Quick answer: Isola I-Speed is a low-loss, glass-reinforced epoxy laminate and prepreg system for multilayer PCBs. Isola lists a 180°C glass-transition temperature, 360°C decomposition temperature, nominal Dk of 3.63 and Df of 0.0060. Those figures describe a material option, not a guaranteed data rate, trace length, board cost or manufacturing yield. Select it only after evaluating the complete channel and the construction your fabricator will build.
| Question | Useful evidence | Decision |
|---|---|---|
| Is the dielectric loss low enough? | Channel loss budget, frequency, trace length, copper roughness and via/connector losses | Model the proposed stackup, not Df alone |
| Is the construction available? | Core, prepreg, glass style, resin content and copper foil | Ask the fabricator for an approved stackup |
| Will it survive assembly? | Thermal profile, via structure and qualification plan | Review process evidence for the actual board |
What is I-Speed?
I-Speed is an Isola FR-4 resin system reinforced with E-glass for multilayer boards. It is supplied as both laminate and prepreg. Isola describes it as a low-loss material with spread-weave glass and lists the nominal electrical and thermal values above in its I-Speed product information. Read the current manufacturer data sheet and construction-specific Dk/Df tables before putting values into an impedance or insertion-loss model.
When does it make sense to consider I-Speed?
Consider it when the existing laminate leaves insufficient channel margin and the board builder can source and qualify the proposed I-Speed construction. Compare total insertion loss at the frequencies relevant to the signaling standard. Dielectric loss is only one term: copper profile, trace geometry, length, vias, connectors and equalization also matter. A protocol name such as PCIe Gen4 or 25G Ethernet is not, by itself, a material approval or a universal maximum trace length.
Before replacing a less expensive material, simulate the channel on both constructions and check whether the change actually closes the design margin. Before replacing a lower-loss laminate with I-Speed, repeat that comparison rather than assuming the nominal Df is sufficient. Price, lead time and yield are quote- and factory-dependent; the earlier percentages and customer examples on this page were removed because they had no verifiable project record.
Which Dk and Df values belong in the design model?
Isola’s 3.63 Dk and 0.0060 Df are useful starting specifications, but the exact dielectric properties vary with frequency and stackup construction. Confirm whether a quoted value applies to laminate or prepreg, and check glass style, resin content and test method. Ask the fabricator which material constructions and copper foils it stocks, then request the matching data for the field solver. Do not treat a catalog Dk as a universal value for every layer or use an unsupported “flat Dk” claim across all frequencies.
What should the fabricator verify?
Request a stackup drawing showing each core and prepreg, dielectric thickness, finished copper, target impedance, and the relevant material part numbers. For a hybrid build, have the fabricator approve the resin systems, bond cycle, dimensional behavior and drill/plating sequence. Isola supplies an I-Speed processing guide; it does not mean every factory can use an identical recipe or that no qualification is needed.
How does it compare with FR408HR?
Isola lists nominal Df of 0.0060 for I-Speed and 0.0092 for FR408HR. That suggests a lower dielectric-loss starting point for I-Speed, not a fixed percentage improvement in finished-board insertion loss. The comparison must use compatible test conditions, copper and board geometry. For the broader family choices, see the QueenEMS PCB materials guide.
What belongs in an I-Speed PCB RFQ?
Send the board drawing and controlled-impedance requirements; the proposed laminate/prepreg construction; copper foil and finished copper; channel frequency or protocol and loss budget; thermal/assembly requirements; and any approved alternate materials. Ask for a construction-specific stackup and a quote that states material availability. Send QueenEMS the stackup and design files for a manufacturability review. We can discuss options, but should not promise a material substitution or performance without checking the design.
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