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TU-872 SLK 20-Layer 3.0mm ENEPIG PCB – HDI & High Speed Digital Applications
1. Introduction to TU-872 SLK HDI PCB
TU-872 SLK is based on a high performance modified epoxy FR-4 resin, reinforced with regular woven E-glass. This material is designed with low dielectric constant and low dissipation factor for high speed low loss and high frequency multilayer circuit board applications.
TU-872 SLK material is suitable for environmental protection lead free processes and is fully compatible with standard FR-4 processing. The laminates exhibit excellent moisture resistance, improved CTE, superior chemical resistance, thermal stability, CAF resistance, and toughness enhanced by an allyl network forming compound.
This 20-layer HDI PCB is constructed with TU-872 SLK as the core material, providing exceptional signal integrity, low loss, and high reliability for demanding high speed digital, telecom, and backplane applications. The board features ENEPIG surface finish, resin plugging, and HDI laser via structures.

2. Key Features of TU-872 SLK
Low dielectric constant (<4.0) Low dissipation factor (<0.010) Stable and flat Dk/Df performance across frequency Tg (DMA) >170°C, Tg (DSC) >340°C, Tg (TMA) >170°C Td (TGA) >340°C Z-axis CTE <3.0% T260 >30 min, T288 >15 min, T300 >2 min Excellent moisture resistance (0.13% water absorption) Lead free reflow process compatible Anti-CAF capability Superior dimensional stability, thickness uniformity and flatness Excellent through-hole and soldering reliability UL 94V-0 flammability rating Max operating temperature: 130°C
3. Benefits of TU-872 SLK HDI PCB
Low loss for high speed signal integrity Compatible with modified FR-4 processes – no special handling required Excellent thermal reliability for lead free assembly Low Z-axis CTE ensures reliable plated through-hole quality HDI capability with laser vias for high density routing Resin plugging for planarized via-in-pad designs ENEPIG surface finish (Ni+Pd+Au) for wire bonding and long shelf life IPC Class-3 high reliability standard
4. PCB Construction Details
| Item | Specification |
| Base material | TU-872 SLK (Tg200 modified epoxy FR-4) |
| Layer count | 20 layers |
| Board dimensions | 215mm x 137mm = 4PCS (2x2 panel array) |
| Finished board thickness | 3.0 mm |
| Finished Cu weight | Outer layers: 1 oz (35 μm) Inner layers: 0.5 oz (18 μm) |
| Surface finish | ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) |
| Solder mask | Top: green, white legend Bottom: green, white legend |
| Special features | HDI (laser vias) Resin plugging (resin filled vias) Impedance control (see impedance table) |
| Acceptance standard | IPC Class-3 |
| Panelization | 2x2 array (4 PCBs per panel) |
| Electrical test | 100% |
5. PCB Stackup (20-Layer HDI Rigid Structure)
*Core and prepreg thicknesses configured to achieve 3.0 mm total thickness with TU-872 SLK and TU-87P SLK prepreg. Laser vias for HDI interconnections between L1-L2 and L19-L20.*
| Layer | Copper Weight | Material |
| L1 (Top) | 1 oz | TU-872 SLK core |
| L2 | 0.5 oz | Prepreg + core |
| L3 | 0.5 oz | Core |
| L4 | 0.5 oz | Prepreg + core |
| L5 | 0.5 oz | Core |
| L6 | 0.5 oz | Prepreg + core |
| L7 | 0.5 oz | Core |
| L8 | 0.5 oz | Prepreg + core |
| L9 | 0.5 oz | Core |
| L10 | 0.5 oz | Prepreg + core |
| L11 | 0.5 oz | Core |
| L12 | 0.5 oz | Prepreg + core |
| L13 | 0.5 oz | Core |
| L14 | 0.5 oz | Prepreg + core |
| L15 | 0.5 oz | Core |
| L16 | 0.5 oz | Prepreg + core |
| L17 | 0.5 oz | Core |
| L18 | 0.5 oz | Prepreg + core |
| L19 | 0.5 oz | Core |
| L20 (Bottom) | 1 oz | TU-872 SLK core |
Total Pressed Thickness: 3.0 mm
6. Impedance Control Table

7. PCB Special Features
HDI Laser Vias: Sequential lamination with microvias for high density interconnect Resin Plugging: All vias resin filled and capped for via-in-pad capability ENEPIG Surface Finish: Electroless Nickel - Electroless Palladium - Immersion Gold (suitable for wire bonding, aluminum wire bonding, and long shelf life) IPC Class-3: Highest reliability standard for mission critical applications 2x2 Panel Array: 4 PCBs per panel (215mm x 137mm each)
8. Primary Application Areas
Radio frequency (RF) circuits Backpanel, high performance computing Line cards, storage systems Servers, telecom, base station equipment Office routers High speed digital designs High reliability mission critical systems
9. Quality Assurance
Artwork supplied: Gerber RS-274-X Accepted standard: IPC Class-3 Availability: Worldwide IPC-4101E Type: /29, /99, /101, /126 IPC-4101E/126 Validation Services QPL Certified UL Designation: ANSI Grade FR-4.0 UL File Number: E189572 Flammability Rating: 94V-0
10. TU-872 SLK High Speed Laminate Introduction
TU-872 SLK is based on a high performance modified epoxy FR-4 resin. This material is reinforced with regular woven E-glass and designed with low dielectric constant and low dissipation factor for high speed low loss and high frequency multilayer circuit board application.
TU-872 SLK material is suitable for environmental protection lead free process and is compatible with FR-4 processes. TU-872 SLK laminates also exhibit excellent moisture resistance, improved CTE, superior chemical resistance, thermal stability, CAF resistance, and toughness enhanced by an allyl network forming compound.
The material is available in various thicknesses from 0.002" to 0.062" with copper cladding from 1/3 oz to 5 oz. Prepregs are available with glass styles including 106, 1080, 3313, 2116 and others upon request.
11. TU-872 SLK Data Sheet
| Property | Typical Value | Units | Conditions | Test Method |
| Tg (DMA) | >170 | °C | E-2/105 | IPC-TM-650 2.4.24 |
| Tg (DSC) | >340 | °C | E-2/105 | IPC-TM-650 2.4.25 |
| Tg (TMA) | >170 | °C | E-2/105 | IPC-TM-650 2.4.24 |
| Td (TGA) | >340 | °C | – | ASTM D3850 |
| CTE (Z-axis) | <3.0 | % | – | IPC-TM-650 2.4.24 |
| T260 | >30 | min | E-2/105 | IPC-TM-650 2.4.24.1 |
| T288 | >15 | min | E-2/105 | IPC-TM-650 2.4.24.1 |
| T300 | >2 | min | E-2/105 | IPC-TM-650 2.4.24.1 |
| Dk (1 GHz / 5 GHz / 10 GHz) | <5.2 / – / – | – | E-2/105 | SPC method/4291B |
| Df (1 GHz / 5 GHz / 10 GHz) | <0.035 / – / – | – | E-2/105 | SPC method/4291B |
| Volume Resistivity | >10¹⁰ | MΩ·cm | C-96/35/90 | IPC-TM-650 2.5.17 |
| Surface Resistivity | >10⁸ | MΩ | C-96/35/90 | IPC-TM-650 2.5.17 |
| Electric Strength | >40 | kV/mm | A | IPC-TM-650 2.5.6 |
| Dielectric Breakdown | >50 | kV | A | IPC-TM-650 2.5.6 |
| Flexural Strength (LW) | >60,000 | psi | A | IPC-TM-650 2.4.4 |
| Flexural Strength (CW) | >50,000 | psi | A | IPC-TM-650 2.4.4 |
| Peel Strength (1 oz RTF) | >4 | lb/in | A | IPC-TM-650 2.4.8 |
| Water Absorption | 0.13 | % | E-1/105+D-24/23 | IPC-TM-650 2.6.2.1 |
| Flammability | 94V-0 | Class | E-24/125 | UL 94 |
12. Typical Applications
Radio frequency (RF) circuits Backpanel, high performance computing Line cards, storage systems Servers, telecom, base station equipment Office routers High speed digital designs High reliability mission critical systems
13. Standard Availability – TU-872 SLK
| Parameter | Options |
| Thickness | 0.002" to 0.062" (0.05mm to 1.58mm) |
| Copper Cladding | 1/3 oz to 5 oz (built-up & double sides) |
| Prepreg | Roll or panel form |
| Glass Styles | 106, 1080, 3313, 2116, and others |
Industry Approvals
| Standard | Designation |
| IPC-4101E | /29, /99, /101, /126 |
| IPC-4101E/126 | Validation Services QPL Certified |
| UL | ANSI Grade FR-4.0, File E189572 |
| Flammability | 94V-0 |
| Max Operating Temp | 130°C |
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