Complete Bergquist PCB material selection guide: compare LTI, MP, HT, HPL dielectrics, base metal options, design rules & datasheets. Written for PCB engineers.

Picking the wrong Bergquist dielectric is one of those decisions that looks fine on paper until the field return report lands on your desk three months after launch. Junction temperatures higher than modeled. Delamination after 200 thermal cycles. A Tg margin that turned out to be thinner than expected. None of it catastrophic on its own, but all of it traceable back to the material selection call made early in the design.

This guide is written for engineers doing Bergquist PCB material selection for real designs — not someone browsing datasheets out of curiosity. It covers the Thermal Clad dielectric family in depth, the key decision variables, base metal choices, design considerations that affect reliability, and a practical selection framework you can actually use. By the end, you should be able to pick a dielectric with confidence rather than defaulting to whatever the previous revision used.

Why Bergquist Thermal Clad Exists and What Problem It Solves

The Bergquist Thermal Clad PCB technology is engineered to improve the efficiency of heat dissipation from electronic components, particularly in devices that generate a significant amount of heat. The fundamental issue it solves is simple: standard FR-4 is a thermal insulator. Its thermal conductivity sits at roughly 0.2–0.3 W/m-K, which means it actively works against you when power-dense components need to dump heat through the board.

Thermal Clad flips this relationship. The dielectric is a proprietary polymer/ceramic blend — glass-free, unlike FR-4 prepreg — that bonds a copper circuit layer to a metal base (typically aluminum). These substrates minimize thermal impedance and conduct heat more effectively and efficiently than standard printed wiring boards. They are more mechanically robust than thick-film ceramics and direct bond copper constructions that are often used in these applications.

The copper substrate offers 390 W/mK conductivity while aluminum substrate offers 205 W/mK conductivity — both significantly higher than typical FR-4 boards. The key point here is that the metal base is the primary heat spreader; the dielectric’s job is to electrically isolate the copper circuit from the base while transferring heat as efficiently as its chemistry allows. Every dielectric family Bergquist offers makes a different trade-off between thermal performance, temperature tolerance, and cost.

The Bergquist Thermal Clad Dielectric Families Explained

Bergquist organizes its Thermal Clad dielectrics into named families. Each family has its own polymer chemistry, thermal performance tier, and target application environment. Getting this choice right is the foundation of good Bergquist PCB material selection.

LTI — Low Temperature Insulator

LTI is the entry point of the Thermal Clad family. It’s a moderate-performance dielectric aimed at applications where the board won’t see sustained high temperatures and budget is a real constraint. Thermal conductivity sits at approximately 1.5 W/m-K with a Tg around 130°C. Consumer electronics, standard LED drivers, audio amplifier output stages, and general-purpose power supply boards are its natural habitat. If your steady-state board temperature comfortably stays below 100°C and thermal cycling isn’t extreme, LTI is the economically sound choice.

MP — Multi-Purpose

The MP dielectric steps up the thermal conductivity to approximately 2.4 W/m-K, making it the most versatile option in the range. When choosing dielectric materials, you have to consider thermal conductivity: this is an important factor you should not overlook. The Bergquist Thermal Clad’s thermal conductivity determines thermal performance — this is especially important when interfacial area and resistance are considered. MP covers most general-purpose power electronics, mid-range LED lighting, and motor drive boards where LTI’s thermal conductivity is insufficient but HT’s temperature capability is more than you need.

HT — High Temperature

The HT dielectric is where Bergquist’s chemistry gets serious. The HT variant delivers a thermal conductivity of 4.1 W/m-K and a thermal resistance of 0.05°C·in²/W. It is, as its name states, resistant to degradation from high temperature exposure and features high dielectric breakdown characteristics. This dielectric is proven in applications such as LED, power supply, motor drives, and solid state relays. HT dielectrics are U.L. solder rated at 325°C/60 seconds, which enables Eutectic Gold/Tin solders and wire bonding with gold wire — options that aren’t available with the lower-tier dielectrics.

HPL — High Power Lighting

HPL is a specialist dielectric, not a general-purpose option. HPL is a dielectric specifically formulated for high power lighting LED applications with demanding thermal performance requirements. This thin dielectric at 0.0015″ (38 µm) has an ability to withstand high temperatures with a glass transition of 185°C, thermal conductivity of 3.0 W/m-K, and thermal impedance of 0.30°C/W. The thin dielectric layer is the enabling factor — less material between the LED junction and the aluminum base means dramatically lower thermal resistance, which translates directly to higher lumen output and longer LED lifespan at the same drive current.

CML — Ceramic-Metal Laminate

CML is the high-end outlier in the Bergquist dielectric lineup. It uses a glass carrier (the only Bergquist dielectric that does, for handling purposes) and is targeted at applications needing maximum thermal performance combined with the ability to replace ceramic substrates. It’s the option you look at when designing thick-film ceramic replacements in motor inverters, high-frequency switching circuits, and bare-die mounting applications.

Full Bergquist Dielectric Comparison Table

Understanding the full picture of Bergquist PCB material selection requires comparing the key parameters across dielectric families side by side.

Dielectric	Thermal Conductivity	Typical Tg	Thermal Resistance	Best Application Tier
LTI	~1.5 W/m-K	~130°C	~0.20°C·in²/W	Consumer electronics, standard LED drivers
MP	~2.4 W/m-K	~130–140°C	~0.13°C·in²/W	General power, mid-range LED, motor drives
HT (3 mil)	~4.1 W/m-K	~150°C	~0.05°C·in²/W	High-power LED, EV inverters, power modules
HPL	~3.0 W/m-K	185°C	~0.02°C·in²/W	High-brightness LED, projectors, backlighting
CML	Highest	High	Lowest	Bare die, ceramic replacement, RF modules

The Naming Convention Decoded

Once you understand how Bergquist names its products, reading a part number becomes straightforward. Take HT-04503 as an example: “HT” is the dielectric family. “045” is the approximate total laminate thickness in mils. “03” is the dielectric layer thickness in mils (3 mil = ~76 µm). So LTI-04503 is a Low Temperature Insulator with a 3-mil dielectric, and MP-06503 is a Multi-Purpose dielectric with a 3-mil dielectric on a 65-mil total laminate.

The dielectric thickness matters significantly: for applications with an expected voltage over 480 Volts AC, Bergquist recommends a dielectric thickness greater than 0.003″ (75 µm). If your application is above that threshold, either choose a product with a thicker dielectric or apply appropriate creepage and clearance margin in your PCB layout per IEC 60664-1.

Five Key Decision Variables for Bergquist PCB Material Selection

1. Operating Temperature and Tg Margin

Your dielectric’s glass transition temperature isn’t just a spec to note — it’s the upper bound of predictable behaviour. The temperature of the operating environment determines a lot: it determines not only the peel strength and CTE, but also the storage modulus. When there is an increase in temperature, the storage modulus decreases. Running a dielectric consistently near its Tg degrades bond strength, increases CTE, and erodes electrical properties over time. The practical rule is to target at least 20–30°C of Tg headroom above your sustained maximum junction-area temperature.

2. Thermal Conductivity vs. Thermal Resistance

These two parameters are related but distinct. Thermal impedance measures how temperature declines across each watt’s stack-up. Lower thermal impedance indicates that more heat moves out of the components. Thermal conductivity is a material property; thermal resistance is a system-level value that depends on both conductivity and the dielectric layer thickness. A thinner dielectric from a lower-conductivity family can outperform a thicker dielectric from a higher-conductivity family in thermal resistance terms. Always compare thermal resistance (°C·in²/W or °C·cm²/W), not just conductivity, when evaluating options.

3. Dielectric Breakdown and Voltage Rating

For any design with significant AC or DC bus voltages, the dielectric breakdown spec is non-negotiable. The standard 3-mil (76 µm) Thermal Clad dielectric typically delivers >3 kVAC breakdown. For industrial or automotive applications running above 480 VAC, move to a thicker dielectric variant. Circuit design is the most important consideration for determining safety agency compliance — layout creepage and clearance distances matter as much as the raw material spec.

4. Base Metal Selection: Aluminum vs. Copper

The base layer is not just structural — it’s the primary heat spreader. The copper substrate offers 390 W/mK conductivity while aluminum offers 205 W/mK conductivity. Aluminum wins on cost, weight, and machinability, making it the right choice for the majority of applications including LED lighting, consumer audio, and standard power conversion. Copper is the choice when matching CTE to ceramic-packaged devices is critical, when the application requires double-sided assembly using the base as part of the circuit, or when maximum heat spreading is paramount.

You should match the base and circuit coefficients of thermal expansion (CTE). Failure to do this may cause excess plated-hole fatigue during thermal cycles. In the application, the CTE of the base material is a dominant contributor to thermal mechanical stress. This is why copper-base Thermal Clad is used in high-reliability designs where components have ceramic packages — the CTE mismatch between aluminum and a ceramic component body creates more stress than many high-cycle applications can tolerate.

5. Assembly Process and Solder Temperature Compatibility

Standard Thermal Clad dielectrics are compatible with SAC305 lead-free reflow at peak temperatures around 260°C. HT dielectrics are rated to 325°C/60 seconds, making them appropriate for higher-temperature solder pastes and gold wire bonding. If your assembly process involves potting compounds, check that the potting material’s cure temperature doesn’t approach the Tg of your chosen dielectric — potting at 150°C with an LTI dielectric (Tg ~130°C) is a common mistake that shows up as delamination failures in the field.

Base Metal Thickness and Circuit Flatness

Circuit flatness can be a concern when the base layer is aluminum. To achieve a flat circuit, maintain the proper ratio of circuit layer thickness to base. If the thickness of the copper circuit layer is kept at 10% of the base layer thickness or thinner, the aluminum base will mechanically dominate, keeping the circuit flat.

In practice, with a 1.57 mm (0.062″) aluminum base, your circuit copper should stay at or below roughly 157 µm — about 4.5 oz — to maintain flatness. Most designs using 1 oz or 2 oz copper are comfortably inside this envelope. Deviation from this ratio shows up as bow and twist that causes solder paste printing issues and component misalignment on automated lines.

Aluminum Base Thickness	Max Copper Thickness for Flatness
0.8 mm (0.031″)	~80 µm (~2.3 oz)
1.0 mm (0.040″)	~100 µm (~2.9 oz)
1.57 mm (0.062″)	~157 µm (~4.5 oz)
2.0 mm (0.079″)	~200 µm (~5.7 oz)
3.2 mm (0.125″)	~320 µm (~9.1 oz)

Bergquist PCB Material Selection: A Practical Decision Framework

The table below is a simplified decision matrix to get engineers to the right dielectric family quickly.

Question	Answer	Dielectric Direction
Is steady-state board temp below 100°C?	Yes	LTI is a candidate
Is thermal conductivity >1.5 W/m-K required?	Yes	MP or above
Will the board see sustained temps above 130°C?	Yes	HT series minimum
Is this a high-brightness LED application?	Yes	HPL or HT
Does the application require bare die mounting?	Yes	HT or CML
Is voltage above 480 VAC?	Yes	Specify thicker dielectric
Is this a cost-sensitive, moderate-power design?	Yes	LTI or MP on aluminum
Is CTE match to ceramic components critical?	Yes	Copper base, HT or CML dielectric

Bergquist Thermal Clad vs. FR-4 and Alternatives

Engineers sometimes ask whether Thermal Clad is actually necessary or whether a thermally enhanced FR-4 (e.g., a high-Tg, thermally filled epoxy laminate) is sufficient. For designs under ~1–2 W/component with good heatsink access and relaxed temperature targets, thermally enhanced FR-4 is a legitimate option. But for power-dense SMD boards where the component body is the only thermal interface to the board, Thermal Clad’s metal base makes a dramatic difference.

Compared to competing IMS products such as Arlon PCB materials and other IMS laminates, Bergquist Thermal Clad benefits from a uniquely well-documented qualification history — new materials undergo a rigorous 12 to 18 month qualification program, and the lab facilities are UL certified with ISO 9001:2000 manufacturing certification. Extensive qualification testing consists of mechanical property validation, adhesion, temperature cycling, thermal and electrical stress — with electrical testing performed at selected intervals to 2000 hours where final evaluation is completed. That paper trail matters for products going through UL, CE, or automotive safety agency review.

Parameter	Standard FR-4	Bergquist LTI	Bergquist MP	Bergquist HT
Thermal Conductivity	0.2–0.3 W/m-K	~1.5 W/m-K	~2.4 W/m-K	~4.1 W/m-K
Max Tg	~130–170°C	~130°C	~130–140°C	~150°C
Metal Base Option	No	Yes (Al/Cu)	Yes (Al/Cu)	Yes (Al/Cu)
UL Recognition	Yes	Yes	Yes	Yes
Relative Cost	Low	Moderate	Moderate-High	High
LED Suitability	Poor	Standard output	Good	Excellent

Assembly and Manufacturing Considerations

Getting a Thermal Clad board assembled correctly requires a few process adjustments compared to FR-4.

Hipot Testing: Due to the capacitive nature of the circuit board construction, it is necessary to control the ramp-up of the voltage to avoid nuisance tripping of the failure detect circuits in the tester and to maintain effective control of the test. Step the voltage up slowly — a sudden ramp to the full test voltage will trip false failures on Thermal Clad boards due to displacement current. This is a common cause of confusion during first-article testing.

Drill and Route Tooling: Aluminum-base MCPCB requires carbide tooling. Standard HSS drill bits wear rapidly on the metal base and will produce rough hole walls and burring that affects via reliability.

Solder Stencil Printing: The standard SMT stencil approach applies without modification for most Thermal Clad designs. Dispensing of solder to specific locations is used for secondary operations or special attachment requirements, particularly for large power devices where controlled solder volume reduces voiding.

Conformal Coating: For outdoor or high-humidity environments, conformal coating can be applied over the assembled Thermal Clad board. Check the curing process temperature against the dielectric Tg before specifying a thermally cured coating.

Useful Resources for Bergquist PCB Material Selection

Resource	Description	Link
Bergquist Thermal Clad Selection Guide (Digikey)	Complete dielectric comparison, design guidelines, circuit and base layer selection	Download PDF
Bergquist Thermal Clad Selection Guide (Semach Mirror)	Alternate hosted version of the full selection guide	Download PDF
Bergquist HT-04503 Datasheet	HT 3-mil dielectric specs, thermal and electrical properties	Download PDF
Bergquist HPL-03015 Datasheet	HPL dielectric specs, high power lighting application data	Download PDF
Bergquist MP-06503 Datasheet	Multi-purpose dielectric specs	Download PDF
Henkel / Bergquist Official Brand Page	Current product catalog, regional distributor contacts	henkel-adhesives.com
IPC-2221B PCB Design Standard	Design guidelines for trace width, clearance, and dielectric considerations	ipc.org
IPC-4101 Base Material Specification	Laminate material specifications including IMS	ipc.org
Digikey – Bergquist Thermal Clad	Stocked parts, pricing, availability	digikey.com

FAQs About Bergquist PCB Material Selection

1. How do I decide between the LTI and MP dielectric in Bergquist PCB material selection?

The core differentiator is thermal load. If your power dissipation per component is moderate, steady-state board temperature stays below 100°C, and you have some tolerance for a slightly elevated junction temperature, LTI at ~1.5 W/m-K is adequate and more cost-effective. If you’re running higher watt-density components, if your thermal model shows the LTI board running within 15°C of its Tg, or if reliability over a long thermal cycling life is critical, step up to MP at ~2.4 W/m-K. The price premium for MP over LTI is typically modest relative to the overall BOM cost and worth it for the extra thermal margin.

2. Can I use Bergquist Thermal Clad for multi-layer PCBs?

Yes, though it’s less common than single-layer Thermal Clad designs. Bergquist dielectrics can be used in multi-layer assemblies by bonding Thermal Clad dielectrics to a metal base using FR-4 or additional Thermal Clad circuit materials, depending on thermal requirements and cost objectives. In power conversion applications especially, replacing FR-4 prepreg with Thermal Clad dielectric in the inner layer stack is done to enhance thermal performance without moving to a full IMS board architecture.

3. What happens if I operate a Bergquist dielectric above its glass transition temperature?

The mechanical and electrical properties of the thermal clad will change when operating above the glass transition. You will notice that the CTE increases and the peel strength reduces. The storage modulus of the thermal clad also declines. In practice this means the dielectric bond to the copper circuit layer becomes weaker, the board becomes more susceptible to delamination under thermal cycling, and electrical properties degrade. Sustained operation above Tg will progressively damage the dielectric and shorten the product’s serviceable life. Always maintain a comfortable margin below Tg under worst-case temperature conditions.

4. Is Bergquist Thermal Clad compatible with standard pick-and-place and reflow assembly?

Yes. One of the practical advantages of Thermal Clad over ceramic or thick-film alternatives is its compatibility with automated SMT assembly. Standard stencil printing, SAC305 reflow profiles (peak ~260°C), and automated optical inspection all apply without special accommodation. The HT dielectric family extends compatibility further, rated for 325°C/60s solder floats, enabling gold wire bonding and higher-temperature attachment processes. The main process adjustment to watch is hipot testing procedure — use a controlled ramp rate rather than a step change to avoid false failures.

5. How does the dielectric thickness affect both thermal and voltage performance in Bergquist materials?

Dielectric thickness is a direct trade-off: thinner dielectric reduces thermal resistance (better heat transfer) but also reduces breakdown voltage and isolation margin. The HPL-03015’s 38 µm (1.5 mil) dielectric achieves exceptional thermal resistance of 0.02°C·in²/W precisely because it is so thin — but its application domain is high-power LED where voltage isolation requirements are moderate. For higher-voltage industrial or automotive applications, the thicker 6-mil (152 µm) or 10-mil (254 µm) dielectric options provide the breakdown voltage headroom needed to meet safety agency requirements. Always match dielectric thickness to both the thermal and voltage requirements of your specific application, not just one or the other.

Conclusion

Getting Bergquist PCB material selection right comes down to honestly characterizing your application: operating temperature, power density, voltage class, assembly process, and cost target. The Thermal Clad family covers a wide performance range — from the economical LTI for consumer applications through the high-performance HT and HPL for demanding LED and power electronics work — and each family member has a legitimate place in that range. The mistake most engineers make is picking a dielectric based on what was used in a previous revision without revisiting whether those assumptions still hold in the new design. Run your thermal model, check your Tg margin, confirm your voltage clearance, and then pick the lowest-tier dielectric that genuinely meets those requirements. That discipline is the core of sound Bergquist PCB material selection.

All specifications should be verified against current official Bergquist/Henkel datasheets before design lock-in. Material properties are subject to revision by the manufacturer.

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Complete Bergquist PCB material selection guide: compare LTI, MP, HT, HPL dielectrics, base metal options, design rules & datasheets. Written for PCB engineers.