IS680-AG PCB | Isola Low-Dk High-Speed Laminate

What Is Isola IS680-AG?

Isola IS680-AG is a glass-reinforced, thermoset hydrocarbon/ceramic laminate with a dielectric constant (Dk) of approximately 3.00 and a dissipation factor (Df) of 0.0025, both measured at 10 GHz. It targets high-speed digital backplanes, advanced driver-assistance systems (ADAS), base-station antenna feeds, and any design where tightly controlled impedance and low insertion loss matter up through Ka-band frequencies. Because it uses standard FR-4 processing—no special PTFE drill bits, plasma desmear, or sodium-etch surface preparation—IS680-AG keeps fabrication costs and lead times closer to conventional multilayer builds than pure PTFE alternatives.

The “AG” suffix denotes Isola’s anti-static glass reinforcement style, which improves dimensional stability during lamination compared to loose-weave or unreinforced options. This makes IS680-AG a practical choice when you need RF-grade loss performance without the mechanical unpredictability of pure unreinforced PTFE substrates.

Key Electrical and Thermal Properties

The table below summarizes the IS680-AG datasheet values that matter most for impedance modeling, loss budgets, and reliability analysis. All electrical values are at 10 GHz per Isola’s published IS680 product family data unless noted otherwise.

A Dk of 3.00 is roughly 25 % lower than standard FR-4 (around 4.0–4.2 at 10 GHz). That difference widens trace widths for a given impedance target, easing fabrication tolerances and improving etch yield on fine-pitch designs. The low Df of 0.0025 places IS680-AG in the “very low loss” tier—comparable to Rogers RO4350B (Df 0.0037 at 10 GHz) or better—making it suitable for insertion-loss-sensitive links up to roughly 30 GHz.

How Dk Drifts with Frequency and Temperature

No laminate has a perfectly flat Dk across all frequencies and temperatures. IS680-AG’s hydrocarbon/ceramic resin system is more stable than standard FR-4 or polyimide, but you still need to account for drift in your impedance model. Typical Dk variation from 1 GHz to 20 GHz is on the order of −0.02 to −0.04 (Dk decreases slightly with frequency in well-cured thermosets). Temperature-induced Dk shift is roughly +0.001 per 10 °C rise below Tg.

Use the estimator below to see how these shifts affect your specific frequency and operating-temperature window. Enter your nominal Dk, target frequency, and expected temperature range to get an adjusted Dk value for your impedance calculation.

For example, starting from Dk 3.00 at 10 GHz and 25 °C, operating at 77 GHz and 85 °C might push the effective Dk down by dispersion but up by temperature, often partially canceling. In practice, many designers use a “design Dk” of 2.98–3.02 for IS680-AG in the 10–30 GHz range and validate with a test coupon. If your application is above 40 GHz, consider whether a tighter-tolerance laminate such as Rogers RO3003G2 with Dk 3.00 ± 0.02 is justified by the link budget.

IS680-AG vs. Competing Laminates

Choosing a low-Dk laminate is always a trade-off among loss, cost, processability, and availability. The comparison below puts IS680-AG alongside materials engineers most often evaluate against it.

Choose IS680-AG when you need the lowest Dk in a thermoset, FR-4-processable package—for instance, wide-trace 50-ohm microstrip on thin cores, or antenna feed networks where Dk uniformity across a large panel directly affects beam pointing. Choose RO4350B when the higher Dk is acceptable and you value its extensive industry track record and broad supply chain benchmarking. Choose Megtron 6 or Shengyi S7136 when the application is primarily high-speed digital (56 Gbps PAM4 or 112G SerDes) and the slightly higher Dk is not a constraint.

Need help narrowing down from Isola’s full product line? The selector below filters by Dk, Df, Tg, and application category so you can compare IS680-AG against IS680-300, Astra MT77, I-Tera MT40, and others in one place.

If the selector suggests I-Tera MT40 for a purely digital 28-Gbps backplane, that is usually the right call—its Dk of 3.45 is higher but its cost per panel is lower, and the Df of 0.0031 is still excellent for NRZ signaling. IS680-AG’s sweet spot is where the lower Dk genuinely buys you something: wider traces, lower phase velocity variation, or better antenna efficiency.

Stackup Design Considerations

Core and Prepreg Availability

IS680-AG cores are available in thicknesses from 3 mil (0.076 mm) to 60 mil (1.524 mm). Matching prepregs (IS680-AG PP) use the same resin system, so the Dk of bonding plies closely tracks the core Dk—a significant advantage over hybrid stackups where mismatched resin chemistries create Dk discontinuities at the bond line. Check the RF laminate thickness chart to verify which thicknesses your fabricator stocks before committing a stackup.

Hybrid Stackups with FR-4

A common cost-reduction strategy is to use IS680-AG only on the RF signal layers and bond them to standard high-Tg FR-4 (such as Isola IS550H) for power, ground, and low-speed digital layers. This works well if:

• The IS680-AG layers are symmetrically placed about the board midplane to minimize bow and twist.
• Lamination temperatures are compatible—IS680-AG laminates at roughly 375–400 °F (190–205 °C), which overlaps most high-Tg FR-4 cure profiles.
• You account for the Dk mismatch when modeling stripline layers that have IS680-AG on one side and FR-4 on the other (asymmetric stripline requires a weighted effective Dk).

Copper Foil Selection

IS680-AG pairs with standard electrodeposited (ED) copper, reverse-treated (RTF) foil, and very-low-profile (VLP) foil. At frequencies above 10 GHz, conductor surface roughness dominates insertion loss more than Df. Using VLP foil (Rz ≤ 3 µm) on IS680-AG can reduce total loss by 0.3–0.5 dB/in at 20 GHz compared to standard 1-oz ED foil (Rz ~ 8–10 µm). Always specify the foil grade in your fabrication notes, because the default at most shops is standard-profile HTE copper.

Fabrication and Processing Tips

One of IS680-AG’s strongest selling points is that it processes like FR-4. That said, a few details are worth calling out:

• Drilling: Standard carbide drill bits work fine. Entry and backup materials are the same as FR-4. Aspect ratios up to 10:1 are achievable with mechanical drilling; laser vias follow normal procedures for glass-reinforced laminates.
• Desmear: Standard permanganate desmear is effective. No plasma cycle is needed, unlike PTFE-based laminates.
• Plating: Electroless copper adhesion is good thanks to the glass reinforcement and the resin’s surface energy. Peel strengths after solder shock typically exceed 6 lb/in.
• Solder compatibility: With a Td of 360 °C and a Tg of 200 °C, IS680-AG handles multiple lead-free reflow cycles (peak 260 °C) without delamination. IPC Class 3 reliability requirements per IPC-6012 are routinely met.
• Routing and scoring: Conventional V-scoring and tab routing apply. No special tooling is needed.

Typical Applications

IS680-AG finds its way into designs where low, stable Dk and FR-4-like processing intersect:

• 77 GHz automotive radar antenna substrates — the Dk of 3.00 allows wider patch elements and feed lines, relaxing etch tolerances at millimeter-wave dimensions.
• 5G massive-MIMO antenna feed networks — Dk uniformity across a 450 × 600 mm panel keeps element-to-element phase error within spec.
• High-speed backplanes (56–112 Gbps per lane) — low Df preserves eye height on long traces; low Dk reduces crosstalk by widening trace spacing for a given impedance.
• Test and measurement fixtures — stable Dk over temperature minimizes calibration drift.
• Satellite communication (Ku/Ka-band) feed assemblies — low moisture absorption (0.09 %) prevents Dk shift in humid or vacuum environments.

For antenna substrates that need an even lower Dk (below 2.5), a hydrocarbon ceramic laminate or PTFE-based material may be necessary, but the processing complexity and cost increase substantially.

Design Checklist for IS680-AG PCBs

1. Confirm the design Dk with your field solver, using 3.00 at 10 GHz as the starting point and adjusting for your actual frequency and temperature per the Dk drift estimator above.
2. Specify copper foil profile explicitly (VLP recommended above 10 GHz).
3. Place IS680-AG layers symmetrically in the stackup to control warpage.
4. Use IS680-AG prepreg—not a different resin system—for bonding RF layers.
5. Call out impedance-controlled routing with ± 5 % tolerance and request test coupons on the production panel.
6. Include a loss-budget calculation in your design review: sum dielectric loss (Df-driven), conductor loss (roughness-driven), and radiation loss for each critical net.
7. Verify your fabricator has IS680-AG in stock or can source it within your lead time; it is less universally stocked than RO4350B.

Frequently Asked Questions

Is IS680-AG the same as IS680?

IS680 is the product family name. IS680-AG specifies the anti-static glass reinforcement variant with Dk 3.00. Other variants in the family (such as IS680-300) may differ in glass style, thickness availability, or Dk tolerance. Always confirm the exact suffix when ordering.

Can IS680-AG replace Rogers RO4350B?

In many RF designs, yes. IS680-AG offers a lower Dk (3.00 vs. 3.48) and lower Df (0.0025 vs. 0.0037), which can improve performance. However, RO4350B has a broader supply chain and more published application notes. A direct swap requires re-running impedance calculations because the Dk difference changes trace widths significantly.

What is the maximum operating frequency for IS680-AG?

There is no hard cutoff. IS680-AG is used in production designs up to 30 GHz and has been prototyped at 77 GHz. Above 40 GHz, conductor roughness and glass-weave effects become the dominant loss mechanisms, so material selection alone does not determine feasibility—foil grade and stackup geometry matter equally.

Does IS680-AG require special via processing?

No. Standard mechanical drilling, permanganate desmear, and electroless copper plating work the same as FR-4. This is a major advantage over PTFE laminates, which typically need plasma desmear and sodium-naphthenate surface treatment.

How does moisture absorption affect IS680-AG performance?

At 0.09 % moisture absorption, IS680-AG is among the lowest in the thermoset laminate category. For comparison, standard FR-4 absorbs roughly 0.15–0.20 %. The practical impact is that Dk shift due to humidity is negligible in most terrestrial environments, making IS680-AG reliable for outdoor base-station and automotive radar applications without hermetic sealing.