370HR Ultra

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370HR Ultra

Industry Leading, Very Low CTE, Epoxy Laminate and Prepreg

370HR Ultra is the industry’s “best in class” very low CTE, lead-free compatible product for high-reliability applications across a wide range of markets.

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Thermal Performance	Electrical Performance	Industry Approvals
Tg: 180°C Td: 360°C	Dk: 4.2 Df: 0.0125	UL Approval Pending and IPC-4101 /126

Thermal Performance

Tg: 180°C
Td: 360°C

Electrical Performance

Dk: 4.2
Df: 0.0125

Industry Approvals

UL Approval Pending and IPC-4101 /126

370HR Ultra laminates and prepregs are engineered using a patented high-performance 180°C Tg FR-4 multifunctional epoxy resin system. Building on the proven foundation of the original 370HR material, 370HR Ultra features targeted modifications to provide a lower Coefficient of Thermal Expansion (CTE) and enhanced thermal performance specifically for HDI and Ultra HDI (UHDI) applications.These advancements build on the proven manufacturability and global availability of the original 370HR material.
We manufacture 370HR Ultra with high-quality E-glass fabric to ensure superior Conductive Anodic Filament (CAF) resistance. This material delivers industry-leading thermal reliability and mechanical, chemical, and moisture resistance properties that meet or exceed traditional FR-4 standards. Proven in thousands of complex designs, 370HR Ultra remains best-in-class for ease of processing and reliability in sequential lamination environments.

Attributes

Markets

Product Summary ▲

Product Features

Industry Recognition
- UL Approval Pending

Performance Attributes
- CAF resistant

Processing Advantages
- FR-4 process compatible
- UV blocking and AOI fluorescence
- Multiple reflow capable
- HDI technology compatible

Production & Manufacturing

Currently manufactured in Asia, North America

Product Availability

Standard Material Offering: Laminate
- 2 to 5 mil (0.05 to 1.3 mm)

Copper Foil Type
- HTE Grade 3
- RTF (Reverse Treat Foil)

Copper Weight
- ½, 1 and 2 oz (18, 35 and 70 µm) available

Standard Material Offering: Prepreg
- Tooling of prepreg panels

Glass Fabric Availability
- E-glass
- Square weave glass
- Mechanically spread glass

Typical Values ▼

Property		Typical Value	Units	Test Method
Property		Typical Value	Metric (English)	IPC-TM-650 (or as noted)
Glass Transition Temperature (Tg) by DSC	Resin Content	180	°C	2.4.25C
Decomposition Temperature (Td) by TGA @ 5% weight loss	Resin Content	360	°C	2.4.24.6
Time to Delaminate by TMA (Copper removed)	A. T260 B. T288	60 50	Minutes	2.4.24.1
Z-Axis CTE	A. Pre-Tg B. Post-Tg C. 50 to 260°C, (Total Expansion)	27 155 1.8	ppm/°C ppm/°C %	2.4.24C
X/Y-Axis CTE	Pre-Tg	11/13	ppm/°C	2.4.24C
Thermal Conductivity		0.5	W/m·K	ASTM E1952
Thermal Stress 10 sec @ 288ºC (550.4ºF)	A. Unetched B. Etched	Pass	Pass Visual	2.4.13.1
Dk, Permittivity	@ 10 GHz	4.20	—	Bereskin Stripline
Df, Loss Tangent	@ 10 GHz	0.0125	—	Bereskin Stripline
Volume Resistivity	A. After moisture resistance B. At elevated temperature	—	MΩ-cm	2.5.17.1
Surface Resistivity	A. After moisture resistance B. At elevated temperature	—	MΩ	2.5.17.1
Dielectric Breakdown	Resin Content	66	kV	2.5.6B
Arc Resistance	Resin Content	120	Seconds	2.5.1B
Electric Strength (Laminate & laminated prepreg)	Resin Content	88	kV/mm (V/mil)	2.5.6.2A
Comparative Tracking Index (CTI)		3 (175-249)	Class (Volts)	—
Peel Strength	A. Low Profile copper foil and very low profile copper foil >17 um B. Standard profile copper 1. After thermal stress 2. At 125ºC (257ºF) 3. After process solutions	1.016 (5.8) 1.016 (5.8) — —	N/mm (lb/inch)	2.4.8C 2.4.8.2A 2.4.8.3 2.4.8.3
Flexural Strength	A. Length direction B. Cross direction	574 (83.2) 460 (66.8)	MPa (kpsi)	2.4.4B
Tensile Strength	A. Length direction B. Cross direction	45 40	MPa (kpsi)	ASTM D3039
Young's Modulus	A. Length direction B. Cross direction	—	ksi	ASTM D790-15e2
Poisson's Ratio	A. Length direction B. Cross direction	—	—	ASTM D3039
Moisture Absorption		0.1	%	2.6.2.1A
Flammability (Laminate & laminated prepreg)		V-0	Rating	UL 94
Relative Thermal Index (RTI)		—	°C	—
The data, while believed to be accurate and based on analytical methods considered to be reliable, is for information purposes only. Any sales of these products will be governed by the terms and conditions of the agreement under which they are sold.

NOTE

Visit our site http://www.isola-group.com for more details.
Revisions:
A. Initial Release 10/21/2026

Constructions ▼

Download Dk/Df Tables PDF

Core Data

Constructions	Resin Content %	Thickness (inch)	Thickness (mm)	100 MHz	500 MHz	1 GHz	2 GHz	5 GHz	10 GHz
Constructions	Resin Content %	Thickness (inch)	Thickness (mm)	Dielectric Constant (DK)/ Dissipation Factor (DF)
1x 106	71.00%	0.0019	0.048	4.03 0.0160	3.99 0.0170	3.95 0.0190	3.91 0.0200	3.86 0.0220	3.81 0.0220
1x 1067	76.00%	0.0029	0.074	3.95 0.0160	3.91 0.0170	3.87 0.0190	3.83 0.0200	3.78 0.0220	3.73 0.0220
1x 1080	67.00%	0.0033	0.084	4.09 0.0150	4.05 0.0160	4.01 0.0180	3.97 0.0190	3.92 0.0210	3.87 0.0210
2x 106	71.00%	0.0038	0.097	4.03 0.0160	3.99 0.0170	3.95 0.0190	3.91 0.0200	3.86 0.0220	3.81 0.0220
1x 1080	72.00%	0.004	0.102	4.01 0.0160	3.97 0.0170	3.93 0.0190	3.89 0.0200	3.84 0.0220	3.79 0.0220
1x 2113	60.00%	0.0044	0.112	4.21 0.0140	4.17 0.0150	4.13 0.0170	4.09 0.0180	4.04 0.0200	3.99 0.0200
1x 1080	76.00%	0.0045	0.114	3.95 0.0160	3.91 0.0170	3.87 0.0190	3.83 0.0200	3.78 0.0220	3.73 0.0220
2x 106	74.00%	0.0046	0.117	3.98 0.0160	3.94 0.0170	3.90 0.0190	3.86 0.0200	3.81 0.0220	3.76 0.0220
1x 2116	57.00%	0.005	0.127	4.27 0.0140	4.23 0.0150	4.19 0.0170	4.15 0.0180	4.10 0.0200	4.05 0.0200

Prepreg Data

Construction	Resin Content %	Thickness (inch)	Thickness (mm)	100 MHz	500 MHz	1 GHz	2 GHz	5 GHz	10 GHz
Construction	Resin Content %	Thickness (inch)	Thickness (mm)	Dielectric Constant (DK)/ Dissipation Factor (DF)
106	71.00%	0.0019	0.048	4.03 0.0160	3.99 0.0170	3.95 0.0190	3.91 0.0200	3.86 0.0220	3.81 0.0220
1027	77.00%	0.002	0.051	3.95 0.0160	3.91 0.0170	3.87 0.0190	3.83 0.0200	3.78 0.0220	3.73 0.0220
106	77.00%	0.0027	0.069	3.95 0.0150	3.91 0.0160	3.87 0.0180	3.83 0.0190	3.78 0.0210	3.73 0.0210
1067	71.00%	0.0028	0.071	4.03 0.0160	3.99 0.0170	3.95 0.0190	3.91 0.0200	3.86 0.0220	3.81 0.0220
1067	76.00%	0.0029	0.074	3.95 0.0160	3.91 0.0170	3.87 0.0190	3.83 0.0200	3.78 0.0220	3.73 0.0220
1080	67.00%	0.0033	0.084	4.09 0.0140	4.05 0.0150	4.01 0.0170	3.97 0.0180	3.92 0.0200	3.87 0.0200
1078	69.50%	0.0035	0.089	4.05 0.0160	4.01 0.0170	3.97 0.0190	3.93 0.0200	3.88 0.0220	3.83 0.0220
1078	73.00%	0.0039	0.099	3.99 0.0160	3.95 0.0170	3.91 0.0190	3.87 0.0200	3.82 0.0220	3.77 0.0220
1080	72.00%	0.004	0.102	4.01 0.0140	3.97 0.0150	3.93 0.0170	3.89 0.0180	3.84 0.0200	3.79 0.0200

NOTE

Revisions:
A - Original - 10/20

Documentation ▼

Resource Title & Summary	Date Updated
370HR Ultra Prepreg Safety Data Sheet	10/21/2026
370HR Ultra Laminate Safety Data Sheet	10/21/2026
370HR Ultra Laminate Prepreg Processing Guide	10/21/2026

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Property		370HR Ultra
Recommended for New Design
Halogen Free		—
Glass Transition Temperature (Tg) by DSC	Resin Content	180
Dk, Permittivity	Resin Content	4.20
Decomposition Temperature (Td) by TGA @ 5% weight loss	Resin Content	360
Df, Loss Tangent	Resin Content	0.0125
Moisture Absorption	Resin Content	0.1
Z-Axis CTE	50 to 260°C, (Total Expansion)	1.8
Peel Strength	Standard profile copper >>> After thermal stress	—

370HR Ultra

Industry Leading, Very Low CTE, Epoxy Laminate and Prepreg

370HR Ultra is the industry’s “best in class” very low CTE, lead-free compatible product for high-reliability applications across a wide range of markets.

Thermal Performance

Electrical Performance

Industry Approvals

Thermal Performance

Electrical Performance

Industry Approvals

Attributes

Markets

Product Features

Production & Manufacturing

Product Availability

Core Data

Prepreg Data

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Questions? Get In Touch With Isola Today