Bergquist ML-11006 Multi-Layer IMS PCB: Specifications & Application Guide

Most engineers who specify insulated metal substrate boards work with the same fundamental picture: one copper circuit layer, one dielectric, one aluminum base. Heat flows down through the dielectric into the metal — the design challenge is keeping that path as short and thermally conductive as possible. The entire Bergquist Thermal Clad family — HT-04503, HT-07006, MP-06503, HPL-03015 — is built around that single-layer architecture. But a real class of power electronics designs cannot be solved with one circuit layer. Motor drives need power and control circuitry coexisting on the same substrate. Compact DC-DC converters need double-sided component mounting. High-density power modules need shielding planes and multi-layer interconnects — while still managing heat through a metal core.

That is the design problem Bergquist ML-11006 was built for. It is the only product in the Thermal Clad family that ships in prepreg form, and it is specifically designed to serve as the thermally conductive interlayer dielectric in multi-layer IMS constructions. In the official Bergquist Thermal Clad Selection Guide, this product carries the designation CML-11006, where CML stands for Circuit Material Laminate. In distributor catalogs and fabricator documentation — particularly across Asia where this material is widely specified — it appears as ML-11006. Both refer to the same material. This guide uses both names, but CML-11006 is the Bergquist/Henkel part number to use when ordering or specifying.

Understanding ML-11006 means understanding why it exists outside the standard Thermal Clad architecture, what its unique glass-reinforced prepreg construction enables, and where the thermal resistance tradeoff it introduces is acceptable in exchange for multi-layer circuit capability.

What Is Bergquist ML-11006 and Why Does It Have a Glass Carrier?

Every standard Thermal Clad dielectric — HT, MP, and HPL — is a glass-free polymer-ceramic blend. Bergquist’s decision to exclude glass from those formulations is deliberate: glass fiber has a thermal conductivity of approximately 1 W/m-K, lower than the ceramic filler in the polymer matrix. Including glass reduces effective thermal conductivity. So for a single-layer MCPCB dielectric that is coated directly onto a metal base in a continuous process, glass-free is always the better thermal choice.

Bergquist PCB ML-11006 cannot be glass-free, because prepreg cannot be glass-free. A prepreg — a B-stage, semi-cured sheet material that flows, bonds, and fully cures under heat and pressure during lamination — needs a mechanical carrier to be handleable as a freestanding sheet. Without glass weave reinforcement, a thin polymer-ceramic film cannot be cut, stacked, registered, and loaded into a multilayer press. The glass carrier is not a performance compromise that crept in — it is the engineering prerequisite for the prepreg format that makes ML-11006 unique in the Thermal Clad lineup.

The part number encodes the key specifications: CML = Circuit Material Laminate, 110 = thermal impedance class reference of 1.1 °C/W, 06 = 6 mil (0.006 inch / approximately 150 µm) dielectric thickness. This naming convention mirrors the rest of the Thermal Clad family — the digits in HT-04503 encode 3 mil thickness, and in HT-07006 they encode 6 mil. ML-11006 at 6 mil thickness shares its thickness class with HT-07006 but delivers lower thermal conductivity due to the glass carrier, while providing the multilayer bonding capability that HT-07006 cannot offer.

Bergquist ML-11006 Complete Specifications

All values below are from the official Bergquist Thermal Clad Selection Guide (Bergquist document Q-6019, current hosted versions at tjk.com.au and Digikey). There is no standalone TDS for CML-11006 — the Selection Guide master dielectric table is the authoritative published reference for this material.

ML-11006 Thermal Properties

Parameter	CML-11006 (ML-11006) Value	Test Method
Dielectric Thermal Conductivity	1.1 W/m-K	ASTM D5470 (Extended)
Thermal Resistance	0.21 °C·in²/W	Calculated from ASTM D5470
Thermal Impedance	1.1 °C/W	Internal TO-220 test (Bergquist RD2018)

The dielectric thermal conductivity of 1.1 W/m-K is the lowest in the Thermal Clad family. Glass-free HT-04503 achieves 2.2 W/m-K, MP-06503 reaches 1.3 W/m-K, and HPL-03015 delivers 3.0 W/m-K. The glass fiber distributed through the ML-11006 dielectric matrix acts as a thermal insulator relative to the ceramic filler, reducing the composite’s effective conductivity. This directly drives the thermal resistance of 0.21 °C·in²/W — the highest of any Thermal Clad dielectric. For a component dissipating 10 W over a 1 cm² footprint, the ML-11006 interlayer contributes approximately 13.5°C of temperature rise across itself alone.

The thermal impedance of 1.1 °C/W, measured in Bergquist’s standard TO-220 test, looks high in isolation. But in a two-layer IMS construction where thermal vias connect the top circuit layer through the ML-11006 dielectric to the metal base, effective thermal impedance drops substantially — thermal via design is the primary tool for managing ML-11006’s thermal resistance, and Bergquist’s own application guidance makes this the central design recommendation for ML-11006 assemblies.

ML-11006 Electrical Properties

Parameter	CML-11006 (ML-11006) Value	Test Method
Dielectric Constant (Permittivity)	7	ASTM D150
AC Breakdown Voltage	10.0 kVAC	ASTM D149
Typical Proof Test Voltage	2500 VDC	500 V/sec ramp, 5 sec hold

The 10.0 kVAC breakdown voltage is the second-highest in the standard Thermal Clad family, behind only HT-09009 at 20.0 kVAC. At 6 mil thickness, this is consistent with the HT-07006 performance class — the glass carrier slightly reduces breakdown voltage versus the glass-free HT dielectric at equal thickness, but 10.0 kVAC is a strong isolation level for the multi-layer circuit applications where ML-11006 is used. The 2500 VDC typical proof test voltage is the fabrication electrical integrity test applied to 6 mil dielectric boards, consistent with HT-07006.

ML-11006 Mechanical and Agency Properties

Parameter	CML-11006 (ML-11006) Value	Test Method / Standard
Dielectric Thickness	6 mil (0.006″ / ~150 µm)	Optical
Glass Transition Temperature (Tg)	90°C	Internal MDSC test RD2014
UL RTI (Electrical / Mechanical)	130°C / 130°C	UL 746E
UL Flammability	V-0	UL 94
Peel Strength	10 lb/in (1.8 N/mm)	ASTM D2861
Solder Limit Rating	260°C / 60 seconds	UL Material Standard
Lead-Free Solder Compatible	Yes	—
RoHS Compliant	Yes	—

Three values here deserve direct attention from a design engineer. The peel strength of 10 lb/in (1.8 N/mm) is the highest in the entire Thermal Clad family — higher than HT-04503 (6 lb/in), MP-06503 (9 lb/in), and HPL-03015 (5 lb/in). The glass reinforcement provides a mechanical backbone for the bond between copper foil and dielectric. In multi-layer construction, that translates into delamination resistance under thermal cycling at the critical interlayer interface.

The 90°C Tg is consistent with the CML/MP dielectric chemistry class rather than the HT family at 150°C. Above 90°C the dielectric transitions to an elastomeric state with lower storage modulus and higher CTE. The Bergquist Selection Guide addresses this directly: the elastomeric state above Tg can actually relieve residual stress at solder joints and dielectric interfaces by allowing CTE mismatch stress to relax — a recognized benefit. The UL RTI of 130°C/130°C, which is 44% above the 90°C Tg, is the continuous operating temperature limit for agency-recognized products.

The solder limit of 260°C/60 seconds is the tightest constraint in the table. SAC305 lead-free reflow peaks at 245–260°C — right at this limit — so reflow profile management is required. AuSn eutectic die attach at 280–320°C is explicitly outside this limit and must not be used on ML-11006 substrates.

How ML-11006 Positions in the Full Thermal Clad Family

Complete Family Comparison: Performance vs Capability

Parameter	HPL-03015	HT-04503	MP-06503	HT-07006	ML-11006 (CML)	HT-09009
Format	Laminate	Laminate	Laminate	Laminate	Prepreg	Laminate
Dielectric Thickness	1.5 mil	3 mil	3 mil	6 mil	6 mil	9 mil
Glass Carrier	No	No	No	No	Yes	No
Thermal Conductivity (W/m-K)	3.0	2.2	1.3	2.2	1.1	2.2
Thermal Resistance (°C·in²/W)	0.02	0.05	0.09	0.11	0.21	0.16
Thermal Impedance (°C/W)	0.30	0.45	0.65	0.70	1.1	0.90
Breakdown Voltage (kVAC)	5.0	6.0	8.5	11.0	10.0	20.0
Proof Test (VDC)	—	1500	1500	2500	2500	—
Tg (°C)	185	150	90	150	90	150
UL RTI Elec/Mech (°C)	140	140/140	130/140	140/140	130/130	150/150
Peel Strength (lb/in)	5	6	9	6	10	6
Solder Limit	325°C	325°C	300°C	325°C	260°C	325°C
Multi-Layer Prepreg	No	No	No	No	Yes	No

ML-11006 occupies the lowest position on thermal performance per layer and the highest on peel strength, and it is the sole product in the family with prepreg capability for multi-layer circuit construction. The 10.0 kVAC breakdown voltage sits well above most power electronics application requirements at the voltages where two-layer IMS construction is used.

The Multi-Layer IMS Construction: Three Ways ML-11006 Is Used

Two-Layer Circuit Pair Bonded to Metal Base

This is the primary application Bergquist documents for ML-11006. The stackup from top to bottom: a top copper circuit layer carrying power components (FETs, diodes, inductors), then an ML-11006 prepreg interlayer, then a bottom copper circuit layer carrying logic, control, or gate driver circuitry, then a Thermal Clad dielectric (such as HT-04503 or LTI-04503), then the aluminum or copper metal base.

During fabrication, the ML-11006 prepreg flows and cures in a heated multilayer press, bonding the two circuit layers into an integral assembly. Power and control circuitry coexist on the same substrate, thermally managed by the metal base below — eliminating the separate power board, control board, and wire harness between them that traditional two-board architectures require.

The Bergquist Selection Guide illustrates this construction explicitly with a cross-section showing thermal vias bridging from the exposed top circuit layer through the ML-11006 interlayer and bottom circuit to the metal base. Via utilization is flagged as the critical thermal design decision in this configuration.

Single-Board Solution Without a Metal Base

ML-11006 can also be used in “ultra-thin circuit” configurations without an aluminum base. Here, ML-11006 bonds two copper-clad circuit layers, and the resulting double-sided board mounts into a heatsink pocket or bonds flat to a chassis surface. Both sides of the board carry components, maximizing component density. The Bergquist Selection Guide calls this a “ceramic submount replacement.” Heat management relies entirely on the external thermal interface. This configuration is used in compact module packaging, power hybrid assemblies, and applications where a metal base would add unacceptable thickness or weight.

FR-4 Prepreg Replacement in Mixed Constructions

Because ML-11006 is a prepreg, it can replace standard FR-4 prepreg in a mixed multilayer construction — using Thermal Clad laminates for outer copper layers and ML-11006 as the interlayer bondply. The Bergquist Selection Guide describes this directly: “Power conversion applications can enhance their performance by replacing FR-4 with Thermal Clad dielectrics in multi-layer assemblies.” Standard FR-4 prepreg has a thermal conductivity of approximately 0.3 W/m-K. Replacing it with ML-11006 at 1.1 W/m-K gives a threefold improvement in interlayer thermal conductivity — a meaningful gain for high-power-density multi-layer boards even without switching to a full metal-base IMS.

Bergquist ML-11006 Applications

DC-DC Power Conversion Modules

High-density DC-DC converters — 48 V to 12 V and 48 V to 5 V brick and half-brick formats for telecom and server applications — need power switches, rectifiers, magnetics drive, and control circuitry at the highest possible power density in a standard form factor. ML-11006 two-layer construction allows power FETs and diodes on the top copper layer and the PWM controller, gate drivers, and compensation network on the bottom copper layer, both sharing a single metal base. Interconnects between power and control stages reduce from connectors and wires to etched copper traces.

Motor Drive Control Integration

Compact motor drives represent one of Bergquist’s highlighted applications for the Thermal Clad system. The Selection Guide states that motor drives on Thermal Clad “have set the benchmark for watt-density.” ML-11006 enables gate driver and control circuitry to share a substrate with the power stage — reducing interconnect inductance between gate driver output and FET gate, improving switching noise immunity, and eliminating the separate control board and inter-board connector that add cost and failure modes in production.

Solid-State Relay and Switch Assemblies

Solid-state relay design needs the power semiconductor (SCR, triac, MOSFET output) and the control/isolation circuitry on separate circuit layers but sharing a common thermal path to the heatsink. An ML-11006 two-layer construction achieves exactly this: power output on one layer, isolated control circuitry on the other, with ML-11006 providing both the interlayer electrical isolation (10.0 kVAC breakdown) and thermal continuity to the metal base.

Power-and-Control Combined Boards in Automotive and Industrial

Any design currently using two separate boards connected by ribbon cable or wiring harness — automotive body control modules with integrated power FETs, industrial actuator and sensor assemblies, appliance motor controllers — can potentially be consolidated onto a single ML-11006 multi-layer IMS. The single-substrate design is thicker than one single-layer MCPCB but far thinner and simpler than the sum of two boards plus connectors. Assembly cost, BOM cost, and failure mode count all decrease.

ML-11006 Design Tips for Engineers

Thermal Via Design Is the Primary Lever

Given ML-11006’s thermal resistance of 0.21 °C·in²/W, thermal vias are not optional in high-power designs — they are the engineering mechanism that makes ML-11006 thermally viable for power components. Copper-plated vias drilled through the interlayer provide direct thermal paths from the top circuit layer to the bottom layer and then to the metal base. Copper’s thermal conductivity (approximately 385 W/m-K) is nearly 350 times higher than ML-11006’s 1.1 W/m-K — each via dramatically reduces effective thermal resistance in proportion to its cross-sectional area.

Practical via sizing: 0.3–0.5 mm drill diameter is typical for thermal vias. Use a pitch of 0.5–1.0 mm within the thermal pad footprint. Calculate required via count from device power dissipation and your target junction temperature, treating the via thermal resistance and dielectric thermal resistance as a parallel combination. The Bergquist Selection Guide’s modeled data shows that via-optimized two-layer Thermal Clad constructions can achieve device case temperatures competitive with single-layer designs.

Selecting Between ML-11006 Multi-Layer and HT-04503 Single-Layer

Design Factor	ML-11006 Multi-Layer	HT-04503 Single-Layer
Two separate circuit layers needed	✓ Enables this	✗ Single layer only
Power + control on one substrate	✓ Primary use case	✗ Not feasible
Thermal via array feasible in layout	✓ Compensates for lower conductivity	n/a
Continuous operation above 130°C	✗ Exceeds UL RTI	✓ 140°C UL RTI
AuSn die attach required	✗ 260°C solder limit	✓ 325°C limit
Standard SAC305 SMT reflow only	✓ Within 260°C limit with care	✓ Comfortable margin
Replacing two-board + connector assembly	✓ Consolidation saves cost	Not applicable

Solder Profiling and Assembly Notes

The 260°C/60-second solder limit requires disciplined reflow profile management. Target peak temperature at 245–255°C rather than the maximum. Keep time above liquidus (TAL) to 30–45 seconds above 217°C for SAC305. No-clean and water-soluble flux chemistries are compatible with ML-11006. Never use AuSn eutectic reflow on ML-11006 — the 280–320°C process temperature is outside the UL-rated solder limit.

Specifying ML-11006 to Fabricators

Not every MCPCB fabricator has run CML-11006 prepreg. Key elements to include in a fabrication specification: interlayer dielectric — Bergquist Thermal Clad CML-11006 (ML-11006) prepreg, 6 mil, no generic substitution without written approval; outer circuit material — specify Thermal Clad laminate or FR-4; metal base alloy and thickness; copper weight per layer; minimum hipot test voltage for the interlayer; thermal via diameter, pitch, and fill requirement; surface finish; IPC Class 2 or 3. Ask fabricators directly whether they have production history with CML-11006 — multilayer IMS lamination press parameters differ from single-layer MCPCB lamination, and a fabricator without specific CML experience may produce inadequate dielectric cure or delamination at the interlayer.

Useful Resources for Bergquist ML-11006 Design and Procurement

Resource	Content	Link
Bergquist Thermal Clad Selection Guide (tjk.com.au)	Complete CML-11006 spec table, multi-layer construction diagrams, thermal via guidance — primary reference	PDF
Bergquist Thermal Clad Selection Guide (Digikey)	Alternate hosted version with full dielectric comparison data	PDF
Bergquist HT-04503 TDS (Henkel)	Reference for the primary single-layer HT laminate used alongside ML-11006 in two-layer constructions	PDF
Bergquist HT-07006 TDS (Henkel)	6 mil HT glass-free dielectric — useful comparison at same thickness with higher thermal conductivity	PDF
Henkel Electronics Portal	Current Thermal Clad product documentation, SDS, and technical support	henkel.com/electronics
IPC-2221B	PCB design standard — via design, current capacity, clearance rules for multi-layer IMS	ipc.org
IPC-6012	Qualification and performance specification for rigid PCBs — quality class specification for ML-11006 fabrication	ipc.org
Digikey — Bergquist Thermal Clad	Stock, pricing, and panel ordering for Bergquist IMS materials	digikey.com

FAQs: Bergquist ML-11006

Q1: Why does ML-11006 have lower thermal conductivity than every other Thermal Clad dielectric, and is that a real problem?

ML-11006’s 1.1 W/m-K dielectric thermal conductivity is a direct consequence of the glass weave carrier required for the prepreg format. Glass fiber has a thermal conductivity around 1 W/m-K — lower than the ceramic filler used in the glass-free HT and MP polymer matrices — so distributing glass through the dielectric composite reduces its effective conductivity. This is the fundamental physics of glass-reinforced laminates, the same reason standard FR-4 prepreg (also glass-reinforced) performs poorly thermally compared to ceramic-filled materials. The 0.21 °C·in²/W thermal resistance is a real design constraint, not something to paper over. The engineering response is a well-designed thermal via array, which provides copper thermal paths through the dielectric that bypass its low conductivity. For designs with power densities under 5 W/cm², uncorrected ML-11006 thermal resistance is often workable. For high-power-density devices, via arrays bring effective thermal resistance into the acceptable range. The cost of the thermal resistance is accepted because ML-11006 provides the multi-layer construction capability that no other Thermal Clad product can.

Q2: What is the relationship between ML-11006 and CML-11006, and which designation should I use?

CML-11006 is the Bergquist/Henkel official part number designation — CML stands for Circuit Material Laminate, and this is the designation used in the Thermal Clad Selection Guide. ML-11006 is the shorthand that became standard in distributor catalogs and fabricator specifications, particularly outside North America. Both refer to the same material: 1.1 W/m-K, 10 kVAC, 90°C Tg, 130°C/130°C UL RTI, 10 lb/in peel strength, 6 mil dielectric thickness, prepreg format. Use CML-11006 as the part number in purchase orders and fabrication specifications, and explicitly note “prepreg format” to prevent any substitution of a laminate product. The confirmation matters because a fabricator unfamiliar with the CML family might otherwise supply a Thermal Clad laminate product, which cannot function as a multi-layer interlayer bondply.

Q3: How do thermal vias work in an ML-11006 two-layer board, and what via density should I target for a 20 W power device?

Thermal vias drilled through the ML-11006 interlayer and plated with copper provide direct thermal paths from the top circuit layer to the bottom layer, bypassing the dielectric. Copper’s thermal conductivity (approximately 385 W/m-K) is nearly 350 times higher than ML-11006’s 1.1 W/m-K — each via contributes a high-conductance path proportional to its cross-sectional area. For a 20 W device in a standard D2PAK footprint (approximately 65 mm²), targeting a thermal resistance across the interlayer of below 1 °C/W: using 0.3 mm drill diameter vias with copper plating, each via provides roughly 0.07 mm² of copper cross-section. An array of 20–30 vias in a 1 mm pitch grid under the device thermal pad is a reasonable starting point for that power level. Bergquist’s thermal models in the Selection Guide confirm that via-optimized two-layer Thermal Clad designs can match single-layer device case temperatures — the via density is the key design variable to iterate on through thermal simulation before committing to board layout.

Q4: Can ML-11006 be used without a metal base, and what applications does that enable?

Yes — the Bergquist Selection Guide explicitly documents “single-board solutions without the metal base” as a valid Thermal Clad configuration. ML-11006 bonds two copper-clad circuit layers into a double-sided board of minimal thickness, which mounts into a heatsink pocket or bonds directly to a chassis surface. Both sides of the board are available for components, enabling combined power and logic on one thin substrate — something a standard metal-base IMS cannot achieve. The Bergquist Selection Guide calls this configuration a “ceramic submount replacement.” Thermal management relies entirely on the external mounting interface rather than the board’s own metal base. This approach appears in compact module packaging, power hybrid assemblies, and applications where the metal base would add unacceptable thickness or weight. The thermal performance of the completed assembly depends critically on the quality and controlled clamping pressure of the thermal interface between the board bottom and the heatsink or chassis — this is not a free thermal lunch but it opens design space unavailable with standard single-layer MCPCB architecture.

Q5: What is the maximum operating temperature for a UL-certified product using ML-11006, and which applications does this affect?

ML-11006 (CML-11006) carries a UL RTI of 130°C/130°C (electrical/mechanical), per the Thermal Clad Selection Guide. This is the maximum temperature at which a UL-certified product can declare continuous operation when ML-11006 is the substrate. HT-04503 carries 140°C/140°C and HT-09009 carries 150°C/150°C for comparison. The 130°C limit is adequate for most DC-DC power conversion, motor drive, and solid-state relay designs where ambient temperatures range from 40°C to 85°C — adding typical thermal rise, the substrate in those applications stays comfortably within 130°C. It is not adequate for under-hood automotive applications with 125–150°C ambient exposure requirements, or for industrial equipment mounted near sustained high-temperature heat sources where junction temperatures push substrate temperature to 135°C or above. For those environments, a single-layer HT-04503 design or an HT dielectric-based multi-layer construction is the correct specification. Always verify the UL recognition file for your specific stackup construction — in a mixed assembly, the RTI constraint comes from the most thermally limiting material, which in any stackup containing ML-11006 is the ML-11006 interlayer.

Conclusion: Where ML-11006 Fits and Where It Doesn’t

Bergquist ML-11006 (CML-11006) has a sharply defined role: it is the product to specify when your design genuinely requires two circuit layers on a thermally managed metal substrate. Power and control on one board, double-sided assembly, power conversion modules with integrated gate drivers, motor drives where gate-to-FET interconnect inductance must be minimized — in every one of these scenarios, ML-11006 enables a board architecture that no other Thermal Clad product can provide.

The thermal resistance tradeoff — 0.21 °C·in²/W versus HT-04503’s 0.05 °C·in²/W — is real and must be managed through thermal via design. The 260°C solder limit requires controlled reflow profiling. The 130°C UL RTI limits the application envelope versus the HT family. None of these are showstoppers in the applications ML-11006 was designed for. Where your design needs one circuit layer and maximum thermal performance, HT-04503 is the answer. Where your design needs two layers with thermally conductive interlayer bonding and a metal thermal base, ML-11006 is the only product in the Bergquist catalog that delivers it.