HPL-03015 vs HT-04503: detailed spec comparison, thermal vs isolation tradeoffs, application guide, and design tips for Bergquist Thermal Clad IMS PCB selection.

When you’re designing a metal core PCB and the Bergquist Thermal Clad lineup is on the table, two grades come up more than almost any other: HPL-03015 vs HT-04503. They’re both high-performance IMS dielectrics. They’re both lead-free compatible, RoHS compliant, and proven in demanding applications. But they are built for fundamentally different design priorities — and picking the wrong one can cost you in thermal headroom, isolation margin, or board reliability down the line.

This guide breaks both materials down from an engineering standpoint: what the datasheets actually say, what the numbers mean in practice, and how to make the call when your design could arguably go either way.

What HPL-03015 and HT-04503 Actually Are

Both materials are dielectrics within Bergquist’s Thermal Clad Insulated Metal Substrate (IMS) family. The naming convention tells you the essentials: “HPL” stands for High Power Lighting, “HT” stands for High Temperature, and the trailing digits describe dielectric thickness — 03015 means 3 mils at 0.0015 inches (38 µm), while 04503 means 3 mils at 0.003 inches (76 µm). That thickness difference is small on paper but significant in practice.

The HPL-03015 was developed specifically for high-brightness LED applications. It uses an extremely thin dielectric at 38 µm to minimize thermal resistance between the LED junction and the aluminum base layer. It achieves a thermal conductivity of 3.0 W/m·K and thermal resistance of just 0.02°C·in²/W — numbers that put it at the top of the Thermal Clad dielectric performance ladder for raw heat transfer.

The HT-04503, by contrast, was designed around high-temperature durability and broad industrial applicability. It has a dielectric thickness of 76 µm (double the HPL), a dielectric thermal conductivity of 2.2 W/m·K, and a glass transition temperature (Tg) of 150°C. It’s proven in applications well beyond LED lighting — motor drives, solid-state relays, power converters, heat rails, and solar receivers.

HPL-03015 vs HT-04503: Full Specification Comparison

This is the comparison table that most datasheets don’t provide side-by-side. Here it is in one place:

Thermal Properties

Parameter	HPL-03015	HT-04503	Test Method
Dielectric Thermal Conductivity	3.0 W/m·K	2.2 W/m·K	ASTM D5470
Product Thermal Conductivity	—	4.1 W/m·K	MET 5.4-01-40000
Thermal Resistance	0.02°C·in²/W	0.05°C·in²/W	ASTM D5470
Thermal Impedance	0.30°C/W	0.45°C/W	MET-5.4-01-40000
Glass Transition Temperature (Tg)	185°C	150°C	ASTM E1356
Max Operating Temperature (UL)	140°C	140°C	UL 796
Max Soldering Temperature	325°C	325°C	UL 796

Electrical Properties

Parameter	HPL-03015	HT-04503	Test Method
Dielectric Thickness	0.0015 in / 38 µm	0.003 in / 76 µm	—
Breakdown Voltage	2.5 kVAC	8.5 kVAC	ASTM D149
Dielectric Strength	2000 V/mil (75 kV/mm)	2000 V/mil (80 kV/mm)	ASTM D149
Dielectric Constant	6.6	7.0	ASTM D150
Dissipation Factor (1kHz/1MHz)	0.003 / 0.005	0.0033 / 0.0148	ASTM D150
Capacitance	925 pF/in²	540 pF/in²	ASTM D150
Volume Resistivity	10¹⁴ Ω·m	10¹⁴ Ω·m	ASTM D257
Operating Voltage (AC cont.)	120 VAC	Higher	—

Mechanical & Agency Properties

Parameter	HPL-03015	HT-04503	Test Method
Peel Strength @25°C	—	6 lb/in (1.1 N/mm)	ASTM D2861
CTE XY/Z below Tg	—	25 µm/m°C	ASTM D3386
Storage Modulus (@25°C/150°C)	—	16/7 GPa	ASTM 4065
UL Flammability	Pending	V-0	UL 94
CTI	Pending	0/600	IEC 60112
Lead-free solder compatible	Yes	Yes	—
RoHS compliant	Yes	Yes	—

Note on HPL-03015 thermal conductivity: Some datasheets show 3.0 W/m·K while product listings occasionally cite 7.5 W/m·K. The 3.0 W/m·K figure is the verified dielectric-only thermal conductivity per ASTM D5470 testing on the official Bergquist/Henkel datasheet. Always verify against the most current datasheet before finalizing a design.

The Core Engineering Difference: Thermal vs. Isolation Priority

Reading the table above, the choice between HPL-03015 vs HT-04503 really comes down to one fundamental tradeoff: thermal performance vs. electrical isolation headroom.

Why HPL-03015 Wins on Thermal Performance

The HPL-03015’s 38 µm dielectric is half the thickness of the HT-04503. Since thermal resistance is proportional to thickness divided by thermal conductivity, thinner is better for heat transfer. The result is a thermal resistance of 0.02°C·in²/W compared to the HT-04503’s 0.05°C·in²/W — that’s 2.5× lower thermal resistance. In a high-density LED array, that difference directly translates to lower junction temperatures, longer LED lifetime, and more lumens per watt at steady state.

The HPL-03015 dielectric was specifically formulated for high power lighting LED applications with demanding thermal performance requirements. This thin dielectric at 0.0015″ (38µm) has the ability to withstand high temperatures with a glass transition of 185°C and phenomenal thermal performance of 0.30°C/W.

Why HT-04503 Wins on Isolation Voltage

The HT-04503 delivers a breakdown voltage of 8.5 kVAC — compared to the HPL-03015’s 2.5 kVAC. That’s more than three times the isolation margin. Its thicker 76 µm dielectric is the reason: more dielectric material between the copper circuit and the aluminum base means more insulation.

The HT-04503 is a dielectric resistant to degradation from high temperature exposure and features high dielectric breakdown characteristics. This dielectric is proven in applications such as LED, Power Conversion, Heat-Rails, Solid State Relays and Motor Drives.

For AC mains-connected designs, industrial motor drives running from a 480 VAC bus, or any application requiring reinforced insulation under IEC 62368-1 or UL 508, the HT-04503’s isolation margin is non-negotiable. The HPL-03015 at 120 VAC continuous simply isn’t usable in those contexts regardless of how good its thermal numbers look.

Application-by-Application: Which Grade to Use

High-Power LED Lighting (Street, Architectural, Horticulture)

Winner: HPL-03015

This is the application HPL was literally named for. High-brightness LED arrays — whether street fixtures, stadium lighting, or grow lights — need the lowest possible thermal resistance between the LED die and the heatsink. Every degree of junction temperature rise reduces lumen output and accelerates lumen depreciation. The HPL-03015’s 0.02°C·in²/W thermal resistance gives LED designers the most direct thermal path available in a polymer-based IMS dielectric.

The Tg of 185°C also helps here. LED arrays in outdoor fixtures can see high ambient temperatures combined with self-generated heat, and a higher glass transition temperature gives additional confidence that the dielectric won’t soften and lose adhesion under worst-case thermal stress.

Automotive LED Headlamps and Backlighting

Winner: HPL-03015 (with caveats)

Automotive LED applications benefit from HPL-03015’s thermal performance and high Tg. The caveat is that automotive-grade designs may require documented UL CTI and flammability ratings — values listed as “pending” on the HPL-03015 datasheet. If your automotive customer requires full UL 94 V-0 documentation, HT-04503 has those ratings confirmed, while HPL-03015 designs may need additional testing and documentation.

Industrial Motor Drives and Variable Frequency Drives (VFDs)

Winner: HT-04503

Motor drive inverter bridges operate from DC bus voltages ranging from 400 VDC to 800 VDC in modern industrial equipment. The continuous AC operating voltage limit of 120 VAC for the HPL-03015 rules it out immediately. HT-04503’s 8.5 kVAC breakdown and proven record in motor drives and solid-state relays make it the correct choice. The HT-04503 offers exceptionally low thermal resistance of only 0.05°C·in²/W (0.32°C·cm²/W), enabling effective heat dissipation and temperature control.

AC-DC Power Converters and Offline SMPS

Winner: HT-04503

Any offline switching power supply operating directly from 120 VAC or 230 VAC mains needs sufficient dielectric isolation between the primary-side switching devices and the chassis/heatsink. HT-04503 at 8.5 kVAC breakdown covers this with margin. HPL-03015 at 2.5 kVAC is inadequate for primary-side components on most mains voltages when safety standards are applied with derating.

DC-DC Converters (Low Voltage Bus, 12–48 VDC Systems)

Winner: Either — consider HPL-03015 if thermal is paramount

For isolated DC-DC converters operating at bus voltages below 48 VDC where isolation requirements are modest, HPL-03015 becomes viable again. If the primary design driver is junction temperature management in a space-constrained converter, HPL-03015’s superior thermal resistance makes it the better performer.

Solar Energy Systems and Concentrator PV

Winner: HT-04503

The HT-04503 is proven in solar receivers as well as power conversion and heat-rail applications. The higher isolation voltage and documented UL ratings make it more suitable for grid-tied solar inverter hardware where safety certifications are mandatory.

Comparing HPL-03015 and HT-04503 with Broader Thermal Clad Family Context

Grade	Dielectric Thickness	Thermal Resistance	Breakdown Voltage	Tg	Primary Use
HPL-03015	38 µm	0.02°C·in²/W	2.5 kVAC	185°C	High-power LEDs
HT-04503	76 µm	0.05°C·in²/W	8.5 kVAC	150°C	Industrial power, LEDs
HT-07006	152 µm	0.09°C·in²/W	11.0 kVAC	150°C	High isolation, 480 VAC
MP-06503	76 µm	0.09°C·in²/W	8.5 kVAC	90°C	Cost-sensitive general purpose
CML-11006	152 µm	0.11°C·in²/W	>11 kVAC	90°C	Multi-layer, max isolation

The HT-07006 is worth mentioning as a natural upgrade path from HT-04503 when you need more isolation voltage (for 480 VAC operation) while keeping the HT dielectric chemistry. It features even higher dielectric breakdown characteristics than the HT-04503, per the HT-07006 datasheet.

Comparing Bergquist IMS Materials vs. Arlon and Competitors

Engineers evaluating the HPL-03015 vs HT-04503 decision should also be aware of how Bergquist compares to alternatives. Arlon PCB materials represent another well-established IMS dielectric option, particularly for military and high-frequency power applications. Direct bond copper (DBC) on alumina outperforms both on thermal conductivity through the substrate but is brittle, fragile under mechanical stress, and significantly more expensive to fabricate. For most commercial power electronics where mechanical robustness and SMT assembly are priorities, Bergquist IMS remains a more practical solution.

Design Considerations for Both Materials

Copper Foil Weight

Both HPL-03015 and HT-04503 support copper foil from 1 oz to 10 oz (35–350 µm). For LED lighting on HPL-03015, 1–2 oz copper is typical. For high-current motor drive or power converter applications on HT-04503, 2–3 oz copper is more common to keep trace temperature rise in check. Heavier copper also improves lateral heat spreading within the circuit layer itself — a secondary thermal benefit.

Assembly and Reflow

Both materials specify a maximum soldering temperature of 325°C and are compatible with standard SAC305 lead-free reflow profiles. The aluminum base layer adds thermal mass compared to FR-4 — plan for a longer soak zone in your reflow profile to bring the board uniformly to reflow temperature, particularly for larger panel sizes or thicker aluminum bases (2.0 mm).

HiPot Testing

The capacitive nature of IMS construction means HiPot testing requires a controlled voltage ramp rate. For HPL-03015 especially, the high capacitance (925 pF/in²) means fast ramp rates can trigger nuisance trips in isolation testers. Use a slow DC ramp, typically 100 V/second, and allow adequate dwell time at test voltage.

Board Routing and Fabrication

Both materials require carbide tooling for CNC routing and drilling through the aluminum base. Standard FR-4 routing parameters will cause rapid tool wear and aluminum burring. If you’re ordering from a fabricator, confirm they have experience with Bergquist IMS materials — not all shops stock carbide tooling suited for metal-clad boards.

Useful Resources and Datasheets

Resource	Description	Link
Bergquist HPL-03015 Official Datasheet	Full thermal, electrical, and mechanical spec table	mclpcb.com PDF
Bergquist HT-04503 Official Datasheet	Full spec table with UL agency ratings	mclpcb.com PDF
Bergquist HT-07006 Datasheet	For higher isolation voltage variant	mclpcb.com PDF
Bergquist Thermal Clad Selection Guide	Complete dielectric comparison chart and design rules	Digikey PDF
Mouser HPL-03015 PDS	Alternate source for HPL datasheet	Mouser PDF
Henkel Bergquist Product Portal	Current product availability, ordering, custom configurations	Henkel Adhesives
IPC-2221 PCB Design Standard	Creepage and clearance rules for voltage isolation design	IPC.org
GlobalSpec HPL-03015 Entry	Third-party spec listing with application notes	GlobalSpec

5 FAQs: HPL-03015 vs HT-04503

Can I use HPL-03015 for an offline LED driver board operating from 120 VAC mains?

Technically no — not for components with traces at mains potential. The HPL-03015 has a continuous AC operating voltage rating of only 120 VAC, and with standard derating practices applied, the usable operating voltage is considerably lower. The aluminum base is typically connected to chassis or safety ground in an offline driver, creating a high-voltage isolation requirement between primary-side circuitry and the base. HT-04503 at 8.5 kVAC breakdown is the appropriate choice for that interface. HPL-03015 is suited for the secondary-side LED array section of the driver, where voltages are typically well below its rating.

Which material runs cooler under an equivalent LED load — HPL-03015 or HT-04503?

HPL-03015, and the gap is meaningful. With thermal resistance of 0.02°C·in²/W versus HT-04503’s 0.05°C·in²/W, the HPL dielectric introduces less than half the temperature drop per watt per unit area. For a typical 1 cm² LED footprint dissipating 5W, that’s roughly a 1.5–2°C improvement through the dielectric alone. In LED system design where color consistency and lumen maintenance are tied to junction temperature, 2°C matters.

Is the HPL-03015 Tg of 185°C an advantage over HT-04503’s 150°C?

For LED applications, yes. A higher Tg means the dielectric retains its mechanical properties at higher temperatures before softening. In high-ambient outdoor or automotive luminaires that also see significant self-heating, the HPL-03015 has more headroom before the dielectric transitions from glassy to rubbery behavior. That said, both materials share the same 140°C UL maximum continuous operating temperature, so the Tg advantage of HPL-03015 is more about margins and reliability during stress events than normal operation.

What’s the difference between HT-04503 and HT-07006, and how do they relate to HPL-03015?

HT-07006 uses the same high-temperature HT dielectric chemistry as the HT-04503 but at 6 mils (152 µm) thickness instead of 3 mils. The thicker dielectric raises breakdown voltage to 11 kVAC and is appropriate for designs operating near 480 VAC. Its thermal resistance is 0.09°C·in²/W — higher than both HT-04503 and HPL-03015. The simple hierarchy for isolation voltage is: HPL-03015 (2.5 kV) < HT-04503 (8.5 kV) < HT-07006 (11 kV). For thermal performance it reverses: HPL-03015 > HT-04503 > HT-07006.

Are HPL-03015 and HT-04503 both available on copper base layers?

Yes. Both materials in the Bergquist Thermal Clad family are available on aluminum and copper metal substrates. Copper base provides approximately 2.4× better lateral heat spreading than aluminum (390 W/m·K vs. 160 W/m·K), which benefits high-density LED arrays on HPL-03015 and high-current bus bar designs on HT-04503. Copper base adds cost and weight — it’s a meaningful choice for the highest watt-density applications but overkill for most standard designs.

Summary: Making the Call on HPL-03015 vs HT-04503

The decision between HPL-03015 vs HT-04503 isn’t complicated once you frame it correctly. Ask two questions about your design: what is the operating voltage relative to the aluminum base, and what is the primary thermal bottleneck?

If your design operates at voltages below 120 VAC at the board-to-chassis interface and thermal resistance is the dominant design concern — LED street lighting, architectural fixtures, horticultural lighting, backlighting panels — HPL-03015 is the right material. Its 0.02°C·in²/W thermal resistance and 185°C Tg give LED designers the best thermal path available in a Bergquist polymer IMS dielectric.

If your design involves mains-connected circuitry, industrial motor drives, DC bus voltages above 170 VDC, or any application where UL V-0 flammability documentation is mandatory, HT-04503 is the correct starting point. Its 8.5 kVAC breakdown, proven industrial application base, and full UL agency ratings make it a more complete solution for safety-critical power electronics designs.

Both materials are excellent products within their intended domains. The engineering mistake isn’t choosing one over the other — it’s choosing the wrong one for the wrong application.