Shengyi S7135 Low-Loss Laminate: Complete RF PCB Design Guide & Datasheet

In the high-frequency design world, we often talk about the “loss budget” as if it’s a finite bank account. Every millimeter of trace and every via is a withdrawal. If you’re designing for 5G small cells, high-gain antennas, or satellite LNBs, you need a substrate that doesn’t bankrupt your signal before it even reaches the connector.

The Shengyi S7135 RF PCB material is a hydrocarbon-based, ceramic-filled laminate designed to be a high-performance alternative to traditional PTFE (Teflon) materials. While PTFE is the undisputed king of low loss, it’s a nightmare to process in a standard PCB shop. S7135 bridges that gap—offering the electrical “quietness” of high-frequency specialty resins with the mechanical “friendliness” of standard thermoset materials.

What is Shengyi S7135? The “Middle Ground” Solution

The S7135 is part of Shengyi’s specialized RF/Microwave portfolio. It is engineered to provide a stable Dielectric Constant ($Dk$) and a very low Dissipation Factor ($Df$) across a broad frequency spectrum, typically from 1 GHz up to 20 GHz.

From an engineering perspective, the S7135 is a thermoset hydrocarbon laminate. Why does that matter? Because unlike PTFE (which is a thermoplastic that “creeps” or flows under heat and pressure), S7135 stays dimensionally stable. This makes it ideal for hybrid multilayer boards—where you might have S7135 on the top RF layers and standard FR-4 (like S1141) on the inner layers for power and ground.

Key Features for RF Designers:

Stable Dk/Df: Minimal drift across temperature ($ -40^{\circ}C$ to $+150^{\circ}C$) and frequency.

Low Z-Axis Expansion: Enhances the reliability of plated-through holes (PTH) in thick boards.

Excellent Thermal Conductivity: At $0.66$ W/m·K, it helps pull heat away from power amplifiers (PAs).

Process Compatibility: Can be fabricated using standard FR-4 processes, avoiding the need for plasma or sodium-etch treatment.

Technical Specifications: S7135 Datasheet Analysis

When you open the Shengyi S7135 RF PCB material datasheet, you’re looking for the parameters that will define your impedance model. Below are the typical values you’ll need for your ADS or HFSS simulations.

Table 1: Electrical Properties

Property	Test Method	Frequency	Typical Value
Dielectric Constant (Process Dk)	IPC-TM-650 2.5.5.5	10 GHz	$3.42 \pm 0.05$
Dielectric Constant (Design Dk)	Differential Phase	10 GHz	$3.61$
Dissipation Factor (Df)	IPC-TM-650 2.5.5.5	10 GHz	$0.0030$
Thermal Coefficient of Dk (TcDk)	IPC-TM-650	-40~150°C	$50$ ppm/$^{\circ}C$
Volume Resistivity	IPC-TM-650 2.5.17.1	–	$1.1 \times 10^8 M\Omega \cdot cm$

Engineer’s Note: Always use the Design Dk (3.61) for your impedance calculations. The Process Dk (3.42) is measured using the “clamped stripline” method, which often includes a tiny air gap that artificially lowers the value. For real-world microstrip traces, the higher Design Dk is more accurate.

Table 2: Thermal and Mechanical Properties

Property	Test Method	Unit	Typical Value
Glass Transition Temp (Tg)	DSC	$^{\circ}C$	$>280$
Decomposition Temp (Td)	TGA (5% loss)	$^{\circ}C$	$390$
Thermal Conductivity	ASTM D5470	W/m·K	$0.66$
CTE (X/Y axis)	TMA	ppm/$^{\circ}C$	$12 / 14$
CTE (Z-axis)	TMA	ppm/$^{\circ}C$	$45$
Water Absorption	IPC-TM-650 2.6.2.1	%	$0.06$

The $Tg$ of $>280^{\circ}C$ is exceptionally high. This means the material is practically “immobile” during lead-free reflow, significantly reducing the mechanical stress on your solder joints and delicate SMT components.

RF Design Guide: Optimizing for S7135

Designing with the Shengyi S7135 RF PCB material requires more than just picking a part number. You have to consider the physical geometry of the signal path.

1. Copper Foil and Skin Effect

At 10 GHz and above, the “skin depth” of the signal is very shallow—about $2 \mu m$. If the copper surface is rough, the signal has to travel a longer physical distance over the “peaks and valleys” of the copper, which increases resistive loss.

Recommendation: Specify Reverse Treated Foil (RTF) or HVLP (Hyper-Very Low Profile) copper for S7135 designs. This can reduce your insertion loss by up to 20% at high frequencies compared to standard ED copper.

2. Hybrid Stackups for Cost Reduction

If your board is 6 layers but only two traces are RF, you don’t need S7135 for the whole stack. You can use S7135 for the top layer and L2, and use a high-reliability FR-4 for the rest.

The “Shengyi Match”: Pair S7135 with <a href=”https://www.pcbsync.com/Shengyi-pcb/“>Shengyi PCB</a> materials like S1000-2M for the core. Their CTEs are reasonably compatible, preventing delamination during thermal cycling.

3. Thermal Management for Power Amplifiers

RF PAs generate significant heat. Standard FR-4 has a thermal conductivity of about $0.25$ W/m·K. S7135 is $0.66$ W/m·K. While it isn’t a “metal core” board, it’s nearly 3x better at dissipating heat than standard material. Use large ground planes and “thermal via farms” under your high-power components to take full advantage of this.

Fabrication Guidelines: Avoiding Common Pitfalls

Since S7135 is a hydrocarbon/ceramic material, your fab shop doesn’t need a specialized PTFE line, but they do need to adjust their standard FR-4 parameters.

Drilling: The ceramic filler is abrasive. Fabricators should use new drill bits and limit the “hit count” to 1000-2000 holes before changing tools. If they use dull bits, you’ll get “smear” or rough hole walls that ruin your PTH plating.

Desmear: Standard chemical desmear works fine, but some high-reliability designs benefit from a light plasma cycle to ensure the resin is perfectly cleaned from the copper interconnects.

Baking: Because it’s a high-frequency material, moisture is the enemy of Df. A pre-bake of $140-150^{\circ}C$ for 2 hours before lead-free soldering or tin spraying is highly recommended to prevent “white spots” or delamination.

Top Applications for S7135

Where does this material provide the most value?

5G Infrastructure: Distributed Antenna Systems (DAS) and MIMO antennas where cost and low loss must be balanced.

Satellite LNBs: Low Noise Block downconverters for residential satellite TV and data.

Automotive Telematics: 2.4 GHz and 5.8 GHz communication modules.

Power Amplifiers: Where thermal management and stable Dk are critical for maintaining the “P1dB” compression point.

Technical Resources & Downloads

To finalize your design, I recommend downloading the following “ground truth” documents:

S7135 Official Datasheet: Download via Syst.com.cn

Shengyi RF Material Selection Guide: Useful for comparing S7135 vs. S7136 or Synamic series.

IPC-4103/11 Slash Sheet: The industry specification that S7135 is designed to meet.

UL File Number E109769: Verification of the 94V-0 flammability rating.

Frequently Asked Questions (FAQs)

1. Is S7135 a direct alternative to Rogers 4350B?

Yes, they are in the same “class” (hydrocarbon ceramic). While the Dk/Df values are slightly different (3.61 vs 3.66), many engineers use S7135 as a cost-effective alternative for high-volume production where Rogers lead times or costs are prohibitive.

2. Can I use S7135 for 77 GHz radar designs?

I wouldn’t recommend it. For 77 GHz, you really need a PTFE-based material like Shengyi mmWave77 or S7439. S7135 is better suited for the “Sub-6GHz” and “X-band” (up to 12-15 GHz) ranges.

3. Does S7135 require plasma treatment?

Generally, no. Unlike PTFE materials, S7135 has a resin chemistry that is compatible with standard chemical desmear. However, for extremely high-reliability military or aerospace projects, plasma is always a “best practice.”

4. What is the shelf life of S7135 prepreg?

Under standard storage ($<23^{\circ}C$, $<50\%$ RH), the shelf life is 3 months. If kept in cold storage ($<5^{\circ}C$), it is 6 months.

5. Why is the CTE so low for this material?

The high loading of ceramic fillers keeps the X/Y expansion at 12-14 ppm/$^{\circ}C$, which is very close to the CTE of copper (17 ppm/$^{\circ}C$). This matching reduces the stress on the copper foil during thermal expansion, preventing “pad cratering.”

Engineer’s Bottom Line: The Shengyi S7135 RF PCB material is a “safe” high-performance choice. It won’t surprise you with erratic electrical drift, and it won’t frustrate your fabricator with PTFE-style processing issues. It is the workhorse of the mid-range RF industry.