Shengyi S7168 PCB Laminate: Low-Dk Material for High-Speed Signal Integrity

In the current landscape of hardware engineering, we are no longer just designing “boards”; we are designing complex waveguides that happen to be made of copper and resin. As data rates climb toward 56G and 112G PAM4, the margins for error in signal integrity (SI) have effectively vanished. If you’ve spent any time in a lab chasing resonance issues or insertion loss spikes in a backplane, you know that the substrate is usually the first place to look.

The Shengyi S7168 PCB laminate is a high-performance, low-loss, and low-dielectric constant (Low-Dk) material engineered specifically to meet these ultra-high-speed challenges. It sits in the “Very Low Loss” category of the Shengyi portfolio, acting as a direct answer to the industry’s demand for stable electricals at millimeter-wave frequencies and beyond.

What is Shengyi S7168? The SI Engineer’s Perspective

From an engineering standpoint, the S7168 is a polyphenylene ether (PPE/PPO) based thermoset system. Unlike standard FR-4, which uses an epoxy resin that becomes “lossy” and electrically unstable as frequency increases, the PPE resin in the Shengyi S7168 PCB laminate maintains a very tight Dielectric Constant (Dk) and Dissipation Factor (Df) curve.

This material is specifically designed for Lead-Free assembly and is optimized for use with Very Low Profile (VLP) or Hyper-Very Low Profile (HVLP) copper foils. In high-speed digital (HSD) design, S7168 provides the low attenuation and phase stability required for long-reach channels in servers, switches, and high-end telecommunications hardware.

Key Performance Drivers:

Stable Dielectric Constant: Prevents impedance mismatches across varying frequencies.

Ultra-Low Dissipation Factor: Minimizes signal attenuation, extending the reach of high-speed traces.

Low Z-axis CTE: Critical for maintaining plated-through hole (PTH) reliability in high-layer count boards.

Glass Fiber Optimization: Often paired with “Low-Dk Glass” (L-Glass) to minimize the fiber-weave effect and differential skew.

Technical Specifications: The S7168 Datasheet Breakdown

When I’m building a stackup at Shengyi PCB for a high-speed project, the first thing I do is pull the “clamped stripline” data. For S7168, the numbers tell a story of extreme stability.

Table 1: Thermal and Physical Properties

Property	Test Method	Unit	Typical Value
Glass Transition Temp (Tg)	DSC	$^{\circ}C$	185
Decomposition Temp (Td)	TGA (5% loss)	$^{\circ}C$	390
T288 (Time to Delamination)	TMA	min	> 60
Z-axis CTE (Before Tg)	TMA	ppm/$^{\circ}C$	38
Z-axis CTE (After Tg)	TMA	ppm/$^{\circ}C$	200
Water Absorption	D-24/23	%	0.05

A $Td$ of $390^{\circ}C$ and a $Tg$ of $185^{\circ}C$ mean this material is incredibly robust during the thermal stress of multiple reflow cycles. The water absorption of 0.05% is almost non-existent, ensuring the board won’t “drift” electrically if it’s deployed in a high-humidity data center environment.

Table 2: Electrical Characteristics (Dk and Df)

Frequency	Dielectric Constant (Dk)	Dissipation Factor (Df)
1 GHz	3.50	0.0028
10 GHz	3.45	0.0032
20 GHz	3.42	0.0035

Note the “flatness” of the Df curve. While standard FR-4 might see its Df double or triple as it approaches 10GHz, the Shengyi S7168 PCB laminate remains virtually constant. This is the difference between a clean eye diagram and a closed one.

Design Considerations for High-Speed Signal Integrity

If you are transitioning a design from a mid-loss material to S7168, you have to account for more than just the Dk value. You are now in the territory where the physical structure of the glass and copper matters as much as the resin.

1. Managing the Fiber Weave Effect

Even with a low-Dk resin, the “knuckles” of the glass weave can cause local Dk variations. For S7168, we highly recommend specifying “Spread Glass” (like 1067 or 1078 styles). This ensures a more uniform dielectric environment, which is essential for minimizing intra-pair skew in differential pairs running at 28Gbps or higher.

2. Copper Foil Selection and Skin Effect

At high frequencies, the current flows on the outer “skin” of the copper. If you use standard ED (Electro-Deposited) copper with a rough surface, your insertion loss will skyrocket regardless of how good the resin is.

Pro Tip: Always pair S7168 with HVLP2 (Hyper-Very Low Profile) copper. This reduces the resistive losses caused by surface roughness and is one of the most cost-effective ways to improve your dB/inch loss budget.

3. Backdrilling and Stub Management

When using a high-performance material like Shengyi S7168 PCB laminate, you cannot afford the parasitic capacitance of via stubs. If your signal transitions from Layer 1 to Layer 3 in a 20-layer board, that remaining via “tail” acts as a resonant stub that will tank your Return Loss (S11). Backdrilling is mandatory for any S7168 design operating above 10GHz.

Fabrication and Processing: The Shop Floor View

One of the reasons S7168 is gaining market share over some Japanese or American competitors is its processability. It doesn’t require the exotic plasma etching associated with PTFE-based materials.

Drilling: Because it is a PPE-based system with specialized fillers, it is relatively “hard” on drill bits. We recommend reduced hit counts to ensure the hole wall quality is high enough for consistent plating.

Desmear: Standard chemical desmear is usually sufficient, though for 24+ layer backplanes, a plasma-plus-chemical desmear cycle provides the best copper-to-inner-layer interconnect reliability.

Lamination: The curing temperature for S7168 is higher than standard FR-4. The press cycle must be carefully controlled to ensure the PPE resin fully cross-links, achieving that $185^{\circ}C$ Tg.

Primary Applications for S7168 Laminate

Where does S7168 truly earn its keep? It’s generally found in the “core” of the global data infrastructure.

Cloud Computing and Data Centers

High-end servers utilizing PCIe Gen 5 and Gen 6 require the thermal stability and low insertion loss that S7168 provides. It allows for longer trace lengths between the CPU and the NVMe storage or NICs without needing expensive retimers.

5G Infrastructure

In 5G base stations and RRUs (Remote Radio Units), signal purity is paramount. S7168 is used in the digital processing sections where high-speed SerDes lines carry massive amounts of data with minimal latency.

Optical Networking

Line cards for 400G and 800G optical modules utilize S7168 to maintain signal integrity from the optical engine to the switch ASIC.

Technical Resources and Downloads

For an accurate simulation in tools like Ansys HFSS or Keysight ADS, you need the official Dk/Df tables.

Official Shengyi S7168 Datasheet: Download PDF – Check for the “High Speed/Low Loss” section.

Shengyi Material Comparison Tool: Useful for comparing S7168 vs. S7439 or S7136.

UL Certificate E109769: Safety and flammability verification.

IPC-4101/102 Specification: The industry standard for PPE-based high-performance laminates.

Frequently Asked Questions (FAQs)

1. How does S7168 compare to Rogers 4350B?

While Rogers 4350B is a hydrocarbon/ceramic material often used in RF, S7168 is a PPE-based material optimized for High-Speed Digital (HSD). S7168 typically offers lower loss (Df) and better processing compatibility for high-layer count multilayer boards compared to the 4350B.

2. Is S7168 “Halogen-Free”?

Shengyi offers halogen-free versions within their high-speed series (look for the “G” or “H” suffixes in related models), but the standard S7168 is focused primarily on achieving the lowest possible Df. Always check the specific part number for environmental compliance requirements.

3. What is the maximum layer count for S7168?

There is no hard limit, but S7168 is commonly used in 24 to 32-layer backplanes. Its low Z-axis CTE (38 ppm/$^{\circ}C$) makes it exceptionally stable for high-aspect-ratio holes in thick PCBs.

4. Can I use S7136 and S7168 in a hybrid stackup?

Yes, but since they are both from the Shengyi high-speed family, they are generally compatible. However, usually, a hybrid stackup involves using S7168 for signal layers and a lower-cost high-Tg FR-4 for power/ground layers to save on the total BOM cost.

5. Why is the water absorption so low?

The PPE resin system is naturally hydrophobic. This is critical because water has a Dk of ~80; even a small amount of moisture absorption in a laminate will cause the Dk to spike, throwing your impedance lines out of spec and increasing signal loss.

Final Summary for Hardware Engineers

The Shengyi S7168 PCB laminate is a surgical tool for signal integrity. It provides the low-Dk and ultra-low-loss performance required to push data rates to the edge of what’s physically possible on a copper substrate. When your loss budget is tight and your frequencies are in the tens of gigahertz, S7168 is one of the most reliable foundations you can build on.