Get straight answers to 25 of the most common Bergquist thermal clad FAQ questions — from dielectric grades and thermal resistance to soldering, voltage ratings, and finding genuine TCLAD suppliers. Engineer-written, datasheet-backed.

If you’ve spent any time specifying IMS boards for LED or power electronics designs, you’ve almost certainly hit the same wall of questions that every engineer hits the first time through: What’s the actual difference between HT and HPL? Can this material handle a standard lead-free reflow profile? Do I really need a soldermask? What happened to Bergquist after Henkel acquired them?

This Bergquist thermal clad FAQ compiles the 25 questions that come up most often — from materials engineers evaluating the technology for the first time to experienced designers troubleshooting a production issue. Answers are drawn directly from the TCLAD selection guide, published datasheets, and real fabrication experience. No filler, no padding — just the answers.

Section 1: Material and Technology Fundamentals

Q1. What exactly is Bergquist Thermal Clad, and how does it differ from a standard aluminum PCB?

Thermal Clad is an Insulated Metal Substrate (IMS) technology built around a proprietary polymer-ceramic dielectric layer bonded between a copper circuit layer on top and an aluminum (or copper) base beneath. The technology of Thermal Clad resides in the dielectric — a polymer chosen for its electrical isolation properties and ability to resist thermal aging, combined with a ceramic filler that enhances thermal conductivity while maintaining high dielectric strength.

The critical difference from generic aluminum PCBs is that standard aluminum boards use conventional prepreg as the dielectric, which achieves 1.0–2.0 W/m·K thermal conductivity. The TCLAD dielectric achieves up to 7.5 W/m·K in the HPL-03015 grade — a 4× to 7× improvement. That performance gap translates directly to lower LED junction temperatures, longer component lifetime, and the ability to run higher watt density without exceeding thermal limits.

Q2. What does the part number mean — for example, HPL-03015 or HT-04503?

The part number encodes three pieces of information:

Part Number Segment	What It Means	Example (HPL-03015)
First letters	Dielectric family	HPL = High Power Lighting
Middle three digits	Thermal resistance × 100 (°C·in²/W)	030 = 0.30 °C·in²/W
Last two digits	Dielectric thickness in tenths of mils	15 = 1.5 mils (38 µm)

So HT-04503 means: High Temperature dielectric, 0.45 °C·in²/W thermal resistance, 3 mils (76 µm) thick. Once you internalize this convention, you can decode any Thermal Clad part number without opening a datasheet.

Q3. What dielectric families are available in the Thermal Clad lineup?

The main commercial families are: HPL (High Power Lighting) optimized for maximum thermal performance at low voltage, HT (High Temperature) offering a balance of thermal performance and high dielectric breakdown up to 6–11 kV depending on thickness, MP (Multi-Purpose) for general purpose cost-sensitive designs, and LM (Low Modulus) for formable applications where the substrate needs to be mechanically shaped after assembly. HT-04503 and MP-06503 are the most widely stocked at fabricators. HPL-03015 requires more lead time at most shops.

Q4. Is Bergquist still the manufacturer, or has the brand changed?

The short version: the material now comes from TCLAD Inc. The Bergquist Company originally developed Thermal Clad, then Bergquist was acquired by Henkel in 2014. In 2021, Polytronics Technology Corp. acquired the Thermal Clad product line from Henkel and formed TCLAD Inc., a Delaware corporation. Manufacturing remains at the 100,000 sq. ft. Innovation Center in Prescott, Wisconsin, with operations also in Frankfurt, Germany and Hsinchu City, Taiwan. All original personnel and part numbers carried over. “Bergquist thermal clad” remains the common industry reference term for the technology, but the official brand is now TCLAD.

Q5. What is the thermal conductivity of Bergquist Thermal Clad, and how is it measured?

Thermal conductivity varies by dielectric grade. The table below summarizes the main grades:

Dielectric	Thermal Conductivity	Dielectric Thickness	Thermal Resistance
HPL-03015	7.5 W/m·K	38 µm / 1.5 mil	0.30 °C/W
HT-04503	2.2 W/m·K	76 µm / 3 mil	0.45 °C/W
HT-07006	2.2 W/m·K	152 µm / 6 mil	0.70 °C/W
LM-04503	1.7 W/m·K	76 µm / 3 mil	0.45 °C/W
MP-06503	1.3 W/m·K	76 µm / 3 mil	0.65 °C/W

Measurement uses two ASTM test methods: ASTM D5470 (steady-state method, direct derived value) and ASTM E1461 (Laser Flash diffusivity, from which conductivity is calculated). Both are referenced in TCLAD datasheets. It’s worth noting that the two methods can yield slightly different values due to their differing assumptions, which is why TCLAD datasheets specify the test method alongside the conductivity figure.

Q6. What does “unit thermal resistance” mean versus “thermal resistance” on the datasheet?

These are related but not interchangeable. Unit thermal resistance (°C·in²/W) is a material property normalized per unit area — use this to calculate the actual resistance for your specific component footprint. Thermal resistance (°C/W) in most TCLAD datasheets refers to the resistance measured across a 1 in² test area.

The working formula: R_dielectric (°C/W) = Unit Thermal Resistance (°C·in²/W) ÷ Component Pad Area (in²)

For a 5mm × 5mm LED pad (0.025 in²) on HPL-03015: R = 0.02 ÷ 0.025 = 0.8 °C/W. On HT-04503: R = 0.05 ÷ 0.025 = 2.0 °C/W. That 1.2 °C/W difference at 3W dissipation means 3.6°C hotter junction temperature on HT vs HPL — significant when you’re managing LED lifetime.

Q7. What base metal options are available, and when would you use copper instead of aluminum?

Aluminum base (1100 alloy or equivalent) is standard and covers the vast majority of LED and power electronics applications. It’s lightweight, cost-effective, and thermally adequate for most designs. Copper base is available and offers higher thermal conductivity and better CTE matching to ceramic and bare die assemblies — but it comes at significantly higher cost. Per the TCLAD selection guide, 0.125″ (3.18mm) aluminum base is equivalent in cost to 0.040″ (1.0mm) copper base. Choose copper base when you need maximum lateral heat spreading, direct die attachment, or CTE compatibility with ceramic substrates. For most LED applications, aluminum is the right call.

Section 2: Design and Layout Questions

Q8. What are the key circuit design guidelines for Thermal Clad boards?

The TCLAD selection guide publishes recommended circuit design limits for standard fabrication:

Design Parameter	Minimum Recommended	Notes
Conductor width	0.004″ / 100 µm	Etching process limitation
Conductor spacing	0.004″ / 100 µm	Dielectric isolation requirement
Conductor to board edge	0.040″ / 1.0 mm	Mechanical and isolation margin
Solder mask coverage	Mandatory	Required per UL and isolation
Copper weight range	0.5 oz to 4 oz	1 oz standard for LED
Minimum drill diameter	0.020″ / 0.5 mm	Aluminum machining limitation

Note that use of a soldermask is mandatory on Thermal Clad — this isn’t optional. It’s required for UL compliance and for maintaining adequate voltage isolation at conductor edges.

Q9. Do you need thermal vias on a Thermal Clad board?

Generally no, and in most single-layer IMS designs they can actually be counterproductive. On IMS PCBs, thermal vias can be problematic since the drill penetrates through the aluminum base and isolation must be maintained through the via annular ring. The aluminum itself handles heat spreading far better than an array of via copper can. The whole point of an IMS board is that the base metal spreads heat laterally to the heatsink contact area — vias in FR-4 are a workaround for the absence of that spreading. Don’t add thermal vias to a Thermal Clad board unless there is a specific electrical reason (not thermal) to connect layers.

Q10. Can Thermal Clad boards be used in multi-layer configurations?

Yes, but it’s a specialty application. TCLAD describes configurations using Bergquist dielectrics bonded to a metal base with FR-4 type circuits or Thermal Clad circuits, depending on thermal requirements and cost objectives. Multi-layer Thermal Clad assemblies are less common than single-layer designs and require more specialized fabrication. For most LED and power supply designs, single-layer IMS is adequate and significantly simpler to fabricate and inspect. Contact TCLAD directly for guidance if your application genuinely requires a multi-layer IMS stack.

Q11. What is the minimum conductor-to-board-edge distance on Thermal Clad?

The standard recommendation from the TCLAD selection guide is 0.040″ (1.0mm) minimum from any conductor to the board edge. This accounts for both electrical isolation and the mechanical stress that occurs at the routed edge. If you’re using edge connectors, a 45° chamfer at the connector edge is recommended — and the minimum conductor-to-edge distance must still be maintained along the chamfered section. This is one of those design details that often gets overlooked in the Gerber review and causes rework on first prototypes.

Q12. What copper weight should I specify for an LED board?

For most LED designs, 1 oz copper (35 µm) is the standard and most cost-effective choice. Thermal Clad trace interconnects can actually carry higher currents than equivalent FR-4 traces of the same width because the base metal dissipates the I²R heating more effectively. Where you need higher current-carrying capacity — motor drive bus bars, high-current LED strings — 2 oz or 3 oz copper is available. Heavy copper requires modified etching chemistry and longer etch times, which your fab house needs to account for in DFM review. Specifying 2 oz on a board that only needs 1 oz adds cost without any thermal benefit, so run the trace width calculation from IPC-2221 first.

Section 3: Assembly and Soldering

Q13. Is Bergquist Thermal Clad compatible with standard lead-free reflow profiles?

Yes, with some attention to profile management. TCLAD boards are compatible with standard SAC305 lead-free reflow — peak temperatures in the 240–260°C range for 30–60 seconds are within the dielectric’s rating. The TCLAD selection guide notes the material is rated at 325°C/60 seconds for eutectic gold/tin solders, so standard lead-free profiles are well within limits. The key consideration for IMS reflow is that the aluminum base has significantly higher thermal mass than FR-4, which means your board takes longer to reach peak temperature and your oven profile needs to account for that. Profile validation on the actual board with thermocouples is essential, not optional.

Q14. What solder thickness is recommended for Thermal Clad assemblies?

The TCLAD selection guide specifies a minimum solder thickness of 0.004″ (100 µm) after reflow. This is thicker than many engineers default to for SMT. The reason is that Thermal Clad’s aluminum base has a different CTE than the component packages, and sufficient solder thickness provides compliance to absorb that differential expansion over thermal cycles. Insufficient solder thickness is one of the most common root causes of premature solder joint failure on IMS boards. Use metal stencils for solder paste application — dispensing is acceptable for secondary operations but harder to control for consistent paste volume.

Q15. What surface finishes are compatible with Thermal Clad, and which is recommended?

The TCLAD selection guide lists HASL (SnPb or lead-free), OSP, and FST (Flow Solderable Tin) as compatible finishes. In practice for LED applications, ENIG is the most commonly specified surface finish because it provides flat, coplanar pads with consistent standoff height — critical for repeatable solder joint thickness and thermal resistance at the LED interface. OSP has a 3–6 month shelf life limitation, which can be a logistics problem for boards that sit in WIP inventory before assembly. HASL is acceptable for non-critical pads and offers better shelf life than OSP. All TCLAD dielectrics are confirmed lead-free solder compatible and RoHS compliant.

Q16. Can Thermal Clad be wave soldered?

Wave soldering of IMS boards is not commonly practiced and not generally recommended for fine-pitch SMT designs. The thermal mass of the aluminum base creates uneven heating across the board during wave solder contact, and the single-layer nature of most IMS boards means all components are on one side anyway — making wave solder unnecessary for most designs. Where through-hole components must be soldered on a Thermal Clad board (pin headers, connectors), selective soldering or hand soldering is typically specified.

Q17. How should I handle and store bare Thermal Clad boards before assembly?

Per the TCLAD technical data sheets, optimal storage is at 5–25°C with a 12-month shelf life for the laminate in unopened containers. Bare fabricated boards with ENIG or HASL finish have similar storage requirements to standard PCBs: low humidity, no ESD sensitive concerns for the board itself, but moisture-sensitive components should be handled per J-STD-033. Aluminum surfaces are susceptible to oxidation if exposed — keep boards in sealed moisture barrier bags if not assembling promptly after receipt.

Section 4: Electrical and Isolation Properties

Q18. What dielectric breakdown voltage should I expect?

Breakdown voltage varies significantly by dielectric family and thickness. This is one of the most important selection criteria for any design with mains voltage or significant working voltage:

Dielectric	Thickness	Breakdown Voltage	Recommended For
HPL-03015	1.5 mil / 38 µm	2.5 kV	Low-voltage LED (< 60V)
HT-04503	3 mil / 76 µm	6.0 kV	LED, automotive, 120–240V isolated
HT-07006	6 mil / 152 µm	11.0 kV	Industrial, high-voltage
MP-06503	3 mil / 76 µm	8.5 kV	General purpose

For applications expecting voltage over 480V AC, TCLAD recommends a dielectric thickness greater than 0.003″ (76 µm). These are breakdown values, not working voltage ratings — apply your appropriate safety factor. Circuit design is the most important consideration for determining safety agency compliance; the dielectric breakdown value alone does not guarantee UL or CE compliance.

Q19. What does the UL RTI rating mean, and why does it matter?

UL RTI (Relative Thermal Index) defines the maximum long-term continuous operating temperature at which the dielectric retains at least 50% of its original electrical or mechanical properties. Many Thermal Clad products have UL ratings up to 45% higher than their glass transition temperature (Tg) — this is intentional and reflects the material’s robust long-term performance. For HT-04503, the UL RTI is 140/140°C (Electrical/Mechanical). Tg for the dielectric is nominally around 150°C. This distinction matters for product qualification under UL 746B and for thermal lifetime calculations in LED luminaire certification.

Q20. Do I need to proof-test every board after fabrication?

For production boards, yes — and the test method requires care. Due to the capacitive nature of the IMS construction, it is necessary to control the ramp-up of voltage during proof testing to avoid nuisance tripping of failure detection circuits and to prevent premature surface arcing. TCLAD documentation recommends a specific ramp rate rather than a step-apply approach. Any micro-fractures, delaminations, or micro-voids in the dielectric will break down or respond as a short under test — which is exactly what you want to detect in production, not in the field. After DC testing, the operator must verify the board is fully discharged before removing from the test fixture. This is a safety step, not just a quality step.

Section 5: Application-Specific and Supplier Questions

Q21. Is Bergquist Thermal Clad suitable for automotive applications?

Yes, and it’s widely used in automotive LED headlamp systems, EV power modules, and DC-DC converters. TCLAD’s advanced thermal management solutions are trusted in the EV sector to prevent overheating of batteries, power electronics, and control units, ensuring safe, reliable operation and charging. For direct automotive supply chain applications, your fabricator should hold IATF 16949 certification in addition to ISO 9001. The HT-04503 dielectric with its 6 kV breakdown rating and 140°C UL RTI is the most commonly specified grade for automotive IMS applications. For automotive applications under 480V bus voltages, HT-04503 provides adequate isolation margin.

Q22. Can Thermal Clad replace ceramic substrates?

In many applications, yes. Thermal Clad can replace large-area ceramic substrates and can be used as a mechanically durable support for ceramic spacers or direct bonded copper subassemblies. The copper circuit layer of Thermal Clad has more current-carrying capability than thick-film on ceramic, and it’s far more mechanically robust than DBC (Direct Bonded Copper) ceramic during handling and assembly. The trade-off is thermal conductivity: alumina ceramic runs 20–25 W/m·K and AlN runs 150–180 W/m·K — substantially higher than even the best TCLAD dielectric. For applications where the highest possible thermal conductivity is the primary constraint (high-density power semiconductor modules, for example), ceramic may still be necessary. For most LED and moderate-power electronics applications, TCLAD offers better mechanical robustness, comparable or better electrical isolation, and simpler fabrication than ceramic at lower cost.

Q23. How do I verify that my PCB fabricator is using genuine TCLAD material?

Request a material certificate (mill cert) with each production lot. This document should reference the TCLAD Inc. part number, lot number, and date of manufacture. A legitimate IMS fabricator using genuine TCLAD laminate will have this documentation available without hesitation. As a secondary check, you can request thermal conductivity test data from a sample of your production lot — genuine HPL-03015 should measure close to 7.5 W/m·K; generic substitutes typically measure 1.0–2.0 W/m·K, a difference that’s clearly detectable with standard ASTM D5470 testing. The price gap between genuine TCLAD and generic aluminum laminate is real — if your quote is suspiciously cheap for an HPL board, that’s worth investigating before committing to production.

For a broader look at IMS board sourcing options including alternative materials, engineers can also review Bergquist PCB options and alternatives at RayPCB, which covers material selection considerations from a fabrication perspective.

Q24. What certifications should a qualified Bergquist Thermal Clad fabricator hold?

The minimum credible certification set for an IMS PCB fabricator includes ISO 9001:2015 for quality management, UL 796 facility recognition for boards going into UL-listed products, and IPC-2221/IPC-A-600 for design and inspection compliance. The TCLAD selection guide states that Bergquist lab facilities are UL certified and manufacturing facilities are ISO certified. For automotive applications, IATF 16949 is mandatory in the automotive Tier supply chain. If your design is going into a CE-marked product, confirm the fab’s process documentation supports the Annex II technical file requirements for relevant directives.

Q25. What has changed in the Thermal Clad product line since the TCLAD Inc. acquisition?

From an engineer’s day-to-day perspective, not much has changed that affects design decisions. The part numbers are the same, the dielectric chemistry is unchanged, and the manufacturing facility in Prescott, Wisconsin continues to produce the same material families. TCLAD continues to innovate from its vertically integrated manufacturing center, delivering thermal management solutions for high-power density applications in LED lighting, automotive EV systems, aerospace and defense, industrial power, and power semiconductors. What has changed at the supply chain level: the company name on purchase orders and certificates of conformance is now TCLAD Inc. rather than Henkel/Bergquist. Authorized distributors including DigiKey continue to stock TCLAD laminate. If you’re working with an overseas fabricator who still refers to the material as “Henkel Bergquist,” that’s not incorrect historically — but your mill cert should now reference TCLAD Inc. as manufacturer.

Quick Reference: Dielectric Selection Summary

Application	Recommended Grade	Key Reason
High-power COB LED, < 60V	HPL-03015	Maximum thermal performance (7.5 W/m·K)
LED luminaire, mains-isolated	HT-04503	6 kV breakdown, 2.2 W/m·K
Industrial / high-voltage	HT-07006	11 kV breakdown
Automotive LED headlamp	HT-04503	6 kV isolation, 140°C RTI
EV power module	HT-04503 or copper base	Isolation + thermal performance
Cost-sensitive general use	MP-06503	Lowest cost TCLAD option
Formable / 3D shaped boards	LM-04503	Flexible after assembly

Useful Resources for Bergquist Thermal Clad Engineering

Resource	What It Contains	Where to Find It
TCLAD Inc. Official Site	Current product line, specs, contact for authorized fabs	tclad.com
TCLAD Selection Guide (DigiKey)	Full dielectric comparison, design rules, assembly guidelines	DigiKey PDF
HPL-03015 Datasheet	Full specs for the high-power lighting dielectric	mclpcb.com PDF
HT-04503 Datasheet	Full specs for the high-temperature 3 mil dielectric	mclpcb.com PDF
HT-07006 Datasheet	Full specs for the 6 mil high-voltage dielectric	mclpcb.com PDF
MP-06503 Datasheet	Specs for the multi-purpose general grade	mclpcb.com PDF
DigiKey TCLAD Catalog	Distributor product listing and stock status	DigiKey Catalog Page
IPC-2221B	PCB design standard for trace width and clearance	ipc.org
Bergquist PCB Guide at RayPCB	Material selection and fabrication overview	raypcb.com/bergquist-pcb
WE-Online IMS Design Rules	Würth Elektronik DFM rules for metal core boards	WE-online PDF
ASTM D5470	Standard test method for thermal conductivity of dielectrics	astm.org

Summary

The 25 questions above cover the majority of what engineers actually need to know when evaluating, designing with, or troubleshooting Bergquist Thermal Clad IMS boards. The technology is mature and well-documented — the TCLAD selection guide alone answers most fabrication and design questions in detail. The most common mistakes in practice are: picking the wrong dielectric grade for the voltage requirements, not accounting for aluminum thermal mass in reflow profiling, specifying insufficient solder thickness for thermal cycling reliability, and failing to verify material traceability on overseas orders.

If you have a question not covered here, TCLAD Inc.’s technical team in Prescott, Wisconsin is actively supporting the product line post-acquisition and is the authoritative source for application-specific guidance.

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