Complete Bergquist HT-04503 specifications — 4.1 W/m-K, 8.5 kVAC, 140°C rating — plus design guide, grade comparisons, and application selection for MCPCB engineers.

When thermal management stops being a footnote and becomes the whole problem, most experienced power electronics engineers end up in the same place: metal core PCBs. And within that category, the Bergquist HT-04503 consistently shows up on short lists for high-watt-density, high-temperature applications. Part of the Thermal Clad family from Bergquist (now a Henkel brand), the HT-04503 is not a general-purpose MCPCB material — it’s an engineered dielectric optimized for applications where standard aluminum PCB substrates run out of headroom.

This guide compiles the full specification data, explains what the numbers actually mean for your design, positions the HT-04503 against other Thermal Clad grades, and gives you the practical design guidance you need to use it correctly.

What Is the Bergquist HT-04503?

The HT-04503 is a Thermal Clad insulated metal substrate (IMS) from Bergquist, characterized by a 3 mil (76 µm) dielectric layer designed for high-temperature service. The product code tells you the key parameters directly: “HT” stands for High Temperature, “045” refers to the dielectric thickness (0.003″ = 3 mil, with “045” being an internal designation tied to thermal resistance), and “03” indicates the 3 mil dielectric thickness in the Bergquist naming convention.

The dielectric itself is a proprietary polymer/ceramic blend — not standard epoxy. The polymer component provides electrical isolation and resistance to thermal aging. The ceramic filler is what drives thermal conductivity while maintaining dielectric strength at thicknesses where standard epoxy resins would begin to show pinholes and breakdown. This combination allows the HT-04503 dielectric to hold a breakdown voltage of 8.5 kVAC at just 76 µm thickness — a figure that should get attention from anyone designing for mains-isolated power electronics.

The “High Temperature” designation is meaningful, not marketing. The HT dielectric maintains its properties at continuous operating temperatures up to 140°C (U.L. 796 rated), with a glass transition temperature of 150°C. That puts it in a different tier from standard MCPCB materials, which typically begin to soften and lose bond strength well below that range.

Bergquist HT-04503 Full Datasheet Specifications

The table below presents the complete published technical data from the official Bergquist HT-04503 datasheet. Every value listed corresponds to a named test method — a point worth emphasizing when comparing competing MCPCB substrates, where thermal conductivity figures are sometimes cited without methodology.

Table 1: Bergquist HT-04503 Complete Technical Specifications

Parameter	Value	Test Method
THERMAL PROPERTIES
Product Thermal Conductivity	4.1 W/m-K	Bergquist MET 5.4-01-40000
Dielectric Thermal Conductivity	2.2 W/m-K	ASTM D5470
Thermal Resistance	0.05°C·in²/W (0.32°C·cm²/W)	ASTM D5470
Thermal Impedance	0.45°C/W	Bergquist MET-5.4-01-40000
Glass Transition Temperature (Tg)	150°C	ASTM E1356
Max Operating Temperature	140°C	U.L. 796
Max Soldering Temperature	325°C	U.L. 796
ELECTRICAL PROPERTIES
Dielectric Constant	7	ASTM D150
Dissipation Factor	0.0033 / 0.0148 (at 1 kHz / 1 MHz)	ASTM D150
Capacitance	540 pF/in² (85 pF/cm²)	ASTM D150
Volume Resistivity	10¹⁴ Ω·m	ASTM D257
Surface Resistivity	10¹³ Ω/sq	ASTM D257
Dielectric Strength	2,000 V/mil (80 kV/mm)	ASTM D149
Breakdown Voltage	8.5 kVAC	ASTM D149
MECHANICAL PROPERTIES
Color	White	Visual
Dielectric Thickness	0.003″ (76 µm)	Visual
Peel Strength at 25°C	6 lb/in (1.1 N/mm)	ASTM D2861
CTE (XY/Z axis) below Tg	25 µm/m·°C	ASTM D3386
CTE (XY/Z axis) above Tg	95 µm/m·°C	ASTM D3386
Storage Modulus at 25°C	16 GPa	ASTM 4065
Storage Modulus at 150°C	7 GPa	ASTM 4065
CHEMICAL PROPERTIES
Water Vapor Retention	0.24% wt.	ASTM E595
Out-Gassing Total Mass Loss	0.28% wt.	ASTM E595
Collect Volatile Condensable Material	0.01% wt.	ASTM E595
AGENCY RATINGS
U.L. Max Operating Temperature	140°C	U.L. 746B
U.L. Flammability Rating	V-0	U.L. 94
Comparative Tracking Index (CTI)	0/600	ASTM D3638 / IEC 60112
Solder Limit Rating	325°C / 60 seconds	U.L. 796
COMPLIANCE
Lead-Free Solder Compatible	Yes	—
Eutectic AuSn Compatible	Yes	—
RoHS Compliant	Yes	—

Understanding the Two Thermal Conductivity Values

A common point of confusion is why the datasheet lists two thermal conductivity values: 4.1 W/m-K for “Product Thermal Conductivity” and 2.2 W/m-K for “Dielectric Thermal Conductivity.” These are not contradictory — they measure different things.

The 4.1 W/m-K figure is a system-level measurement (Bergquist’s proprietary MET test method using a TO-220 setup) that accounts for the full substrate stack including the aluminum base and copper circuit layer. The 2.2 W/m-K value is the intrinsic thermal conductivity of the dielectric layer alone, measured via ASTM D5470. When you’re modeling thermal resistance in a design tool, the 2.2 W/m-K dielectric-only value is what you’ll use alongside the dielectric thickness to calculate junction-to-baseplate thermal resistance. The 4.1 W/m-K figure is useful for comparative benchmarking against competing products but cannot be directly substituted into a layer-by-layer thermal model.

The thermal resistance specification of 0.05°C·in²/W at 3 mil dielectric thickness is a direct output of that ASTM D5470 measurement. To put it in context: standard aluminum MCPCB materials at equivalent dielectric thicknesses typically land between 0.10 and 0.20°C·in²/W. The HT-04503 essentially halves the thermal resistance of a typical entry-level MCPCB dielectric.

Bergquist HT-04503 vs. Other Thermal Clad Grades

The HT-04503 doesn’t exist in isolation — it’s one product in the Thermal Clad lineup. Engineers selecting MCPCB materials should understand where the HT series sits relative to the Multi-Purpose (MP) and High Power Lighting (HPL) grades.

Table 2: Bergquist Thermal Clad Grade Comparison

Parameter	HT-04503 (High Temp)	MP-06503 (Multi-Purpose)	HT-07006 (High Temp 6 mil)	HPL-03015 (High Power Lighting)
Dielectric Thickness	3 mil (76 µm)	6 mil (152 µm)	6 mil (152 µm)	1.5 mil (38 µm)
Dielectric Thermal Conductivity	2.2 W/m-K	2.4 W/m-K	2.2 W/m-K	~3.0+ W/m-K
Thermal Resistance	0.05°C·in²/W	0.09°C·in²/W	—	0.02°C·in²/W
Breakdown Voltage	8.5 kVAC	6.0 kVAC	11.0 kVAC	~3.5 kVAC
Max Operating Temp (UL)	140°C	130°C	140°C	150°C+
Glass Transition Temp	150°C	~130°C	150°C	185°C
Primary Application	Power conversion, SSR, motor drives	General-purpose, multi-application	High-isolation power	High-power LED
Lead-Free Compatible	Yes	Yes	Yes	Yes

The comparison reveals how each grade trades off thermal resistance against electrical isolation. The HT-04503 occupies the sweet spot for most high-power industrial applications: thinner dielectric than the HT-07006 (lower thermal resistance, higher temperature capability), more isolation voltage than the HPL-03015 (which is optimized for LED boards where mains isolation is not the priority), and significantly better high-temperature performance than the MP-06503 general-purpose grade.

If your design is a mains-connected power converter running at sustained high ambient temperatures, the HT-04503 is the appropriate choice. If you’re building a high-bay LED fixture operating at lower ambient temperatures with modest isolation requirements, the HPL-03015 may offer better thermal performance at the cost of isolation voltage margin.

Decoding the Part Number and Available Configurations

The Bergquist Thermal Clad HT-04503 is available on both aluminum and copper metal substrates — a point sometimes overlooked in procurement. Aluminum is the standard choice for cost and weight, but copper-base variants are available for applications where higher thermal spreading (leveraging copper’s roughly 4× higher thermal conductivity vs. aluminum) justifies the cost and weight penalty.

Standard MCPCB Stack-Up Using HT-04503

A typical single-layer HT-04503 MCPCB consists of three layers from top to bottom:

Circuit Layer (Copper Foil): The component mounting and interconnect layer. Standard offerings are 1 oz (35 µm) copper, with 2 oz (70 µm) available for higher current carrying capacity. The copper foil is certified to an area weight requirement per IPC-4562 rather than measured directly for thickness — a nuance worth noting when specifying to a fabricator.

Dielectric Layer (HT-04503): The 3 mil (76 µm) polymer-ceramic blend. This is the thermal and electrical performance layer. Its CTE of 25 µm/m·°C below Tg provides reasonable match to both the aluminum base (~23 µm/m·°C) and copper circuit layer (~17 µm/m·°C), reducing interfacial stress during thermal cycling.

Metal Base (Aluminum or Copper): Typically 1.0 mm, 1.5 mm, or 2.0 mm thick aluminum (6061 or 5052 alloy). Acts as the primary heat spreader and mechanical substrate. The base attaches to a heatsink via thermal interface material or direct bolted contact.

Table 3: Standard HT-04503 Board Configuration Options

Parameter	Standard Options	Notes
Metal Base Material	Aluminum (standard), Copper (premium)	Al 5052 or 6061 typical
Base Thickness	0.8 mm, 1.0 mm, 1.5 mm, 2.0 mm	1.5 mm most common
Copper Weight	1 oz (35 µm), 2 oz (70 µm), 3 oz (105 µm)	Specify per current needs
Surface Finish	HASL (lead-free), ENIG, OSP	ENIG preferred for fine-pitch SMT
Solder Mask Color	White (standard for LED), Black, Green	White maximizes LED light reflection
Dielectric Thickness	3 mil (76 µm) — fixed for HT-04503	Use HT-07006 for 6 mil
Max Panel Size	Typically up to 500 × 600 mm	Verify with fabricator

PCB Design Guide: Getting the Best from Bergquist HT-04503

Selecting the right material is step one. Getting the design right to exploit its properties is the part that separates boards that perform from boards that just test okay.

Thermal Via and Pad Design Considerations

One critical difference between designing for MCPCB and standard FR-4: through-holes in MCPCB are electrically isolated blind stubs, not continuous barrels connecting to the metal base. In standard Thermal Clad construction, drilled holes are lined with the same dielectric system and do not penetrate the metal base. This means conventional thermal vias to the baseplate aren’t available — the dielectric provides the only thermal path from the circuit layer to the aluminum base.

For surface-mount power components, this makes pad geometry critical. Thermal pads under components should be maximized within DFM constraints to spread the heat flux over the largest possible dielectric area. Since thermal resistance scales inversely with contact area (R_th = R_material / A), doubling the effective pad area under a MOSFET or LED package halves the component’s contribution to junction-to-baseplate thermal resistance.

Direct screw-mount thermal pads — with the dielectric separating the component’s thermal slug from the aluminum baseplate — are a particularly effective topology. The HT-04503’s 8.5 kVAC breakdown voltage provides ample margin for most industrial mains-connected designs using this approach.

Solder Mask and Surface Finish Selection

The HT-04503 is rated for maximum soldering temperatures of 325°C for 60 seconds (U.L. 796). Lead-free SAC305 reflow peaks at approximately 250–260°C, leaving substantial margin. Eutectic AuSn (80/20) compatibility at higher process temperatures is also specified, which matters for die-attach applications in solid-state relay and power module constructions.

ENIG (Electroless Nickel Immersion Gold) surface finish is generally preferred over HASL on MCPCB for fine-pitch surface mount components because HASL can produce uneven deposit thickness that complicates coplanarity on small packages. For LED applications, a white solder mask significantly improves optical efficiency by reflecting secondary light emission from the PCB surface rather than absorbing it.

Trace Width and Current Carrying Capacity on MCPCB

The copper circuit layer on an HT-04503 board carries current just like any other PCB copper, but with an important advantage: because the dielectric efficiently transfers heat to the aluminum baseplate, traces on MCPCB can sustain higher continuous current than the same geometry on FR-4 at the same temperature rise. IPC-2152 current-carrying capacity tables, which are derived from FR-4 data, are conservative for MCPCB — but unless you have empirical data for your specific thermal configuration, using IPC-2152 as a starting point and applying a derating factor remains the safe engineering approach.

For high-current applications (motor drive bus bars, power converter output stages), 2 oz or 3 oz copper is available and worthwhile. The thermal dissipation from I²R losses in the copper itself becomes a secondary heat source that the dielectric must also conduct — heavier copper reduces this contribution.

Mechanical Mounting and Assembly Considerations

The aluminum base of an HT-04503 MCPCB can be mounted directly to a heatsink using thermal interface material (TIM). Bergquist also offers compatible Bond-Ply and Hi-Flow TIM products for this interface, which is convenient for supply chain management if you’re already specifying Bergquist for the MCPCB substrate.

For designs with multiple MCPCBs in a chassis, consider the CTE mismatch between the 3003/5052 aluminum base (~23 µm/m·°C) and steel or cast aluminum chassis hardware when designing fastener patterns for boards that experience wide temperature swings. The HT-04503 dielectric’s CTE of 25 µm/m·°C below Tg closely tracks the aluminum base, which keeps internal stress at the dielectric-metal interface controlled through the normal operating range.

Application Profiles: Where Bergquist HT-04503 Excels

Table 4: HT-04503 Application Suitability Guide

Application	Why HT-04503 Works	Key Spec Drivers	Notes
High-power LED modules	Lowest thermal resistance at 3 mil; white solder mask	0.05°C·in²/W thermal resistance	HPL may win at very thin dielectrics if isolation <3.5 kV acceptable
AC/DC power converters	High isolation voltage + elevated temperature operation	8.5 kVAC breakdown; 140°C operating temp	Mains-connected designs benefit from breakdown margin
Solid state relays (SSR)	Direct component-to-baseplate topology; high-temp dielectric	8.5 kVAC; 150°C Tg	CTE match reduces dielectric fatigue in cycling
Motor drives and inverters	Sustained high-temp operation; high current density	140°C UL rating; 2–3 oz copper options	IGBT and MOSFET thermal management
Solar/concentrator PV	Outdoor ambient temp + self-heating; UV stable polymer	High-temp dielectric; low outgassing	Low CVCM (0.01%) suits sealed enclosures
Automotive electronics	-40 to 125°C cycling; vibration; lead-free assembly	150°C Tg; CTE <Tg = 25 µm/m·°C; lead-free rated	Verify AEC-Q compatibility with full qualification
Heat-rail assemblies	Long, distributed heat paths on single substrate	Product thermal conductivity 4.1 W/m-K	Copper base variant improves lateral spreading

Comparing HT-04503 to Alternative High-Performance MCPCB Materials

For completeness, engineers evaluating the HT-04503 should understand where it sits against other premium MCPCB substrate families. The Arlon PCB material portfolio offers alternative high-temperature IMS options for applications where different thermal/electrical trade-offs are needed. Ceramic substrates (AlN, Al₂O₃) offer better CTE matching to silicon but at significantly higher cost and with brittleness constraints. The HT-04503’s polymer-ceramic dielectric falls between standard MCPCB and ceramic in performance — closer to ceramic in thermal capability but with the manufacturing flexibility and cost profile of a conventional PCB process.

Table 5: HT-04503 vs. Alternative Thermal Management Substrates

Substrate Type	Thermal Conductivity	Isolation Voltage	Max Temp	Relative Cost	PCB-Compatible Process
Bergquist HT-04503 (MCPCB)	2.2 W/m-K (dielectric)	8.5 kVAC	140°C (UL)	Moderate	Yes
Standard MCPCB (generic)	1.0–1.5 W/m-K	3–5 kVAC	105–130°C	Low	Yes
Bergquist HPL-03015	~3.0+ W/m-K (dielectric)	~3.5 kVAC	150°C+ (Tg)	Moderate	Yes
Ceramic (Al₂O₃)	20–25 W/m-K	>10 kV	>300°C	High	No (specialized)
Ceramic (AlN)	150–180 W/m-K	>10 kV	>300°C	Very High	No (specialized)
Direct Bond Copper (DBC)	24–28 W/m-K	Moderate	>300°C	High	No (specialized)
FR-4 with thermal vias	Effective 1–3 W/m-K	3–5 kVAC	130°C (Tg limited)	Very Low	Yes

Fabrication Notes: Working With HT-04503 MCPCB Material

A few process details worth knowing before sending files to your fabricator:

Dielectric Testing. Because micro-fractures or micro-voids in the dielectric can manifest as electrical shorts under voltage, Bergquist recommends testing finished boards with a controlled voltage ramp rate. The capacitive nature of the MCPCB construction (capacitance of 540 pF/in² is substantial) can cause nuisance trips if testers apply voltage too rapidly. Specify a controlled ramp-up per Bergquist fabrication guidelines.

Drilling. MCPCB drilling requires carbide tooling and controlled parameters to prevent dielectric cracking or delamination at hole walls. Through-hole components work, but pad connections to the base metal are not electrically available — all through-holes are dielectrically isolated from the aluminum base.

Solder Mask Application. Standard liquid photoimageable (LPI) solder masks are compatible. For white solder mask on LED boards, verify that your fabricator’s white LPI formulation has been qualified with MCPCB substrates — adhesion characteristics differ from FR-4.

Storage. Bergquist specifies optimal storage at 5–25°C with a 12-month shelf life in unopened packaging. Moisture absorption (0.24% water vapor retention per ASTM E595) is relatively controlled, but pre-baking before assembly is recommended if material has been stored in humid conditions.

Useful Resources for Engineers Working With HT-04503

Bookmark these references for material qualification, design validation, and procurement:

Official Datasheets and Documentation

• Bergquist HT-04503 Official Datasheet (PDF via mclpcb.com) — Full specification table with test methods
• Bergquist Thermal Clad Selection Guide (PDF via Digikey) — Comprehensive guide comparing all Thermal Clad dielectrics, stack-up options, and design guidelines
• Henkel Bergquist Product Portfolio — Current product listing after Bergquist acquisition by Henkel

Standards Referenced in HT-04503 Datasheet

• ASTM D5470 — Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials
• ASTM D149 — Standard Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials
• IPC-2152 — Standard for Determining Current Carrying Capacity in Printed Board Design

Distributor and Procurement

• Digikey — Bergquist Thermal Clad Products — Stock and pricing data for HT-04503 and related products
• Mouser — Bergquist IMS Materials — Alternative distributor with lead time information

Frequently Asked Questions About Bergquist HT-04503

What makes the HT-04503 a “high temperature” MCPCB material?

The designation refers to the dielectric polymer system, which is formulated to resist thermal degradation at sustained elevated temperatures. The glass transition temperature of 150°C and U.L.-certified maximum operating temperature of 140°C distinguish it from standard MCPCB dielectrics (typically Tg ~130°C, operating limit ~105–125°C). In practice this means the HT-04503 maintains its mechanical integrity, bond strength, and electrical isolation properties through repeated excursions toward 140°C, where a standard MCPCB dielectric would begin softening and losing peel strength.

What is the difference between the HT-04503 and HT-07006?

Both are High Temperature series Thermal Clad materials, but the HT-07006 uses a 6 mil (152 µm) dielectric instead of the 3 mil (76 µm) in the HT-04503. The thicker dielectric in the HT-07006 raises breakdown voltage to 11 kVAC (vs. 8.5 kVAC for HT-04503) at the cost of higher thermal resistance. Choose the HT-04503 when thermal performance is the priority and 8.5 kVAC isolation is sufficient. Choose the HT-07006 when your isolation requirements demand greater voltage margin — for instance, in 480 VAC industrial equipment where creepage and clearance requirements plus safety margins push isolation needs above what the 3 mil product provides.

Can the Bergquist HT-04503 be used for double-sided or multilayer MCPCB?

Single-sided construction (one copper circuit layer over the dielectric and metal base) is the standard and most common configuration. Double-sided MCPCB is technically possible but requires specialized construction — typically two single-sided substrates bonded back-to-back with a thermally conductive adhesive, or use of Bergquist’s Bond-Ply adhesive films to build up multilayer assemblies with thermal vias in the dielectric. True through-hole multilayer MCPCB with the base metal as a middle layer is a specialty construction that should be explicitly discussed with your fabricator before committing to the design.

Is the Bergquist HT-04503 suitable for automotive applications?

The material properties — 150°C Tg, 140°C UL operating temperature, lead-free solder compatibility, and CTE of 25 µm/m·°C — are consistent with automotive under-hood requirements. However, “suitable” in the automotive sense requires AEC-Q component-style qualification, which is application-specific. The material passes the thermal, electrical, and mechanical benchmarks that automotive designs demand. Whether it meets your specific OEM’s supplier qualification requirements is a separate process that requires engaging Henkel/Bergquist directly through their automotive channel.

How does the HT-04503 thermal resistance compare to using thermal vias in FR-4?

An optimized via-in-pad array in FR-4, filled with thermally conductive epoxy, can achieve effective thermal conductivity of roughly 1–3 W/m-K through the via cluster — considerably less than the HT-04503 dielectric’s 2.2 W/m-K over its full surface. More importantly, the thermal path in FR-4 with vias is discontinuous and sensitive to via fill quality, while the HT-04503 dielectric provides a continuous, uniform thermal path across the entire component footprint. For component junction temperatures above ~100°C under sustained load, or for designs where thermal resistance budget is tight, the MCPCB approach using HT-04503 consistently outperforms FR-4 with thermal vias.

The HT-04503 is one of those materials that rewards the engineer who takes the time to understand its specifications properly. The thermal resistance number is exceptional, the isolation voltage is better than it has any right to be at 3 mil thickness, and the temperature capability puts it in territory that FR-4 and generic MCPCB materials simply can’t reach. Design it right, specify your fabricator’s process correctly, and this material will outlast the components mounted on it.