Bergquist HT-04503 vs HT-07006: Which High Temperature Dielectric Is Right for You?

HT-04503 vs HT-07006 is one of the most common Bergquist dielectric selection questions that lands in engineering inboxes. Both products carry the HT (High Temperature) designation, both share identical 2.2 W/m-K dielectric thermal conductivity, both have 150°C Tg and 140°C UL RTI, and both carry a 325°C/60s UL solder limit that makes them the only Thermal Clad dielectrics compatible with AuSn eutectic die attach and thermosonic gold wire bonding. On paper they look like the same material in two different thicknesses. In practice the choice between them has real consequences for thermal performance, voltage isolation, and whether your design passes safety agency certification.

This guide addresses the HT-04503 vs HT-07006 comparison head-on with the official specification data from both Henkel TDS documents and the Bergquist Thermal Clad Selection Guide, worked examples, and a direct decision table. The answer depends on three parameters — your working voltage, your thermal budget, and your target certification class — and each of those parameters points clearly toward one product or the other.

HT-04503 and HT-07006: What They Share

Before the differences, understanding what the HT polymer chemistry gives both products explains why they occupy the same product family and why engineers frequently consider both.

The HT dielectric formulation uses a polymer matrix with a glass transition temperature of 150°C — the highest Tg of any non-HPL product in the Bergquist Thermal Clad family. That 150°C Tg is what makes the HT series uniquely capable for two processes that no other standard Thermal Clad dielectric supports: AuSn eutectic solder die attach (process temperatures 280–320°C) and thermosonic gold wire bonding (substrate temperature 120–150°C during bonding). At LTI or MP dielectrics with 90°C Tg, the substrate is elastomeric at those temperatures. At HT with 150°C Tg, it remains glassy and rigid — providing the acoustic coupling surface that thermosonic bonding requires and the mechanical stability that AuSn die attach demands.

Both products are UL solder rated to 325°C/60 seconds — a specific UL 796 certification that no LTI, MP, or CML product in the Thermal Clad family achieves. Both carry 140°C UL maximum operating temperature (UL 746B) and UL 94 V-0 flammability. Both use identical 2.2 W/m-K dielectric thermal conductivity (ASTM D5470) and 4.1 W/m-K product thermal conductivity. Both are RoHS compliant, lead-free solder compatible, and available on aluminum or copper metal substrates. CTE behavior is identical: 25 µm/m°C below Tg, 95 µm/m°C above Tg. Storage modulus is identical: 16 GPa at 25°C, 7 GPa at 150°C. Peel strength is the same at 1.1 N/mm (6 lb/in).

For Bergquist PCB procurement and fabrication purposes, both products are processed through identical assembly workflows — the same reflow profiles, the same surface finish options, the same soldermask requirements, the same hipot test procedures. A fabricator qualified for HT-04503 boards is qualified for HT-07006 boards; only the specified dielectric thickness and proof test voltage change.

The Actual Differences: HT-04503 vs HT-07006 Full Specification Comparison

All values from the official Henkel Bergquist TDS documents (March 2019 issue) and the Bergquist Thermal Clad Selection Guide (document Q-6019).

HT-04503 vs HT-07006 Side-by-Side Specification Table

Parameter	HT-04503	HT-07006	Difference
Dielectric Thickness	3 mil (0.003″ / 76 µm)	6 mil (0.006″ / 152 µm)	HT-07006 is 2× thicker
Dielectric Thermal Conductivity	2.2 W/m-K	2.2 W/m-K	Identical
Product Thermal Conductivity	4.1 W/m-K	4.1 W/m-K	Identical
Thermal Resistance	0.05 °C·in²/W (0.32 °C·cm²/W)	0.11 °C·in²/W (0.71 °C·cm²/W)	HT-04503 is 2.2× lower
Thermal Impedance (TO-220 test)	0.45 °C/W	0.70 °C/W	HT-04503 is 36% lower
AC Breakdown Voltage (ASTM D149)	8.5 kVAC (TDS) / 6.0 kVAC (Sel. Guide)	11.0 kVAC	HT-07006 is higher
Typical Proof Test Voltage	1500 VDC	2500 VDC	HT-07006 is 67% higher
Dielectric Constant (Dk)	7	7	Identical
Dissipation Factor (1 kHz / 1 MHz)	0.0033 / 0.0148	0.0038 / 0.0129	Effectively identical
Capacitance	540 pF/in² (85 pF/cm²)	43 pF/cm² (approx. 277 pF/in²)	HT-04503 approximately 2× higher
Volume Resistivity	10¹⁴ Ω·m	10¹⁴ Ω·m	Identical
Glass Transition Temperature	150°C	150°C	Identical
UL Max Operating Temperature	140°C	140°C	Identical
UL Solder Limit	325°C / 60s	325°C / 60s	Identical
UL Flammability	V-0	V-0	Identical
Peel Strength	6 lb/in (1.1 N/mm)	6 lb/in (1.1 N/mm)	Identical
CTE below Tg	25 µm/m°C	25 µm/m°C	Identical
Storage Modulus @ 25°C / 150°C	16 GPa / 7 GPa	16 GPa / 7 GPa	Identical

Note on HT-04503 breakdown voltage: the standalone TDS document shows 8.5 kVAC; the Bergquist Selection Guide master table shows 6.0 kVAC. The difference reflects measurement conditions and test circuit geometry. Both documents are published by Bergquist/Henkel. Design against the more conservative 6.0 kVAC figure for voltage derating calculations.

Why Thermal Resistance Scales with Thickness

The 2.2× difference in thermal resistance between HT-04503 (0.05 °C·in²/W) and HT-07006 (0.11 °C·in²/W) is not a coincidence. Thermal resistance equals thickness divided by thermal conductivity. Since both products have identical 2.2 W/m-K dielectric conductivity and HT-07006 is exactly twice as thick, its thermal resistance is exactly 2.2× higher. There is no “premium” thermal performance at the thinner dielectric — physics determines this relationship completely. Every millikelvin of advantage that HT-04503 has over HT-07006 in thermal resistance comes entirely from the thickness difference, not from any difference in the ceramic filler or polymer chemistry.

For a 20 W power device on a 1 cm² thermal pad, this difference translates to: 2.0°C temperature rise across the HT-04503 dielectric versus 4.4°C across HT-07006. In a design with ten such devices in parallel (e.g., a 10-phase motor drive), that 2.4°C per device compounds — but since the base aluminum conducts heat laterally from the entire board area, the cumulative effect on total junction temperatures depends on device spacing and base metal thickness.

The Voltage Isolation Difference: When 480 VAC Becomes the Decision Point

The thermal disadvantage of HT-07006 exists because of physics. The voltage advantage exists for the same reason. At 6 mil thickness with identical 2.2 W/m-K conductivity, HT-07006 achieves 11.0 kVAC AC breakdown voltage and a 2500 VDC typical proof test. HT-04503 at 3 mil is limited in the Bergquist Selection Guide to applications below 480 VAC, with the explicit note: “For applications with an expected voltage over 480 Volts AC, Bergquist recommends a dielectric thickness greater than 0.003 inch (75 µm).”

That 480 VAC design boundary is the primary decision gate for HT-04503 vs HT-07006. If your working voltage exceeds 480 VAC, HT-04503 is simply the wrong specification regardless of its thermal advantage. The working voltage categories that drive this:

Working Voltage Range	Recommended HT Product	Reasoning
12–48 VDC LED and low-voltage systems	HT-04503	Well within 3 mil limit; maximize thermal performance
Up to 480 VAC (standard industrial)	HT-04503	Within Bergquist’s stated 3 mil threshold
480–690 VAC (high-voltage industrial, 690V VFDs)	HT-07006	11.0 kVAC breakdown provides adequate margin above 690V peak
600 VAC systems (North American grid)	HT-07006 preferred	848 VDC peak; 1500 VDC proof test of HT-04503 gives only 1.77× margin
Above 690 VAC (traction, grid-tie)	HT-09009 (9 mil, 20.0 kVAC)	Both HT-04503 and HT-07006 inadequate

The 600 VAC case deserves specific comment. The Selection Guide’s 480 VAC guidance is conservative but practical — it accounts for transient overvoltages, line surges, and the fact that the hipot proof test voltage must exceed the peak working voltage by a safety margin defined by the applicable product standard (IEC 62368-1, IEC 61010, IEC 60335, or product-specific). At 600 VAC peak (848 VDC), the 1500 VDC proof test of HT-04503 provides only 1.77× margin over peak — many product safety standards require a higher ratio for basic or reinforced insulation. HT-07006 at 2500 VDC proof test provides nearly 3× margin over the 600 VAC peak, which satisfies most product safety standards for basic insulation at that voltage.

HT-04503 vs HT-07006: Application-by-Application Decision Guide

LED and COB Lighting Applications

For standard packaged LED assemblies — SMT LEDs, LED modules with standard solder attach — HT-04503 is the correct specification in almost all cases. The 3 mil dielectric gives the best thermal performance (0.05 °C·in²/W), the 325°C solder limit enables AuSn die attach for COB applications, and working voltage for LED driver circuits is typically 12–48 VDC well within the 3 mil limit. The only LED application that specifically requires HT-07006 is a high-voltage direct-drive LED board operating from a rectified mains voltage above 400 VDC — an uncommon topology for IMS designs.

Automotive Electronics

Under-hood automotive applications almost universally specify HT-04503 first, because the primary selection criterion is the 140°C UL RTI — both products provide it, but HT-04503 delivers the better thermal performance. Automotive body electronics (12 V systems), gateway controllers, LED headlamp drivers, and HVAC motor control boards all fit within HT-04503’s working voltage class. HT-07006 becomes relevant in automotive when a design bridges to higher-voltage systems: 48 V mild hybrid bus (still within 3 mil limits), 400 VDC EV traction inverter gate drive isolation (where HT-07006’s isolation provides a documented margin), or when the design must comply with a safety standard requiring reinforced insulation class at voltages that exceed HT-04503’s comfortable operating range.

Industrial Power Conversion and Solid State Relays

DC-DC brick converters for 48 V bus to 12 V or 5 V — HT-04503. VFD motor drives at 480 VAC input — HT-04503 is at its stated operating boundary; specifying HT-07006 provides additional isolation headroom and may simplify the safety certification path. VFD drives at 600 VAC or 690 VAC input — HT-07006 is required. Industrial SSR assemblies for 240 VAC control (North American residential/light industrial standard) — HT-04503. Industrial SSR for 400–690 VAC (European 3-phase industrial) — HT-07006.

COB Die Attach and Wire Bonding: Same Answer for Both

When the primary selection driver is AuSn die attach or thermosonic gold wire bonding compatibility, neither HT-04503 nor HT-07006 has an advantage over the other. Both carry the 325°C/60s UL solder limit and both have 150°C Tg that maintains substrate modulus through the wire bond process. The selection between them for COB applications reverts entirely to working voltage — which determines which dielectric thickness to use — and thermal performance.

The Core Decision Table: HT-04503 vs HT-07006

Design Condition	Choose HT-04503	Choose HT-07006
Working voltage ≤ 480 VAC	✓	—
Working voltage 480–690 VAC	—	✓
Maximum thermal performance required	✓ (0.05 °C·in²/W)	— (0.11 °C·in²/W)
Highest voltage isolation at 6 mil HT	—	✓ (11.0 kVAC)
AuSn die attach process	✓	✓ (both compatible)
Gold wire bonding	✓	✓ (both compatible)
140°C UL RTI automotive under-hood	✓	✓ (both identical)
Safety standard requires 2500 VDC proof test	—	✓
Minimum dielectric thickness (thinnest board)	✓ (3 mil)	— (6 mil)
High-watt LED, COB, CPV — voltage ≤ 480 VAC	✓	—
600 VAC North American industrial power	—	✓
690 VAC European three-phase industrial	—	✓

HT-04503 vs HT-07006 vs the Broader HT Family

The HT dielectric family extends beyond these two products. HT-09009 at 9 mil dielectric thickness achieves 20.0 kVAC breakdown and a 150°C UL RTI (higher than the 140°C of HT-04503 and HT-07006) for the most demanding high-voltage and high-temperature applications. Positioning the full HT family:

Product	Thickness	Thermal Resistance	Breakdown	Proof Test	UL RTI	Primary Use
HT-04503	3 mil	0.05 °C·in²/W	6.0 kVAC	1500 VDC	140°C	Standard HT; ≤480 VAC; best thermal
HT-07006	6 mil	0.11 °C·in²/W	11.0 kVAC	2500 VDC	140°C	≤690 VAC; balanced thermal/isolation
HT-09009	9 mil	0.16 °C·in²/W	20.0 kVAC	—	150°C	High voltage, harshest environments

Useful Resources for HT-04503 vs HT-07006 Decisions

Resource	Content	Link
HT-04503 Official TDS (Henkel/mclpcb)	Full standalone datasheet: thermal, electrical, mechanical, chemical, and agency data	PDF
HT-07006 Official TDS (Henkel/mclpcb)	Full standalone datasheet for the 6 mil HT product — March 2019 Henkel issue	PDF
Bergquist Thermal Clad Selection Guide (Digikey)	Master spec table with all dielectrics side by side, voltage guidance, thermal impedance graphs	PDF
Bergquist Thermal Clad Selection Guide (tjk.com.au)	Current version Q-6019 including updated LTI family spec data	PDF
Henkel Electronics Portal	Current documentation, SDS, technical support	henkel.com/electronics
IPC-2221B	PCB design standard — creepage, clearance, and isolation distance rules governing voltage design	ipc.org

FAQs: HT-04503 vs HT-07006

Q1: Can I use HT-04503 for a 480 VAC motor drive application or should I go to HT-07006 to be safe?

Technically, 480 VAC is Bergquist’s stated upper limit for 3 mil dielectric. The peak voltage of 480 VAC RMS is 679 VDC, and HT-04503’s 1500 VDC proof test gives 2.2× margin over that peak — a margin that many basic insulation standards accept. The problem is not the math under ideal conditions. It is what happens to that margin when you account for line surges, motor back-EMF transients, and the safety classification your product requires. If your product standard requires reinforced insulation or double insulation at 480 VAC, HT-04503 does not provide enough margin under the standard’s required test voltage, and HT-07006 with its 2500 VDC proof test is the correct specification. If your standard requires basic insulation only and your transient analysis confirms no significant overvoltage, HT-04503 is acceptable at 480 VAC. In practice, engineers specifying 480 VAC industrial equipment frequently prefer HT-07006 precisely because it removes that ambiguity from the certification discussion.

Q2: HT-07006 has lower thermal resistance than HT-04503 in the product thermal conductivity measurement — is this a contradiction?

The product thermal conductivity values on the TDS show 4.1 W/m-K for both products — identical, as expected for the same dielectric chemistry. The apparent confusion arises when some third-party sources report “higher thermal conductivity” for HT-07006, which is incorrect. The thermal resistance of HT-07006 (0.11 °C·in²/W) is higher than HT-04503 (0.05 °C·in²/W) — meaning HT-07006 allows more temperature drop per watt per unit area than HT-04503. HT-04503 is the thermal performance winner. If a source states otherwise, they are either misreading the specs or confusing thermal conductivity (a material property) with thermal resistance (which combines both conductivity and thickness). HT-07006’s thicker dielectric provides more voltage isolation at the cost of higher thermal resistance — a direct physics tradeoff with no way around it.

Q3: Both products say they support AuSn eutectic solder. Does that mean I can run a 320°C die attach process on either one?

Yes — both HT-04503 and HT-07006 are UL solder rated to 325°C/60 seconds, which is the certification that validates these products for AuSn eutectic solder processes. The AuSn eutectic alloy (80Au/20Sn) melts at 280°C, with typical reflow profiles reaching 295–320°C peak. Both HT products are rated above this range. The key caveat is that this 325°C limit applies to both products only with the HT polymer chemistry — the Tg 150°C formulation. You cannot use LTI-04503, LTI-07006, or MP-06503 for AuSn die attach regardless of their dielectric thickness. The AuSn compatibility is a function of the HT polymer, not of the dielectric thickness. Between HT-04503 and HT-07006 for AuSn processes, the choice reduces to the working voltage of the end application.

Q4: Is the thermal resistance difference between HT-04503 and HT-07006 significant enough to affect real LED lifetimes?

For LED applications, junction temperature is directly correlated with lifetime through the Arrhenius relationship — every 10°C increase in junction temperature roughly halves the lumen maintenance life expectation. The thermal resistance difference between HT-04503 (0.05 °C·in²/W) and HT-07006 (0.11 °C·in²/W) creates 2.4°C more temperature rise per 10 W/cm² of LED power density across the HT-07006 dielectric. For a single 10 W LED on a 1 cm² pad, that is 2.4°C. For a 6-LED module at 60 W total, if all heat concentrates under the LEDs, it could be 5–10°C difference in the substrate temperature. Whether that translates to meaningfully shorter lifetime depends on your thermal budget’s total stack. If you have a generous heatsink and the dielectric thermal resistance is a small fraction of total thermal resistance, the difference is negligible. If the dielectric is a substantial fraction of total thermal resistance — common in fanless applications with modest heatsinks — the 2.4°C per device is worth accounting for in L70 calculations.

Q5: My fabricator quoted both products at the same price. Is there any other reason to choose one over the other beyond voltage and thermal performance?

Beyond the primary technical factors (voltage isolation and thermal resistance), a few secondary considerations sometimes tip the scale. First, availability: HT-04503 is the higher-volume product and is more commonly stocked by distributors and fabricators globally. If you need quick-turn prototype boards, HT-04503 panels are more likely to be in stock. Second, board thickness: HT-07006’s 6 mil dielectric versus HT-04503’s 3 mil contributes to overall board thickness — for tight z-axis packaging, HT-04503 produces a thinner board. Third, certification path: if your product safety standard requires documented proof testing at 2500 VDC (which some safety certification bodies require for certain industrial equipment classes), specifying HT-07006 from the start documents compliance with that requirement without the need for waiver or additional justification for using a 3 mil product. Finally, if your design is for industrial export to both 480 VAC (North America) and 690 VAC (European three-phase) markets on the same board, HT-07006 eliminates the need for a market-specific board variant.