FAQ: What Nanya PCB Materials Are Best for High-Voltage Applications?

In the power electronics world, specifying a “standard FR-4” isn’t just lazy engineering—it’s a safety hazard. When you’re designing motor drives, solar inverters, or EV charging stations, the dielectric strength and surface tracking resistance of your substrate are the only things standing between a functional product and a catastrophic arc-over.

Among the Tier 1 laminate suppliers, Nan Ya Plastics offers a specialized portfolio that bridges the gap between low-cost consumer boards and high-end specialty ceramics. If you are looking for the right Nanya PCB laminate high voltage application choice, you need to understand the relationship between CTI (Comparative Tracking Index) and the resin’s chemical purity.

The Core Metric: Comparative Tracking Index (CTI)

For high-voltage designs, the Glass Transition Temperature (Tg) is actually secondary to the CTI. CTI measures the voltage at which the material’s surface begins to break down into a conductive carbon path under standardized contamination.

In a high-voltage environment, dust and moisture on the board surface can create “leakage currents.” These currents carbonize the resin, eventually forming a permanent short circuit (tracking).

Nanya CTI Material Classification

Nanya Grade	Material Class	CTI Rating (Volts)	Material Group (IEC)	Best For
NP-140	Standard FR-4	175V – 250V	Group IIIa	Low-voltage consumer
NP-155F	Mid-Tg FR-4	250V – 400V	Group II	Standard Industrial
NP-175FM	High-Tg / High-CTI	600V+	Group I	EV, Power Grids, PV
NPG-170D	Halogen-Free	300V – 500V	Group II	Green Power Supplies

Note: For applications exceeding 600V, engineers often specify “Group I” materials like NP-175FM to allow for tighter creepage distances per IPC-2221B.

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Why NP-175FM is the “Gold Standard” for High Voltage

From an engineering perspective, NP-175FM (the ‘M’ often denotes Modified or High-CTI) is the standout performer in Nanya’s catalog. Most standard FR-4 materials struggle to pass 250V in tracking tests. NP-175FM uses a highly refined, dicy-free epoxy resin filled with inorganic fillers that are naturally resistant to carbonization.

Dielectric Breakdown vs. Dielectric Strength

While CTI handles surface tracking, Dielectric Breakdown handles the “bulk” insulation through the board layers.

Dielectric Strength: Nanya high-voltage grades typically offer >40 kV/mm.

Z-Axis Reliability: Because NP-175FM is a “filled” material, it has a lower Coefficient of Thermal Expansion (CTE), meaning it expands less during heat spikes, preserving the integrity of the resin-to-glass bond which is where internal arcing often starts.

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Design Guidelines for Nanya High-Voltage Boards

Selecting the material is only half the battle. You must design the board to play to the material’s strengths.

1. Prepreg Selection: The 1080 Rule

In high-voltage multilayer boards, air bubbles (voids) are your enemy. Air has a much lower breakdown voltage than resin. I always recommend using prepregs with higher resin content (like type 1080 or 2116) rather than heavy glass styles (like 7628) for high-voltage layers. This ensures the Nanya PCB laminates fully “wet out” and eliminate potential partial discharge sites.

2. Creepage and Clearance (IPC-2221B)

Using a Group I material like NP-175FM (CTI 600) allows you to reduce your creepage distance compared to a Group III material.

Example: At a working voltage of 500V, a Group III material might require 5.0mm of creepage. A Group I Nanya material might allow you to drop that to 2.5mm, significantly shrinking your footprint.

3. Copper Weight and Edge Treatment

High-voltage boards often carry high current. Specifying 2oz or 3oz copper on Nanya NP-175F is common. However, remember that thicker copper creates “cliffs” that are harder for the solder mask to cover. Ensure your fabricator uses a high-build solder mask to prevent exposed copper edges where arcing can initiate.

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Manufacturing and Fabrication Tips

If you are specifying Nanya for a high-voltage build, keep these fabrication “gotchas” in mind:

Hole Wall Quality: Rough drilling can create micro-cracks in the Nanya resin. These cracks can trap moisture or plating chemicals, leading to CAF (Conductive Anodic Filament) growth. Always specify a “desmear” process to ensure hole walls are smooth and clean.

Surface Finish: For high-voltage boards, ENIG (Electroless Nickel Immersion Gold) is often preferred over HASL. ENIG provides a much flatter surface, reducing the “pointy” peaks of solder that can act as lightning rods for electrical discharge.

Cleanliness: Ionic contamination is the #1 killer of CTI. Even the best Nanya material will fail if there are flux residues or salt on the surface. Specify an ionic contamination test (ROSE test) to ensure the board is clean before shipping.

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Useful Resources for Power Engineers

Nanya High-CTI Datasheet Portal: Technical Specs for NP-Series

IPC-2221B Calculator: Creepage and Clearance Logic

UL Product iQ: Search File E98983 — Check for “Comparative Tracking Index” ratings specifically.

Material Cross-Reference: Compare Nanya vs. Isola/Rogers

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FAQs: Nanya PCB Laminate High Voltage Application

1. Can I use standard NP-140 for a 400V power supply?

Technically, you can if you have enough space for massive creepage distances. However, it’s risky. NP-140 has a low CTI, meaning any dust or moisture will quickly cause tracking. Moving to NP-175FM (CTI 600) is a much safer “insurance policy” for industrial designs.

2. Does “Halogen-Free” (NPG series) mean better high-voltage performance?

Not necessarily. While NPG materials are great for the environment, their resin systems can sometimes be more brittle. For pure high-voltage reliability, the “filled” dicy-free NP series (like NP-175F) is often more robust mechanically.

3. What is the maximum voltage a Nanya board can handle?

With proper design (slots, potting, and correct material selection), Nanya FR-4 laminates are regularly used in applications up to 5kV – 10kV. Beyond that, you may need to look at specialized ceramic or teflon-based substrates.

4. Why are “slots” used in high-voltage Nanya boards?

A slot (an air gap) effectively resets the creepage distance to “Clearance” (distance through air). Since air doesn’t “track” like a resin surface does, cutting a slot between high-voltage nodes is the most effective way to prevent surface failure on any laminate.

5. How do I verify the CTI of the Nanya material my shop used?

Ask for the UL Yellow Card for the specific material used. It will list the CTI Performance Level Category (PLC). PLC 0 is the best (600V+), and PLC 4 is the worst (100V-175V).

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Final Thoughts for the Power Designer

When you’re dealing with high voltage, the substrate is an active participant in your circuit’s safety. By selecting NP-175FM or other high-CTI Nanya grades, you are providing a foundation that resists the inevitable environmental degradation that leads to field failures.

Would you like me to help you calculate the creepage requirements for your specific voltage and Nanya material group?