DE-104 PCB material from Isola: Tg 135ยฐC, Dk 4.37 @ 1GHz, railway EN 45545-2 approved. Full specs, Df tables, competitor comparison & engineering guide.
If your project sits in that common middle ground โ not a simple consumer gadget running at DC, but not a 10 GHz mmWave radar module either โ there’s a good chance the DE-104 PCB material from Isola Group deserves a spot in your laminate shortlist. It’s one of those workhorses that never gets glamorous press coverage, but shows up in automotive electronics, industrial controls, medical instrumentation, and consumer products by the millions.
This guide breaks down every property that matters, where this material actually makes sense versus where you’d be leaving performance on the table, and how it compares to some common alternatives engineers evaluate at the same time.
What Is DE-104 PCB Material?
DE-104 is a low-Tg copper-clad laminate and prepreg system manufactured by Isola Group, one of the oldest and most recognized names in PCB substrate materials (founded 1912). It is classified as FR-4 under NEMA grades and meets the requirements of IPC-4101 slash sheet /21, the standard specification for epoxy/woven-glass base materials.
Despite the “low Tg” classification, DE-104 has a special resin system that delivers notably better thermal resistance than plain commodity FR-4 โ particularly in Z-axis CTE control and decomposition temperature. It’s manufactured in Isola’s European facility, which matters for supply chain qualification in some regulated sectors like railway and medical.
The product is available in both laminate (core) and prepreg form, covering a thickness range from 0.05 mm to 2.4 mm, making it usable across single-layer, double-sided, and complex multilayer stackups.
DE-104 PCB Material: Full Technical Specifications
Here’s the complete property table you’d pull when running a material qualification assessment:
| Property | Condition / Test Method | Typical Value |
| Glass Transition Temp (Tg) | DSC โ IPC-TM-650 2.4.25C | 135ยฐC |
| Decomposition Temp (Td) | TGA 5% weight loss โ 2.4.24.6 | 315ยฐC |
| Time to Delaminate (T260) | TMA, copper removed โ 2.4.24.1 | 12 minutes |
| Z-Axis CTE (50โ260ยฐC) | IPC-TM-650 2.4.24C | 4.2% total |
| Z-Axis CTE (pre-Tg) | IPC-TM-650 2.4.24C | 70 ppm/ยฐC |
| X/Y-Axis CTE (pre-Tg) | IPC-TM-650 2.4.24C | 16 / 13 ppm/ยฐC |
| Thermal Conductivity | ASTM E1952 | 0.36 W/mยทK |
| Dk @ 1 GHz | IPC-TM-650 2.5.5.9 | 4.37 |
| Df @ 1 GHz | IPC-TM-650 2.5.5.9 | 0.022 |
| Dk @ 5 GHz | IPC-TM-650 2.5.5.5 | 4.32 |
| Df @ 5 GHz | IPC-TM-650 2.5.5.5 | 0.024 |
| Dielectric Breakdown | IPC-TM-650 2.5.6B | >50 kV |
| Arc Resistance | IPC-TM-650 2.5.1B | 105 seconds |
| Moisture Absorption | IPC-TM-650 2.6.2.1A | 0.3% |
| Flexural Strength (length) | IPC-TM-650 2.4.4B | 579 MPa |
| Flexural Strength (cross) | IPC-TM-650 2.4.4B | 450 MPa |
| Peel Strength (after thermal stress) | IPC-TM-650 2.4.8C | 1.58 N/mm |
| Flammability | UL 94 | V-0 |
| Relative Thermal Index (RTI) | UL 94 | 130ยฐC |
| RoHS Compliance | EU 2011/65/EU | Yes |
UL File Number: E41625. IPC-4101 slash sheet: /21.
Understanding DE-104’s Dk/Df Across Frequency
This is where it gets interesting for engineers doing any kind of controlled-impedance or sub-5 GHz signal routing. DE-104’s dielectric properties shift predictably with frequency, which is typical of epoxy-glass systems:
| Frequency | Dk (Permittivity) | Df (Loss Tangent) |
| 100 MHz | 4.46 | 0.020 |
| 500 MHz | 4.40 | 0.021 |
| 1 GHz | 4.37 | 0.022 |
| 2 GHz | 4.35 | 0.023 |
| 5 GHz | 4.32 | 0.024 |
The Dk variation from 100 MHz to 5 GHz is only about 3.1%, which is actually quite good consistency for an epoxy/glass system. This frequency-stable behavior means your impedance calculations hold up reasonably well from DC to the lower end of the microwave band.
The Df of 0.022โ0.024 up to 5 GHz puts it firmly in the “usable but not optimized for RF” zone. For comparison, Rogers RO4350B hits Df of ~0.0037 at 10 GHz. If your signal path insertion loss budget is tight at 3โ5 GHz, you’ll feel the difference. But for many industrial and consumer applications running sub-2 GHz interfaces โ think Zigbee, Sub-GHz IoT, LPWAN, lower-band LTE modules, or CAN bus systems โ DE-104’s loss profile is entirely acceptable.
Prepreg Constructions and Resin Content
One of the practical advantages of DE-104 for multilayer design is the range of prepreg constructions available. Resin content directly affects both Dk/Df and bondline thickness, so having options matters when you’re targeting specific impedance in a dense stackup.
| Glass Style | Resin Content | Thickness (mm) | Dk @ 1 GHz | Df @ 1 GHz |
| 106 | 73% | 0.058 | 4.02 | 0.024 |
| 1080 | 64% | 0.077 | 4.18 | 0.022 |
| 2113 | 54% | 0.100 | 4.37 | 0.020 |
| 2116 | 50% | 0.120 | 4.45 | 0.019 |
| 7628 | 45% | 0.198 | 4.56 | 0.018 |
The higher resin content in fine-weave styles like 106 and 1080 yields lower Dk values โ useful when you need thinner dielectrics with tighter impedance control on outer signal layers. The 7628 glass with lower resin content gives you a stiffer mechanical construction better suited for core layers carrying power planes.
DE-104 vs. Competing FR-4 Class Laminates
Here’s how DE-104 stacks up against materials engineers commonly evaluate in the same application tier:
| Material | Manufacturer | Tg (ยฐC) | Td (ยฐC) | Dk @ 1GHz | Df @ 1GHz | Notable Difference |
| DE-104 | Isola | 135 | 315 | 4.37 | 0.022 | Railway EN 45545-2 approved |
| IS400 | Isola | 135 | 310 | 4.40 | 0.021 | Standard commodity FR-4 |
| IT-180A | Iteq | 180 | 340 | 4.40 | 0.021 | Higher Tg for lead-free intensive |
| FR408 | Isola | 185 | 370 | 3.69 | 0.012 | Low-loss, next tier up |
| TU-768 | TUC | 175 | 340 | 4.60 | 0.021 | Halogen-free option |
| S1141 | Sytech | 130 | 300 | 4.50 | 0.022 | Budget commodity FR-4 |
The standout differentiator for DE-104 isn’t a single electrical property โ it’s the combination of reliable batch-to-batch Dk consistency, railway fire standard approvals (EN 45545-2:2025), UV blocking for AOI, and being recommended for new designs by Isola as of their current product portfolio. That last point matters if you’re starting a new design and don’t want to build on a material Isola is planning to phase out.
Where DE-104 PCB Material Actually Makes Sense
Automotive and Transportation PCBs
DE-104’s railway approval under EN 45545-2 (both R24 and R25 revisions) makes it one of the few standard FR-4 class materials that can go into rail applications without the qualification headache of exotic materials. For automotive body electronics โ BCM, HVAC, seat control modules โ the 135ยฐC Tg and 315ยฐC Td provide adequate thermal margin for typical under-hood ambient plus lead-free assembly cycles.
Industrial Controls and Instrumentation
Motor drives, PLC backplanes, sensor interface boards, and test equipment all benefit from DE-104’s combination of dimensional stability, good peel strength after thermal cycling, and RoHS compliance. The 579 MPa flexural strength (length direction) handles board edge connector engagement loads without drama.
Medical Equipment PCBs
Medical procurement increasingly mandates RoHS compliance plus documented supply chain traceability. Isola provides RoHS declarations and Safety Data Sheets for DE-104 laminate and prepreg separately โ clean documentation that simplifies the technical file for CE marking under MDR.
Consumer Electronics โ Mid-Complexity Boards
Anything from set-top boxes and smart home hubs to power adapters and LED driver boards falls comfortably within DE-104’s performance envelope. The UV blocking feature speeds up AOI (automated optical inspection) on high-volume SMT lines, which your contract manufacturer will appreciate.
Sub-5 GHz RF-Adjacent Designs
For boards that route controlled-impedance traces to RF connectors, antenna feed traces at 900 MHz/2.4 GHz, or Bluetooth/Zigbee module interfaces, DE-104 can work if you’ve modeled insertion loss with its Dk/Df values and confirmed the budget. It’s not an RF laminate, but it’s not blindly incompatible with RF either.
Where DE-104 PCB Material Is the Wrong Call
Be direct with your stackup review:
If your design has signal frequencies above 3โ4 GHz with a real loss budget (filters, power amplifiers, phased-array feed networks), the Df of 0.022+ is going to hurt. Look at FR408HR (Df ~0.009 @ 10 GHz) or Rogers RO4350B (Df ~0.0037) instead.
If you need lead-free assembly with repeated thermal cycling in a high-layer-count board, the 135ยฐC Tg becomes marginal. For those cases, consider Isola’s own 370HR (Tg 200ยฐC) or IT-180A.
If halogen-free is a hard requirement from your customer, DE-104 uses standard brominated resin โ it’s RoHS compliant, but it is not halogen-free per IEC 61249-2-21. Isola has separate halogen-free products for that requirement.
Processing Notes for DE-104
Drilling: Fully compatible with standard carbide drill bits and routing. No special tooling required. Adjust feed/speed per your laminate thickness and copper weight as normal.
Copper foil: Ships standard with HTE Grade 3 copper in ยฝ oz, 1 oz, and 2 oz (18, 35, 70 ยตm). Thinner copper foils are available for fine-line outer layer work.
Lamination: Standard FR-4 press cycles apply. No exotic cure schedules needed.
Surface finishes: Compatible with ENIG, OSP, immersion silver, immersion tin, and lead-free HASL.
UV blocking / AOI: The base material has built-in UV blocking and AOI fluorescence enhancement, which gives contrast between copper and substrate under the inspection wavelengths most AOI systems use. On high-volume lines with tight placement tolerances, this is a real productivity benefit.
Storage: Keep in sealed packaging at 15โ30ยฐC, below 60% RH. Pre-bake at 120ยฐC for 2 hours if panels have been stored outside recommended conditions before layup.
For detailed process parameters including drill feeds, lamination profiles, and copper plating guidelines, refer to the DE-104 Processing Guide available from Isola.
Useful Resources for DE-104 PCB Material
| Resource | Description | Link |
| Isola DE-104 Product Page | Official specs, Dk/Df tables, all compliance docs | isola-group.com |
| DE-104 Datasheet PDF | Full typical values, constructions tables | Download PDF |
| DE-104 Processing Guide | Drill, laminate, and fab parameters | Processing Guide |
| DE-104 RoHS Declaration | EU RoHS compliance certificate | RoHS Doc |
| IPC-4101 Standard | Base materials specification (slash /21 applies) | ipc.org |
| IPC-TM-650 Test Methods | All IPC laminate test method references | ipc.org/TM-650 |
| UL Product iQ | Verify UL E41625 certification | iq.ul.com |
| Doosan PCB Laminates | Alternative mid-range laminate options | Doosan PCB |
| IsoDesign Tools (Isola) | Dk/Df stack planning tools | isola-group.com/resources/design-tools |
5 FAQs About DE-104 PCB Material
Q1: Is DE-104 a good choice for a 2.4 GHz Bluetooth or Wi-Fi board? It depends entirely on your loss budget. At 2.4 GHz, Dk is ~4.35 and Df is ~0.023. For a short antenna feed trace (say, under 30 mm from module to connector), the additional insertion loss compared to a proper RF laminate is measurable but often acceptable โ especially if you’re using an integrated module with its own matching network. Run the numbers with your trace geometry. If you’re routing long RF traces or designing the matching network on the PCB itself, switch to a lower-loss material.
Q2: Can DE-104 survive lead-free reflow for a 16-layer board? Yes, with caveats. The T260 of 12 minutes means a single lead-free reflow at 260ยฐC peak is fine. For a thick 16-layer board going through multiple reflow cycles (top side, bottom side, rework), watch the cumulative thermal exposure carefully. Double-sided assembly with one rework cycle is typically fine. For designs that anticipate heavy rework or high layer counts above 20, stepping up to a higher-Tg material like Isola 370HR gives more headroom.
Q3: What does the railway EN 45545-2 approval mean practically? EN 45545-2 is the European fire protection standard for railway vehicles. The DE-104 holds approvals under both R24 and R25 (the 2020 and 2025 versions). This means the material meets fire reaction requirements โ specifically the glow-wire temperature tests and hazard level ratings needed for equipment installed in railway rolling stock. If your customer is a rail integrator in Europe, this saves a significant qualification step.
Q4: Is DE-104 the same as DE104 โ is the hyphen just a naming convention? Yes, DE-104 and DE104 refer to the same Isola product. Isola’s official naming on their product page and datasheets uses “DE104” without a hyphen, but both forms appear in distributor catalogs, fab house material libraries, and procurement documents. When quoting to a fab house, use “DE104” to match Isola’s official designation.
Q5: Where can I source DE-104 in small quantities for prototyping? Isola sells direct via their Quick Turnaround Program for prototyping quantities. Many authorized distributors โ including Ventec, Biltrite, and regional Isola distributors in Europe and Asia โ stock standard DE104 constructions. Your PCB fab house in most cases already stocks common thicknesses (0.8 mm, 1.0 mm, 1.6 mm) as standard inventory, so simply specifying DE104 in your fab notes is usually enough for prototype runs.
Final Thoughts
The DE-104 PCB material from Isola is precisely what it claims to be: a reliable, well-documented, FR-4 class laminate with better-than-commodity thermal resistance, consistent Dk/Df up to 5 GHz, railway fire certification, and a clean regulatory compliance profile. It isn’t trying to compete with Rogers PTFE laminates, and it doesn’t need to. For the vast majority of industrial, automotive, medical, and sub-5 GHz consumer PCBs, it covers the requirement matrix without the processing complexity or cost premium that true RF laminates introduce.
The key thing to take from Isola’s own classification โ “recommended for new designs” โ is that this is an actively supported product, not an end-of-life carryover. That matters more than most engineers give it credit for when you’re planning a product with a 5-to-10-year production run.
