Bergquist LTI-04503 Low Thermal Impedance IMS PCB: Full Specifications & Guide

When engineers first encounter the Bergquist Thermal Clad family and look at the dielectric selection table, one question comes up almost immediately: LTI-04503 and HT-04503 have identical thermal performance numbers — the same 2.2 W/m-K thermal conductivity, the same 0.45 °C/W thermal impedance, the same 0.05 °C·in²/W thermal resistance — so what exactly is different, and which one should you use?

That is the central question this guide answers. Bergquist LTI-04503 (Low Thermal Impedance) is the general-purpose IMS workhorse of the Thermal Clad family — a 3 mil dielectric delivering HT-class thermal performance at a 90°C glass transition temperature rather than the HT formulation’s 150°C Tg. It shares the LTI dielectric chemistry with two companion products, LTI-06005 (5 mil) and LTI-07006 (6 mil), all three of which are plotted as the “Low Thermal Impedance” series in the Bergquist Selection Guide’s dielectric performance charts. The LTI series and the HT series appear side by side in those charts as the two highest-performance dielectric families — distinguishable in application by operating temperature environment rather than by thermal conductance.

Understanding LTI-04503 means understanding what the 90°C Tg actually implies in practice, how Bergquist’s UL RTI data allows operation well above that Tg, and where LTI-04503 belongs versus HT-04503 in your selection logic.

What Is Bergquist LTI-04503? The LTI Dielectric Explained

Bergquist PCB Thermal Clad materials all share the same fundamental construction: copper circuit foil, a proprietary polymer-ceramic dielectric, and an aluminum or copper metal base. What differentiates each product is the dielectric formulation — the specific polymer chemistry and ceramic filler blend that determines thermal conductivity, mechanical properties at temperature, voltage isolation capability, and glass transition temperature.

The LTI designation stands for Low Thermal Impedance. The Bergquist Thermal Clad Selection Guide places the LTI dielectric family alongside HT (High Temperature) in its thermal model comparison as the two highest-performing families for watt-density applications, explicitly contrasting them against the MP (Multi-Purpose) and CML (Circuit Material Laminate) families. The thermal model images in the guide show LTI and HT dielectrics with similar heat-spreading profiles — because at 3 mil thickness with 2.2 W/m-K conductivity, they deliver equivalent heat flow through the dielectric.

The part number decodes as: LTI = Low Thermal Impedance dielectric family, 045 = Bergquist internal impedance class reference, 03 = 3 mil (0.003 inch / 75–76 µm) dielectric thickness. The family extends to LTI-06005 at 5 mil and LTI-07006 at 6 mil for applications requiring higher voltage isolation, following the same pattern as the HT family’s HT-04503 and HT-07006.

The key practical distinction is the polymer chemistry. The LTI formulation uses a polymer matrix with a glass transition temperature of 90°C — significantly lower than the HT formulation’s 150°C Tg. Both formulations incorporate the same 2.2 W/m-K ceramic filler system, which is why thermal performance is identical at the measurement level. The difference shows up in mechanical and electrical stability at elevated temperatures, in the UL RTI rating, and in the suitability for high-temperature operating environments like automotive under-hood applications.

Bergquist LTI-04503 Complete Specifications

All values below are from the official Bergquist Thermal Clad Selection Guide (Bergquist document Q-6019, current version hosted at tjk.com.au and Digikey). The Selection Guide is the authoritative published reference for LTI-04503 specifications.

LTI-04503 Thermal Properties

Parameter	LTI-04503 Value	Test Method
Dielectric Thermal Conductivity	2.2 W/m-K	ASTM D5470 (Extended)
Thermal Resistance	0.05 °C·in²/W	Calculated from ASTM D5470
Thermal Impedance	0.45 °C/W	Internal TO-220 test (Bergquist RD2018)

The 2.2 W/m-K dielectric thermal conductivity is identical to HT-04503 at the same 3 mil thickness. This equivalence is not a coincidence — both LTI and HT formulations use the same 2.2 W/m-K ceramic filler blend; only the polymer chemistry differs. At the level of thermal resistance measurement (ASTM D5470), they produce the same result: 0.05 °C·in²/W and 0.45 °C/W. A design that is thermally viable on HT-04503 will be thermally viable on LTI-04503, and vice versa — the selection decision must then rest on operating temperature environment, electrical isolation requirements, and solder process compatibility.

For context: the thermal impedance of 0.45 °C/W means a 10 W device on a standard 1 cm² thermal pad sees approximately 2.9°C of temperature rise across the LTI-04503 dielectric alone. That is the same dielectric thermal resistance contribution as HT-04503, and substantially lower than MP-06503 (0.65 °C/W) or CML-11006 (1.1 °C/W).

LTI-04503 Electrical Properties

Parameter	LTI-04503 Value	Test Method
Dielectric Constant (Permittivity)	7	ASTM D150
AC Breakdown Voltage	6.5 kVAC	ASTM D149
Typical Proof Test Voltage	1500 VDC	500 V/sec ramp, 5 sec hold

The AC breakdown voltage of 6.5 kVAC is marginally higher than HT-04503’s 6.0 kVAC at the same 3 mil thickness. Both are in the same practical tier for standard industrial power electronics applications below 480 VAC. Bergquist’s own note in the Selection Guide states: “For applications with an expected voltage over 480 Volts AC, Bergquist recommends a dielectric thickness greater than 0.003 inch (75 µm).” This applies equally to LTI-04503 and HT-04503 — at 3 mil, both are appropriate for standard industrial voltages up to 480 VAC with proper safety margin, but higher-voltage applications (600 VAC, 1000 VDC) require LTI-06005 (5 mil, 9.5 kVAC), LTI-07006 (6 mil, 11.0 kVAC), or the HT-07006 equivalent.

The typical proof test voltage of 1500 VDC is the fabrication electrical integrity test voltage for 3 mil dielectric Thermal Clad boards. This is the standard hipot test voltage applied at the fabrication level to verify dielectric integrity — it is not the maximum operating voltage, which must include appropriate derating from the breakdown value.

The dielectric constant of 7 is consistent across the LTI, HT, and CML families. It is slightly higher than MP-06503’s Dk of 6, which has no practical significance for typical power electronics frequencies but becomes relevant if the substrate is being used for mixed-signal assemblies with RF components.

LTI-04503 Mechanical and Agency Properties

Parameter	LTI-04503 Value	Test Method / Standard
Dielectric Thickness	3 mil (0.003″ / 75–76 µm)	Optical
Glass Transition Temperature (Tg)	90°C	Internal MDSC test (Bergquist RD2014)
UL RTI (Electrical / Mechanical)	130°C / 130°C	UL 746E
UL Flammability	V-0	UL 94
Peel Strength	6 lb/in (1.1 N/mm)	ASTM D2861
Lead-Free Solder Compatible	Yes	—
RoHS Compliant	Yes	—

The 90°C Tg is the specification that separates LTI-04503 from HT-04503 (Tg 150°C) in application suitability. The glass transition temperature marks where the polymer transitions from glassy to elastomeric behavior — above Tg, storage modulus drops, CTE increases, and peel strength reduces. At 90°C, LTI-04503 will be operating in its elastomeric state during the reflow solder process (typical peak 245–260°C) and potentially during high-temperature continuous operation above 90°C.

The Bergquist Selection Guide addresses this directly: “Many Thermal Clad products have UL rating up to 45% higher than their glass transition temperature and are used extensively in applications above rated Tg.” The UL RTI of 130°C/130°C is 44% above the 90°C Tg — this is not an error or anomaly. Bergquist has qualified LTI-04503 for continuous operation at 130°C even though the Tg is 90°C. Above Tg, the dielectric’s elastomeric state can actually relieve residual stress at solder joints and dielectric interfaces through CTE mismatch relaxation, which can be a reliability benefit in thermally cycled assemblies. The 130°C UL RTI is the hard operating temperature limit for certified products using LTI-04503.

The peel strength of 6 lb/in (1.1 N/mm) matches HT-04503 exactly. This is the expected result since the ceramic filler system and the bond chemistry are similar between LTI and HT at 3 mil thickness.

LTI-04503 vs HT-04503: The Definitive Selection Decision

This is the question that most engineers searching for LTI-04503 actually need answered. The answer is a single-row table followed by the application logic that governs the choice.

Side-by-Side Comparison: LTI-04503 vs HT-04503

Parameter	LTI-04503	HT-04503	Difference
Thermal Conductivity (W/m-K)	2.2	2.2	Identical
Thermal Resistance (°C·in²/W)	0.05	0.05	Identical
Thermal Impedance (°C/W)	0.45	0.45	Identical
Dielectric Thickness	3 mil / 76 µm	3 mil / 76 µm	Identical
Breakdown Voltage (kVAC)	6.5	6.0	LTI slightly higher
Proof Test (VDC)	1500	1500	Identical
Dielectric Constant (Dk)	7	7	Identical
Glass Transition (Tg)	90°C	150°C	HT 60°C higher
UL RTI Elec/Mech (°C)	130/130	140/140	HT 10°C higher
Peel Strength (lb/in)	6	6	Identical
AuSn Wire Bond Compatibility	Limited (Tg 90°C)	Yes (Tg 150°C)	HT preferred for COB
Max Solder Process Temp	Standard reflow	325°C (AuSn capable)	HT broader range

The selection logic follows directly from this table. When your application meets all of these conditions, LTI-04503 is the correct specification: operating temperature stays within the 130°C UL RTI; assembly uses standard SAC305 lead-free reflow (peak 245–260°C); wire bonding or AuSn die attach is not required; and standard industrial voltages below 480 VAC are the working voltage. When any of those conditions is not met — operating temperature above 130°C, automotive under-hood application requiring 140°C+ certification, direct die attach with thermosonic gold wire bonding, or AuSn solder die attach above 280°C — specify HT-04503 instead.

The Bergquist Selection Guide explicitly states that for direct die application using thermosonic gold wire bonding, “it is important to use HT dielectric because of its high Tg (thus higher modulus) at wire bond temperatures.” Wire bonding requires the substrate to be at 120–150°C during the bonding process, at which temperature LTI-04503 is above its 90°C Tg and in its elastomeric state — the reduced modulus creates a compliant surface that does not support the ultrasonic energy transfer needed for reliable wire bonding. HT-04503 at 150°C Tg stays in its glassy, high-modulus state through the wire bond process.

How LTI-04503 Fits in the Full Thermal Clad Family

Complete Family Specification Comparison

Product	Dielectric	Thickness	Conductivity	Thermal Resist.	Breakdown	Tg	UL RTI	Peel Strength
HPL-03015	HPL	1.5 mil	3.0 W/m-K	0.02 °C·in²/W	5.0 kVAC	185°C	140°C	5 lb/in
LTI-04503	LTI	3 mil	2.2 W/m-K	0.05 °C·in²/W	6.5 kVAC	90°C	130/130°C	6 lb/in
HT-04503	HT	3 mil	2.2 W/m-K	0.05 °C·in²/W	6.0 kVAC	150°C	140/140°C	6 lb/in
MP-06503	MP	3 mil	1.3 W/m-K	0.09 °C·in²/W	8.5 kVAC	90°C	130/140°C	9 lb/in
LTI-06005	LTI	5 mil	2.2 W/m-K	0.09 °C·in²/W	9.5 kVAC	90°C	130°C	6 lb/in
HT-07006	HT	6 mil	2.2 W/m-K	0.11 °C·in²/W	11.0 kVAC	150°C	140/140°C	6 lb/in
LTI-07006	LTI	6 mil	2.2 W/m-K	0.11 °C·in²/W	11.0 kVAC	90°C	130°C	6 lb/in
CML-11006	CML	6 mil	1.1 W/m-K	0.21 °C·in²/W	10.0 kVAC	90°C	130/130°C	10 lb/in
HT-09009	HT	9 mil	2.2 W/m-K	0.16 °C·in²/W	20.0 kVAC	150°C	150/150°C	6 lb/in

LTI-04503 sits between HPL-03015 and HT-04503 in the thermal performance column — delivering the second-best thermal conductance in the family at a thickness that balances thermal performance with voltage isolation. Within the LTI dielectric series, LTI-04503 at 3 mil is the thermal performance choice; LTI-06005 at 5 mil and LTI-07006 at 6 mil extend voltage capability at proportionally higher thermal resistance.

Bergquist LTI-04503 Applications

DC-DC Power Conversion: The Classic LTI Application

High-density DC-DC power conversion is listed in the Bergquist Thermal Clad Selection Guide as the application that originally drove Thermal Clad adoption: “Due to the size constraints and watt-density requirements in DC-DC conversion, Thermal Clad has become the favored choice.” LTI-04503 is the standard specification for DC-DC converter IMS boards where the operating temperature does not require the HT family’s higher Tg and where the slightly higher 6.5 kVAC breakdown voltage of LTI-04503 versus HT-04503’s 6.0 kVAC is useful for hipot test margins. Low-voltage bus converters (48 V to 12 V, 24 V to 5 V), isolated DC-DC modules in industrial equipment, and point-of-load converters in telecom and server systems all fit this profile.

Solid State Relays and Power Switches

SSR assemblies mount thyristors, TRIACs, or MOSFETs directly on an IMS substrate with the dielectric providing both the thermal path to the heatsink and the electrical isolation between the power semiconductor and chassis. LTI-04503 at 6.5 kVAC breakdown and 0.05 °C·in²/W thermal resistance covers the thermal and isolation requirements of standard industrial SSR designs (24–480 VAC operating range) at optimal thermal performance. The 130°C UL RTI is adequate for SSR applications where ambient temperatures are in the 40–85°C range and total substrate temperature rise keeps the LTI-04503 dielectric within its rated limit.

LED Lighting Applications — Consumer and Commercial

While HPL-03015 is Bergquist’s specialized LED product, LTI-04503 is frequently specified for LED lighting boards where the operating voltage is within the 480 VAC limit, the assembly uses standard SMT reflow, and the thermal performance of 2.2 W/m-K is sufficient for the LED power density in the design. Commercial LED drivers and power modules for LED streetlights, downlights, and architectural luminaires commonly specify LTI-04503 as a cost-optimized alternative when the higher Tg of HT-04503 is not required.

Motor Control and Variable Speed Drives

Compact motor drive assemblies — particularly in consumer appliances, HVAC systems, and light industrial equipment — frequently operate within the 130°C UL RTI of LTI-04503. The power FETs, gate drivers, and rectifier diodes in a VFD (Variable Frequency Drive) for a 0.5–5 kW motor generate substantial heat at a single-layer IMS board, and LTI-04503’s 2.2 W/m-K dielectric performance handles the watt density without requiring the higher-temperature HT formulation. Bergquist’s Selection Guide explicitly highlights motor drives as a core Thermal Clad application, and the LTI family is positioned at the higher-performance end of the dielectric chart for these power-density-sensitive designs.

Heat-Rail and Forming Applications

Thermal Clad’s forming capability — the ability to mechanically shape the metal base into three-dimensional heatsink and mounting structures — is highlighted in the Bergquist Selection Guide for automotive, audio, and motor control applications. LTI-04503 supports forming operations because the polymer chemistry at 90°C Tg provides some mechanical compliance during the forming process. The Selection Guide notes that heat-rail applications have grown significantly and are used in automotive (non-under-hood), audio amplifier assemblies, motor control modules, and power conversion designs. For under-hood automotive with sustained temperature above 130°C, HT-04503 is required; for body electronics, audio systems, and infotainment power modules where operating temperatures stay within 130°C, LTI-04503 is appropriate.

Design Tips for LTI-04503 IMS Boards

Operating Above the 90°C Tg — Understanding the Practical Reality

The 90°C Tg causes engineers to instinctively question whether LTI-04503 can be used in designs where the substrate temperature may reach 100–120°C. The answer is yes, within the 130°C UL RTI limit, and the Bergquist Selection Guide explains why. Above Tg, the dielectric enters its elastomeric state — storage modulus drops, CTE increases — but the material does not fail. In fact, the lower modulus above Tg can reduce residual stress at solder joints and dielectric interfaces by allowing CTE mismatch strain to relax, which can improve solder joint thermal fatigue life in thermally cycled assemblies. The critical rule is: keep continuous operating temperature within the 130°C UL RTI. Transient excursions above 130°C should be avoided in UL-certified product designs.

Choosing Between LTI-04503, LTI-06005, and LTI-07006

The LTI dielectric family offers three thickness options that trade thermal resistance for voltage isolation:

Product	Thickness	Thermal Resistance	Breakdown	Proof Test	Best For
LTI-04503	3 mil / 76 µm	0.05 °C·in²/W	6.5 kVAC	1500 VDC	Standard industrial ≤480 VAC
LTI-06005	5 mil / 125 µm	0.09 °C·in²/W	9.5 kVAC	2000 VDC	Medium voltage 480–690 VAC
LTI-07006	6 mil / 150 µm	0.11 °C·in²/W	11.0 kVAC	2500 VDC	High voltage, reinforced isolation

LTI-04503 is the thermal performance choice within the LTI family. LTI-06005 and LTI-07006 increase breakdown voltage at the cost of proportionally higher thermal resistance, following the same physics as the HT family’s thickness progression.

Surface Finish Selection for LTI-04503 PCBs

Surface Finish	Application	Notes
ENIG (Electroless Nickel Immersion Gold)	General SMT, fine-pitch, long shelf life	Standard finish for most LTI-04503 designs; flat surface improves solder joint formation
Lead-Free HASL	Cost-sensitive production, larger thermal pads	Good for power device thermal pads; less precise for fine-pitch
OSP (Organic Solderability Preservative)	Immediate-assembly production	Short shelf life; requires controlled assembly window
Immersion Silver	High-reflectivity LED boards	Slightly higher reflectivity than ENIG; oxidation management required

ENIG is the standard default for LTI-04503 boards in production. Its flat, consistent surface supports accurate solder paste printing, which is critical for void-free joints under power device thermal pads.

Fabrication and Specification Notes

When specifying LTI-04503 to a fabricator, the most important clause is: no generic IMS substrate substitution. The LTI dielectric’s specific 2.2 W/m-K thermal conductivity and 6.5 kVAC breakdown voltage are what you are paying for. A generic 1 W/m-K aluminum MCPCB looks similar in photographs and fabrication documentation but delivers thermal resistance four times higher. Require a Certificate of Conformance with Bergquist/Henkel lot number traceability, a hipot test at 1500 VDC (or confirm test voltage with your fabricator based on your isolation requirement), and UL 94 V-0 flammability per material. Specify copper weight (1 oz or 2 oz), aluminum base thickness (typically 1.0 mm or 1.6 mm), and surface finish explicitly.

Useful Resources for Bergquist LTI-04503 Design and Procurement

Resource	Content	Link
Bergquist Thermal Clad Selection Guide (tjk.com.au)	Complete LTI-04503 specification table, LTI vs HT vs MP vs CML comparison, circuit design guidelines, assembly recommendations — primary reference	PDF
Bergquist Thermal Clad Selection Guide (Digikey)	Alternate hosted version with full dielectric comparison data and current-carrying capability charts	PDF
Bergquist HT-04503 TDS (Henkel/mclpcb)	Reference for HT-04503 — the 150°C Tg alternative at identical thermal performance	PDF
Bergquist HT-07006 TDS (Henkel/mclpcb)	Reference for the 6 mil HT dielectric — useful when LTI-06005 or LTI-07006 higher voltage is needed and HT Tg is required	PDF
Bergquist HPL-03015 TDS (mclpcb)	HPL dielectric — reference for designs needing maximum thermal performance at low voltage	PDF
Henkel Electronics Portal	Current Thermal Clad product documentation, SDS, technical support	henkel.com/electronics
IPC-2221B	PCB design standard — trace width, current capacity, creepage and clearance rules applicable to LTI-04503 IMS design	ipc.org
Digikey — Bergquist Thermal Clad	Stock, pricing, and panel ordering	digikey.com

FAQs: Bergquist LTI-04503

Q1: LTI-04503 and HT-04503 have identical thermal specs. Why would I choose one over the other?

The thermal specs are identical because both use the same 2.2 W/m-K ceramic filler system at the same 3 mil dielectric thickness — thermal performance is governed by those two parameters, not by the polymer chemistry. The polymer chemistry determines everything else: Tg, UL RTI, and solder process compatibility. Choose LTI-04503 when your design operates continuously within 130°C, uses standard SAC305 lead-free reflow, and does not require direct die attach with thermosonic gold wire bonding. Choose HT-04503 when any of those conditions is not met — operating above 130°C, automotive under-hood certification at 140°C, or COB die assembly requiring wire bonding or AuSn die attach at temperatures where LTI-04503 would be operating above its 90°C Tg. For most standard DC-DC power conversion, LED driver, SSR, and motor control applications below 130°C operating temperature, LTI-04503 is the appropriate choice and may offer a slight cost advantage depending on your supply chain.

Q2: LTI-04503 has a 90°C Tg but a 130°C UL RTI. Can I really run it continuously at 115°C?

Yes — this is explicitly supported by Bergquist’s qualification data and the UL RTI rating. The glass transition temperature marks a material property change (from glassy to elastomeric), not a product failure point. Above 90°C, LTI-04503’s dielectric is in its elastomeric state: storage modulus is lower, CTE is higher, and peel strength is reduced. But “reduced” does not mean zero — the Bergquist Selection Guide shows that peel strength maintains above 3 lb/in even at 175°C for Thermal Clad dielectrics. The UL 746E RTI test is a long-term thermal endurance test at elevated temperature that validates material performance — a 130°C/130°C electrical/mechanical RTI means the material passes UL’s endurance criteria at 130°C, and Bergquist has earned that rating through rigorous testing. Running at 115°C is well within the 130°C RTI limit. The caveat is that above Tg, electrical properties including permittivity, dielectric loss, and breakdown strength begin to change at high frequencies (above 1 MHz) — for standard power electronics at switching frequencies well below 1 MHz, these changes are not functionally significant.

Q3: What is the LTI-04503 breakdown voltage, and how should I determine the safe operating voltage for my design?

The ASTM D149 AC breakdown voltage of 6.5 kVAC is a material characterization value, not a working voltage specification. It is measured under ideal conditions on flat, defect-free samples using a controlled voltage ramp. Real-world operating voltage must be substantially lower. Bergquist’s own note in the Selection Guide recommends limiting designs to below 480 VAC on 3 mil dielectric. The derating logic is: the 1500 VDC proof test voltage at fabrication verifies dielectric integrity at 1500 VDC, providing confidence in the dielectric as shipped. For a 480 VAC working voltage, peak voltage is 679 VDC — the proof test at 1500 VDC provides more than a 2× margin above peak working voltage. For designs above 480 VAC, switch to LTI-06005 (5 mil, 9.5 kVAC, 2000 VDC proof test) or LTI-07006 (6 mil, 11.0 kVAC, 2500 VDC proof test). The working voltage your safety certification body (UL, IEC, VDE) requires must ultimately be determined by the applicable product safety standard, not purely by the IMS substrate breakdown voltage — creepage and clearance distances on the circuit layer are equally important.

Q4: What surface finishes are compatible with LTI-04503, and which is best for high-power SMT components?

LTI-04503 is compatible with all standard surface finishes: ENIG, lead-free HASL, immersion silver, OSP, and ENEPIG. For high-power SMT components — power FETs with exposed thermal slugs, rectifier diodes with large thermal pads, power modules — ENIG is the preferred finish for most production designs. The flat, consistent gold surface produced by ENIG improves solder paste printing accuracy and paste release from the stencil, both of which directly affect solder void percentage under large thermal pads. Voids under the thermal pad of a power FET increase effective thermal resistance — the path for heat to travel from the package is blocked wherever a void exists, forcing heat through narrower copper cross-sections around the void. HASL is acceptable for larger thermal pads where the slight surface topology of the HASL finish doesn’t create printability issues. OSP requires careful assembly scheduling because shelf life is short, but it is cost-effective for immediate-assembly production runs. ENEPIG is appropriate when wire bonding to the circuit layer is required for any mixed SMT + wire bond assembly — but as noted, wire bonding on LTI-04503 is not recommended for thermosonic gold bonding due to the 90°C Tg; ENEPIG becomes relevant only for aluminum wire bonding at lower temperatures.

Q5: Can LTI-04503 be used in automotive applications?

LTI-04503 can be used in automotive applications where the substrate operating temperature does not exceed the 130°C UL RTI. This covers many body electronics applications — LED interior and exterior lighting (non-headlamp), body control modules, HVAC blower controls, seat heater controllers, and audio amplifiers where sustained temperatures stay within 130°C. It is not appropriate for under-hood applications where ambient temperatures can reach 85–125°C, where the additional thermal rise from component dissipation would push the LTI-04503 substrate above its 130°C RTI limit. For under-hood automotive, HT-04503 (140°C UL RTI) is the standard Thermal Clad specification, and in the most demanding locations (near exhaust, transmission tunnel) the HT-09009 with 150°C UL RTI may be required. Additionally, automotive applications that require AEC-Q200 or AEC-Q101 component qualification and involve direct die attach (bare-die COB) must use HT-04503 for the wire bonding reason described in FAQ #1. Always confirm the maximum continuous substrate temperature in your specific automotive application before selecting LTI-04503 over HT-04503 — the 10°C RTI difference is meaningful in applications where thermal margins are tight.

Conclusion: When LTI-04503 Is the Right Call

Bergquist LTI-04503 is the correct IMS specification for the large majority of standard power electronics designs where operating temperature is within 130°C, standard lead-free SMT reflow is the assembly process, direct die wire bonding is not needed, and working voltage is within the 480 VAC range. It delivers the same thermal performance as HT-04503 at 2.2 W/m-K and 0.05 °C·in²/W, with a slightly higher 6.5 kVAC breakdown voltage, at a Tg of 90°C supported by a 130°C/130°C UL RTI. DC-DC power conversion, solid-state relays, LED driver boards, HVAC motor controls, and heat-rail audio and power assemblies all fall in this category.

The decision is not complex: when your design needs operation above 130°C, AuSn die attach, or thermosonic wire bonding, specify HT-04503. In every other high-performance 3 mil dielectric application, LTI-04503 is the efficient, appropriately specified choice from the Bergquist Thermal Clad catalog.