Bergquist HT-09009: Multi-Layer High Temperature Dielectric for Advanced MCPCB

Most engineers reach for Bergquist HT-04503 or HT-07006 when specifying a Thermal Clad insulated metal substrate. Those two dielectrics cover the majority of single-layer power electronics applications cleanly. But there is a category of design where neither of them is right — one where the working voltage climbs above 1000 VDC, where multi-layer construction is non-negotiable, or where a direct ceramic substrate replacement needs to survive qualification with a 20 kVAC proof test. That’s the territory Bergquist HT-09009 was designed to own.

HT-09009 is the thickest and highest-voltage dielectric in Bergquist’s High Temperature Thermal Clad family: 9 mil (229 µm), 20 kVAC breakdown voltage, 150°C glass transition temperature, and a 150°C UL Relative Thermal Index — the highest RTI of any standard Thermal Clad product. The Selection Guide explicitly lists it under the “Multi-Layer” category of the dielectric summary table, distinguishing it from the three single-layer HT products. Understanding what that means in practice, where it gets specified, and what tradeoffs it imposes is the purpose of this guide.

What Is Bergquist HT-09009 and Where Does It Sit in the Thermal Clad Family?

Bergquist PCB materials — the full Thermal Clad product line — are insulated metal substrates (IMS) built on a three-layer architecture: copper circuit foil on top, a thermally conductive polymer-ceramic dielectric in the middle, and a metal base (aluminum or copper) below. The dielectric is glass-free, which is why Thermal Clad can achieve 2.2 W/m-K conductivity in the HT formulation while prepreg-based solutions with glass fiber carriers are limited to far lower values. The ceramic filler in the polymer matrix simultaneously enhances thermal conductivity and maintains dielectric strength at elevated temperatures — properties that cannot coexist in a conventional organic dielectric without the ceramic loading.

The HT-09009 part number follows Bergquist’s standard naming: HT = High Temperature dielectric, 090 = thermal impedance class reference, 09 = 9 mil (0.009 inch / 229 µm) dielectric thickness. It uses the same polymer-ceramic base chemistry as HT-04503 and HT-07006, scaled to a thicker dielectric layer that delivers proportionally higher breakdown voltage at the cost of proportionally higher thermal resistance. That tradeoff is the central engineering reality of every dielectric thickness selection in the Thermal Clad HT family.

Bergquist HT-09009 Complete Specifications

All specifications below are from the official Bergquist Thermal Clad Selection Guide (Digikey hosted, Bergquist/Henkel, September 2009) and represent typical properties of cured material. These are the authoritative reference values for design and specification work.

HT-09009 Thermal Properties

Parameter	HT-09009 Value	Test Method
Dielectric Thermal Conductivity	2.2 W/m-K	ASTM D5470 (Guarded Hot Plate)
Thermal Impedance	0.90 °C/W	Internal TO-220 test RD2018
Thermal Resistance	0.16 °C·in²/W (1.03 °C·cm²/W)	Calculated from ASTM D5470

The dielectric thermal conductivity of 2.2 W/m-K is identical to HT-04503 and HT-07006 — all three share the same HT polymer-ceramic formulation. What changes with thickness is the thermal resistance, which scales linearly with dielectric thickness: HT-09009 at 9 mil produces 0.16 °C·in²/W thermal resistance versus HT-07006 at 6 mil producing 0.11 °C·in²/W and HT-04503 at 3 mil producing 0.05 °C·in²/W. The thermal impedance measured in the TO-220 test configuration is 0.90 °C/W for HT-09009. For a component with a 1 cm² thermal footprint dissipating 10 W, the HT-09009 dielectric alone contributes approximately 10.3°C of temperature rise — over 3× the contribution of HT-04503 at the same power level.

HT-09009 Electrical Properties

Parameter	HT-09009 Value	Test Method
AC Breakdown Voltage	20 kVAC	ASTM D149
Dielectric Constant (Permittivity)	7	ASTM D150
Dissipation Factor @ 1 kHz	~0.004	ASTM D150

The 20 kVAC breakdown voltage is the defining electrical specification of HT-09009 and is the highest in the entire standard Thermal Clad product range. To put that in context: a design with a 1000 VDC working voltage requires a hipot test at roughly 2× working voltage plus 1000V under IEC 62477 — approximately 3000 VAC. HT-09009 at 20 kVAC provides over 6× margin above that requirement, which explains its use in high-voltage power electronics where qualification margins matter as much as the nominal specification.

HT-09009 Mechanical and Agency Properties

Parameter	HT-09009 Value	Test Method / Standard
Dielectric Thickness	9 mil (0.009″ / 229 µm)	Optical
Glass Transition Temperature (Tg)	150°C	Internal MDSC test RD2014
UL RTI (Electrical / Mechanical)	150°C / 150°C	UL 746E
Peel Strength	6 lb/in (1.1 N/mm)	ASTM D2861
Flammability	V-0	UL 94
Solder Limit Rating	325°C / 60 seconds	UL Material Standard
Lead-Free Compatible	Yes	—
AuSn Eutectic Compatible	Yes	—
RoHS Compliant	Yes	—

The UL RTI of 150°C/150°C (electrical/mechanical) is notable: it is higher than HT-04503 and HT-07006, which are both rated at 140°C/140°C. This 10°C difference in UL rating reflects the thicker dielectric’s superior resistance to thermal aging degradation in the test protocol — a meaningful advantage for designs that will be submitted for safety certification and must declare a maximum operating temperature in the product’s UL file. For applications targeting 150°C continuous operation with UL recognition — advanced automotive inverters, high-ambient industrial controls, down-hole electronics — HT-09009’s 150°C RTI is a genuine specification differentiator.

The 325°C/60-second solder limit rating covers eutectic AuSn solder, enabling bare-die assembly with gold-tin attach materials for maximum thermal performance and reliability in demanding environments.

The Full Thermal Clad Dielectric Comparison: Where HT-09009 Fits

The Bergquist Selection Guide explicitly categorizes the Thermal Clad dielectrics into tiers based on their primary application profile. Understanding the full table is essential for correct product selection.

Parameter	HPL-03015	HT-04503	HT-07006	HT-09009	MP-06503	CML-11006
Category	High Power LED	Single-Layer	Single-Layer / Multi-Layer	Multi-Layer	Single-Layer	Multi-Layer
Dielectric Thickness	1.5 mil / 38 µm	3 mil / 76 µm	6 mil / 152 µm	9 mil / 229 µm	3 mil / 76 µm	6 mil / 152 µm
Dielectric Conductivity	3.0 W/m-K	2.2 W/m-K	2.2 W/m-K	2.2 W/m-K	1.3 W/m-K	1.1 W/m-K
Thermal Resistance (°C·in²/W)	0.02	0.05	0.11	0.16	0.09	0.21
Thermal Impedance (°C/W)	0.30	0.45	0.70	0.90	0.65	1.10
Breakdown Voltage (kVAC)	2.5	6.0*	11.0	20.0	8.5	10.0
Dielectric Constant (Dk)	6	7	7	7	6	7
Glass Transition Tg (°C)	185	150	150	150	90	90
UL RTI (°C)	Pending	140/140	140/140	150/150	130/140	130/130
Peel Strength (lb/in)	5	6	6	6	9	10
AuSn Compatible	—	Yes	Yes	Yes	Yes	Yes
Solder Limit	—	325°C	325°C	325°C	300°C	260°C

*Note: The Selection Guide lists HT-04503 at 6.0 kVAC breakdown while the standalone HT-04503 TDS lists 8.5 kVAC. The standalone TDS is the more specific and reliable reference for that product. HT-09009’s 20 kVAC is consistent across both sources.

Why the Selection Guide Lists HT-09009 Under “Multi-Layer”

The Bergquist Selection Guide’s categorization reflects engineering intent, not a hard restriction on single-layer use. HT-09009 is categorized under multi-layer because its primary value proposition — very high breakdown voltage and the highest UL RTI in the HT family — becomes most relevant in multi-layer MCPCB constructions, specifically the two-layer configurations the guide describes for applications requiring a second interconnect layer, shielding, or internal heavy copper.

In a two-layer Thermal Clad construction using HT-09009 as the core dielectric between a copper circuit layer and an aluminum base, the 20 kVAC isolation allows the assembly to function as a certified isolation barrier between a high-voltage circuit layer and a second circuit layer or the chassis. This architecture appears in advanced DC-DC converters, high-voltage motor drive gate driver boards, and EV power modules where the PCB assembly itself must provide primary isolation rated for the full bus voltage.

For single-layer use, HT-09009 is perfectly valid — it simply means accepting 0.16 °C·in²/W thermal resistance in exchange for 20 kVAC isolation. Whether that tradeoff makes sense depends entirely on the design’s voltage requirements and thermal budget.

HT-09009 Applications: The Specific Designs That Need 20 kVAC Isolation

High-Voltage DC Bus Power Conversion (1000–1500 VDC)

Utility-scale solar inverters and energy storage systems now commonly operate at 1000–1500 VDC string voltage on the DC bus. At 1500 VDC, the required hipot test voltage under IEC 62477-1 for reinforced insulation approaches 6000–7000 VAC. HT-09009 at 20 kVAC delivers approximately 3× safety margin above that requirement. For the power stage MCPCB in these high-voltage inverters — where SiC MOSFETs or IGBTs switch at 1200–1700 V ratings directly on the substrate — HT-09009 is the appropriate Thermal Clad selection.

EV Traction Inverter Power Modules

Battery electric vehicle traction inverters operate at 400–800 VDC bus voltages. The power semiconductor substrates in these modules must satisfy automotive functional safety requirements (ISO 26262), AEC-Q102 qualification for substrate materials, and both working voltage and hipot test requirements across the -40°C to 150°C operating temperature range. HT-09009’s 150°C UL RTI (matching the 150°C maximum operating temperature common in EV drivetrain environments), 20 kVAC breakdown voltage, and AuSn solder compatibility for bare SiC die attachment make it a technically sound substrate specification for automotive traction inverter development.

Direct Ceramic Substrate Replacement

One of the explicit use cases in the Bergquist Selection Guide is Thermal Clad as a replacement for ceramic substrates — specifically alumina (Al₂O₃) DBC and thick-film ceramic used in power hybrid circuits. Ceramic provides very high breakdown voltage and can survive elevated temperatures, but it is brittle, expensive, geometrically constrained (limited panel sizes, no forming or punching), and requires specialized equipment for die mounting. HT-09009 brings the high-voltage capability of ceramic in a substrate that processes on standard PCB equipment, can be punched or formed, and is available in large panel formats. The Selection Guide notes that HT-09009 (with its 9 mil thickness and 20 kVAC rating) is best positioned for this ceramic replacement role among the Thermal Clad dielectrics.

Industrial High-Voltage Solid State Relays Above 1000 VAC

Solid-state relays for industrial equipment operating on 690 VAC three-phase (common in European heavy industrial power distribution) require isolation levels above what HT-07006 provides. IEC 60950 and IEC 62368 safety standards for equipment on 690 VAC systems require hipot test voltages in the range of 4000–5000 VAC for basic insulation and higher for reinforced insulation. HT-09009 at 20 kVAC provides a substantial margin above those requirements. In high-current SSR designs for industrial motor starters and contactor replacement applications, HT-09009 on an aluminum substrate handles both the isolation and the thermal management of the power semiconductor elements simultaneously.

Down-Hole Oil and Gas Electronics

Down-hole drilling electronics routinely operate at ambient temperatures exceeding 150°C, sometimes approaching 200°C for brief periods. The combination of high operating temperature and the high-voltage requirements of the power supply and control electronics in these systems points directly to HT-09009. The 150°C UL RTI, 150°C Tg, and compatibility with AuSn die attach for down-hole bare-die assembly makes HT-09009 the most appropriate Thermal Clad dielectric for this application space.

Aerospace Auxiliary Power Unit (APU) Electronics

Military and commercial aerospace power electronics — including the APU control electronics, electromechanical actuator drives, and high-voltage bus power converters in more-electric aircraft (MEA) designs — operate in environments that combine high voltage (270 VDC to 540 VDC military bus, up to 800 VDC in newer MEA architectures), elevated temperature (125–175°C ambient at the electronics bay), and strict agency certification requirements. HT-09009’s 150°C RTI and 20 kVAC breakdown voltage, combined with the AuSn solder compatibility for mil-spec die attachment, positions it for these environments.

HT-09009 Multi-Layer MCPCB Construction: How It Actually Works

The Bergquist Selection Guide describes two-layer Thermal Clad constructions using the HT dielectric family, and HT-09009 is the preferred dielectric for multi-layer builds where maximum isolation is the design driver. The construction approach for a two-layer HT-09009 board works as follows:

A copper circuit foil (layer 1) is laminated to the top surface of the HT-09009 dielectric. The bottom surface of the dielectric is bonded to a second copper layer (layer 2) or directly to the aluminum or copper base. Where a second copper layer is used between the dielectric and the metal base, that internal copper layer can serve as a heavy copper heat spreader, a power plane, or a ground plane. Thermal vias can connect from the top circuit layer through the internal copper layer to the base metal, though via isolation in the aluminum base requires the same insulating plug fill process as in single-layer MCPCB construction.

The guide includes a modeled thermal comparison showing that with proper via utilization, two-layer Thermal Clad constructions using HT dielectrics achieve device case temperatures competitive with single-layer designs — the additional copper layer and via thermal path partially compensate for the higher dielectric thermal resistance. Without vias, the additional thermal resistance of HT-09009 is fully added to the thermal stack.

Thermal Via Design for HT-09009 Multi-Layer Boards

Because HT-09009’s 0.16 °C·in²/W thermal resistance is the highest in the HT family, thermal via design is more critical than for HT-04503 or HT-07006. For power devices mounted on HT-09009 multi-layer boards, a thermal via array under the device thermal pad — connecting through the upper dielectric and internal copper to the base metal via the lower dielectric — provides a parallel thermal path that significantly reduces effective thermal resistance. The via fill material, drill diameter, and via pitch all affect the improvement, and thermal simulation using the substrate manufacturer’s thermal parameters is strongly recommended before committing to a via pattern for production.

HT-09009 vs Competing High-Voltage MCPCB Solutions

Solution	Breakdown Voltage	Thermal Resistance	Temperature Rating	Process Compatibility	Cost
Bergquist HT-09009	20 kVAC	0.16 °C·in²/W	150°C UL RTI	Standard MCPCB	Medium
Bergquist HT-07006	11 kVAC	0.11 °C·in²/W	140°C UL RTI	Standard MCPCB	Medium
Alumina (Al₂O₃) DBC	Very high	Very low	300°C+	Specialized ceramic	High
AlN DBC	Very high	Extremely low	300°C+	Specialized ceramic	Very High
Standard FR-4 with TIM	Limited (~1 kV)	Poor (6+ °C/W effective)	130–170°C Tg	Standard PCB	Low
Generic MCPCB 1.0 W/m-K	Varies	~0.6 °C/W per cm²	Varies	Standard MCPCB	Low

HT-09009 fills the space between standard Thermal Clad MCPCB products (adequate for up to ~600 VAC working voltage in the case of HT-07006) and ceramic DBC (optimal performance but specialist process, high cost, size constraints). For applications that need more than 11 kVAC isolation in a standard PCB process flow, HT-09009 is the only Bergquist standard product that delivers it.

Design Considerations Specific to HT-09009

Managing the Higher Thermal Resistance

The thermal resistance of HT-09009 (0.16 °C·in²/W) is 3.2× that of HT-04503 (0.05 °C·in²/W). For a design migrating from HT-04503 to HT-09009 driven by voltage requirements, that thermal resistance increase must be absorbed somewhere in the thermal budget. Practical approaches include: increasing the copper circuit layer weight to improve lateral heat spreading before heat reaches the dielectric; increasing aluminum base thickness to improve spreading resistance in the base layer; reducing component power dissipation through circuit optimization; accepting a lower maximum ambient operating temperature; or designing a more aggressive heatsink or cold plate.

If the thermal budget cannot absorb the HT-09009 thermal resistance penalty, the design may need to use HT-07006 (11 kVAC) and verify that the lower breakdown voltage remains within safety factor requirements — or redesign the power architecture to reduce bus voltage.

IEC 60664 Creepage and Clearance Compliance

As with HT-07006, HT-09009’s 20 kVAC dielectric breakdown voltage addresses vertical isolation only. Horizontal creepage and clearance between conductors at different potentials still must comply with IEC 60664-1 for the design’s working voltage, overvoltage category, and pollution degree. The CTI of the HT dielectric family is 600 (IEC 60112, Material Group I), which gives the most favorable creepage distance requirements under IEC 60664. For 1000 VDC working voltage at Pollution Degree 2, the minimum creepage distance under IEC 60664-1 for CTI Group I material is approximately 8–10 mm depending on overvoltage category — these horizontal distances must be realized in the PCB layout regardless of the substrate’s vertical isolation rating.

Specifying HT-09009 to Fabricators

When ordering HT-09009 MCPCB fabrication, include these elements in your drawing notes and purchase specification: dielectric: Bergquist Thermal Clad HT-09009 (9 mil), no generic substitution without written engineering approval; base metal alloy and thickness (e.g., 5052 aluminum, 1.5 mm or 2.0 mm); copper circuit foil weight (1 oz, 2 oz, or 3 oz); surface finish (ENIG is recommended for AuSn and wirebond applications, lead-free HASL for standard SMT); required hipot test voltage and dwell time; IPC Class 2 or Class 3 per application; whether via isolation plugs are required for plated through-holes. Confirm the fabricator has specific experience with Bergquist Thermal Clad HT materials and understands the via isolation requirements — not all MCPCB shops are equipped for 9 mil dielectric work with 20 kVAC test requirements.

Useful Resources for Bergquist HT-09009 Design and Procurement

Resource	Content	Link
Bergquist Thermal Clad Selection Guide (Digikey PDF)	Complete family comparison table including HT-09009, dielectric selection methodology, multi-layer construction guidance, fabrication recommendations	Digikey PDF
Bergquist HT-07006 Datasheet (Henkel)	Adjacent product reference: 6 mil HT dielectric at 11 kVAC — useful for comparison when evaluating HT-09009 vs HT-07006 tradeoffs	mclpcb.com PDF
Bergquist HT-04503 Datasheet (Henkel)	3 mil HT baseline; use for thermal resistance comparison against HT-09009	mclpcb.com PDF
Henkel Electronics Portal	Current Bergquist Thermal Clad product documentation, Safety Data Sheets, technical support	henkel.com/electronics
IEC 60664-1	Insulation coordination for equipment — creepage and clearance requirements at high working voltages	iec.ch
IEC 62477-1	Safety requirements for power electronic converter systems — hipot test voltage derivation for solar inverters, drives	iec.ch
IPC-2221B	Generic PCB design standard — current capacity, clearance, and via design applicable to MCPCB	ipc.org
Digikey — Bergquist Thermal Clad	Stock, pricing, and ordering for Bergquist MCPCB panel and circuit products	digikey.com

FAQs: Bergquist HT-09009

Q1: Why is HT-09009 listed under “Multi-Layer” in the Bergquist Selection Guide while HT-04503 and HT-07006 appear under “Single-Layer”?

The categorization in the Bergquist Selection Guide reflects the primary engineering use case for each product, not a hard restriction. HT-09009’s 9 mil thickness and 20 kVAC breakdown voltage are most relevant in multi-layer MCPCB constructions where the dielectric must provide primary isolation between a high-voltage circuit layer and a second copper layer or the metal base — applications where reinforced or double insulation is required by the safety standard and the substrate is the isolation element. That said, HT-09009 is entirely valid for single-layer use cases where the application simply needs 20 kVAC isolation in a single dielectric layer. The multi-layer designation is best understood as “optimized for multi-layer” rather than “restricted to multi-layer.”

Q2: What is the practical significance of HT-09009’s 150°C UL RTI versus 140°C for HT-04503 and HT-07006?

The UL Relative Thermal Index (RTI) is the continuous operating temperature at which the material maintains its electrical and mechanical properties to UL’s satisfaction per UL 746B aging test methodology. When a product is submitted for UL certification, the maximum declared operating temperature in the UL file cannot exceed the substrate’s UL RTI. For a product targeting 150°C maximum operating temperature — common in automotive inverters, EV chargers, and industrial equipment near heat sources — HT-04503 and HT-07006 at 140°C RTI cannot support that certification temperature. HT-09009 at 150°C RTI can. This one specification difference directly affects whether a product can be certified for 150°C continuous operation without using a more expensive ceramic substrate. For HT-04503 or HT-07006, the workaround is either accepting a 140°C certified maximum temperature or conducting additional thermal testing — HT-09009 eliminates that constraint.

Q3: How does HT-09009 compare to alumina DBC for high-voltage power electronics, and when would you choose one over the other?

This is the core selection decision for engineers designing above 600 VAC. Alumina (Al₂O₃) Direct Bond Copper (DBC) provides lower thermal resistance than HT-09009 and inherently higher breakdown voltage in thick tiles, but it requires specialized ceramics processing equipment for fabrication, has practical panel size limitations compared to standard MCPCB, is brittle (it cannot be punched, formed, or drilled without risk of cracking), carries a cost premium of 5–15× versus standard MCPCB, and has limited via options. HT-09009 processes on standard PCB equipment, can be punched and formed, is available in large panel formats, has no brittleness risk in handling, and costs far less per unit area. The tradeoff is thermal resistance: AlN DBC achieves 0.02–0.04 °C·in²/W versus HT-09009 at 0.16 °C·in²/W. The selection comes down to whether the thermal budget can be met with HT-09009’s thermal resistance. If it can — which is the case in many high-voltage but moderate watt-density designs — HT-09009 delivers the voltage capability of ceramic in a process-friendly, cost-effective substrate.

Q4: Can HT-09009 be used with bare-die SiC or GaN devices, and what surface finish and assembly process does it require?

Yes — HT-09009’s 325°C/60-second solder limit rating and AuSn eutectic solder compatibility make it suitable for bare-die SiC and GaN assembly. The Bergquist Selection Guide specifically addresses direct die attachment as an application for HT dielectrics, noting that ENEPIG (Electroless Nickel/Electroless Palladium/Immersion Gold) is recommended for gold wire bonding and ENIG (Electroless Nickel/Immersion Gold) for aluminum wire bonding. For eutectic AuSn die attach at 280–320°C, ENIG is the standard surface finish. The die attach process for SiC on HT-09009 should be developed with care for the substrate’s thermal expansion coefficient (CTE ~25 µm/m·°C below Tg) relative to the SiC die (CTE ~3–4 µm/m·°C) — the CTE mismatch is substantial and requires appropriate die attach material selection and package design to manage thermal cycling stress on the solder joint. This is not an HT-09009-specific constraint; it applies to all organic-based MCPCB with bare SiC or GaN die.

Q5: Is there a newer or updated version of the Bergquist HT-09009 datasheet beyond the 2009 Selection Guide, and how do I access it?

The Bergquist Thermal Clad Selection Guide (September 2009) remains the primary published reference for the HT-09009 dielectric characteristics, as Bergquist/Henkel typically issues individual TDS documents for high-volume products (HT-04503, HT-07006) and covers lower-volume products like HT-09009 in the Selection Guide. The Henkel Electronics product portal (henkel.com/electronics) is the authoritative source for current documentation — if an individual HT-09009 TDS has been issued since 2009, it will be found there. For design work, the Selection Guide values (20 kVAC, 0.16 °C·in²/W, 150°C RTI) are consistent across all secondary references and can be used with confidence as design parameters, with the standard caveat from Bergquist that material should be tested in your specific application before production commitment. For formal procurement specification, request a current TDS from your Bergquist/Henkel sales contact or authorized distributor before finalizing drawing notes.

Conclusion

Bergquist HT-09009 is the high-voltage ceiling of the Thermal Clad HT family. Its 20 kVAC breakdown voltage, 150°C UL RTI, and 2.2 W/m-K dielectric thermal conductivity address a specific class of power electronics design where neither standard MCPCB products nor the cost and fragility of ceramic DBC is the right answer. The thermal resistance penalty — 0.16 °C·in²/W versus 0.05 °C·in²/W for HT-04503 — is real and must be accounted for in the thermal budget before committing to HT-09009. But for designs targeting 1000 VDC or higher bus voltages, 150°C continuous operating temperature with UL certification, direct ceramic replacement in high-voltage power modules, or multi-layer MCPCB construction with reinforced isolation, HT-09009 is a technically sound choice that processes in standard MCPCB fabrication and delivers its 20 kVAC rating with the same reliability and agency certifications as the rest of the Thermal Clad family.