Isola 370HR PCB laminate
Isola 370HR PCB: High-Tg, CAF-Resistant FR-4
A 180 °C Tg, 340 °C Td FR-4-class laminate built for repeated lead-free reflow, thick high-layer-count boards and long field life, processed on standard FR-4 lines.
- Tg (DSC)
- 180 °C
- Td
- 340 °C
- Dk @ 1 GHz
- ≈4.04
- Z-CTE 50–260 °C
- 2.7%
Overview
What is Isola 370HR?
Isola 370HR is a high-performance FR-4-class epoxy laminate with a glass transition temperature of 180 °C (DSC), a decomposition temperature of 340 °C and enhanced resistance to conductive anodic filament (CAF) growth. It is one of the most widely specified laminates for multilayer boards that see several lead-free reflow cycles at 260 °C.
370HR sits between commodity FR-4 and specialty low-loss laminates such as Megtron or Rogers. It is far more reliable than standard FR-4 for a modest material premium, and it processes on the same equipment, so switching to it rarely changes lead time or needs process re-qualification.
Key properties
Isola 370HR material properties.
| Property | Typical value | Why it matters |
|---|---|---|
| Tg (DSC) | 180 °C | Less z-axis expansion during reflow |
| Td (5% weight loss) | 340 °C | Margin for rework, wave and selective solder |
| Z-axis CTE (50–260 °C) | ≈ 2.7% | Lower stress on via barrels |
| Dk @ 1 GHz | ≈ 4.04 | Impedance calculation input |
| Df @ 1 GHz | ≈ 0.021 | Fine for digital to a few Gbps; not low-loss |
| Flammability | UL 94 V-0 | Safety listing |
These thermal properties let multilayer constructions survive multiple 260 °C lead-free reflow cycles without delamination or barrel cracking. The electrical properties are adequate for digital signal integrity up to several gigahertz, but 370HR is not intended for low-loss RF or 25 Gbps+ SerDes channels.
CAF resistance
Why CAF resistance matters.
CAF (conductive anodic filament) is an electrochemical failure in which copper ions migrate along glass-fiber/resin interfaces under voltage bias and humidity. Over time they form a conductive filament that shorts adjacent holes or conductors. It is a latent failure: boards pass test and then fail in the field after months or years.
370HR uses a resin system with strong glass-to-resin adhesion that resists CAF formation in accelerated testing. That is why it is a standard choice for automotive, industrial and aerospace boards with long service lives, especially where hole-to-hole spacing is tight and bias voltages are high.
- Keep hole-to-hole wall spacing generous on high-voltage nets
- Avoid aligning holes along a single glass bundle direction where possible
- Specify a CAF-resistant laminate on the drawing for automotive and industrial boards
When to specify
When to specify Isola 370HR.
Use 370HR when standard FR-4 (Tg 135–150 °C) is not enough but specialty laminates are not justified. Automotive electronics such as ADAS, body control and powertrain modules often specify it because IATF 16949 programs need proven CAF resistance and thermal-cycling endurance. Industrial controls in hot environments benefit from the higher Td and lower z-expansion. Server and networking boards that see multiple rework cycles value its thermal margin above the lead-free reflow peak.
When not to
When to choose something else.
For 10 Gbps+ SerDes channels or RF front-end sections, 370HR’s Df of about 0.021 costs too much loss. Consider Megtron 6 for high-speed digital or Rogers 4350B for RF. For flex, high-temperature rigid or very hot zones, use polyimide. 370HR is optimized for thermal and mechanical reliability rather than high-frequency electrical performance.
Stackup guidance
Stackup and construction guidance.
We keep 370HR in standard core thicknesses and prepreg styles for multilayer constructions from 4 to 20+ layers. It processes like production FR-4, with no special drill parameters, plating chemistry or lamination changes, so a move from commodity FR-4 usually does not affect lead time.
For hybrid stack-ups, such as Megtron cores for signal layers with 370HR for power and ground, Tg and CTE compatibility between the materials must be evaluated for reliable lamination and thermal cycling. We confirm this during stack-up planning and return the construction with your quote.
- Use the laminate’s published Dk for impedance, not a generic 4.2
- Balance copper on mirrored layers
- Specify finished thickness and tolerance
- Allow equivalent high-Tg substitutes if lead time matters
Reflow & rework
Surviving lead-free reflow and rework.
A typical lead-free assembly puts a board through two reflow passes (top and bottom side), sometimes a wave or selective-solder step, and occasionally one or two rework cycles. Each excursion above Tg expands the resin in the z-axis and strains the copper barrel of every plated hole. With standard FR-4 the cumulative strain can crack barrels in thick boards. 370HR’s higher Tg and lower z-CTE reduce that strain on every cycle.
Moisture also matters. Laminate that has absorbed moisture can blister or delaminate during reflow. Boards should be packed in moisture-barrier bags and baked if exposure limits are exceeded before assembly.
| Process step | Peak temperature (typical) |
|---|---|
| Lead-free reflow | 245–260 °C |
| Wave / selective solder | ≈ 260–270 °C (local) |
| Hand / BGA rework | Local, repeated |
Comparison
370HR vs other high-Tg laminates.
| Laminate | Tg | Df @ 1 GHz (approx.) | Positioning |
|---|---|---|---|
| Standard FR-4 | 130–140 °C | ≈ 0.020 | Low cost, tin-lead or simple lead-free |
| Isola 370HR | 180 °C | ≈ 0.021 | Reliability and CAF resistance |
| Shengyi S1000-2M | ≈ 180 °C | ≈ 0.02 | Cost-effective high-Tg alternative |
| Isola FR408HR | ≈ 190 °C | ≈ 0.009–0.012 | Lower loss for faster digital |
| Megtron 4 | ≈ 175 °C | ≈ 0.005–0.007 | Bridge to low-loss |
| Megtron 6 R-5775(N) | 185 °C | 0.002 | Low-loss option; confirm channel budget |
RFQ
How to specify 370HR in an RFQ.
- Name Isola 370HR (or “370HR or equivalent high-Tg, CAF-resistant”)
- Layer count, finished thickness and tolerance
- Impedance targets and reference layers
- IPC class and any automotive addendum
- Whether substitution is allowed
- Quantity and schedule
FAQ
Material questions.
What is the Tg of Isola 370HR?
180 °C by DSC, with a Td of 340 °C.
What makes 370HR suitable for high-reliability boards?
High Tg and Td, low z-axis expansion and strong CAF resistance, which together improve plated-hole reliability through reflow and thermal cycling.
How does 370HR compare to standard FR-4?
Higher Tg (180 °C vs 130–140 °C), better z-expansion control and CAF resistance, processed on the same equipment. Material cost is modestly higher.
Is 370HR lead-free compatible?
Yes, it is designed for multiple 260 °C lead-free reflow cycles.
Is 370HR good for high speed?
Up to roughly 10 Gbps depending on channel length. For 25 Gbps+, use Megtron 6 or 7.
Can 370HR be substituted?
Equivalent high-Tg, CAF-resistant grades such as Shengyi S1000-2M can be proposed if your drawing allows substitution.
Ready when your files are
Send your stack-up for a material check.
Upload Gerber, ODB++ or IPC-2581 data. Every quote includes a written engineering DFM review, typically within one business day.