[{"data":1,"prerenderedAt":376},["ShallowReactive",2],{"blog-what-is-dielectric-constant-fr":3,"header-nav-fr":47},{"title":4,"description":5,"date":6,"lastUpdated":6,"category":7,"image":8,"readingTime":9,"wordCount":10,"timeRequired":11,"htmlContent":12,"tags":13,"slug":21,"jsonld":22},"Qu'est-ce que la constante diélectrique (Dk) ? Formule, unités et PCB","Constante diélectrique (permittivité relative) expliquée : formule, unités, valeurs pour l'air, le FR-4 et les laminés RF, et impact sur l'impédance.","2026-10-09T00:00:00.000Z","Technologie","/assets/img/pcb/high-frequency/pcb-high-frequency-pcb-hero.webp",4,686,"PT4M","\u003Cp>En électronique rapide et radiofréquence (RF), le substrat isolant soutenant les pistes de cuivre n'est jamais un simple support mécanique neutre. Il agit comme un milieu électromagnétique actif. Le paramètre physique prépondérant régissant la vitesse et l'intégrité des signaux est la \u003Cstrong>constante diélectrique\u003C/strong>, couramment abrégée en \u003Cstrong>Dk\u003C/strong> ou notée $\\varepsilon_r$ (permittivité relative).\u003C/p>\n\u003Cp>Que vous adaptiez une ligne 50 Ω pour un émetteur-récepteur 5G ou calculiez le déphasage sur des paires différentielles, la maîtrise de la constante diélectrique est indispensable pour réussir vos conceptions.\u003C/p>\n\u003Cp>Ce guide technique détaille la définition, la formule, les unités et le comportement en fréquence de Dk, tout en précisant quand migrer du standard FR-4 vers des laminés RF haute performance.\u003C/p>\n\u003Ch2 id=\"points-cles\" data-anchor-en=\"key-takeaways\">Points clés\u003C/h2>\n\u003Cul>\n\u003Cli>\u003Cstrong>Définition :\u003C/strong> La constante diélectrique quantifie la capacité d'un isolant à stocker de l'énergie électrostatique sous l'effet d'un champ électrique par rapport au vide.\u003C/li>\n\u003Cli>\u003Cstrong>Unités et symbole :\u003C/strong> Rapport scalaire de permittivités ($\\varepsilon / \\varepsilon_0$), la constante diélectrique est \u003Cstrong>sans dimension\u003C/strong> et sans unité physique. Symbole : $\\varepsilon_r$ ou Dk.\u003C/li>\n\u003Cli>\u003Cstrong>Vitesse de propagation :\u003C/strong> La vitesse du signal est inversement proportionnelle à la racine de la constante diélectrique effective : $v_p = c / \\sqrt{\\varepsilon_{\\text{eff}}}$. Un Dk élevé ralentit le signal.\u003C/li>\n\u003Cli>\u003Cstrong>Contrôle d'impédance :\u003C/strong> À épaisseur diélectrique égale, un Dk plus élevé requiert des pistes plus étroites pour atteindre 50 Ω.\u003C/li>\n\u003Cli>\u003Cstrong>Stabilité en fréquence :\u003C/strong> Le Dk diminue avec l'augmentation de la fréquence (dispersion). Les laminés RF haut de gamme conservent une courbe plate dans les GHz, contrairement au FR-4 classique.\u003C/li>\n\u003C/ul>\n\u003Cdiv data-component=\"BlogQuickQuoteInline\">\u003C/div>\n\n\u003Ch2 id=\"qu39est-ce-que-la-constante-dielectrique-definition-et-symbole\" data-anchor-en=\"what-is-dielectric-constant-definition-and-symbol\">Qu'est-ce que la constante diélectrique ? Définition et symbole\u003C/h2>\n\u003Cp>Lorsqu'un champ électrique alternatif traverse un diélectrique isolant, les molécules se polarisent et stockent de l'énergie électrostatique. La \u003Cstrong>constante diélectrique\u003C/strong> exprime cette aptitude par rapport au vide. Les normes IPC et les fabricants utilisent quasi exclusivement la désignation \u003Cstrong>Dk\u003C/strong>.\u003C/p>\n\u003Cp>Le vide possède un Dk exact de 1,0. L'air sec affiche environ 1,0006. Les substrats pour circuits imprimés s'échelonnent entre 2,1 (PTFE pur) et 9,8 (céramique d'alumine $\\text{Al}_2\\text{O}_3$), tandis que le FR-4 standard se situe entre 4,0 et 4,6.\u003C/p>\n\u003Ch2 id=\"formule-unites-et-permittivite\" data-anchor-en=\"formula-units-and-permittivity-explained\">Formule, unités et permittivité\u003C/h2>\n\u003Cp>$$\\varepsilon_r = \\frac{\\varepsilon}{\\varepsilon_0}$$\u003C/p>\n\u003Cp>Où $\\varepsilon_r$ est relatif et sans dimension, $\\varepsilon$ est la permittivité absolue en Farads par mètre (F/m), et $\\varepsilon_0 \\approx 8{,}854 \\times 10^{-12} \\text{ F/m}$. Les unités s'annulant au numérateur et au dénominateur, \u003Cstrong>Dk est sans unité\u003C/strong>.\u003C/p>\n\u003Ch2 id=\"tableau-comparatif-des-materiaux-pcb\" data-anchor-en=\"dielectric-constant-units\">Tableau comparatif des matériaux PCB\u003C/h2>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth>Matériau\u003C/th>\n\u003Cth>Référence / Norme\u003C/th>\n\u003Cth align=\"right\">Dk (1 GHz)\u003C/th>\n\u003Cth align=\"right\">Dk (10 GHz)\u003C/th>\n\u003Cth align=\"right\">Tangente de perte (Df @ 10 GHz)\u003C/th>\n\u003Cth>Application principale\u003C/th>\n\u003C/tr>\n\u003C/thead>\n\u003Ctbody>\u003Ctr>\n\u003Ctd>\u003Cstrong>Vide\u003C/strong>\u003C/td>\n\u003Ctd>Référence idéale\u003C/td>\n\u003Ctd align=\"right\">1,0000\u003C/td>\n\u003Ctd align=\"right\">1,0000\u003C/td>\n\u003Ctd align=\"right\">0,0000\u003C/td>\n\u003Ctd>Référence physique\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Air\u003C/strong>\u003C/td>\n\u003Ctd>Air sec ambiant\u003C/td>\n\u003Ctd align=\"right\">1,0006\u003C/td>\n\u003Ctd align=\"right\">1,0006\u003C/td>\n\u003Ctd align=\"right\">~0,0000\u003C/td>\n\u003Ctd>Lignes coaxiales à air\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>PTFE pur\u003C/strong>\u003C/td>\n\u003Ctd>Fluoropolymère\u003C/td>\n\u003Ctd align=\"right\">2,10\u003C/td>\n\u003Ctd align=\"right\">2,10\u003C/td>\n\u003Ctd align=\"right\">0,0004\u003C/td>\n\u003Ctd>Radar hyperfréquence\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>PTFE tissé\u003C/strong>\u003C/td>\n\u003Ctd>Rogers RT/duroid 5880\u003C/td>\n\u003Ctd align=\"right\">2,20\u003C/td>\n\u003Ctd align=\"right\">2,20\u003C/td>\n\u003Ctd align=\"right\">0,0009\u003C/td>\n\u003Ctd>Télécoms spatiales\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Hydrocarbure céramique\u003C/strong>\u003C/td>\n\u003Ctd>Rogers RO4350B\u003C/td>\n\u003Ctd align=\"right\">3,66\u003C/td>\n\u003Ctd align=\"right\">3,48\u003C/td>\n\u003Ctd align=\"right\">0,0037\u003C/td>\n\u003Ctd>Stations de base 5G, radar 24 GHz\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Époxy haute vitesse\u003C/strong>\u003C/td>\n\u003Ctd>Panasonic Megtron 6\u003C/td>\n\u003Ctd align=\"right\">3,71\u003C/td>\n\u003Ctd align=\"right\">3,65\u003C/td>\n\u003Ctd align=\"right\">0,0040\u003C/td>\n\u003Ctd>Fond de panier 112G, PCIe 5.0\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>FR-4 standard\u003C/strong>\u003C/td>\n\u003Ctd>Kingboard KB-6160\u003C/td>\n\u003Ctd align=\"right\">4,40\u003C/td>\n\u003Ctd align=\"right\">4,15\u003C/td>\n\u003Ctd align=\"right\">0,0200\u003C/td>\n\u003Ctd>Électronique grand public, industrie\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Céramique Al2O3\u003C/strong>\u003C/td>\n\u003Ctd>Alumine pure\u003C/td>\n\u003Ctd align=\"right\">9,80\u003C/td>\n\u003Ctd align=\"right\">9,60\u003C/td>\n\u003Ctd align=\"right\">0,0008\u003C/td>\n\u003Ctd>Modules de puissance, hybrides\u003C/td>\n\u003C/tr>\n\u003C/tbody>\u003C/table>\n\u003Ch2 id=\"quand-quitter-le-fr-4-pour-des-lamines-haute-frequence\" data-anchor-en=\"capacitor-formula-representation\">Quand quitter le FR-4 pour des laminés haute fréquence ?\u003C/h2>\n\u003Cp>Le FR-4 standard atteint ses limites physiques au-delà de 3 GHz ou 10 Gbps. Les pertes diélectriques (Df) et les variations de Dk imposent de migrer vers des technologies de \u003Ca href=\"/fr/pcb/high-frequency-pcb\">PCB haute fréquence\u003C/a> pour sécuriser le diagramme de l'œil et l'atténuation.\u003C/p>\n\u003Chr>\n\u003Ch2 id=\"faq\">Foire aux questions (FAQ)\u003C/h2>\n\n\u003Cp>\u003Cstrong>Q: La constante diélectrique a-t-elle des unités ?\u003C/strong>\nA: Non, il s'agit d'un rapport de permittivités sans dimension physique.\u003C/p>\n\u003Cp>\u003Cstrong>Q: Pourquoi le Dk du FR-4 varie-t-il selon l'empilage ?\u003C/strong>\nA: Le FR-4 associe fibres de verre ($Dk \\approx 6{,}0$) et résine époxy ($Dk \\approx 3{,}2$). La proportion volumique de résine dans les préimprégnés (1080 vs 7628) modifie la valeur globale finale.\u003C/p>\n\n\u003Csection class=\"related-links\" aria-label=\"Related\">\u003Ch3>Related links\u003C/h3>\u003Cul>\u003Cli>\u003Ca href=\"/fr/pcb/high-frequency-pcb\">PCB haute fréquence\u003C/a>\u003C/li>\u003C/ul>\u003C/section>",[14,15,16,17,18,19,20],"Constante diélectrique","Matériaux PCB","Permittivité relative","PCB haute fréquence","Contrôle d'impédance","FR4 Dk","Intégrité du signal","what-is-dielectric-constant",{"blog":23,"breadcrumb":32,"faq":46},{"@context":24,"@type":25,"headline":4,"description":5,"image":8,"url":26,"datePublished":6,"dateModified":6,"timeRequired":11,"keywords":27,"articleSection":7,"author":28,"publisher":31},"https://schema.org","BlogPosting","https://aptpcb.com/fr/blog/what-is-dielectric-constant","Constante diélectrique, Matériaux PCB, Permittivité relative, PCB haute fréquence, Contrôle d'impédance, FR4 Dk, Intégrité du 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