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MIL‑I‑24768 stands as the backbone for military thermoset laminates used in applications requiring rigorous insulation, durability, and reliability. This specification ensures that every laminate—whether for electronic circuit boards or for high-temperature structural components—meets both stringent performance and safety standards. By dictating criteria for material composition, precise dimensions, electrical and mechanical performance, and environmental endurance, MIL‑I‑24768 helps streamline quality and interoperability throughout military and aerospace supply chains.
MIL‑I‑24768 categorizes laminates according to the underlying fiber used and the resin system that bonds the layers. This classification is key to matching materials with application-specific demands:
Cotton-Fabric-Based Laminates
Predominantly employ phenolic-resin binders.
Variants are designated FBE, FBG, FBI, and FBM, reflecting differences in electrical performance, mechanical robustness, and machining qualities.
Glass-Fabric-Based Laminates
Epoxy-Resin Grades: Such as GEE and GEB, with flame-resistant versions like GEE‑F and GEB‑F.
Melamine-Resin Grades: Including GME for high-performance insulation and GMG for general purpose use.
Silicone-Resin Grades: Identified as GSG to offer improved thermal endurance.
Polytetrafluoroethylene (Teflon) Grades: Such as GTE provide unique dielectric properties.
Divided by resin type:
Other Laminates
Nylon and Paper-Based Systems: NPG and various paper-based grades (PBE, PBG, PBM, and derivatives) deliver a spectrum of insulation properties with a balance of strength and cost efficiency.
The MIL‑I‑24768 specification encompasses three primary laminate forms:
Commonly used as circuit boards, spacers, and voltage barriers.
Must exhibit a consistent semigloss finish and uniform thickness.
Formed either by rolling impregnated sheets around a mandrel or by molding processes.
Dimensional tolerances for the inside and outside diameters, as well as wall thickness, are rigorously controlled.
Rods:
Manufactured by molding layered laminates into cylindrical shapes and finely grinding them to size.
Typically applied in applications requiring precise dimensions and reliable insulating performance.
MIL‑I‑24768 demands outstanding performance across several key areas:
Electrical Properties:
Dielectric Breakdown & Strength: Ensures that laminates can withstand high voltages without failure.
Dielectric Constant and Dissipation Factor: Maintains insulation efficiency and low energy loss.
Resistivity Measures: High volume and surface resistivity are critical to minimize leakage currents.
Mechanical Properties:
Impact and Flexural Strength: Guarantees the laminate’s resilience against mechanical shocks and bending stresses.
Compressive Strength: Affirms that the material can support loads without deformation.
Bonding Strength: Ensures robust adhesion between layers for long-term durability.
In addition to electrical and mechanical performance, the standard also addresses:
Water Absorption: Minimizing moisture uptake to prevent degradation.
Thermal Endurance: The laminate must retain key properties under elevated temperatures.
Flammability: Strict testing for burning rate and flame resistance is mandated.
Fungal Resistance: Ensures that the insulation remains reliable even in humid, variable environments.
MIL‑I‑24768 is segmented into various sub-specifications, each addressing different material types based on resin and fiber configurations:
MIL‑I‑24768/1 (GME): Glass Melamine Laminate
MIL‑I‑24768/2 (GEE): G-10 Glass Epoxy Laminate (non‑brominated)
MIL‑I‑24768/3 (GEB): G-11 Glass Epoxy Laminate
MIL‑I‑24768/4 (GPO‑1): Glass Polyester Laminate
MIL‑I‑24768/5 (GPO‑2): Glass Polyester Laminate
MIL‑I‑24768/6 (GPO‑3): Glass Polyester Laminate
MIL‑I‑24768/7 (GTE): Glass Teflon Laminate
MIL‑I‑24768/8 (GMG): G-5 Glass Melamine Laminate
MIL‑I‑24768/9 (NPG): Nylon Fabric Phenolic Laminate
MIL‑I‑24768/10 (PBE): Paper Base XXX Phenolic Laminate
MIL‑I‑24768/11 (PBG): Paper Base XX Phenolic Laminate
MIL‑I‑24768/12 (PBM): Paper Base X Phenolic Laminate
MIL‑I‑24768/13 (FBE): Cotton LE Phenolic Laminate
MIL‑I‑24768/14 (FBG): Cotton CE Phenolic Laminate
MIL‑I‑24768/15 (FBI): Cotton L Phenolic Laminate
MIL‑I‑24768/16 (FBM): Cotton C Phenolic Laminate
MIL‑I‑24768/17 (GSG): G-7 Glass Silicone Laminate
MIL‑I‑24768/18 (GPG): G-3 Glass Phenolic Laminate
MIL‑I‑24768/19 (PBM‑P): Paper Phenolic Laminate
MIL‑I‑24768/20 (PBM‑PC): Paper Phenolic Laminate
MIL‑I‑24768/21 (PBG‑P): Paper Phenolic Laminate
MIL‑I‑24768/22 (PBE‑P): Paper Phenolic Laminate
MIL‑I‑24768/23 (PBE‑PC): Paper Phenolic Laminate
MIL‑I‑24768/24 (PBM‑PF): Paper Phenolic Laminate
MIL‑I‑24768/25 (PBE‑PCF): Paper Phenolic Laminate
MIL‑I‑24768/26 (PEE): Paper Epoxy Laminate
MIL‑I‑24768/27 (GEE‑F): G-10/FR‑4 Glass Epoxy Laminate
MIL‑I‑24768/28 (GEB‑F): Glass Epoxy Laminate
Each grade is tailored to deliver distinct performance attributes essential for the diverse operational conditions encountered in military applications.
MIL‑I‑24768 is underpinned by strict quality assurance procedures to ensure every batch of laminates meets defined standards:
First Article Inspection: Prior to full production, sample materials are exhaustively tested to verify adherence to all specifications.
Lot Sampling: Continuous quality inspections are performed on production lots, with defined sampling plans and rejection criteria ensuring no defective products are released.
Detailed Documentation: Manufacturers are required to maintain thorough records of tests, inspections, and traceability data for compliance verification.
Proper marking and packaging play critical roles in maintaining quality and ensuring safe transportation:
Identification Labels: Each laminate sheet, tube, or rod must include clear, permanent markings with the manufacturer’s identity and material grade.
Packaging Requirements: Products are packaged using military-approved methods to prevent damage and to protect against environmental conditions during storage and transit.
MIL‑I‑24768 remains a pivotal specification in the world of military thermoset laminates, driving innovation, quality, and reliability in materials critical to defense and aerospace applications. As technology evolves and operational requirements become increasingly sophisticated, manufacturers continue to innovate within the framework provided by MIL‑I‑24768. This ensures that high-performance laminates not only meet current rigorous standards but are also poised to address future challenges in harsh environments.
By understanding the detailed requirements, classification systems, and rigorous testing protocols of MIL‑I‑24768, industry professionals can confidently select and produce advanced laminates that safeguard the performance and safety of military systems. At Fenhar, we empower our clients with a diverse portfolio of cutting-edge laminated insulation solutions—from advanced FR‑4, G‑10, G‑11, and G‑7 series to specialized products like GPO‑3, copper‐clad laminates, and precision CNC or molded parts—ensuring robust, adaptable performance tailored for today’s demanding electrical, mechanical, and industrial applications.
