the outer diameter unchanged). This adjustment ensures reliable copper plating and high product quality.

4. Optimal Via Size and Annular Ring Ratio

When board space permits, standard via sizes between 0.3mm and 0.5mm (inner diameter) are optimal. To maintain a reliable annular ring, the outer pad diameter should ideally be at least 12 mils larger than the inner drill hole (e.g., a 12-mil hole should have a 24-mil pad). The size of the outer ring directly impacts production alignment and product reliability.

Manufacturing processes inherently have tolerances; if the outer ring is too small, standard drilling and alignment deviations can lead to "annular ring breakout" (often called a "broken pad" by manufacturers). A broken pad not only compromises the physical connection but also risks reducing the current-carrying capacity of the circuit.