Circuito stampato TUC TU-872 SLK per progetti ad alta velocità FR-4 e resistenti al CAF.

TUC TU-872 SLK is a modified-epoxy FR-4 system designed to bridge the gap between ordinary high-Tg FR-4 and more specialized low-loss laminates. TUC positions it for high-speed, low-loss, and high-frequency multilayer boards while retaining compatibility with modified FR-4 processing. The material also combines moisture resistance, improved z-axis expansion, anti-CAF capability, dimensional stability, and lead-free reflow compatibility.

This combination is relevant to servers, storage, backplanes, high-performance computing, line cards, telecom equipment, base stations, routers, and selected RF boards. The public product data list typical Dk 3.8 and Df 0.009 at 10 GHz for a 50% resin-content condition, Tg values of 190°C by TMA, 200°C by DSC, and 220°C by DMA, plus 2.3% z-axis expansion from 50–260°C.

TU-872 SLK should not be marketed as an extreme-low-loss substitute for every long channel. Its strongest value is a balanced package: better electrical performance than general-purpose FR-4, high thermal reliability, broad construction availability, and process compatibility for cost-sensitive high-speed multilayers.

What TU-872 SLK Solves in High-Speed FR-4

A standard FR-4 board can become loss-limited as route length and lane rate increase, but moving directly to a premium ultra-low-loss laminate may add cost and supply-chain complexity that the channel does not need. TU-872 SLK provides an intermediate option for designs that need lower Dk/Df and stronger environmental reliability while remaining close to familiar FR-4 fabrication.

TUC identifies the core as TU-872 SLK and the matching prepreg as TU-87P SLK. This pairing matters because a high-speed stackup should not mix an approved core with an unspecified prepreg that has different dielectric or flow behavior.

Typical problems addressed by the material

TU-872 SLK can help when a project needs:

• lower distributed channel loss than standard high-Tg FR-4;
• controlled impedance with Dk below 4.0;
• high-layer-count thermal endurance;
• improved moisture and CAF performance;
• broad glass-style and copper availability;
• a material compatible with modified FR-4 processing;
• a cost/performance step below very-low-loss or ultra-low-loss families.

The material does not correct poor routing, excessive via stubs, rough copper, or discontinuous return planes. The stackup and layout must still be engineered from the protocol and route length.

Applications should be separated by channel demand

TUC lists backplanes, HPC, line cards, storage, servers, telecom, base stations, office routers, and RF as applications. Within that list, the electrical demands vary widely. A short server daughtercard and a long backplane should not use the same loss assumption. The design team should quantify channel attenuation before deciding whether TU-872 SLK is sufficient or whether TU-872 SLK Sp or a lower-loss family is needed.

Material Snapshot

The following values are published by TUC for TU-872 SLK. They are typical material data and should be matched to the actual core/prepreg construction used in production.

Dk and Df are construction-dependent

The published 3.8/0.009 values use a 50% resin-content reference. Higher-resin prepregs and different glass styles can have different effective properties. The field solver should use design values supplied for the selected construction and should include the finished copper thickness and solder-mask condition.

Electrical tier and material naming

“SLK” and “SLK Sp” are different products. The Sp version uses novel woven glass and is positioned with extra-low Dk and lower-loss behavior. A quotation should not shorten the name to “TU-872” because the base TU-872, LK, SLK, and SLK Sp variants have different electrical performance.

Moisture Resistance, CTE and CAF

High-speed boards are often also high-density boards, and the reliability risk can be dominated by moisture and spacing rather than by insertion loss. TU-872 SLK’s moisture resistance, improved z-axis expansion, and CAF positioning should be connected to specific layout and process requirements.

Moisture changes more than insulation resistance

Moisture can reduce insulation resistance, increase loss, alter effective dielectric behavior, and increase the risk of delamination during reflow. Prepreg storage, layup-room exposure, finished-board packaging, dry storage, and pre-assembly conditioning should be controlled.

The fabricator and assembler should define:

• prepreg storage temperature and humidity;
• shelf-life and retest procedure;
• finished-board dry-pack condition;
• maximum floor exposure before assembly;
• baking triggers and limits;
• humidity indicators and desiccant;
• handling after partial package opening.

CAF risk around dense vias

CAF grows along glass-resin interfaces under moisture and electrical bias. Anti-CAF material reduces susceptibility, but feature spacing and cleanliness remain decisive. The DFM review should examine hole-to-hole spacing, hole-to-copper spacing, voltage difference, glass style, and resin coverage.

Usa il DFM checks for reliability builds to connect material capability to annular ring, drill pitch, copper balance, and process tolerance.

Low CTE and through-hole reliability

The published 2.3% total z expansion is favorable for a high-speed FR-4 class material, but board thickness and hole geometry still control fatigue. Specify minimum hole-wall copper, avoid unnecessary aspect ratio, and test representative coupons after the intended reflow cycles.

For press-fit connectors, include insertion force and finished-hole tolerance in the reliability review. Mechanical loading can combine with thermal fatigue at the same plated-hole barrel.

Pianificazione dello stacking e dell'impedenza

The stackup should be chosen from the required channel reach and manufacturable dielectric constructions. TU-872 SLK can support high-speed multilayers, but the electrical model must use the actual glass styles, resin contents, and copper foil.

Assegnazione dei livelli

Place the most critical channels on stripline layers with continuous reference planes and controlled dielectric thickness. Keep high-speed pairs away from plane voids, board edges, noisy power regions, and large changes in copper density. Outer-layer microstrip can be useful for short routes or launches but is more sensitive to solder mask, surface finish, and environmental variation.

Copper roughness and foil selection

A Df of 0.009 does not eliminate conductor-loss sensitivity. Low-profile or reverse-treated copper may be needed for long routes. The foil type should be listed in the stackup notes, and the roughness model used in simulation should match the production foil and inner-layer treatment.

Impedance release data

The controlled-impedance table should include:

• target and tolerance;
• layer and reference plane;
• finished trace width and spacing;
• finished copper thickness;
• target dielectric thickness;
• design Dk by construction;
• solder-mask assumption;
• coupon location and test method.

The fabricator should propose trace compensation before tooling. A post-fabrication report that only says “passed” is less useful than a released stackup showing the modeled geometry and measured coupon result.

Via and backdrill planning

High-speed backplanes and line cards often need backdrill to control residual stubs. Specify stub length, depth tolerance, breakout limits, and verification. Return vias should be placed near signal transitions to preserve the return path. If blind or buried vias are used, account for sequential lamination cost and registration.

Produzione e ispezione

TU-872 SLK is compatible with modified FR-4 processes, but the fabricator should use the TUC process guideline and its own qualified parameters for lamination, drilling, desmear, plating, and soldering.

Lamination and thickness control

The matching TU-87P SLK prepreg should be selected from resin-fill and pressed-thickness needs. Copper pattern density affects resin flow, so the stackup review should include local copper distribution, heavy copper, and large clearance fields. A symmetric construction and balanced copper help control bow and twist.

High-layer panels require registration compensation and controlled cooling. The first article should confirm finished dielectric thicknesses, total board thickness, and panel flatness.

Perforazione e rimozione delle smear

Drill parameters should be qualified for the cured resin and glass styles. Tool wear, smear, fiber protrusion, and positional error should be inspected through representative microsections. Desmear must clean the wall without excessive resin recession.

Through-hole copper thickness, inner-layer connection, and corner quality should be verified after thermal stress. High aspect-ratio boards may need additional plating controls and coupon locations that represent the panel center.

Piano di ispezione

A robust plan can include:

• AOI and electrical test;
• TDR impedance coupons;
• insertion-loss or S-parameter coupons for tight channels;
• microsections through through holes and backdrills;
• finished dielectric and copper measurements;
• bow/twist and dimensional inspection;
• CAF, IST, or thermal-cycle evidence where required.

When the board is delivered as PCBA, align fabrication evidence with controlled assembly and inspection so the reflow and test plan does not invalidate the bare-board qualification.

TU-872 SLK vs Other High-Speed FR-4 Options

The closest decision is often between TU-872 SLK, TU-872 SLK Sp, and a standard high-Tg FR-4.

When to choose SLK Sp

Choose SLK Sp when the full channel model shows that SLK does not provide enough loss or skew margin and the novel-glass construction is available and qualified. Do not substitute it silently because the Dk, trace geometry, pressed thickness, and dimensional behavior may change.

RFQ and FAQ

Specify TU-872 SLK laminate and TU-87P SLK prepreg, layer count, board size, finished thickness, glass styles, resin contents, copper profile, lane rate, route length, impedance and loss limits, minimum hole, aspect ratio, backdrill plan, reflow profile, CAF conditions, surface finish, coupon plan, IPC/UL requirements, and annual volume. Ask the fabricator to state the design Dk for every dielectric.

Is TU-872 SLK ordinary FR-4?

It is an FR-4.0 modified-epoxy material engineered for lower Dk/Df and higher thermal, moisture, CAF, and through-hole reliability than general-purpose FR-4.

Is Df 0.009 low enough for every high-speed backplane?

No. Channel reach, copper roughness, vias, connectors, and lane rate determine whether this tier is sufficient.

What is the difference between TU-872 SLK and SLK Sp?

SLK Sp uses novel woven glass and is positioned for extra-low Dk and lower-loss performance. It requires a separate stackup and impedance model.

Can standard FR-4 processing be used?

TUC states compatibility with modified FR-4 processes. The exact press, drill, and desmear parameters should still be qualified for the selected construction.

What should be tested on the first article?

Confirm dielectric thickness, impedance, critical dimensions, plated-hole quality, backdrill depth, and—when margin is tight—insertion loss or S-parameters.

Riferimenti del produttore

• TUC TU-872 SLK product page and public data
• TUC TU-872 SLK Sp comparison page