What Is G10 Material? Meaning, FR-4, and Verification

G10 is a rigid thermoset composite laminate consisting of continuous woven fiberglass reinforcement and cured epoxy resin. The fiberglass serves as structural support, while the epoxy serves to wet, bind, and protect the woven fiberglass support material. G10 is therefore categorized as a composite material; it is not simply fiberglass, nor is it a standard melt-processable type of plastic, nor is it a single standard formulation with fixed attributes.

The grade name further specifies the category of laminate material; however, the grade designation does not completely cover the information that needs to be provided to assure successful material selection. Successful selection of the product requires identification of the specific named product and other technical data regarding that product (the method used to perform the testing and the condition of the sample tested), as well as identification of the specific sheet supplied and traceability of all the above information in order to ascertain the ability of the laminate to perform as required. For an overview of the different substrate families of the PCB, refer to the PCB Material Overview.

What Is G10 Material?

G10 is a rigid, high-pressure industrial laminate material based on woven-glass reinforcement and an epoxy matrix. Woven glass provides the primary structural support of the laminate. During the curing process, the epoxy develops into a network of interconnected molecules. This interconnected structure creates a solid thermoset matrix that transfers mechanical loads between fibers and enables the laminate to maintain its shape. The laminate does not soften and reshape once cured as is common for thermoplastic-based products. While the designation defines a class of materials, this does not provide a comprehensive datasheet or brand indication. Consequently, products identified as the same grade may vary significantly regarding thickness, color, resin formulations, glass styles, cure history, finish and performance characteristics. Glass epoxy and Garolite are examples of the types of words that sellers use to describe their products but are not adequate to provide consumers with a clear understanding of the particular grade being offered.

Norplex-Micarta defines NP500A as a woven glass cloth with a non-brominated epoxy system and specifies it as NEMA G-10. Thus, the details of chemistry for NP500A belong to NP500A and may not be generalized to all sheets designated as G10.

How G10 Is Manufactured

G10 is prepared by layering multiple sheets of woven glass cloth and impregnating them with an epoxy resin system. These layers are consolidated and cured using controlled heat and pressure. The exact resin formulation, the type of glass cloth, the cure cycle and press settings are each individual to manufacturers. Therefore, the generic description of G10 preparation should describe the process sequence without implying universal process values.

1. Preparation of the glass cloth. The reinforcement material must be chosen and prepared to allow for adequate wetting. If the glass cloth is contaminated, wrinkled or damaged, the resulting interface may have reduced bonding strength and local dimensional variation.
2. Impregnation of resin. The epoxy resin is applied in a controlled manner to saturate the glass cloth. This method will generally produce staged material that can be laid up later. If the amount of resin applied is too low, dry areas may be present. Conversely, excessive resin could affect thickness control and the fiber-to-resin ratio.
3. Lay-up. Stacked plies must be aligned to produce consistent thicknesses and surface quality and to ensure consistent directional properties in the final laminate.
4. Pressing and curing. The curing of a structural laminate takes place as a result of heat being applied to activate the epoxy polymerization reaction and pressure consolidating the stack of layered glass and reducing excess void space. An incomplete cure or poor consolidation can reduce mechanical, electrical, and moisture performance.
5. Cooling and finishing. Following the curing process, the laminate must be cooled in a controlled environment, trimmed, finished and cut into stock sizes. The presence of residual stresses, edge damage, or aggressive machining can affect flatness and local durability even if the base laminate is sound.

G10 possesses layers of woven glass cloth and therefore can have different properties in different directions. Machining exposes glass fibers as well as cured resin. Lastly, if a sheet looks similar to another, it is inaccurate to assume that both materials are identical based solely on appearance. There can be significant differences in the resin formulation, reinforcement characteristics, cure quality, and qualification status.

G-10 Is a Grade Designation, Not a Property Table

Like other industrial laminated thermosetting materials, NEMA defines a grade, which is G-10, in ANSI/NEMA LI 1 with a grade specification. The grade name supports the classification; a named product record provides decision-grade values and tolerance specifications for a specific product. The hyphen in a G-10 designation is for notation and not evidence of a different product material.

Because there is no evidence in the public standards information of a reliable hidden meaning for the G-10 number, there is no reliable defined meaning to be attached to the number 10 in terms of resin %, glass type, temperature rating, or performance ranking. These claim types would create a claim that the governing sources do not state. This designation does not establish one thickness, color, glass transition temperature, strength, moisture value, electrical rating, or flame class for all products.

A technical data bulletin provides a stronger link between results and product, test method, direction, and condition of the test. It may also report only typical values rather than guaranteed specification limits. Typical results outline the behaviors one may expect from the material when tested in a specific manner, whereas a purchasing limit or design minimum requires reference to an applicable specification or certificate as well as a controlled requirement.

G10 vs. FR-4: Related, but Not Interchangeable

G10 and FR-4 are related glass-cloth/epoxy laminate grades but are not interchangeable names.

A paired product example to illustrate the dividing line is: G10 non-flame-retardant product NP500A; whereas NP510A is an FR-4 product with a GEE-F declaration. This comparison illustrates those products only and does not prove that every modern FR-4 formulation uses identical chemistry.

UL states that plastics are classified according to how they burn based on controlled tests; the test method, the way the test specimen was positioned, its thickness, and the recorded test conditions are all important in determining the classification of a plastic. This does not mean that a particular type of plastic is nonflammable in every type of geometry or assembly.

The G10 connection is product specific. A named G10 product can declare an IPC-4101 slash sheet. However, an unidentified G10 product does not automatically meet the requirements for an IPC-4101 material specification sheet or meet the various criteria for the following types of applications: board stack-up, copper construction, fabrication processes, electrical modeling, and qualification plans. See What Is FR4 Material? for a more complete discussion of the identity and use of the FR-4 type of material.

G10 Properties: Read Test Results, Not Constants

The properties listed as typical values for a G10 material are based on a specific sample tested under a specific set of conditions. In general, properties listed as data points are based on the sample tested, the named G10 product such as NP500A, the sample direction, its conditioning state, and the temperature and method of testing. For the table below, these are NP500A typical values, not universal G10 constants or guaranteed purchasing limits; conversions are rounded from the source values.

Woven laminates do not have identical properties in all directions. Therefore, the technical data for woven G10 laminates may distinguish between LW direction results and CW direction results. Other variables related to the condition of G10 specimens must be considered when interpreting the meaning of a result in service.

The results of the directional strength test show that a simple claim such as “G10 has a tensile strength of 43,000 psi” is not sufficient. This is an example of a typical LW result of one product under one condition, whereas a product with holes, notches, thin walls, damaged edges, or loaded across the laminate may fail through a different mechanism.

A product’s stiffness and high tensile or flexural strength do not prevent chipping, delamination or sensitivity to impacts.

Electrical properties must be kept apart as well. Dielectric strength concerns breakdown under a particular geometry or configuration. Volume and surface resistivities represent different leakage paths. Dk indicates the relative permittivity and Df indicates the dielectric loss at a given frequency and construction. If impedance or high-frequency losses are important, use manufacturer-specific data and the separate guide to FR4 dielectric constant rather than assuming one value of G10 as the constant for all designs.

Thermal conductivity, Tg, temperature index, continuous-use temperature, and short exposure define different technical questions. Tg indicates a polymer transition as defined by a particular test method, but it does not indicate the maximum operating temperature for the polymer. The temperature index is defined by long-term aging tests and retained-property evaluations, described by UL in Thermal Aging Tests for Plastics. Continuous use depends on the load and environment of the application, as well as the thickness of the material and the amount of allowable property change.

Where G10 Is Used

When considering G10 for a particular application, it is essential to determine the specific grade of G10 to ensure it can sustain the expected load and environmental conditions, as well as any geometry, fabrication method, and safety requirements.

Electrical Insulation and Power Equipment

When used as an electrical insulator or in electrical equipment, G10 can serve as insulating barriers, terminal supports, switchgear components, transformer spacers, and structural standoffs while keeping conductive components separated and providing mechanical stability and support. It is essential to consider the dielectric strength at the relevant thickness, creepage and clearance geometry, surface and volume resistivity, moisture conditioning, contamination, operating temperature, and any applicable flame requirements when selecting G10 for insulation applications. A high dry-state value does not describe a humid enclosure, a contaminated surface, or a thin machined part. Also, it is critical to inspect the edges and drilled holes carefully, as damage can shorten an electrical path or concentrate mechanical stress.

PCB and Electronics

Since G10 is a glass-epoxy laminate, it is familiar in electronic applications. However, because G10 by itself does not specify complete PCB materials, when selecting a particular product, confirm whether it declares an IPC-4101 specification sheet. A named product may be suitable for fixtures, carriers, test adapters, insulating supports, or particular board constructions. PCB design must still define the copper and resin construction, cured thickness, process compatibility, dimensional behavior under the expected conditions, electrical performance at the desired frequencies, and qualification evidence. To achieve controlled impedance or to work with high frequencies, the Dk and Df of a laminate should match the actual laminate construction and test method. Therefore, relying on the catalog label, which is a generic way of identifying your laminate, is not a replacement for documenting your actual stack-up or your approved-materials list.

Fixtures, Spacers, and Structural Supports

The use of machined G10 as a jig, assembly fixture, alignment block, spacer, wear-resistant support, or robotic component is frequently preferred to metal where it eliminates the potential creation of an unwanted conductive path. G10’s stiffness, combined with good dimensional stability, allows for good retention of geometry. G10 comes in sheet form, which allows profiles and holes to be machined from sheets of G10. The design must also take into consideration the directional characteristics of the material and bearing stresses around fasteners, as well as notch sensitivity, edge distance, and long-term temperature exposure. When loading is concentrated at a corner or on a thin ligament, it is better to distribute the load through the use of washers, shoulders, or generous radii. If sliding wear is central, the named grade should be compared with purpose-made bearing materials.

Handles, Grips, and Outdoor Components

Because of its machinability, traction-generating texture, and availability in many colors, G10 is commonly used in the design of knife and tool handles, grips, and various rigid panels. The key properties of G10 are its stable laminate structure and the ability to produce a controlled surface finish. Care must be taken to avoid assumptions regarding the safety and durability of finishes. Poorly finished thin edges are prone to chipping; overly aggressive textures are uncomfortable to use; and countersunk fasteners over-tightened on the laminate can result in splitting through the local layers of the laminate. For outdoor use and exposure to moisture, temperature cycling, UV exposure, cleaning chemicals, and color stability, evidence of weatherability and durability specific to the product will also need to be provided. In addition to evidence of weatherability, the laminate material (G10) should be treated and finished according to the product hygiene and handling requirements.

Low-Temperature and Marine Service

Certain named glass-epoxy laminates may be used to provide insulation and structural support in cryogenic, marine, or moisture-prone conditions. However, the use of these laminates for those applications should not be assumed. When using a laminate intended for low-temperature service, mechanical and dimensional data at the operating temperature must be considered, as well as thermal contraction and joint performance characteristics. For a product such as NP500A, the published in-plane thermal expansion is approximately 12.1 ppm/°C along one axis and 9.6 ppm/°C along the other, and this directional difference is exactly what a metal fastener or a mating part needs to accommodate across wide-ranging temperature changes. Marine applications also impose additional exposure to salt, temperature cycling, and galvanic effects around fasteners made of other metals. If these conditions are critical to a product, you must obtain a product bulletin or report that covers the application-specific performance of the part or assembly regarding the exposure conditions described above. A general statement that G10 resists moisture cannot substitute for application-specific evidence.

Machining and Handling

When cutting, drilling, sanding, and grinding G10, there is the potential to create dust made up of glass and epoxy resin; in addition, the glass reinforcement can abrade machining tools. The current G10 and NP500A SDS, when combined with the specifics regarding your processes and assessments of your work environment for exposure to dust, should be utilized in your hazard assessment of working with these materials. Use effective dust-collection systems, avoid generating uncontrolled dry dust, and inspect parts for chipouts, local-layer separation, and edge chipping on parts made of G10. The cutting parameters, the type of tooling to be used, the resulting surface-finish quality, and production controls will vary based on the thickness of the part, the machine type, and the cutting conditions; therefore, creating one machining recipe to cover all applications would be incorrect.

When G10 Is Not the Right Material

Not every instance of stiffening and insulating will indicate that G10 is the optimal material. A flame requirement may point to a properly documented FR-4 product. For electrical services with a higher temperature requirement, you would want to get either a G11 or FR-5 grade and have the required thermal testing evidence instead of going purely off a reputation for the grade.

Electrical panels that are cost-sensitive may favour phenolic laminates and/or GPO-3 provided that all mechanical, moisture, flame, and fabricating properties match the use. When dealing with heat spreading, ductility, threaded strength, impact resistance, or thin-section load capacity, often a metal will be a better choice. Complex molded geometries may need to be made from a thermoplastic, as well as lower mass production cost or multiple snap-fit behaviours. High-stiffness-to-weight performance can be achieved with carbon-fiber composites; however, due to the electrical conductivity of carbon-fiber composites, they are not a valid substitute when electrical isolation is required.

How to Verify That a Sheet Is Really G10

The verification of a G10 sheet can start with visual identification and progress through to records tied to the exact product and lot you received; color, pattern, surface feel, and seller terminology are clues, not proof.

1. Collect visual evidence; photographs of labels and packaging, manufacturing colour, any dimensions, and the source of the product. Do not consider visual evidence as definitive proof.
2. Determine the manufacturer and exact grade of the sheet material. Listing G10, G-10, glass epoxy, Garolite, or G10/FR4 does not create sufficient identification.
3. Ensure you have the current technical data and governing specification for this product. Ensure that they are the same product/form/revision context/method/unit and conditioning.
4. Request evidence for the requirement. This would include certificates, test reports, UL recognitions, qualification records, or declarations appropriate for the requirement.
5. Trace the revealed records back to the lot that was supplied. This will prevent you from applying a correct document on one grade to another sheet material erroneously.

The same verification process applies for materials intended for substitution. Two sheets can only be candidates for interchange after fulfilling all the same requirements for mechanical, electrical, thermal, environmental, flame, fabrication, and traceability requirements. A common colour and description of the glass and epoxy in the two sheets cannot establish equivalency.

Conclusion

G10 is a grade of woven-glass/cured-epoxy thermoset laminate. It is not a brand name, bare-glass sheet, or universal property table. You must separate G10 and FR-4 evidence and verify the appropriate evidence for an unknown stock by exact product records and traceability to the lot.