Wangling TF440 25mil DK4.4 Laminate Immersion Gold 2-Layer Copper-filling Vias PCB

Wangling TF440 25mil DK4.4 Laminate Immersion Gold 2-LayerCopper-filling Vias  PCB

A Glass-Free PTFE/Ceramic Platform for Stable Microwave Circuits

This article describes a two-layer rigid PCB built on Taizhou Wangling TF440, a woven-glass-free PTFE/ceramic composite on a 25 mil (0.635 mm) core with immersion gold. 

Part 1 covers construction, stackup, statistics, design choices and applications; 

Part 2 explains theTF440 laminate with a complete data sheet, standard offerings and a CCL photograph. The combination targets microwave, antenna and RF front-end work needing stable dielectric constant, low loss and a wide temperature range.

1. The TF440 25 mil Immersion Gold PCB

1.1 Product overview

The TF440 25 mil immersion gold board is a double-sided, single-core RF panel, supplied as one 45 × 66.04 mm piece at ±0.15 mm tolerance. Both faces are clad with 1 oz (35 µm) copper on a 0.635 mm (25 mil) dielectric. It is built bare—no silkscreen or solder mask—so the controlled copper sits directly on the ceramic-filled PTFE.

The exposed copper is protected by immersion gold, with selected vias on a designated IC pad copper filled. Minimum trace/space is 7/8 mils, and the smallest drilled hole is 0.4 mm. The board is made to IPC Class 2 from Gerber RS-274-X artwork with 100% electrical test.

Table 1 lists the board’s key construction and finishing attributes.

Table 1. PCB construction details.

Table 2 shows equal 1 oz copper on both faces of the 25 mil core.

Table 2. PCB stackup (2-layer rigid).

Table 3 summarizes the pad, via and net counts.

Table 3. PCB design statistics.

1.2 Engineering choices and differentiation

The bare-board configuration is the defining choice. On a microwave panel, a solder mask is itself a dielectric whose thickness, dielectric constant and coverage are poorly controlled. Leaving both faces without mask or silkscreen removes that variable from impedance and insertion-loss calculations, so every trace sees only the known 4.4 environment. The gold finish keeps the copper from oxidizing while preserving coplanarity for SMT and attach.

The copper-filling vias on the IC pad solve two problems at once: a filled and capped via gives the device a solid planar pad while creating a low-inductance path to the opposite face for grounding and RF return. With a single core and no lamination, faces stay in tight registration; the routing, holes and plating leave margin for IPC Class 2 yield.

1.3 Typical applications

With stable dielectric performance, low loss and a −80 to +200 °C service range, the board targets：

• Microwave and millimeter-wave circuits
• Phased-array and phase-sensitive antennas
• RF front-end modules and low-noise amplifiers
• Satellite systems; and aerospace equipment.

1.4 Conclusion (PCB)

The TF440 25mil PCB combines a symmetric single-core 2-layer build, 7/8 mil routing, 0.4 mm holes and a gold-finished, mask-free RF surface with copper-filled IC-pad vias. The result is a simple, reproducible, well-controlled platform for microwave and antenna work that values stable impedance and low parasitics over added layers or cosmetic coverings.

2. Understanding the Taizhou Wangling TF440 Laminate (CCL)

2.1 Material introduction

The board’s RF behavior is governed by its laminate. The Wangling TF series is a substrate made from PTFE resin, valued for its microwave properties, combined with ceramic fillers and no woven glass. Adjusting the ceramic-to-PTFE ratio controls the dielectric constant precisely, while a special process yields consistent performance and reliability.

The naming follows its cladding: TF is unclad, TF-1 single-sided clad and TF-2 double-sided clad. TF440 is the 4.4 grade, supplied here as double-sided clad with ED copper. The series offers dielectric constants from 3 to 16 with low dielectric loss.

2.2 Complete data sheet

Table 4 consolidates the complete published properties of TF440.

Table 4. TF440 typical properties (complete data sheet).

Dk is measured in the Z direction by the stripline method (IPC-TM-650 2.5.5.5). Values are typical for selection, not a warranty; validate suitability for each application.

2.3 Standard offerings

Table 5 lists the standard foil, panel and thickness options.

Table 5. TF series standard offerings.

Thickness may be total copper-clad or dielectric; specify which when ordering.

2.4 Technical analysis

The absence of woven glass is the key structural fact. Glass-reinforced laminates show a “glass-weave effect,” alternating between resin-rich and fiber-rich zones and causing periodic impedance variation and fiber-weave skew. TF440 instead disperses ceramic through a continuous PTFE matrix for a homogeneous dielectric, with ceramic loading fixing the nominal Dk. A Dk of 4.4 is a useful middle ground near FR-4, while its 0.0010 dissipation factor at 10 GHz sits in the low-loss PTFE regime rather than the several-thousandths of epoxy boards, reducing attenuation in feed lines.

The −60 ppm/°C TCDK describes a modest Dk drift, and water absorption ≤0.05% keeps properties stable in humidity. The grade supports continuous operation from −80 to +200 °C with radiation resistance and low outgassing for satellite hardware; density is 2.58 g/cm³ and thermal conductivity 0.32 W/(m·K). Chemical etching leaves its dielectric properties unchanged, and PTFE’s inert surface requires sodium-naphthalene or plasma activation for reliable hole metallization.

Figure 1. TaizhouWangling TF440 copper-clad PTFE/ceramic laminate sheets

Conclusion (CCL)

Wangling TF440 is a glass-free, ceramic-filled PTFE laminate pairing an FR-4-like 4.4 dielectric constant with PTFE-level low loss, very low water absorption, stable behavior and a −80 to +200 °C service range. Its homogeneous structure avoids the glass-weave effect, and its low-outgassing, radiation-resistant character suits microwave, antenna, satellite and aerospace RF circuits.