{
  "id": 5504076,
  "title": "FR-4 PCB Material: Properties, Grades, and Specification Guide for Engineers",
  "url": "https://urgent.news/2026/09/04/fr-4-pcb-material-properties-grades-and-specification-guide-for",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-09-04T05:59:57.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/abc_8b09c7009ee0029b85665/fr-4-pcb-material-properties-grades-and-specification-guide-for-engineers-4oc8"
  },
  "original_language": "en",
  "account": "FR-4 is a specific grade of PCB material defined by the National Electrical Manufacturers Association. It refers to a range of flame-retardant woven-glass-reinforced epoxy laminates with UL94 V-0 flammability rating. FR-4 does not specify resin chemistry, glass transition temperature, dielectric properties, or thermal decomposition threshold. Engineers commonly assume FR-4 as a standard material, typically meaning a 1.6mm thick laminate with a glass transition temperature of 130-140°C, dielectric constant around 4.4 at 1GHz, and low cost. However, this mental model may not apply to modern designs with lead-free solder, higher signal frequencies, and strict reliability requirements.\n\nFR-4 consists of three components: E-glass fiber cloth, epoxy resin system, and flame-retardant additive. The performance of FR-4 depends on these components, especially the epoxy resin system which contributes to variations in glass transition temperature, dielectric properties, and thermal stability. The flame-retardant additive varies between brominated chemistry in traditional FR-4 and phosphorus or nitrogen-based systems in halogen-free variants.\n\nTwo key properties influencing design decisions are glass transition temperature (Tg) and thermal decomposition temperature (Td). Tg signifies the temperature at which epoxy resin transitions from a rigid state to a softer rubbery state, affecting coefficient of thermal expansion in the Z-axis and causing barrel cracking in plated through-holes. Td is the temperature at which resin system begins to decompose irreversibly. Tg values range from 130-140°C for standard FR-4, 150-155°C for mid-Tg, and 170-180°C for high-Tg. The choice between these options depends on assembly process and operating environment.",
  "summary": "Reviewed by AtlasPCB Engineering Team What FR-4 Actually Is — And What It Is Not Every PCB designer has written \"FR-4\" on a fabrication drawing. Most assume they are specifying a material. They are not. FR-4 is a grade designation defined by the National Electrical Manufacturers Association under the NEMA LI-1 standard, and it describes a broad class of flame-retardant woven-glass-reinforced…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}