6-Layer Isola Astra MT77 PCB with Blind Via & Resin Plug Immersion Silver Finish

6-Layer Isola Astra MT77 PCB with Blind Via & Resin Plug Immersion Silver Finish

Product Overview

The 6-layer Astra MT77 Immersion Silver PCB represents a state-of-the-art solution for millimeter-wave (mmWave) and RF/microwave applications demanding exceptional signal integrity, thermal reliability, and manufacturing precision. Built upon Isola’s breakthroughAstra MT77 laminate system—a very low-loss dielectric constant (Dk) product specifically engineered for millimeter wave frequencies and beyond—this 6-layer board delivers near-PTFE electrical performance without the processing complexities and costs typically associated with PTFE-based materials.

Designed with a finished board thickness of 0.994mm and compact dimensions of 131mm x 107mm, this PCB incorporates three 0.127mm Astra MT77 core boards combined with Astra MT77 prepreg materials to achieve a homogeneous dielectric structure throughout all six layers. The use of identical resin systems across both cores and prepregs ensures consistent dielectric properties, minimized signal distortion, and reliable impedance control—critical factors for high-frequency circuit performance.

The board features blind vias (L1-L2 and L5-L6) with G12 resin plug hole technology and electroplating filling, enabling high-density interconnect (HDI) designs while maintaining signal integrity through reduced via stub effects. The Immersion Silver surface finish provides excellent solderability, flatness, and low contact resistance, making it ideal for high-frequency applications where surface roughness can significantly impact insertion loss. With 0.5oz copper on inner layers and 1oz copper on outer layers, this PCB balances current-carrying capacity with fine-feature etching capability.

1. PCB Construction Details

This table fully enumerates all mechanical, electrical, process and surface treatment specifications of the finished6-layer RF PCB for direct manufacturing verification.

2. PCB Layer Stack-Up Configuration

This stack-up table clarifies the dielectric structure, copper thickness and interlayer bonding medium of the 6-layer stack, supporting impedance simulation and lamination process control.

3. Core Technical Feature Deep Analysis

3.1 Low-Loss Astra MT77 Full Substrate Design

The entire PCB adopts 3 pieces of 0.127mm Astra MT77 rigid core plus matched MT77 prepreg without mixed FR-4 materials, eliminating dielectric mismatch that causes inconsistent Dk/Df across layers.Isola MT77 delivers stable Dk=3.00 and ultra-low Df=0.0017 at 2–10 GHz, with dielectric constant unchanged from -40°C to +140°C, critical for automotive radar modules operating under wide temperature fluctuation. Unlike PTFE high-frequency substrates, MT77 supports standard FR-4 lamination, drilling and desmear processes, cutting production cost without sacrificing RF performance.

3.2 Differentiated Inner & Outer Copper Weight

Outer layers use 1oz copper (35μm nominal) to enhance high-current carrying capacity for antenna feedlines and power interfaces, while inner layers adopt thinner 0.5oz copper (18μm) to reduce interlayer dielectric thickness variation and improve stripline impedance precision. This asymmetric copper design balances power delivery capability and high-density inner signal routing, effectively lowering crosstalk between adjacent RF traces.

3.3 Dual-Side Blind Microvia HDI Architecture

L1-L2 and L5-L6 blind vias adopt sequential laser drilling instead of through-hole structures, removing long signal stubs that generate severe insertion loss at mmWave bands. Blind vias shorten vertical signal transmission paths, raise wiring density by over 200% compared to traditional 6-layer through-hole PCBs, and reserve more board area for RF matching networks and passive component placement.

3.4 G12 Resin Plug with Electroplating Filling

All through-holes are fully filled with G12 high-temperature resin, followed by surface grinding and full copper electroplating planarization. This process prevents solder wicking during SMT reflow, eliminates air void expansion and board delamination under multiple lead-free reflow cycles, and provides flat pad surfaces for BGA and millimeter-wave chip mounting. Resin plug also strengthens interlayer bonding stability of the thin 0.994mm finished board, reducing Z-axis thermal expansion stress during thermal cycling.

3.5 Immersion Silver Surface Finish for RF Applications

Immersion silver eliminates nickel barrier layers required by ENIG, avoiding extra high-frequency loss caused by low-conductivity nickel. Silver possesses superior electrical conductivity among common PCB surface finishes, maintaining smooth trace skin effect transmission path for GHz-level signals. The RoHS-compliant lead-free process offers consistent solderability for automated high-volume assembly, perfectly matching radar antenna, RF front-end and high-speed sensor circuit demands.

4.Target Applications

This6-layer Astra MT77 PCB is ideally suited for:

Automotive Radar Systems: Adaptive cruise control, pre-crash detection, blind spot detection, lane departure warning, and stop-and-go systems operating at 77GHz

• 5G Wireless Infrastructure: mmWave base station and small cell RF front-end circuits

• Aerospace and Defense: Airborne RF systems, radar, and communication equipment

• Commercial RF/Microwave: Long antennas and high-frequency communication modules

• Test and Measurement: High-frequency probing and characterization fixtures

5. PCB Product Conclusion

This 6-layer Astra MT77 PCB integrateslow-loss high-frequency substrate, HDI blind via technology and full resin plug electroplating filling, forming a targeted circuit carrier for automotive millimeter-wave radar, 5G small cell RF modules and aerospace low-interference communication equipment. The differentiated copper weight stack-up, controlled 0.994mm thin finished thickness and nickel-free immersion silver finish collectively solve three core pain points of high-frequency PCB design: excessive signal attenuation, limited wiring density and poor thermal cycle reliability.

Adopting fully matched Isola MT77 core and prepreg ensures uniform dielectric performance across all layers, while FR-4-compatible manufacturing flow guarantees stable mass production yield. The standardized construction table and clear stack-up specification eliminate ambiguity in fabrication communication, supporting seamless prototype verification and batch production handover.

Supplementary Technical Document: Isola Astra® MT77 RF/Microwave Laminate & Prepreg CCL Knowledge

1. Material Product Profile

Astra MT77 is Isola Group’s ultra-low-loss glass-reinforced hydrocarbon laminate and prepreg series, certified per IPC-4103/17 and UL File Number E41625, specially developed for millimeter-wave, automotive ADAS radar and high-speed RF circuits. It acts as a cost-effective alternative to expensive PTFE substrates, combining ultra-stable dielectric constants, low dissipation factor, high thermal resistance and standard PCB manufacturability. Key target markets include automotive adaptive cruise control radar, blind spot detection sensors, 5G mmWave communication antennas, aerospace avionics and high-precision industrial measurement equipment.

2. Complete MT77 Typical Performance Data Table (From Official Datasheet)

3. Core Material Advantages & Manufacturing Compatibility

3.1 Electrical Performance Superiority

The fixed Dk=3.00 and ultra-low Df=0.0017 deliver minimal signal insertion loss at mmWave frequencies, with dielectric properties nearly unchanged across -40°C to +140°C operating temperature range. This eliminates frequency drift of radar detection distance and communication signal distortion caused by temperature variation, a critical advantage over conventional high-Tg FR-4 (Df≥0.02).

3.2 Outstanding Thermal Reliability

200°C high Tg and 360°C Td enable the material to withstand multiple lead-free reflow cycles without layer separation or resin decomposition. Low X/Y CTE of 12 ppm/°C provides excellent dimensional stability during lamination, drilling and thermal cycling, preventing pad shifting and trace cracking on thin 0.994mm multi-layer boards. Only 0.1% moisture absorption avoids bubble generation during high-temperature assembly for outdoor vehicle-mounted radar equipment.

3.3 Simplified PCB Fabrication Process

Unlike PTFE substrates requiring specialized etching and plasma treatment, Astra MT77 is fully FR-4 process compatible:

• No mandatory plasma desmear after laser drilling, reducing production cycle time;
• Good resin flow and filling performance matching resin plug HDI technology;
• Lower drill bit abrasion extends tool service life for mass production;
• Supports multiple lamination cycles and Any-Layer / VIPPO HDI structures;
• RoHS compliant and compatible with lead-free solder assembly processes.

3.4 Standard Available Specifications

• Laminate core thickness stock: 

0.0635mm, 0.127mm, 0.1905mm, 0.254mm, 0.3175mm, 0.381mm, 0.510mm, 0.760mm, 1.50mm (the 0.127mm core adopted in this PCB is a mainstream standard thickness);

• Copper foil options: 

HVLP (VLP2) low-profile foil, embedded resistor foil; standard copper weight 0.5oz, 1oz, 2oz;

• Matching prepreg series: 

Formulated with identical resin system to core sheets, guaranteeing interlayer dielectric consistency without impedance jump.

4. CCL Material Conclusion

Isola Astra MT77 is a balanced high-frequency substrate solution that compromises neither electrical performance nor manufacturing efficiency. Its ultra-low loss, wide-temperature stable dielectric parameters and high thermal resistance make it irreplaceable for modern automotive radar and mmWave communication PCBs. Full compatibility with standard FR-4 production lines significantly lowers mass manufacturing cost compared to fluoropolymer substrates, while standardized core and prepreg thickness specifications support flexible multi-layer stack-up design for thin HDI boards like the 0.994mm 6-layer PCB.

Uniform resin system between core and prepreg eliminates interlayer dielectric mismatch risk, ensuring consistent impedance control and long-term structural reliability under complex temperature and humidity operating environments. As a UL-listed, RoHS-compliant material with mature industrial application cases, Astra MT77 provides stable, repeatable high-frequency circuit performance for both prototype development and large-volume commercial production.