Drill Hole 1
Before determining via sizes, it’s essential to understand how holes are created in PCB production. The process starts with panel cutting, where large copper-clad laminates are cut into specific sizes using automated equipment. Next, CNC drilling machines create precise holes at predetermined positions. Since drill bits are round, square holes are not feasible with standard mechanical drilling.
Drill bit 1
In PCB manufacturing, vias smaller than 0.3mm are classified as “small vias.” While miniaturization demands smaller vias in dense designs, they introduce significant manufacturing challenges centered around the aspect ratio (the ratio of board thickness to via diameter). A higher aspect ratio increases processing difficulty, leading to three key issues:
Plating Challenges: Smaller hole diameters make it difficult to achieve uniform copper deposition during electroplating. This often results in incomplete copper coverage (voids) or even non-conductive holes, directly reducing via reliability. Simply put, smaller vias mean lower plated-through-hole (PTH) yield rates.
Reduced Production Efficiency: Small drill bits have shorter effective working lengths, limiting the number of PCB panels that can be drilled in a single batch. To prevent bit breakage, machines must operate at slower feed rates and higher rotational speeds—extending processing time and increasing tool wear.
Outer Diameter Constraints: For both through-holes and component mounting holes, matching inner and outer diameter specifications is critical. Mismatched sizes can disrupt soldering processes or compromise mechanical stability.
Recommendation: Whenever possible, design vias larger than 0.3mm to ensure manufacturing efficiency and reduce costs. Reserve small vias (≤0.3mm) only for space-constrained high-density designs.
At FUMAX, our advanced manufacturing capabilities—including high-layer count technology and in-pad via (IPV) processes—support designs with up to 60 layers, minimum via diameters of 0.2mm, and minimum line/space of 0.1mm. Our IPV process for 6+ layer PCBs uses resin filling and plating capping, allowing vias to be placed directly on pads. This delivers flatter pad surfaces and maximizes routing space, solving common small-via challenges for high-density boards.
The annular ring (the copper pad surrounding a via) is another critical design element often overlooked. If the annular ring is too small, drilling equipment tolerances and alignment errors can cause “hole misalignment”—where the drilled hole shifts from the pad’s center on the film.
This misalignment reduces the pad’s effective conductive area, increases manufacturing defects, and may even lead to complete electrical connection failure. To avoid this, always design annular rings with sufficient size to accommodate typical manufacturing tolerances (usually ±0.1mm), ensuring reliable electrical contact and mechanical strength.
Slot holes (oblong vias) are essential for specific component packages (e.g., connectors with rectangular pins) but present unique manufacturing challenges. Two critical rules apply:
Avoid “Short Slots”: Slots where length is less than twice the width are classified as “short slots”—the most difficult to drill. When drilling short slots, the drill bit is partially supported by the PCB material and partially suspended after the first hole, causing uneven force distribution. This often results in skewed or undersized slots. Best practice: Design slots with a length-to-width ratio of ≥2.5
Process Selection for Long Slots: For slots longer than 5mm, prioritize hot air solder leveling (HASL) or electroless nickel immersion gold (ENIG) processes. Ensure the annular ring width on both sides of the slot exceeds 0.3mm (minimum 0.2mm for tight spaces). Slots with annular rings <0.3mm are prone to “solder blowout” during HASL—where high-pressure solder causes the hole to rupture. This risk is even higher for slots with only one-sided copper rings.
For densely packed slots, the PCB substrate’s fiber structure may be damaged during drilling, increasing blowout risk. In such cases, ENIG is recommended for its gentler processing and superior surface protection.
A common design mistake is misclassifying vias (electrical connections) and component holes (mounting pads). Their distinct functions require different manufacturing treatments:
Consequences of confusion:
At FUMAX, we understand that precise via design is the foundation of reliable PCBs—especially for industrial and automation electronics where downtime is costly. Our engineering team works with you from the early design stage to:
Whether you’re designing high-density control boards or rugged industrial PCBs, our advanced manufacturing processes and design expertise ensure your vias perform reliably in the most demanding environments.
Don’t let via design mistakes delay your project or compromise quality. Partner with FUMAX for PCB solutions that combine technical excellence with manufacturing efficiency.
To discuss your project’s via design requirements or request a DFM review:
