Bergquist HT-04503 MCPCB: Datasheet, Specifications & Design Guide

If you’re designing power electronics, high-brightness LED lighting, solid-state relays, or motor drives, thermal management is the problem that doesn’t go away by itself. Standard FR-4 boards have thermal conductivity around 0.2–0.3 W/m-K. That’s roughly the same as a piece of wood. For a power board where a single MOSFET is dissipating 5–15 watts in a confined footprint, that number isn’t just inadequate — it’s a reliability failure waiting to happen.

The Bergquist HT-04503 is one of the most specified thermal management substrates in high-power electronics. It’s a Thermal Clad Metal Core PCB (MCPCB) dielectric engineered specifically for high-temperature, high-watt-density applications where standard MCPCB dielectrics aren’t enough. This article covers the complete HT-04503 datasheet, explains every key specification and what it means in practice, compares it to other Thermal Clad materials in the family, and gives you a design and fabrication guide for implementing it correctly.

What Is Bergquist Thermal Clad and How Does HT-04503 Fit In?

Bergquist (now part of Henkel following a 2014 acquisition) developed the Thermal Clad product family as an insulated metal substrate (IMS) platform — a three-layer construction consisting of a copper circuit foil, a thermally conductive polymer-ceramic dielectric layer, and an aluminum or copper metal base that acts as the primary heat spreader.

The key to Thermal Clad’s performance is not in the metal substrate — any aluminum PCB has a metal base. The differentiation sits entirely in that dielectric layer. Bergquist’s proprietary polymer-ceramic blend achieves very high thermal conductivity within a thin, electrically isolating dielectric, without sacrificing the dielectric breakdown voltage that isolation requires. The polymer matrix is chosen for electrical isolation, resistance to thermal aging, and high bond strength. The ceramic filler enhances thermal conductivity and maintains dielectric strength at very thin thicknesses — maintaining those properties even at the 3 mil (76 µm) thickness of HT-04503.

The HT designation in HT-04503 stands for High Temperature. It’s the dielectric formulation designed for applications where operating temperatures are elevated continuously — motor drives, solid state relays, power converters in confined enclosures, and high-wattage LED applications where junction temperatures push the limits of what standard MCPCBs can sustain. The “04503” part of the part number encodes key construction parameters: 045 = 4.5 oz (referring to the product thermal impedance category) and 03 = 3 mil (0.003 inch / 76 µm) dielectric thickness.

As a leading Bergquist PCB fabrication material, the HT-04503 sits at the top of the standard single-layer Thermal Clad dielectric family in terms of thermal resistance performance, and is available on both aluminum and copper metal substrates.

Bergquist HT-04503 Full Specifications: Complete Datasheet Data

The following specifications are extracted from the official Bergquist / Henkel HT-04503 technical datasheet and represent typical values based on standardized test methods.

Thermal Properties

Parameter	HT-04503 Value	Test Method
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 (UL)	140°C	UL 796
Max Soldering Temperature	325°C	UL 796

The “Product Thermal Conductivity” of 4.1 W/m-K is the system-level figure that includes the copper circuit layer and the aluminum or copper substrate in the calculation. The “Dielectric Thermal Conductivity” of 2.2 W/m-K represents the dielectric layer alone, measured by ASTM D5470 — the controlled, comparable figure used when benchmarking dielectric materials against each other. The thermal resistance of 0.05 °C·in²/W is the spec that matters most for thermal design calculations.

Electrical Properties

Parameter	HT-04503 Value	Test Method
Dielectric Constant (Dk)	7	ASTM D150
Dissipation Factor	0.0033 @ 1 kHz / 0.0148 @ 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	2000 V/mil (80 kV/mm)	ASTM D149
AC Breakdown Voltage	8.5 kVAC	ASTM D149

The relatively high Dk of 7 is a consequence of the ceramic filler content that gives the dielectric its thermal conductivity — higher ceramic content gives better thermal performance but also raises the dielectric constant. For power electronics and LED applications, this is not a problem. For impedance-controlled RF/microwave designs, MCPCB materials are not the appropriate substrate anyway.

The 8.5 kVAC breakdown voltage at 3 mil (76 µm) dielectric thickness is particularly important for mains-connected power electronics. For designs with expected voltages above 480 VAC, Bergquist recommends using a dielectric thickness greater than 3 mil — at which point HT-07006 (6 mil dielectric) or HT-09009 (9 mil dielectric) become appropriate choices within the HT family.

Mechanical Properties

Parameter	HT-04503 Value	Test Method
Color	White	Visual
Dielectric Thickness	0.003″ (76 µm)	Visual
Peel Strength @ 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 @ 25°C	16 GPa	ASTM 4065
Storage Modulus @ 150°C	7 GPa	ASTM 4065

The peel strength of 6 lb/in confirms reliable copper adhesion to the dielectric under thermal cycling and mechanical stress. The CTE of 25 µm/m·°C below Tg is relevant for solder joint reliability calculations — this value is dominated by the aluminum substrate’s CTE (~22 ppm/°C) and copper’s CTE (~17 ppm/°C) in the assembled system.

Chemical and Environmental Properties

Parameter	HT-04503 Value	Test Method
Water Vapor Retention	0.24% wt.	ASTM E595
Outgassing — Total Mass Loss (TML)	0.28% wt.	ASTM E595
Collect Volatile Condensable Material (CVCM)	0.01% wt.	ASTM E595

Agency Ratings and Durability

Parameter	HT-04503 Rating	Standard
UL Maximum Operating Temperature (RTI)	140°C	UL 746B
UL Flammability	V-0	UL 94
Comparative Tracking Index (CTI)	0/600	ASTM D3638 / IEC 60112
UL Solder Limit Rating	325°C / 60 seconds	UL 796

The CTI of 600 — the maximum value in the IEC 60112 classification system — means HT-04503 achieves Material Group I status, the highest level of resistance to electrical tracking. This is significant for safety-certified products where spacing requirements depend on CTI material group.

The UL solder limit rating of 325°C/60 seconds enables Eutectic Gold/Tin (AuSn) solder use, which requires higher process temperatures than standard SAC305 lead-free solder. This capability distinguishes HT-04503 from general-purpose MCPCB materials and makes it appropriate for high-reliability assemblies where AuSn solder joints are specified.

Bergquist Thermal Clad Family Comparison: HT-04503 vs HT-07006 vs MP-06503

Understanding where HT-04503 fits within the broader Bergquist Thermal Clad product family helps engineers choose the right dielectric for their application.

Thermal Clad Dielectric Comparison Table

Parameter	HT-04503	HT-07006	MP-06503	HPL-03015
Dielectric Thickness	3 mil (76 µm)	6 mil (152 µm)	3 mil (76 µm)	1.5 mil (38 µm)
Thermal Impedance (°C/W)	0.45	0.70	0.65	0.30
Thermal Resistance (°C·in²/W)	0.05	0.11	0.09	0.02
Dielectric Thermal Cond. (W/m-K)	2.2	2.2	1.3	3.0
Breakdown Voltage	8.5 kVAC	11.0 kVAC	8.5 kVAC	2.5 kVAC
Dielectric Constant (Dk)	7	7	6	6
Glass Transition Temp (Tg)	150°C	150°C	90°C	185°C
UL Max Operating Temp	140°C	140°C	130°C	See note
Peel Strength (N/mm)	1.1	1.1	1.6	0.9
RoHS / Lead-free Compatible	Yes	Yes	Yes	Yes
AuSn Compatible	Yes	Yes	Yes	—
Primary Use Case	High temp, high power density	High voltage + high temp	General purpose	Ultra-thin, high-brightness LED

HT-04503 is the correct choice when: operating temperature is sustained above 130°C, applications require AuSn solder compatibility, the lowest thermal resistance with adequate voltage isolation is the priority, and the board will cycle through extreme thermal ranges.

HT-07006 shares identical dielectric thermal conductivity (2.2 W/m-K) with HT-04503 but at twice the dielectric thickness (6 mil). This doubles the breakdown voltage to 11.0 kVAC and increases thermal resistance to 0.11 °C·in²/W. The HT-07006 is the right call when working voltage exceeds 480 VAC, or where the design is operating at the boundary of the HT-04503 isolation margin.

MP-06503 (Multi-Purpose) is the general-purpose entry in the Thermal Clad family — same 3 mil dielectric thickness as HT-04503 but with lower dielectric thermal conductivity (1.3 W/m-K vs 2.2 W/m-K) and a lower Tg of 90°C. It costs less and works well for moderate-temperature applications below 130°C continuous. For applications that don’t push sustained temperatures above that threshold, MP-06503 provides a cost-effective alternative to HT-04503.

HPL-03015 (High Power Lighting) is the ultra-thin dielectric at 1.5 mil — the thinnest in the Thermal Clad family. It delivers the lowest thermal resistance (0.02 °C·in²/W) and highest thermal conductivity (3.0 W/m-K) but at a significantly lower breakdown voltage of 2.5 kVAC. HPL-03015 is designed specifically for LED applications operating at lower voltages (typically 12–48 V) where the voltage isolation requirement is modest but thermal performance at the LED package is critical.

HT-04503 Applications: When Is It the Right Substrate?

Power Conversion and Switch-Mode Power Supplies

In switch-mode power supplies handling significant power density, MOSFETs and GaN devices can generate localized heat fluxes that FR-4 simply cannot handle. HT-04503 on an aluminum substrate provides a thermal path directly from the device thermal pad through the 3 mil dielectric into the aluminum base, which then conducts heat to the chassis or an external heat sink. The thermal resistance of 0.05 °C·in²/W means that a 1 cm² power device dissipating 20 W produces a temperature drop across the dielectric of only 0.05 × 20/6.45 = approximately 0.15°C — negligible compared to the junction-to-case resistance of the device itself. That’s the value proposition: the substrate stops being the bottleneck.

Motor Drives and Solid State Relays

Motor drive applications subject MCPCB substrates to extended high-temperature operation combined with thermal cycling as the motor starts, runs, and stops. The HT-04503’s Tg of 150°C and UL RTI of 140°C give engineers a genuine continuous-use margin above the 130°C maximum that general-purpose MCPCB materials provide. In solid-state relay applications, the combination of high sustained temperature, AuSn solder compatibility, and UL V-0 flammability rating are often all required simultaneously — which is exactly the combination HT-04503 was designed to deliver.

High-Power LED Lighting

High-brightness LEDs — particularly COB (chip-on-board) arrays and high-wattage single emitters — generate heat fluxes at the junction that must be removed as efficiently as possible to maintain lumen output and extend lifespan. Bergquist’s Thermal Clad HT-04503 has been specifically proven in high-power LED applications. The white color of the dielectric provides an incidental benefit in LED applications: it enhances the reflectivity of the PCB surface, contributing to the overall efficiency of the lighting fixture by reflecting light that would otherwise be absorbed by the board surface.

Solar Receivers and Photovoltaic Applications

Concentrating solar panel systems use optical elements to focus sunlight onto small receiver areas, creating extreme local heat flux on the receiving electronics. HT-04503’s thermal performance, high operating temperature rating, and environmental robustness make it a listed application in the official Bergquist datasheet.

Heat-Rails

The “Heat-Rail” application is a configuration where Thermal Clad boards are used not just as a PCB substrate but as a structural thermal management component — a rail that simultaneously provides the circuit interconnect function and conducts heat from components along the length of the rail to heat dissipation points. This is common in aircraft avionics and telecommunications base station equipment.

HT-04503 Design Guide: Stackup, Substrate, and Layout Recommendations

Choosing the Metal Substrate: Aluminum vs Copper

HT-04503 is available on both aluminum and copper metal substrates. The choice is driven by several factors:

Parameter	Aluminum Substrate	Copper Substrate
Thermal Conductivity	~160–205 W/m-K	~385 W/m-K
Weight	Low (~2.7 g/cm³)	High (~8.9 g/cm³)
CTE	~22 ppm/°C	~17 ppm/°C
CTE match to copper circuit	Moderate	Better
Typical Alloy	5052 (recommended)	1100
Relative Cost	Lower	Higher (2–4×)
Best For	LED, power supplies, most applications	Very high power density, CTE-sensitive devices

The 5052 aluminum alloy is Bergquist’s recommended substrate for most applications — it offers good thermal conductivity and good mechanical strength. For designs with extremely high power density or applications where the CTE mismatch between the aluminum substrate and bare-die semiconductor devices causes reliability concerns, the copper substrate reduces CTE mismatch and increases the lateral heat spreading significantly.

Standard aluminum substrate thickness choices are 0.6mm, 0.8mm, 1.0mm, 1.5mm (most common), and 2.0mm. Thicker substrates improve rigidity and heat spreading but add weight and material cost.

Circuit Layer: Copper Weight Selection

The copper circuit layer in HT-04503 MCPCB construction is certified per IPC-4562 (area weight requirement) rather than nominal thickness measurement. Standard copper weights and their implications for current-carrying and thermal performance:

Copper Weight	Nominal Thickness	Common Applications
1 oz (35 µm)	35 µm	Low to medium current signal and power traces
2 oz (70 µm)	70 µm	Medium-high current power electronics (most HT-04503 designs)
3 oz (105 µm)	105 µm	High current applications, motor drives

Higher copper weight increases current-carrying capacity and improves lateral heat spreading in the copper layer before heat transfers through the dielectric. However, heavier copper requires adjusted etching processes and may require double-pass solder mask printing due to the depth differential between etched trace surfaces and base board.

Layout and Pad Design for High-Power Components

For power devices (MOSFETs, IGBTs, LEDs), the thermal pad design directly determines how effectively heat transfers from the device into the HT-04503 dielectric and substrate system. Key design principles from Bergquist’s fabrication guidelines and MCPCB design-for-manufacturability best practices:

Maximize the thermal pad area in contact with the copper circuit layer. For power devices with an exposed thermal pad, extend the copper pad area beyond the minimum footprint by at least 200% of the device base area where board real estate allows. More copper pad area means more dielectric cross-section conducting heat downward into the aluminum.

Use thermal via arrays under power devices if the design uses a multi-layer or thermal via configuration. Via arrays of 0.3mm diameter at 1.0mm pitch, filled with thermally conductive material, improve vertical heat conduction and prevent hot-spot formation.

Maintain minimum insulation clearance of 0.2mm between SMD pads and any exposed metal substrate edge. For mains-voltage designs, consult safety standards for required creepage distances — circuit design is the most important consideration for safety agency compliance, as noted in Bergquist’s own selection guide. A 45° chamfer is recommended on edge connectors.

Vias and Through-Holes on HT-04503 MCPCB

Through-holes on MCPCB substrates require careful attention because the metal base must be isolated from plated holes to prevent short circuits. For HT-04503 boards:

The minimum punched non-plated through-hole diameter is 0.030″ (0.76mm). Drilled and plated via minimum hole size is 0.010″ (0.25mm). For through-holes that must pass through the aluminum substrate without shorting to it, a common approach is to drill an oversized hole in the metal core (typically 2× the final hole diameter), fill it with thermally and electrically insulating resin, allow full cure, then drill the final hole size through the filled plug. This isolates the plated barrel from the metal substrate. Most MCPCB designs favor surface-mount components specifically to avoid the complexity of through-hole isolation.

Surface Finish Selection

The surface finish on HT-04503 MCPCB copper traces affects solderability, wire bonding capability, and long-term oxidation resistance. Common options:

Lead-free HASL (Hot Air Solder Level) is the most economical option and works well for standard SMT assembly with larger component pads. ENIG (Electroless Nickel / Immersion Gold) is recommended for wire bonding applications (required with the aluminum wire bonding capability that HT dielectrics support), fine-pitch QFN or BGA footprints, and applications requiring long shelf life. OSP (Organic Solderability Preservative) is suitable for immediate assembly in controlled production environments where extended shelf life isn’t required.

For high-reliability applications using Eutectic AuSn solder — where HT-04503’s 325°C/60s UL solder rating comes into play — ENIG finish is standard.

Solder Mask

White solder mask is standard for HT-04503 boards in LED applications, where the white surface provides reflectivity above 85% to maximize light extraction efficiency. Black solder mask is used for products where aesthetics call for it or where visible light reflection is not desired. The two-pass solder mask printing process is often used with heavier copper weights (2 oz and above) to ensure full coverage over the trace height differential.

Bergquist HT-04503 vs FR-4: Understanding the Thermal Difference

The thermal resistance comparison between HT-04503 MCPCB and standard FR-4 is worth quantifying explicitly, because the numbers explain why FR-4 simply cannot serve in high-power-density applications.

Substrate	Thermal Conductivity	Thermal Resistance (1.5mm board, 1 cm² footprint)
Standard FR-4	~0.25 W/m-K	~6 °C/W
High-Tg FR-4	~0.30 W/m-K	~5 °C/W
Generic MCPCB (1.0 W/m-K dielectric)	~1.0 W/m-K	~0.6 °C/W
Bergquist MP-06503	1.3 W/m-K dielectric	0.09 °C·in²/W
Bergquist HT-04503	2.2 W/m-K dielectric	0.05 °C·in²/W
Bergquist HPL-03015	3.0 W/m-K dielectric	0.02 °C·in²/W

For a 1 cm² device dissipating 10 W, FR-4 imposes roughly 60°C of temperature rise across the dielectric. HT-04503 at 0.05 °C·in²/W imposes approximately 0.77°C for the same area and power. The difference between a substrate that allows 10 W/cm² and one that doesn’t is frequently the difference between a working product and a burned-out field return.

Useful Resources for Bergquist HT-04503 MCPCB Design

Resource	What You’ll Find	Link
Bergquist HT-04503 Official Datasheet (PDF)	Full thermal, electrical, mechanical, and agency rating specifications	mclpcb.com (datasheet host)
Bergquist Thermal Clad Selection Guide (Digikey PDF)	Complete Thermal Clad product family guide including all dielectric comparisons and design recommendations	media.digikey.com
Bergquist MP-06503 Datasheet (PDF)	Comparison reference: Multi-Purpose Thermal Clad dielectric specs	mclpcb.com
Bergquist HT-07006 Datasheet (PDF)	Comparison reference: 6 mil HT dielectric for higher voltage applications	mclpcb.com
Henkel / Bergquist Product Portal	Current Thermal Clad documentation and request access	henkel.com/electronics
IPC-2221 PCB Design Standard	General PCB design for manufacturability guidelines applicable to MCPCB design	ipc.org
ASTM D5470 Standard	Test method for thermal conductivity of dielectric materials — referenced in HT-04503 datasheet	astm.org

FAQs: Bergquist HT-04503 MCPCB

Q1: What is the actual dielectric thermal conductivity of HT-04503, and why is the “product thermal conductivity” figure higher at 4.1 W/m-K?

The dielectric thermal conductivity is 2.2 W/m-K, measured on the dielectric layer alone by ASTM D5470. The product thermal conductivity of 4.1 W/m-K is a system-level figure that includes the thermal contribution of the copper circuit layer and the aluminum substrate in the measurement stack, not the dielectric alone. When comparing dielectric materials from different manufacturers, always use the dielectric-only figure (2.2 W/m-K for HT-04503) or, better still, use the thermal resistance specification (0.05 °C·in²/W) which is a direct, application-relevant measurement. Thermal conductivity in W/m-K only becomes meaningful when combined with the material thickness — thermal resistance = thickness / thermal conductivity / area — which is why Bergquist publishes thermal resistance directly.

Q2: What is the difference between HT-04503 and HT-07006, and when should I use HT-07006 instead?

Both are in the HT (High Temperature) dielectric family and share identical dielectric thermal conductivity (2.2 W/m-K) and Tg (150°C). The difference is dielectric thickness and the performance parameters it affects. HT-04503 uses a 3 mil (76 µm) dielectric with 8.5 kVAC breakdown voltage and thermal resistance of 0.05 °C·in²/W. HT-07006 doubles the dielectric thickness to 6 mil (152 µm), raising breakdown voltage to 11.0 kVAC and increasing thermal resistance to 0.11 °C·in²/W. Bergquist recommends moving to HT-07006 (or greater dielectric thickness) for designs where expected working voltage exceeds 480 VAC. If your working voltage stays below 480 VAC and thermal performance is the primary optimization target, HT-04503 is the better choice within the HT family.

Q3: Can HT-04503 be used for double-sided or multilayer MCPCB designs?

Standard Thermal Clad HT-04503 is a single-signal-layer construction: copper circuit on top of dielectric on top of metal substrate. Double-sided or multilayer MCPCB configurations are possible but require Bergquist’s multi-layer Thermal Clad configurations (such as HT-09009 for 9 mil multi-layer dielectric), specialized bonding processes, or sequential lamination approaches using additional dielectric layers between copper layers. These are more complex builds and should be discussed directly with a qualified Thermal Clad fabricator. Standard HT-04503 is not simply doubled up for multilayer use — the metal substrate is always the single bottom reference layer.

Q4: Is HT-04503 compatible with standard PCB assembly processes, and how does soldering work on aluminum MCPCB?

Yes — HT-04503 is designed to be compatible with standard surface-mount assembly including solder paste screen printing, pick-and-place, and reflow soldering. It is lead-free compatible and RoHS compliant. The solder mask and copper pads on the circuit layer are processed exactly like standard PCB pads from the assembly line’s perspective. The critical difference versus FR-4 assembly is that the board is significantly more thermally conductive, which means the reflow oven profile may need adjustment to ensure the board itself reaches adequate solder reflow temperature — the metal substrate can act as a heat sink and draw heat away during reflow if the profile isn’t tuned. Additionally, the UL solder limit rating of 325°C/60 seconds enables AuSn eutectic solder processing, which requires higher peak temperatures than standard SAC305 lead-free solder.

Q5: How does Bergquist HT-04503 compare to generic low-cost MCPCB materials claiming similar specifications?

The generic MCPCB market offers dielectrics with stated thermal conductivity of 1.0–3.0 W/m-K at prices significantly below Bergquist materials. Several factors differentiate HT-04503: the combination of 2.2 W/m-K dielectric thermal conductivity with a 150°C Tg and 8.5 kVAC breakdown voltage in a 3 mil dielectric is a technically difficult combination that low-cost alternatives frequently fail to actually achieve consistently in production. HT-04503 carries UL 94 V-0 certification, UL 746B Relative Thermal Index of 140°C, CTI 600 (Material Group I), and full ASTM-method traceability for every specification. Generic suppliers often publish nominal dielectric thermal conductivity values measured by less stringent methods that are not comparable to the ASTM D5470 values on the Bergquist datasheet. For applications requiring UL recognition, safety agency compliance, long-term reliability in high-temperature environments, and process consistency across production lots, the certified Bergquist material is the appropriate specification — not a substitution risk.

Conclusion

The Bergquist HT-04503 is a mature, well-characterized MCPCB dielectric that earns its position as the go-to High Temperature Thermal Clad choice for high-power-density applications. Its combination of 2.2 W/m-K dielectric thermal conductivity, 0.05 °C·in²/W thermal resistance, 150°C Tg, 8.5 kVAC breakdown voltage, CTI 600 electrical tracking resistance, and AuSn solder compatibility in a 3 mil dielectric package is a genuine engineering achievement that generic alternatives consistently fail to match in certified production.

For power conversion designs, motor drives, solid-state relays, and high-power LED boards where the thermal substrate is a critical part of the reliability engineering — not just a mounting surface for components — specifying HT-04503 with the correct metal substrate, copper weight, and fabrication parameters is the right starting point. Verify your thermal budget against the 0.05 °C·in²/W thermal resistance, check your working voltage against the 8.5 kVAC breakdown margin, confirm your operating temperature against the 140°C UL RTI, and then finalize the rest of the design from there.