PCB Via Current Capacity: Why I Almost Burned a Power Board

Introduction

PCB via current capacity refers to the maximum amount of electric current a via can safely carry without overheating or causing damage to your circuit board. When current flows through a via, it encounters resistance that generates heat—a phenomenon called Joule heating. Understanding how to calculate via size in PCB design is critical for beginners because undersized vias can overheat, melt solder joints, and destroy expensive boards. I learned this the hard way when a 6-mil via on my power supply board started heating up to dangerous levels, nearly causing a complete board failure because I hadn’t calculated the via current capacity properly.​

How PCB Via Current Capacity Works

Via current capacity depends on three main factors: via diameter, copper plating thickness, and the board’s thermal management. When you pass current through a via, the resistance of the copper creates heat, and if this heat cannot dissipate quickly enough, the via temperature rises. A typical 10-mil via with 1 oz copper plating can safely carry around 1 amp with a 10°C temperature rise, while a 20-mil via can handle over 2 amps.

The relationship between via size and current isn’t linear—doubling the via size doesn’t double the current capacity. Industry experts recommend that 10-12 mil vias are optimal for most conventional PCB designs because they balance current capacity with board space efficiency. The PCB via current capacity formula uses trace modeling calculations. The basic formula is: I = 0.048 × T^0.44 × A^0.75, where I is the maximum allowable current in amperes, T is the temperature rise in °C, and A is the cross-sectional area of the via wall in square mils.

Via Size vs Current: Reference Table

Via Size (mils)	Via Size (mm)	Maximum Current Capacity
6 mils	0.15 mm	0.2 A
8 mils	0.20 mm	0.5 A
10 mils	0.25 mm	0.8-1.0 A
12 mils	0.30 mm	1.0-1.2 A
16 mils	0.41 mm	1.5 A
20 mils	0.51 mm	2.0 A
24 mils	0.61 mm	2.5 A
30 mils	0.76 mm	3.0 A

Step-by-Step Guide: How to Calculate Via Size in PCB

Step 1: Determine Your Current Requirements
Identify the maximum current that will flow through the via in your circuit. Add a 20-30% safety margin for transient spikes and thermal variations.

Step 2: Measure Via Physical Dimensions
Note your via diameter (e.g., 0.3 mm or 12 mils) and copper plating thickness. Standard copper weights are 1 oz/ft² (35 μm thick) or 2 oz/ft² (70 μm). You can check different free software for PCB design that help calculate these parameters automatically.​

Step 3: Calculate Via Resistance
Use the formula R = ρ × L / A, where ρ is copper resistivity (1.68 × 10^-8 ohm-meters), L is via length (board thickness, typically 1.6 mm), and A is the cross-sectional area of copper plating. For a 0.3 mm via with 35 μm plating, resistance is approximately 0.5 milliohms.​

Step 4: Estimate Power Loss and Temperature Rise
Power loss is calculated as P = I² × R. For 1 amp through a via with 0.5 milliohms resistance, power loss equals 0.0005 watts. Most designs allow a maximum temperature rise of 10-20°C for safe operation.

Step 5: Use Altium via current capacity Calculator or IPC-2152 Standards
Use professional calculators based on IPC-2152 standards that account for internal vs external traces, board material, and ambient conditions. These tools provide accurate results faster than manual calculations. The IPC-2152 standard offers comprehensive guidance on determining current-carrying capacity in printed circuit boards based on extensive empirical testing.

Step 6: Apply Multiple Vias for High Current
If a single via cannot handle your current requirement, use multiple vias in parallel. For example, to supply 5 amps, use 5 large vias rated at 1 amp each with thick plating. Ensure proper spacing to avoid thermal coupling.​

Step 7: Verify with Thermal Simulation
Run DC simulation tools like Allegro’s IR Drop to verify via performance under actual operating conditions. This helps predict hot spots and optimize via placement. Consider solder temperature for PCB when evaluating thermal limits.​

Quick Answer: How Much Current Can Vias Handle?

A standard 12-mil via with 1 oz copper plating can handle approximately 1-1.2 amps safely with acceptable temperature rise. Smaller 6-mil vias are limited to 0.2 amps, while larger 20-mil vias can carry up to 2 amps. The exact capacity depends on copper thickness, board material, and thermal dissipation conditions.

Cost Impact and Failure Risks

Using undersized vias causes serious reliability problems. When a via overheats, it can melt the solder around it, creating intermittent connections that are nearly impossible to troubleshoot. I once had a client lose $3,000 worth of boards because 8-mil vias carrying 0.8 amps gradually degraded over weeks, causing random device resets.​

Oversizing vias also wastes money—larger drill sizes cost more in fabrication, reduce routing space, and can create impedance mismatches in high-speed designs. Finding the optimal via size saves both production costs and long-term reliability headaches. Proper via sizing extends board lifespan significantly. A correctly sized via maintains stable resistance over years, while an undersized via degrades progressively as heat stress accumulates. Understanding how much current PCB traces handle alongside via capacity prevents cascading failures where trace heating compounds via heating.

Common Mistakes and Pro Tips

Mistake 1: Ignoring Temperature Rise Limits
Many beginners calculate via resistance but forget to check if the resulting temperature rise is acceptable. Always verify that temperature rise stays below 20°C for reliable operation.​

Mistake 2: Not Accounting for Copper Weight
Using 1 oz copper calculations when your manufacturer uses 0.5 oz copper will give you wrong results. Always confirm copper specifications with your PCB fabricator.​

Mistake 3: Forgetting About Via Height
Board thickness directly affects via resistance—a 1.6mm board has twice the via length of a 0.8mm board, doubling resistance. Thicker boards need larger vias or multiple parallel vias.​

Pro Tip: Follow the 0.5A Conservative Rule
For quick estimates, design engineers often use 0.5A per standard via as a conservative guideline. This works for most low-to-medium current applications without detailed calculations.​

Pro Tip: Use Via-in-Pad for Power Components
Placing vias directly under component pads improves thermal management and current distribution in high-power designs. This technique is especially useful for voltage regulators and power MOSFETs where exposed copper on PCB aids heat dissipation.​

Pro Tip: Reference IPC-2152 Over IPC-2221
The newer IPC-2152 standard provides more accurate via current guidelines by accounting for board material, internal vs external placement, and various ambient conditions. IPC-2221 is over 50 years old and less conservative. The IPC-2152 standard replaced the older IPC-2221 standard and is based on extensive empirical testing that addresses thermal conductivity, vias, copper planes, power dissipation, and board thickness factors.

How Many Amps Can PCB Traces Handle?

PCB trace current capacity follows similar principles to via capacity. A 10-mil wide trace with 1 oz copper on an external layer can handle approximately 1 amp with a 10°C rise. Internal traces surrounded by FR4 dissipate heat differently than external traces exposed to air, requiring wider traces for the same current.​​

The trace width calculator formula is similar to via calculations: I = k × ΔT^0.44 × A^0.75, where k is a constant, ΔT is temperature rise, and A is cross-sectional area. When designing power paths, you must ensure both traces AND vias can handle the required current—the weakest link will fail first. For circuits requiring complex routing like single throw double pole switch PCB designs, matching trace and via current capacities prevents bottlenecks in power distribution paths.​

For detailed technical specifications and comprehensive guidance on PCB current-carrying capacity standards, the IPC-2152 documentation provides industry-validated methods based on extensive testing across various configurations. You can learn more about IPC standards and access technical resources at the official IPC website: https://www.ipc.org/.​

FAQs

Conclusion

Calculating PCB via current capacity correctly prevents expensive board failures and ensures long-term reliability. By understanding via size vs current relationships, using proper formulas, and following IPC-2152 standards, you can confidently design vias that handle your circuit’s power requirements. Remember that a 12-mil via handles about 1-1.2 amps safely, and when in doubt, use multiple vias in parallel or consult via current capacity calculators. Start with conservative estimates, verify with thermal simulation, and always add safety margins—your future self will thank you when boards work flawlessly in production.

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Author Bio:
Sumit Patil is an electronics repair specialist and PCB design enthusiast with hands-on experience in PCB manufacturing, troubleshooting, and real-world circuit failures. He shares practical, beginner-friendly electronics knowledge to help technicians avoid costly mistakes.