Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
What Is Df (Dissipation Factor) in PCB Laminates? A Complete Guide
If you have been designing RF boards or high-speed digital circuits for any length of time, you already know that material selection can make or break a design before you ever fire up your layout tool. And somewhere in that stack of laminate datasheets, two numbers keep showing up: Dk and Df. Most engineers grasp Dk fairly quickly — it’s about how fast signals travel through the substrate. But PCB dissipation factor Df is the one that quietly kills your signal budget when you are not paying attention.
This guide breaks down everything you need to know about Df in PCB laminates — what it means physically, how it affects your design at real-world frequencies, how to compare materials using it, and where to find reliable data. Written from a working PCB engineer’s perspective, not a textbook.
What Is the Dissipation Factor (Df) in PCB Laminates?
The dissipation factor (Df), also called loss tangent or tan δ, is a measure of how much electromagnetic signal energy is converted into heat as it passes through the dielectric material of a PCB laminate. The lower the Df value, the less energy the material absorbs, and the cleaner your signal arrives at the other end of the trace.
Think of it this way: every time a signal travels through the dielectric, the alternating electric field causes the polar molecules in the resin to continuously try to realign themselves. This molecular friction generates heat. Df quantifies exactly how much of that conversion is happening.
Mathematically, Df is expressed as:
Df = tan δ = ε” / ε’
Where:
ε” is the imaginary part of the complex permittivity (the lossy component)
ε’ is the real part of the complex permittivity (the storage component, related to Dk)
In practical terms, the dissipation factor tells a designer how lossy a material may be — it defines the ability of an insulator to store versus lose energy. A high Df means the material is working more like a resistor than an insulator when RF energy is present.
Df vs. Loss Tangent vs. Tan δ — Are They the Same Thing?
Yes, completely. You will see all three terms used interchangeably on datasheets and in design literature:
Df — common in PCB laminate datasheets (e.g., Rogers, Isola, Panasonic)
Tan δ — common in microwave and RF literature
Loss tangent — more common in academic and signal integrity contexts
They all refer to the same physical quantity. When you see any of these on a datasheet, you are looking at the same number.
Why PCB Dissipation Factor Df Matters for Signal Integrity
Df and Dielectric Loss
Df shows how much of the signal energy turns into heat as it travels through the dielectric. This heat loss is called dielectric loss, and it is one of two major loss mechanisms in a PCB transmission line. The other is conductor loss, caused by skin effect in the copper trace.
At lower frequencies (below 1 GHz), conductor loss often dominates and dielectric loss is relatively minor. But as you push into multi-GHz territory — think 10G/25G Ethernet, PCIe Gen 4/5, 5G mmWave, SERDES lanes at 56 Gbps — dielectric loss becomes the primary constraint. At these speeds, a poorly chosen laminate can eat your entire link budget before the signal ever reaches the far-end receiver.
How Df Increases with Frequency
Here is something that catches engineers off guard: Df is not a fixed number. Dk and Df are not constant across all frequencies. As signal frequency increases, Df increases slightly with frequency. This is why datasheets from responsible manufacturers like Rogers and Isola publish Df values at multiple frequency points — typically 1 GHz, 2 GHz, 5 GHz, 10 GHz, and sometimes up to 40 GHz.
If you are designing for 28 Gbps SERDES (where the fundamental content reaches 14 GHz and harmonics go higher), using the 1 GHz Df figure from a datasheet in your simulation will give you an overly optimistic loss estimate. Always use the Df value measured at or near your operating frequency.
Df and Its Impact on Insertion Loss
Insertion loss in a transmission line is directly proportional to Df. The relationship is approximately:
Dielectric Attenuation (dB/in) ∝ f × √Dk × Df
Where f is signal frequency. This tells you that for a given frequency and Dk, cutting your Df in half roughly halves the dielectric portion of your insertion loss. That can be the difference between a passing and failing channel at 25 Gbps.
Typical Df Values for Common PCB Laminate Materials
Understanding where different materials fall on the Df spectrum helps set expectations during early stack-up planning. Here is a practical reference:
Values are representative and may vary by glass style, resin content, and test method. Always verify with manufacturer datasheets.
Df by Application Category
Df Range
Classification
Typical Applications
> 0.015
High loss
General-purpose consumer PCBs, <1 GHz
0.008 – 0.015
Medium loss
Industrial control, <5 Gbps links
0.003 – 0.008
Low loss
10–25 Gbps SERDES, 5G sub-6 GHz
0.001 – 0.003
Very low loss
mmWave radar, 56 Gbps+ SERDES
< 0.001
Ultra-low loss
Satellite, military, phased array radar
What Affects the Df of a PCB Laminate?
Resin Chemistry
The resin system is the single biggest driver of Df. Standard epoxy (as used in FR-4) has higher polar molecular content, which means more molecular friction under an alternating electric field. Modified polyphenylene ether (PPE/PPO) resins like those in Megtron 6 have lower polarity and thus lower Df. PTFE (Teflon) is essentially non-polar, which is why it delivers the lowest Df values of any commercial laminate family.
Glass Fiber Content and Weave Style
Differences in resin content percent have a significant effect on the Dk and Df values. The resin content percent varies based on the glass style, on target thickness for a given glass style, and manufacturing tolerances. More resin in a given prepreg generally means slightly higher Df because the resin carries more of the dielectric loss burden than the glass fibers.
Frequency
As discussed earlier, Df climbs with frequency. The rate of increase varies significantly between material families. Standard FR-4 shows a steep upward slope past 1 GHz, while PTFE-based laminates remain nearly flat well into the millimeter-wave range. This slope behavior is why some materials that look acceptable at 1 GHz become completely unworkable at 28 GHz.
Temperature and Moisture Absorption
An additional concern arises around the effect of operating temperatures upon the effective Dk and Df of PCB materials. Due to thermal radiation from active IC devices, power supplies, etc., the operating temperature of PCBs within a network equipment chassis is typically higher than the 23–25°C value at which Dk and Df are measured and reported.
Moisture absorption has a similar effect. Standard PCB laminates have moisture absorption values of 2% or more, which means in a humid environment the laminate can absorb moisture readily and the electrical properties change significantly. High-performance RF laminates, particularly PTFE-based materials, are specifically engineered for low moisture absorption to maintain stable electrical properties in variable environments.
Copper Roughness (an Indirect Effect)
While not a property of the dielectric itself, copper surface roughness affects how accurately you can extract Df from measurements. Industry-standard methods assume the smooth copper case, with consequent frequency-dependent error introduced into extracted values of Df. The main errors induced in extracted values of Df result from increased conductor losses due to surface roughness. This is particularly important to understand when comparing Df values measured using different test vehicles.
How to Read Df on a PCB Laminate Datasheet
If you are looking at a datasheet and feeling confused about which Df number to use, here is a quick field guide.
Test Method Matters
One of the complications with laminate vendor-supplied data is that a lot come from different IPC test methods. The most common ones you will encounter include IPC-TM-650 2.5.5 (clamped stripline), the split-post dielectric resonator method, and the full-sheet resonance (FSR) method. Each can yield slightly different numbers for the exact same material. When comparing two competing laminates, make sure the Df values you are looking at were measured using the same test method — otherwise you are comparing apples to oranges.
Frequency of Measurement
Check what frequency the Df was measured at. Many standard FR-4 datasheets report Df at 1 MHz using the IPC-2.5.5 method — a number that is essentially useless for any design running above a few hundred MHz. For modern high-speed designs, you want Df at 1 GHz as a minimum, and ideally at your actual operating frequency.
Datasheet Reading Checklist
Parameter to Check
Why It Matters
Test frequency
Df climbs with frequency — match to your application
Test method (IPC-TM number)
Ensures apples-to-apples comparison between vendors
Resin content %
Df varies with resin content, not just material type
Conditioning (dry vs. humid)
Some datasheets show wet conditioned values
Temperature of measurement
Usually 23°C; may differ under real operating conditions
FR-4 vs. High-Frequency Laminates: Df in the Real World
When FR-4 Df Is Acceptable
Standard FR-4 works perfectly well for the vast majority of digital PCB designs. If your fastest signals are below about 1 GHz, or you are designing general-purpose MCU boards, power supplies, or anything not specifically involving RF or multi-gigabit serial links, the Df of FR-4 is not going to cause you problems. The cost advantage is enormous, and the manufacturing ecosystem is universally available.
When FR-4 Df Becomes a Problem
FR-4 has a higher dissipation factor than laminates engineered for high-frequency use, so circuits fabricated on FR-4 will suffer higher losses. Typical values are about 0.020 for FR-4 and about 0.004 for a high-frequency laminate — a dissipation factor about one-fourth that of FR-4. This difference directly translates into a meaningful difference in insertion loss at GHz frequencies.
With typical Df values at ~0.020 at 10 GHz, using a standard FR4 board yields much higher losses as PCB frequency rises — an unacceptable degradation in performance that calls for custom dielectrics which dissipate less RF energy at higher frequencies.
A practical rule of thumb many RF engineers use: if your design exceeds 2 GHz operating frequency, or if you are running SERDES links above 10 Gbps, it is time to seriously evaluate whether FR-4 Df is going to blow your loss budget.
PTFE vs. Hydrocarbon Ceramic Laminates
Within the high-performance laminate world, there is a further choice between PTFE-based materials and ceramic-filled hydrocarbon systems like the Rogers RO4000 series.
PTFE has a very low dissipation factor, around 0.0001 to 0.0020, so signals stay strong at high frequencies. In contrast, FR-4 has higher values between 0.008 and 0.022, which causes more signal loss.
The RO4000 series lands in the middle — Df values around 0.003 to 0.004, but with the fabrication-friendly processing characteristics of standard FR-4. Rogers laminates boast very low Df values, often below 0.004, and unlike pure PTFE, the RO4000 series does not require special through-hole preparation or extra technological processes.
How to Choose the Right Df for Your PCB Design
Step 1 — Establish Your Frequency and Data Rate
Before touching a material datasheet, know your operating frequency. For RF designs, this is your carrier frequency. For SERDES designs, it is roughly half your data rate (the Nyquist frequency), though you need to consider harmonics as well. A 28 Gbps NRZ link has significant energy content up to around 28 GHz when harmonics are considered.
Step 2 — Calculate Your Loss Budget
Work out the maximum allowable insertion loss for each channel. Subtract estimated connector and via losses. What remains is your trace loss budget. From this, you can back-calculate the maximum Df you can tolerate for a given trace length.
Step 3 — Shortlist Materials
As Df decreases, material cost tends to increase. For cost-sensitive products, trade-offs between performance and price must be carefully managed. Use the Df comparison tables above to narrow your shortlist to two or three candidate materials that meet your electrical target at an acceptable price point.
Step 4 — Verify with Simulation
Use field-solver tools (Ansys SIwave, HyperLynx, Cadence Clarity, or even Saturn PCB Toolkit for quick estimates) to run insertion loss simulations using the Df values at your actual operating frequency. Do not rely solely on hand calculations at this stage.
Step 5 — Pilot Build and Measure
For production designs, especially at 25 Gbps and beyond, always build a pilot board with your chosen material and measure actual insertion loss using a VNA. Material batches can vary, and simulation never tells the complete story.
Useful Df and PCB Material Resources
Below is a curated list of authoritative resources that every PCB engineer dealing with dissipation factor should bookmark:
Frequently Asked Questions About PCB Dissipation Factor Df
1. What is a good Df value for a high-speed PCB?
It depends entirely on your data rate and trace length. As a practical starting point: for 10 Gbps links, a Df below 0.010 is generally acceptable for moderate trace lengths. For 25 Gbps, aim for Df below 0.005. For 56 Gbps PAM4 or mmWave RF, you want Df below 0.003. Run a proper loss budget calculation with your specific stack-up parameters rather than relying on rules of thumb alone.
2. Is Df the same as dielectric loss?
Not exactly. Df (loss tangent) is a material property — a dimensionless ratio describing how lossy the dielectric is relative to how much energy it stores. Dielectric loss (or dielectric attenuation) is the actual signal loss that results in your specific design, expressed in dB/inch. Dielectric loss depends on Df, Dk, frequency, and trace geometry all together. Df is the material input; dielectric attenuation is the design output.
3. Why does my laminate Df value change between datasheets from the same manufacturer?
Several reasons: the test method used (IPC-TM-650 clamped stripline vs. split-post resonator), the frequency of measurement, the resin content of the specific sample, and whether the sample was measured dry or after humidity conditioning. Always check the test conditions footnote on the datasheet, and when comparing two materials, insist on data from the same test method and frequency.
4. Can I use FR-4 for a 5G antenna PCB?
For sub-6 GHz 5G designs, modified epoxy laminates (like Isola FR408HR or Panasonic Megtron 6) can sometimes work with careful engineering. Standard FR-4 is generally not suitable due to its Df of 0.015–0.022, which creates excessive insertion loss at 3.5–6 GHz carrier frequencies. For mmWave 5G at 28 GHz or above, PTFE or high-quality ceramic hydrocarbon laminates are required — FR-4 of any grade will not perform acceptably.
5. Does copper roughness affect Df measurements?
Yes, and this is an often-overlooked subtlety. When Df is extracted from insertion loss measurements using stripline test vehicles, the measured insertion loss includes both dielectric loss and conductor loss. If the copper is rough (standard electrodeposited copper can have Rz values of 2–6 µm), the increased conductor loss gets partially attributed to Df in the extraction algorithm, inflating the apparent Df value. Smoother copper (reverse-treated foil or HVLP foil) gives more accurate Df extraction and also reduces conductor loss directly in your design.
Summary: Key Takeaways for PCB Engineers
PCB dissipation factor Df is not just a number on a datasheet — it is one of the primary constraints that separates a design that works from one that barely passes compliance testing. As data rates and carrier frequencies continue climbing, understanding Df and choosing materials accordingly becomes less of an advanced specialization and more of a basic engineering requirement.
The core principles are simple: lower Df means less signal energy converted to heat, which means better signal integrity and more margin in your loss budget. PTFE delivers the lowest Df, hydrocarbon ceramics offer an excellent middle ground, and modified epoxy systems bridge the gap between standard FR-4 and full RF-grade laminates. Match your material to your frequency, validate with simulation, and measure on real hardware before committing to production volumes.
Material selection and stack-up planning early in the design cycle is far cheaper than re-spins caused by link failures discovered in compliance testing.
Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
