Megtron 8 (written MEGTRON 8 by Panasonic) is Panasonic’s ultra-low-loss laminate and prepreg family for high-speed, high-layer-count boards such as 800GbE switches and routers, servers, AI servers, base stations and semiconductor test equipment. On Panasonic’s datasheet (July 2024) it has a Tg of 220°C (DMA), a Td of 370°C, T288 over 120 minutes, and a Dk of 3.08 with a Df of 0.0012 at 14 GHz in its ultra-low-Df glass version. This page gathers the official numbers, explains the different Megtron 8 part numbers, and lists what to verify and specify when you order a Megtron 8 PCB. For other laminates, see our PCB materials guide.
1. What Is Megtron 8?
The newest member of Panasonic’s MEGTRON family of low-loss materials, after MEGTRON 6 and 7. Panasonic states that MEGTRON 8 improves transmission loss by about 30% compared with MEGTRON 7 at 28 GHz, and that it can be processed with standard multilayer fabrication methods (Panasonic announcement).
“Megtron 8” is a family, not one material. The part numbers you will see:
| Part number | What it is |
|---|---|
| R-5795 (N) | Laminate, low-Dk glass cloth |
| R-5795 (U) | Laminate, ultra-low-Df glass cloth |
| R-579Y (N) / R-579Y (U) with R-569Y prepreg | UL-recognized laminate grade with matching prepreg |
| R-5795S / R-579YS | MEGTRON 8S versions |
Panasonic notes that the UL 94 V-0 rating on the R-5795 datasheet is from its internal testing; if you need a UL-recognized grade, use R-579Y. Write the exact part number and glass type on your drawing.
2. What Does the Megtron 8 Datasheet Say?
Typical values for R-5795, 0.75 mm test laminate (1078 glass × 10 plies):
| Property | R-5795 (N), low-Dk glass | R-5795 (U), ultra-low-Df glass | Method |
|---|---|---|---|
| Tg | 220°C | 220°C | DMA |
| Td | 370°C | 370°C | TGA |
| T288 (with copper) | > 120 min | > 120 min | IPC-TM-650 2.4.24.1 |
| X/Y CTE below Tg | 17–20 ppm/°C | 17–20 ppm/°C | IPC-TM-650 2.4.24 |
| Z-axis CTE below / above Tg | 50 / 270 ppm/°C | 50 / 270 ppm/°C | IPC-TM-650 2.4.24 |
| Dk at 14 GHz | 3.13 | 3.08 | Balanced-type circular disk resonator (IEC 63185) |
| Df at 14 GHz | 0.0016 | 0.0012 | Same |
| Water absorption | 0.06% | 0.06% | IPC-TM-650 2.6.2.1 |
| Flammability | 94V-0 (internal test) | 94V-0 (internal test) | UL 94 method |
Source: Panasonic R-5795 datasheet, July 2024. Panasonic states these are typical, not guaranteed, values. The MEGTRON 8 product page lists the same values for R-579Y.
Why does Df change between constructions?
Because resin and glass have different loss. For thin R-5795 (U) cores at 14 GHz, Panasonic lists Df from 0.0011 (1035 glass, 78% resin) to 0.0013 (1078 glass, 62% resin). Use the values for the constructions in your stackup, not the headline number, and compare materials only at the same frequency and test method.
3. When Is Megtron 8 Worth the Cost?
When channel loss is the limiting factor: long high-speed routes, 800GbE-class networking, backplanes, and high-layer-count server and AI boards where every decibel matters. If the design has a comfortable loss budget, a lower-cost low-loss material may meet it; Siemens makes the same point about not overspending on stackup materials.
A practical way to decide:
- Model the channel with the candidate materials, using construction-specific Dk and Df and your copper roughness.
- If you meet the loss budget with margin on a cheaper material, use it.
- If you are near the limit, Megtron 8 (or another ultra-low-loss laminate qualified by your customer) is the safer choice.
- Check availability and lead time for the exact construction before you commit.
Panasonic lists AI servers among its applications, but that does not mean every AI or GPU board uses Megtron 8; only the board maker or material maker can confirm a specific design.
4. Why Do Copper Profile and Glass Style Matter?
At these frequencies, rough copper adds conductor loss that can cancel much of the laminate’s advantage, so Megtron 8 boards are usually built with very-low-profile copper such as HVLP3, which Panasonic lists with its peel strength data. Glass style affects how evenly the dielectric looks to the two traces of a differential pair, which drives skew. Specify the copper type and glass styles, or approve the fabricator’s proposal; otherwise both can be substituted. For plane and return-path layout, see our copper pour vs ground plane guide.
5. What Are the Fabrication Risks on High-Layer-Count Boards?
Panasonic says MEGTRON 8 works with standard multilayer processes, but the boards it is used on are rarely standard. Risk rises with:
- 20 or more layers, large panels and thick boards;
- tight registration for dense BGA fanout;
- backdrilling to remove via stubs;
- via-in-pad, HDI or sequential lamination (HDI vs standard PCB cost);
- hybrid stackups that mix Megtron 8 with other materials.
The thermal numbers help: a Tg of 220°C and T288 over 120 minutes give margin for multiple laminations and lead-free assembly. Registration, drilling, plating and dielectric thickness control still decide whether the board meets the electrical model.
6. How Do You Specify a Megtron 8 PCB?
| Item | What to write |
|---|---|
| Material | Exact part number and glass type, e.g. “Panasonic R-579Y(U) / R-569Y” |
| Substitutes | “No substitution without written approval,” or approved alternatives |
| Stackup | Layer order, dielectric thicknesses and glass style per layer |
| Copper | Foil type (e.g. HVLP3) and weight per layer |
| Impedance | Targets, tolerance and reference layers (controlled impedance guide) |
| Loss testing | Insertion-loss coupons, if your customer requires them |
| Via structure | Backdrill depth and stub limit, HDI, via-in-pad |
| Evidence | Material certificate, stackup report, TDR or impedance report |
How Can We Help?
Send your stackup, the Megtron 8 part number you specified, impedance targets and Gerber files, and we will confirm material availability, constructions and impedance in the quote; bare-board quotes come back within 2 hours. If you are also comparing other materials, include your data rate and channel length, and we can quote alternatives side by side. For the assembly stage, see our PCB assembly RFQ checklist.
Conclusion
Megtron 8 is Panasonic’s ultra-low-loss laminate family: Tg 220°C, Td 370°C, T288 over 120 minutes, and Dk 3.08 / Df 0.0012 at 14 GHz in the ultra-low-Df glass version (3.13 / 0.0016 with low-Dk glass). Choose it when channel loss is the limit, specify the exact part number, glass, copper and constructions, and use construction-specific Dk and Df in your model. Contact us with your stackup for a quote.
FAQ
What is Megtron material? Panasonic’s family of low-loss circuit board laminates and prepregs for high-speed digital boards; MEGTRON 4, 6, 7 and 8 have progressively lower loss.
What are the Megtron 8 specs? On Panasonic’s R-5795 datasheet: Tg 220°C (DMA), Td 370°C, T288 over 120 minutes, Z-axis CTE 50/270 ppm/°C, and Dk/Df of 3.08/0.0012 (ultra-low-Df glass) or 3.13/0.0016 (low-Dk glass) at 14 GHz.
Is Megtron 8 better than Megtron 7? For loss, yes: Panasonic states about 30% lower transmission loss at 28 GHz. Whether you need it depends on your channel budget.
Is Megtron 8 only for AI servers? No. Panasonic also lists routers, switches, optical transmission equipment, base stations, semiconductor test equipment and probe cards.
Can I substitute another material for Megtron 8? Only if your customer allows it and the alternative meets your modeled Dk, Df, copper, reliability and test requirements at the same frequency and method.
Sources
- Panasonic Industrial Devices, R-5795 datasheet (July 2024)
- Panasonic Industrial Devices, MEGTRON 8 product page
- Panasonic Industrial Devices, MEGTRON8 / MEGTRON8S product page
- Panasonic Industrial Devices, Low-loss MEGTRON 8 joins the MEGTRON family
- Siemens EDA, Avoid overspending on stackup materials in your PCBs
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