KEM-828 Low Loss Laminate: High Frequency PCB Material for RF and 5G Applications

The rollout of 5G infrastructure and the proliferation of high-frequency RF devices have fundamentally changed the requirements for printed circuit board (PCB) substrates. In the previous era of 4G/LTE, standard FR-4 materials were often sufficient for most consumer and industrial designs. However, as we move into the sub-6GHz and millimeter-wave (mmWave) spectrums, the dielectric performance of the laminate becomes the limiting factor for signal integrity and system efficiency.

As a PCB engineer, you know that “Low Loss” isn’t just a marketing buzzword—it is a survival requirement for high-speed signals. The KEM-828 low loss laminate has emerged as a critical material in this transition. This guide provides a comprehensive technical breakdown of KEM-828, exploring its electrical properties, thermal stability, and its specific role in the 5G ecosystem.

Understanding the KEM-828 Low Loss Laminate Material System

KEM-828 (frequently referenced in the industry alongside high-performance series like EM-828) is a halogen-free, high-Tg (Glass Transition Temperature) substrate engineered for low dielectric loss and stable permittivity across a wide frequency range. While traditional laminates rely on standard brominated epoxy resins, KEM-828 utilizes a modified multifunctional epoxy or PPE (Polyphenylene Ether) blend to achieve its superior electrical profile.

The “Low Loss” designation specifically refers to the material’s Dissipation Factor (Df). In high-frequency applications, energy is lost as heat within the dielectric material. KEM-828 is designed to minimize this energy absorption, ensuring that the maximum amount of signal reaches the receiver without distortion or excessive attenuation.

Key Characteristics of the KEM-828 System

Halogen-Free Chemistry: Meets global environmental standards (RoHS/REACH) while providing better thermal resistance than older brominated systems.

High Glass Transition Temperature (Tg): Usually ranging between 170°C and 190°C, providing stability during lead-free reflow.

Optimized Resin Content: Balanced to provide the necessary flow for high-density interconnect (HDI) filling while maintaining a low dielectric constant.

Moisture Resistance: Extremely low water absorption ensures that the Dk (Dielectric Constant) does not drift in humid environments.

Technical Specifications: The Engineer’s Datasheet

When specifying a laminate for an RF project, the datasheet is the first point of contact. KEM-828 is designed to compete with industry-standard mid-to-low loss materials, providing a more cost-effective alternative to premium PTFE (Teflon) substrates without sacrificing the reliability needed for 5G base stations.

Table 1: Technical Property Profile of KEM-828 Low Loss Laminate

Property	Typical Value	Test Method
Glass Transition Temp (Tg)	180°C (DSC) / 200°C (DMA)	IPC-TM-650 2.4.25
Dielectric Constant (Dk) @ 10GHz	3.6 – 3.8	Cavity Resonator
Dissipation Factor (Df) @ 10GHz	0.007 – 0.009	Cavity Resonator
Decomposition Temp (Td)	380°C	TGA (5% weight loss)
CTE Z-Axis (Before Tg)	40 – 45 ppm/°C	TMA
CTE Z-Axis (After Tg)	220 – 240 ppm/°C	TMA
Total Z-Axis Expansion (50-260°C)	2.6% – 2.9%	TMA
Water Absorption	0.08%	IPC-TM-650 2.6.2.1
Peel Strength (1 oz Copper)	1.4 – 1.6 N/mm	IPC-TM-650 2.4.8
Flammability	UL 94 V-0	UL94

RF Performance and Dielectric Stability

For 5G and RF designs, the stability of the Dielectric Constant (Dk) and Dissipation Factor (Df) across both frequency and temperature is more important than the nominal value itself. If the Dk shifts significantly as the board heats up, the impedance of your transmission lines will drift, leading to signal reflections and degraded “eye diagrams” in digital circuits.

Frequency Response

KEM-828 shows remarkable flatness in its Dk/Df curve from 1GHz up to 20GHz. In sub-6GHz 5G applications (n77, n78 bands), this stability allows designers to use standard impedance calculators with high confidence. Even as we enter the lower mmWave bands (24GHz – 28GHz), KEM-828 maintains sufficient signal integrity for short-reach interconnects and antenna arrays.

Temperature Coefficient of Dielectric Constant (TCDk)

Materials like KEM-828 are specifically formulated to have a low TCDk. This means that as the 5G base station outdoor unit (ODU) experiences seasonal temperature swings from -40°C to +85°C, the phase stability of the RF signals remains within acceptable tolerances. This is a critical advantage over standard FR-4, which can see Dk swings of 5% or more over that same range.

5G Applications: Where KEM-828 Shines

The 5G ecosystem is divided into various hardware categories, each with different material requirements. KEM-828 fits perfectly into the “Performance-to-Cost” sweet spot for several key 5G components.

1. 5G Small Cells and Macro Base Stations

In a 5G macro cell, the Massive MIMO (Multiple Input, Multiple Output) antenna systems require hundreds of RF paths. Using pure PTFE for these large boards is prohibitively expensive. KEM-828 is often used in the digital-to-analog conversion layers and the RF distribution network because it processes like FR-4 but performs like a high-speed material.

2. High-Speed Servers and Data Centers

The backbone of 5G is the edge computing and data center infrastructure. These systems use high-speed SerDes (Serializer/Deserializer) interfaces operating at 56Gbps or 112Gbps. The KEM-828 low loss laminate is frequently specified for these high-layer-count (20+ layers) backplanes because its low Z-axis expansion ensures via reliability even in very thick boards.

3. Automotive Radar and V2X

Vehicle-to-Everything (V2X) communication and ADAS (Advanced Driver Assistance Systems) rely on 77GHz radar and sub-6GHz communication. While the 77GHz sensor head might use an ultra-low-loss PTFE material, the main processing board—which handles massive amounts of high-speed data—regularly utilizes KEM-828 to maintain signal integrity without the mechanical fragility of PTFE.

Comparative Analysis: KEM-828 vs. Competitors

To understand the value proposition of KEM-828, we must compare it to industry benchmarks like Panasonic’s Megtron series and Rogers Corporation’s hydrocarbon laminates.

Table 2: Comparative Analysis of High-Performance Laminates

Material	Category	Df @ 10GHz	Relative Cost	Ease of Fab
KEM-828	Low Loss	0.008	Medium	Excellent
Megtron 6	Ultra-Low Loss	0.004	High	Good
Rogers 4350B	RF / Hydrocarbon	0.0037	Very High	Fair
Standard FR-4	General Purpose	0.022	Low	Excellent
kingboard PCB (KB-6167G)	High-Tg / Low Loss	0.009	Medium-Low	Excellent

As shown in the table, while Rogers 4350B and Megtron 6 offer lower loss tangents, KEM-828 provides a significant performance jump over standard FR-4 while remaining much more affordable and easier to manufacture than the ultra-premium options. For many 5G designs, a Df of 0.008 is more than sufficient for the loss budget, making KEM-828 the more efficient choice for the bill of materials.

PCB Fabrication and Manufacturing Insights

One of the biggest advantages of the KEM-828 material system is that it does not require the specialized processing equipment or chemicals (like sodium etch) that PTFE-based materials demand.

Drilling and Desmear

Because KEM-828 is a thermoset epoxy-based system, it can be drilled using standard carbide bits. However, engineers should be aware that the fillers used to achieve “low loss” can be more abrasive than those in standard FR-4.

Tip: Ensure your fabricator uses a “shorter hit count” for drill bits to maintain hole wall quality.

Desmear: KEM-828 responds well to standard plasma or permanganate desmear processes, ensuring a clean copper-to-copper interconnect in multilayer boards.

Lamination Parameters

The multifunctional resin in KEM-828 has a specific viscosity window. For complex multilayer builds, the lamination press cycle should include a controlled ramp rate (typically 1.5°C to 2.5°C per minute) to prevent resin-starved areas or voids. The high Td (Decomposition Temperature) of 380°C makes it exceptionally robust against delamination during sequential lamination cycles.

Designing for High-Speed: Copper Foil and Glass Weave

When using a high-performance material like the KEM-828 low loss laminate, your design should also consider the “secondary” loss factors: copper roughness and the glass weave effect.

Copper Foil Selection

At 5G frequencies, the “skin effect” means that current travels on the very outer surface of the copper trace. If the copper is rough (standard ED copper), the signal has to travel a longer path, increasing the effective resistance and loss.

HVLP Copper: It is highly recommended to specify Very Low Profile (VLP) or Hyper Very Low Profile (HVLP) copper when ordering KEM-828. This can reduce total insertion loss by 20% compared to standard copper.

Mitigating the Glass Weave Effect

High-speed differential pairs can suffer from “skew” if one trace runs over a glass bundle while the other runs over a resin-rich area (the Dk mismatch).

Flat Glass: Specify “spread glass” or “flat glass” styles (like 1067 or 1086) for KEM-828 prepregs to ensure a more uniform dielectric constant across the board surface.

Useful Resources and Database Links

For engineers needing deeper technical integration, the following resources are essential:

IPC-4101 Slash Sheets: KEM-828 generally falls under the /126, /129, or /131 categories for high-Tg, halogen-free materials.

Material Databases: Many manufacturers provide Z-axis expansion and Dk/Df data for Altium or Cadence Allegro material libraries.

Kingboard PCB Technical Center: Detailed fabrication guidelines and comparative data for high-reliability substrates.

UL iQ Database: Search for manufacturer UL files to verify flammability and RTI (Relative Thermal Index) for the KEM-828 series.

Frequently Asked Questions (FAQs)

1. Is KEM-828 compatible with lead-free soldering?

Yes. With a Td of 380°C and a Tg of 180°C+, KEM-828 is fully compatible with lead-free reflow profiles (peak 260°C) and can withstand multiple heat cycles without risk of delamination or pad lifting.

2. Can KEM-828 be used for mmWave applications above 28GHz?

While KEM-828 is excellent for sub-6GHz and 10-20GHz signals, it is often used as a “hybrid” material for mmWave. Designers may use a premium PTFE material for the antenna layer and KEM-828 for the inner signal and power layers to balance performance and cost.

3. Does KEM-828 help with CAF (Conductive Anodic Filament) resistance?

Absolutely. The high-Tg halogen-free resin system in KEM-828 is designed with superior CAF resistance, making it suitable for high-reliability automotive and telecom designs where small via-to-via spacing is required.

4. How does the cost of KEM-828 compare to FR-4?

KEM-828 is more expensive than standard FR-4 (roughly 1.5x to 2x the base material cost) but is significantly cheaper than RF-specific materials like Rogers 4000 or 3000 series.

5. What are the storage requirements for KEM-828 prepregs?

Like most high-performance prepregs, they should be stored in a temperature-controlled environment (<20°C) and at low humidity (<50% RH) to maintain the resin’s flow properties and prevent moisture absorption before lamination.

Final Engineering Perspective on KEM-828

The KEM-828 low loss laminate represents the pragmatic side of high-frequency design. While there will always be a need for “exotic” PTFE materials at the very edge of the millimeter-wave spectrum, the bulk of 5G infrastructure—from the backhaul to the edge servers—requires a material that is reliable, easy to build, and cost-conscious.

By providing a stable Dk, low loss tangent, and excellent thermal properties, KEM-828 allows engineers to push the boundaries of 5G and RF performance without reinventing the manufacturing wheel. When your loss budget is tight, but your project budget is tighter, KEM-828 is a standout candidate for your next high-speed stackup.