G10/FR4 Glass Epoxy Sheet

FR-4 is G-10 with a flame retardant designed into the resin, and it is the most widely used printed-circuit substrate and the most commonly stocked grade in this family. It meets NEMA FR-4 - now ANSI/NEMA IM 60000-2021 - along with MIL-I-24768/27 Type GEE-F and ASTM D709 Type IV Grade FR-4. Published lengthwise flexural strength runs from 65,000 to 80,000 psi and tensile strength from 40,000 to 62,000 psi depending on the maker, against NEMA required minimums of 60,000 psi flexural lengthwise and 50,000 crosswise. Thinner stock reads lower - one maker publishes 55,000 psi lengthwise at.125 inch - so check the figure against your thickness rather than taking the headline number.

The temperature index is 130 to 140C. Volume resistivity is around 3 x 10^15 ohm-cm, the dielectric constant 4.4 to 5.0 and the dissipation factor 0.014 to 0.032 at 1 MHz, with breakdown voltage parallel to the laminations around 65 kV. Water absorption is 0.10% at.125 inch and 0.20% at.062. Dielectric strength perpendicular is published from 630 V/mil upward, and the spread between sources is mostly test thickness rather than material - never compare a V/mil figure across thicknesses.

On flammability, FR-4 is defined as the flame-retardant grade and the US makers we buy from publish UL 94 V-0 for it. Ratings on imported stock are not always documented to the same standard, so if the rating is a requirement rather than a preference, ask us for the certificate on the lot. One more thing worth knowing before you cut, grind or laser it: heating this grade above 300C decomposes the flame-retardant package and releases hydrogen bromide along with carbon monoxide. G-10 and G-11 contain no bromine and cannot do this.

It is the standard substrate for printed circuit boards, and beyond that goes into terminal boards and barrier strips, switchgear and motor control insulation, battery module and EV pack insulation, insulating washers, spacers and standoffs, transformer components, structural insulators and machined test fixtures. Natural stock is light green; black is pigmented through.

Machining and handling. The glass abrades tooling, so carbide is the floor and diamond-coated or PCD cutters are what hold tolerance in production; run high spindle speeds with secure workholding and design in generous internal radii, because small tools wear out fast against glass. Threaded holes are normally milled rather than tapped and external threads turned or thread-milled, since the plies can delaminate. The laminate has no hazards as shipped, but cutting it releases a fine dust, and the epoxy resin in that dust is classified as a skin and respiratory sensitiser - use local exhaust, a dust respirator, eye protection and gloves, and work to your own site's exposure limit, because published limits for glass dust differ by jurisdiction and by whether total or respirable dust is measured. It comes off as powder rather than chips, so vacuum it up rather than blowing it airborne. These are our shop notes, not a manufacturer specification.