Mixed-substrate multilayer stackup
Timelines and summary
Due to a stock outage, our supplier could not use FR408-HR cores for a duration in June 2026. The boards were fabbed with FR408HR pre-preg and an EM528 core.
- 2026-JUN-09: First date EM528 may have been used in production
- 2026-JUN-16: FR408HR availability issues resolved.
During this time, some boards would have an EM528 core, which is identifiable with a red substrate. Any affected customers were notified.
- 2026-JUL-21: Notice of FR408HR supply shortage recieved
- 2026-AUG 3: Estimated resupply date.
During this period, a few orders in process were fabbed with this stackup, and users notified. Most orders were with-held unless opted into this stackup.
What do to if this substrate is unacceptable
We know how demanding our customers are, and that equivilent is not identical. If this substrate does not work for your application, please contact us.
4 Layer FR408HR+EM528 Stackup
This fabricated stackup maintains the typical FR408HR prepreg between layers 1+2 and 3+4, maintaining compatibility with expected impedences.
The change is only to the core material, which will be a red color.
| Layer | Material | Dk | Df |
|---|---|---|---|
| 1oz copper | |||
| 7.87 mil prepreg | FR408HR 2113 prepreg | 3.61 | |
| 0.5oz copper | |||
| 39.00mil core | EM-528 5x7628 | 4.11 | 0.005 |
| 0.5oz copper | |||
| 7.87 mil prepreg | FR408HR 2113 prepreg | 3.61 | |
| 1oz copper |
6 Layer FR408HR+EM528 Stackups
This fabricated stackup maintains the typical FR408HR prepreg between layers 1+2+3 and 4+5+6, maintaining compatibility with expected impedences.
The change is only to the core material, which will be a red color.
| Layer | Material | Dk | Df |
|---|---|---|---|
| 1oz copper | |||
| 4.36 mil (0.1107mm) | FR408HR 106 75% prepreg | 3.23@1Ghz | 0.011 |
| 0.5oz copper | |||
| 4 mil (0.1016mm) | FR408HR 2113 core | 3.66@1Ghz | 0.009 |
| 0.5oz copper | |||
| 21mil core | EM-528 - 3x7628 | 4.11 | 0.005 |
| 0.5oz copper | |||
| 4 mil (0.1016mm) | FR408HR 2113 core | 3.66@1Ghz | 0.009 |
| 0.5oz copper | |||
| 4.36 mil (0.1107mm) | FR408HR 106 75% prepreg | 3.23@1Ghz | 0.011 |
| 1oz copper |
Comparison of cores
The boards are visually distinguishable; The EM528 is a visible reddish color, compared to a milky white of FR408-HR. This is visible on the sides of the board, or on any exposed board surface.
These are the major changes between the cores
| Value | FR408HR | EM528 | - |
|---|---|---|---|
| Datasheet | FR408-HR | EM528 | |
| Volume Resistivity | 4.4*10^7 | >10^10 | Mohm-CM |
| Surface Resistivity | 2.6*10^6 | > 10^9 | Mohm |
| Td(TGA) | 360 | 420 | °C |
| Tg (DMA) | 230 | 250 | °C |
| Tg (TMA) | 220 | °C | |
| Tg (DSC) | 190 | °C | |
| Thermal Conductivity | 0.4 | 0.6 | W/mK |
| Water Absorption | 0.061 | 0.11 | % |
| Flame Resistance | UL-94 V-0 | UL-94 V-0 | |
| Substrate color | white | red |
The following information is not currently available.
- Outgassing information
- Dielectric Breakdown
- Arc Resistance
- CTI
- RTI
