In the electronics industry, Epoxy FR4 Yellow Sheets and Green FR4 Sheets are two terms often mentioned together. Many engineers and buyers wonder: Are they different materials, or just different colors?
The truth is that both yellow and green FR4 sheets share the same substrate material — FR4, a composite made of fiberglass cloth reinforced with epoxy resin. The core properties are identical; the difference lies only in the color of the solder mask coating applied during the final production stage.
Before comparing yellow and green FR4 boards, it is important to clarify what FR4 actually means:
FR: Short for Flame Retardant, indicating the material’s inherent fire resistance.
4: Refers to the material grade classification of this composite.
FR4 is manufactured by impregnating electronic-grade fiberglass cloth with epoxy resin, then curing it under heat and pressure to form a laminate. This gives FR4 a balanced set of properties:
High mechanical strength to withstand stress.
Excellent electrical insulation to ensure safety in circuits.
Reliable heat resistance and flame retardancy, suitable for demanding electronic environments.
The natural color of FR4 substrate is typically light yellow or light green. The final visible color comes from the solder mask layer applied afterward.
The distinction between Yellow FR4 and Green FR4 arises from the solder mask stage of PCB production:
Green FR4 Board
Uses a green solder mask ink applied over the copper circuitry.
Openings are developed to expose solder pads for assembly.
Yellow FR4 Board
Follows the same process, but with yellow solder mask ink.
The end result is a yellow board appearance, with no difference in performance compared to green FR4.
Although both yellow and green FR4 are technically identical, green dominates the global market (around 99%) due to several reasons:
1. Superior Visibility and Contrast
White silkscreen markings and silver solder pads stand out clearly on a green background.
This improves accuracy in manual inspections and automated optical inspection (AOI) systems.
2. Established Supply Chain
Green solder mask has been widely used for decades, benefiting from economies of scale.
This ensures lower costs, mature technology, and reliable availability.
3. Eye Comfort
From an ergonomic perspective, green is easier on the eyes during long inspection tasks.
This helps reduce eye fatigue for workers in electronics manufacturing lines.
Although not mainstream, yellow FR4 boards are still chosen in certain applications:
1. Educational and Laboratory Use
The copper traces are more visible on yellow boards, making them suitable for teaching PCB layout concepts.
2. Brand Differentiation
Some manufacturers use yellow or other custom colors to stand out in the market.
This is common in premium products such as development boards or graphic cards.
3. Customized Aesthetic or Functional Preferences
In niche applications, product designers may prefer yellow FR4 for visual identity or specific project requirements.
In essence:
Yellow FR4 Sheet = Standard FR4 Substrate + Yellow Solder Mask
Green FR4 Sheet = Standard FR4 Substrate + Green Solder Mask
Their electrical, mechanical, and thermal properties are identical. The decision comes down to cost, supply chain stability, and application needs:
Choose Green FR4 for standard electronic device manufacturing — cost-effective, widely available, and AOI-friendly.
Choose Yellow FR4 for education, branding, or special customer requirements.
Both options fully meet the requirements of electronic applications, and the choice depends mainly on appearance and usage scenario, not on performance differences.
The comparison between Epoxy FR4 Yellow Sheet and Green FR4 highlights that the substrate is the same, and only the solder mask color differs. While green remains the global industry standard, yellow FR4 has its place in niche markets.
At YILONG INSULATION, we provide both yellow and green FR4 sheets, ensuring consistent quality, excellent mechanical strength, and reliable electrical insulation. Whether for mass production or specialized projects, we offer solutions tailored to your needs.
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