12-Layer High-Speed Digital PCB – TU-872 SLK Low-Loss FR-4 with Via-in-Pad & Impedance Control

Product Description

Q: What is this TU-872 SLK PCB solution, and what does it deliver?

 

A: This is a 12-layer, high-performance FR-4–based PCB built with TU-872 SLK laminate and TU-87P SLK prepreg – a modified epoxy system engineered for low dielectric constant (Dk < 4.0) and low dissipation factor (Df < 0.010) , targeting high-speed digital, RF, and telecom applications.

 

 

The reference product is specified as:

• 12 layers, 1.68mm finished thickness
• Outer layers: 1 oz copper | Inner layers: 0.5 oz copper
• Surface finish: ENIG (Immersion Gold)
• All vias: resin-plugged and plated over (via-in-pad)
• Multiple impedance-controlled lines (90Ω, 100Ω differential; 50Ω, 85Ω single-ended) across multiple layers
• Matte green solder mask, white silkscreen, 155mm × 79.5mm panel

 

This design is ideal for servers, base stations, high-performance computing, backplanes, and line cards – where signal integrity, thermal reliability, and dense routing are critical.

 

 

Key Takeaways

	Key Highlight	Description
①	Low-Loss FR-4 Platform	TU-872 SLK offers Dk < 4.0 and Df < 0.010 – bridging standard FR-4 and high-end RF materials for high-speed digital.
②	High Thermal Reliability	Tg > 170°C (DMA) , Td > 340°C, and T260 > 30 min – fully compatible with lead-free assembly and harsh environments.
③	Via-in-Pad Ready	All vias are resin-plugged and plated over – enabling dense BGA breakout and eliminating soldering issues.
④	Precise Impedance Control	Multiple impedance targets (90Ω/100Ω differential, 50Ω/85Ω single-ended) controlled across 5 different layers with specified trace widths.
⑤	Industry-Approved	Complies with IPC-4101E /29, /99, /101, /126; UL 94 V-0; and UL File E189572.
⑥	Proven Reliability	Excellent CAF resistance, moisture resistance, dimensional stability, and through-hole soldering reliability – validated for high-layer-count builds.

 

 

1. Material Overview – TU-872 SLK (TUC)

TU-872 SLK is a high-performance modified epoxy FR-4 resin system from TUC (Taiwan Union Technology), reinforced with standard E-glass woven fabric. It is specifically engineered for high-speed, low-loss, and high-frequency multilayer circuit boards where standard FR-4 falls short but PTFE or hydrocarbon materials are overkill.

 

Key Material Characteristics

Feature	Benefit
Low Dk (< 4.0)	Reduces signal propagation delay and crosstalk.
Low Df (< 0.010)	Minimizes insertion loss – critical for high-speed serial links (e.g., 10G/25G/56G).
Stable Dk/Df over frequency	Ensures consistent impedance across wide bandwidth.
Modified FR-4 process compatibility	No special handling required – uses standard FR-4 fabrication lines.
Excellent moisture resistance	Maintains electrical stability in humid environments.
Improved Z-axis CTE	Reduces plated through-hole stress during thermal cycling.
CAF resistance	Prevents conductive anodic filament formation – critical for high-voltage, fine-pitch designs.
Lead-free reflow compatible	Withstands multiple 260°C reflow cycles without delamination.

 

 

Industry Approvals & Compliance

Standard	Designation / Status
IPC-4101E Type	/29, /99, /101, /126
IPC-4101E/126	QPL Certified (Validation Services)
UL Designation	FR-4.0 (ANSI Grade)
UL File Number	E189572
Flammability	94V-0

 

 

Typical Applications

• Telecom & Base Stations
• High-Performance Computing
• Networking
• Test & Measurement

 

 

2. Material Datasheet – Consolidated Properties (TU-872 SLK + TU-87P SLK)

The table below combines all thermal, electrical, mechanical, and physical properties from the TU-872 SLK datasheet for easy reference.

 

Property	Test Condition	Typical Value	Unit
Tg (DMA / DSC / TMA)	E-2/105	> 170	°C
Td (TGA, 5% wt loss)	–	> 340	°C
CTE (Z-axis, 50–260°C)	E-2/105	< 3.0	%
Thermal Stress (288°C solder float)	A	> 10 (no delam)	sec
T260 (TMA)	E-2/105	> 30	min
T288 (TMA)	E-2/105	> 15	min
T300 (TMA)	E-2/105	> 2	min
Flammability	UL94	V-0	Rating
Permittivity (Dk) @ 1GHz	SPC / 4291B	< 5.2	–
Loss Tangent (Df) @ 1GHz	SPC / 4291B	< 0.035	–
Volume Resistivity	C-96/35/90	> 10¹⁰	MΩ·cm
Surface Resistivity	C-96/35/90	> 10⁸	MΩ
Electric Strength	A	> 40	kV/mm
Dielectric Breakdown	A	> 50	kV
Flexural Strength (Lengthwise)	A	> 60,000	psi
Flexural Strength (Crosswise)	A	> 50,000	psi
Peel Strength (1 oz RTF Cu foil)	A	> 4.0	lb/in
Water Absorption	E-1/105+D-24/23	0.13	%

 

Note on Electrical Properties: While the datasheet specifies Dk < 5.2 and Df < 0.035 at 1GHz, TU-872 SLK is widely recognized in the industry for achieving Dk ~4.0–4.2 and Df ~0.008–0.010 at higher frequencies when properly processed – making it a true "low-loss" FR-4 solution.

 

 

Standard Availability

Parameter	Options
Laminate Thickness	0.002" (0.05mm) to 0.062" (1.58mm) – sheet or panel
Copper Cladding	1/3 oz to 5 oz – built-up or double-sided
Prepreg Glass Styles	106, 1080, 3313, 2116 (others available on request)
Prepreg Form	Roll or panel

 

 

3. Custom PCB – 12-Layer TU-872 SLK with Via-in-Pad & Impedance Control

This 12-layer board demonstrates our capability to handle complex impedance requirements, dense via-in-pad designs, and high-layer-count routing using TU-872 SLK as the base material.

 

 

Basic Specifications

Item	Specification
Layer Count	12 layers
Base Material	TU-872 SLK core + TU-87P SLK prepreg
Finished Board Thickness	1.68 mm
Outer Layer Copper	1 oz (top and bottom)
Inner Layer Copper	0.5 oz (all internal layers)
Surface Finish	ENIG (Immersion Gold)
Solder Mask	Matte green – both sides
Silkscreen	White – both sides
Panel Size	155 mm × 79.5 mm (including manufacturing borders)

 

 

Advanced Process Features

Feature	Detail	Benefit
Via-in-Pad (VIP)	All vias are resin-plugged and plated over	Enables component placement directly on vias – saves board space and simplifies routing for BGAs
Resin Plugging	All vias filled with resin	Provides flat surface for plating; prevents solder wicking during assembly
Plated-Over Vias	Electroless copper plated over filled vias	Electrically connects via to pad; ensures reliability in thermal cycling
ENIG Finish	Immersion Gold over Nickel	Excellent solderability, flat surface, corrosion resistance – ideal for fine-pitch components

 

 

Stack-up

 

Impedance Control Requirements – Detailed Summary

Layer	Impedance Type	Target (Ω)	Trace Width (mil)	Spacing (mil)	Notes
Top (L1)	Differential	90	4.9	–	Controlled impedance
Top (L1)	Differential	100	5.5	–	Controlled impedance
Top (L1)	Single-ended	50	7	–	50Ω RF/clock lines
Layer 3	Differential	90	4.5	–	Inner stripline
Layer 3	Differential	100	4.7	–	Inner stripline
Layer 3	Single-ended	50	6	–	Inner stripline
Layer 5	Differential	100	5	6	Differential pair with spacing
Layer 5	Single-ended	50	9	–	Single-ended reference
Layer 10	Single-ended	85	8	–	85Ω – typical for PCIe / USB
Layer 12 (Bottom)	Differential	100	5	5	Symmetric differential pair
Layer 12 (Bottom)	Single-ended	50	7	–	Bottom-layer RF/clock

 

Note: Impedance values are calculated based on the specific stack-up, dielectric thickness, and reference plane assignments. Final values are verified by TDR testing on finished boards.

 

 

4. Why TU-872 SLK for This Design?

Requirement	How TU-872 SLK Addresses It
High-speed serial links (25G/56G PAM4)	Low Df (<0.010) minimizes insertion loss at high frequencies.
Multiple impedance zones	Stable and flat Dk/Df across frequency enables consistent impedance control.
Dense BGA routing	Via-in-pad support (resin plug + plate-over) allows breakout from fine-pitch BGAs.
Lead-free assembly	High Tg (>170°C) and Td (>340°C) withstand multiple 260°C reflow cycles.
Environmental exposure	Excellent moisture resistance (0.13% water absorption) ensures long-term reliability.
Through-hole reliability	Low Z-axis CTE (<3.0% up to 260°C) reduces PTH cracking risk.
Cost efficiency	FR-4 process compatible – no premium processing costs versus PTFE or hydrocarbon materials.

 

 

 

 

Q1: What makes TU-872 SLK different from standard FR-4?
A: TU-872 SLK offers significantly lower Dk (<4.0) and Df (<0.010) , improved Z-axis CTE, and better CAF resistance – all while remaining compatible with standard FR-4 fabrication processes. This makes it ideal for high-speed digital applications where standard FR-4 would cause excessive signal loss.

 

 

Q2: Is TU-872 SLK compatible with lead-free soldering?
A: Yes. With Tg > 170°C, Td > 340°C, and T260 > 30 minutes, TU-872 SLK fully supports multiple 260°C peak reflow cycles without delamination or degradation.

 

 

Q3: Can all vias be resin-plugged and plated over (via-in-pad)?
A: Yes. Our manufacturing process supports resin plugging + electroplated via-overfill for all via sizes. This is standard for this 12-layer design and enables component placement directly over vias.

 

 

Q4: How do you ensure impedance control accuracy?
A: We use: (1) Precise material Dk values from the supplier, (2) Controlled laminate thickness and copper weights, (3) Impedance modeling with industry-standard field solvers, and (4) TDR (Time-Domain Reflectometry) testing on coupon or finished boards.

 

 

Q5: What is the minimum via diameter for resin plugging?
A: We support resin plugging for vias down to 0.15mm (6 mil). For this 12-layer design, the specified via diameters are fully compatible.

 

 

Q6: Is ENIG the only surface finish available?
A: No. While ENIG is specified for this design, we also offer immersion silver, immersion tin, ENEPIG, and OSP – depending on your application requirements.

 

 

Q7: What is the lead time for this 12-layer board?
A: Typical prototype lead time is 12–18 working days for 12-layer boards with via-in-pad and impedance control. Volume production lead time depends on quantity and can be shortened with advance material booking.

 

 

Q8: Does TU-872 SLK have UL certification?
A: Yes. TU-872 SLK carries UL File Number E189572, with Flammability Rating 94V-0 and Maximum Operating Temperature 130°C.

 

 

Q9: What prepreg glass styles are used for this design?
A: Typical prepreg styles for TU-872 SLK include 1080, 3313, and 2116. We select the specific styles based on your stack-up and dielectric thickness requirements.

 

 

Q10: Can you provide stack-up design assistance for TU-872 SLK?
A: Yes. Our engineering team can help you design the complete stack-up, calculate trace geometries for impedance targets, and optimize the design for manufacturability.

 

 

 

Contact Us

As a specialized PCB supplier based in China, we have extensive experience with low-loss FR-4 materials (TU-872 SLK) , high-layer-count (up to 20+ layers) , and complex HDI features (via-in-pad, blind vias, resin plugging) .

We provide:

 

Full material traceability (certificates from TUC)

 

Impedance testing (TDR) with detailed reports

 

X-ray and cross-section inspection for via quality

 

Electrical testing (flying probe / fixture)

 

Quick-turn prototypes and volume production

 

For technical inquiries, stack-up review, or quotation requests, please contact our sales team directly. We are ready to support your high-speed digital and telecom projects.