6-Layer RO3003+370HR Hybrid PCB with Blind Vias (Layers 1–2) and plugged with conductive copper paste (0.15mm)

Product Description

 

This article presents a detailed design strategy for a 6-layer hybrid PCB that combines the superior high-frequency performance of Rogers RO3003™ with the excellent thermal reliability and cost-effectiveness of Isola 370HR FR-4. This hybrid construction is ideal for demanding RF/microwave applications requiring controlled impedance, blind vias, and reliable thermal management in a compact form factor.

 

By integrating RO3003 as the high-frequency material and 370HR as the bonding/prepreg layers, this design achieves an optimal balance of electrical performance, mechanical robustness, and manufacturability for small-to-medium-sized RF modules.

 

 

Rogers RO3003™ High-Frequency Laminate

RO3003™ is a ceramic-filled PTFE composite laminate from Rogers Corporation’s RO3000® series, designed for commercial microwave and RF applications. This material offers exceptional electrical and mechanical stability at competitive prices.

 

Key Features:

1. Low dielectric loss – can be used in applications up to 77 GHz
2. Stable dielectric constant versus temperature and frequency – ideal for band pass filters, microstrip patch antennas, and voltage-controlled oscillators
3. Excellent mechanical properties versus temperature – reliable stripline and multilayer board constructions
4. Low in-plane expansion coefficient (matched to copper) – allows for more reliable surface-mounted assemblies and excellent dimensional stability
5. Volume manufacturing process – economical laminate pricing

 

Key Specifications (RO3003):

Property	Typical Value	Unit	Test Condition
Dielectric Constant (Dk)	3.00 ± 0.04	—	10 GHz / 23°C
Dissipation Factor (Df)	0.001	—	10 GHz / 23°C
TCDk	-3	ppm/°C	-50 to 150°C / 10 GHz
CTE – X axis	17	ppm/°C	-55 to 288°C
CTE – Y axis	16	ppm/°C	-55 to 288°C
CTE – Z axis	25	ppm/°C	-55 to 288°C
Thermal Conductivity	0.5	W/(m·K)	50°C
Moisture Absorption	0.04	%	D48/50
Density	2.1	g/cm³	23°C
Flammability	V-0	—	UL 94
Lead-Free Process Compatible	Yes	—	—

 

 

Isola 370HR High-Performance FR-4

370HR is a high-performance 180°C glass transition temperature (Tg) FR-4 system designed for multilayer Printed Wiring Board (PWB) applications where maximum thermal performance and reliability are required. 370HR laminate and prepreg products are manufactured with a unique high-performance multifunctional epoxy resin, reinforced with electrical grade (E-glass) glass fabric.

 

Key Features:

1. High Thermal Performance: Tg 180°C (DSC); Td 340°C (TGA @ 5% wt loss)
2. Low CTE for reliability: T260: 60 minutes; T288: 30 minutes
3. RoHS Compliant
4. UV Blocking and AOI Fluorescence – maximum compatibility with Automated Optical Inspection (AOI) systems
5. CAF Resistant
6. Superior Processing – closest to conventional FR-4 processing
7. Proven best in class for sequential lamination designs

 

 

Key Specifications (370HR):

Property	Typical Value	Unit	Test Method
Glass Transition Temperature (Tg)	180	°C	IPC-TM-650 (DSC)
Decomposition Temperature (Td)	340	°C	ASTM D3850
T260	60	Minutes	ASTM D3850
T288	30	Minutes	ASTM D3850
CTE – Z-axis (Pre-Tg)	45	ppm/°C	—
CTE – X,Y axes (Pre-Tg)	13/14	ppm/°C	—
Z-axis Expansion (50–260°C)	2.8	%	—
Thermal Conductivity	0.4	W/m·K	—
Dk @ 1 GHz	4.17	—	IPC-TM-650 2.5.5.9
Df @ 1 GHz	0.0161	—	IPC-TM-650 2.5.5.9
Moisture Absorption	0.15	%	—
Flammability	V-0	Rating	UL 94

 

 

Design Strategy: Performance Advantages of the Hybrid Stackup

 

Argument 1: Balancing RF Performance and Cost

RO3003 offers a low dielectric constant (Dk 3.00) and ultra-low dissipation factor (Df 0.0010 at 10 GHz), making it ideal for RF and microwave signal transmission while minimizing high-frequency insertion loss. The 5mil thin dielectric layer allows for precise control of differential and single-ended impedance.

 

370HR is a high-Tg, heat-resistant prepreg that provides excellent resistance to delamination and withstands multiple SMT reflow cycles. This addresses the poor thermal stability and high costs associated with boards made entirely of ceramic-based materials.

 

Hybrid Construction Logic:

 

RF Signal Layers: Use RO3003 for critical high-frequency signal layers (L1, L3, L6) to maintain low loss and stable Dk.

 

Bonding Layers: Use 370HR prepreg for bonding the RO3003 cores, providing reliable mechanical connection and thermal stability.

 

Inner Layers: Use 370HR for power/ground planes and digital signal routing, leveraging its cost-effectiveness and FR-4 process compatibility.

 

Cost Consideration: Hybrid stackups place Rogers on the RF signal layers and FR-4 on digital/power layers, reducing cost by 40–60% versus all-Rogers construction while maintaining RF performance. The bonding layer (370HR prepreg) must be selected for compatible Dk and processing temperature.

 

 

Argument 2: Process Control for 0.82mm-Thick 6-Layer Hybrid PCBs

 

Thickness Control

Precise control of the total board thickness (0.82mm) is achieved through the specific combination of 5mil ceramic dielectric and 5mil 370HR prepreg (PP), adhering to strict thickness tolerance standards.

 

Stackup Design:

 

Note: The exact prepreg thicknesses are optimized to achieve the target finished thickness of 0.82 mm.

 

CTE Mismatch Management

Given the difference in the Coefficient of Thermal Expansion (CTE) between RO3003 and 370HR, specialized multi-stage lamination heating profiles and anti-delamination process strategies are employed.

 

CTE Comparison:

 

RO3003: X/Y = 17/16 ppm/°C, Z = 25 ppm/°C

 

370HR: X/Y = 13/14 ppm/°C (Pre-Tg), Z = 45 ppm/°C (Pre-Tg)

 

The Z-axis CTE mismatch is significant (RO3003: 25 ppm/°C vs. 370HR: 45 ppm/°C). To manage this, the lamination process should use:

 

Slow ramp rates in the critical Tg region (150–200°C)

 

Extended dwell time at peak temperature to allow stress relaxation

 

Controlled cooling to prevent warpage

 

 

Addressing Thin 6-Layer Board Defects

Potential defects in thin 6-layer boards include lamination misalignment and warpage. Root-cause analysis and corrective measures include:

Defect	Root Cause	Corrective Measure
Lamination Misalignment	Uneven pressure, CTE mismatch	Precision tooling pins, optimized press cycle
Warpage	Asymmetric stackup, CTE mismatch	Symmetric construction, balanced copper distribution
Delamination	Insufficient prepreg flow, contamination	Proper prepreg selection, controlled environment
Via Barrel Cracking	Z-axis CTE mismatch	Resin-filled vias, optimized drill parameters

 

 

Blind Vias (Layers 1–2)

Blind vias (L1–L2) reduce via stub effects and improve high-frequency performance by eliminating unnecessary via lengths.

 

This is critical for maintaining signal integrity in high-layer-count designs.

 

Implementation: Sequential lamination is required. The first lamination step bonds L1–L2 (RO3003 core), followed by the second lamination step to bond the remaining layers.

 

 

Conductive Copper Paste Vias (0.15mm)

The 0.15mm vias are plugged with conductive copper paste. This technology involves filling the through-holes with a via paste containing Cu particles and a curable resin component.

 

Advantages of Conductive Paste Vias:

1. Smaller Via Diameter: Allows vias as small as 0.15mm, increasing routing density
2. Elimination of Fanout: Vias can be drilled directly through contact pads, reducing signal length and propagation delay
3. Cost-Effective: Avoids electroplating for via filling, reducing processing steps
4. Reliable Interconnection: Cu particles form plane contact under compression, creating low-resistance connections

 

 

Processing Considerations:

1. The via paste is applied to completely fill the through-holes
2. Protective films are removed to create protrusions
3. Compression bonding is performed at a temperature below the eutectic temperature of the solder particles
4. The Cu particles deform in plane contact with one another, forming a joined unit for electrical connection

 

 

PCB Construction Details

Parameter	Specification
Base Material (High-Frequency Layers)	Rogers RO3003 (5 mil)
Bonding Material (Prepreg)	Isola 370HR (5 mil)
Number of Layers	6
Finished Board Size	83 mm × 42 mm (1 piece)
Finished Board Thickness	0.82 mm
Outer Layer Copper Weight	1 oz (35 μm)
Inner Layer Copper Weight	0.5 oz (18 μm)
Surface Finish	ENIG (Electroless Nickel Immersion Gold)
Top Solder Mask	Blue
Bottom Solder Mask	Blue
Top Silkscreen	White
Bottom Silkscreen	White
Blind Vias	L1–L2
Via Plugging	0.15mm vias, conductive copper paste
Electrical Testing	100% prior to shipment
Accepted Quality Standard	IPC-Class-2
Artwork Format	Gerber RS-274-X
Global Availability	Worldwide shipping

 

 

Features & Benefits Summary

Feature	Benefit
Hybrid RO3003 + 370HR Construction	Optimizes high-frequency performance and cost-effectiveness
6-Layer Design	Supports complex RF/microwave circuits with power/ground planes
5mil RO3003 Core	Precise impedance control for 50Ω and differential signals
370HR Prepreg (Tg 180°C)	High thermal reliability, multiple reflow capable
Blind Vias (L1–L2)	Reduces stub effects, improves signal integrity
Conductive Copper Paste Vias	Enables 0.15mm micro-vias, increases routing density
ENIG Surface Finish	Flat, solderable, wire-bondable, and corrosion-resistant
Blue Solder Mask / White Silkscreen	Comprehensive protection with clear component identification
0.82mm Finished Thickness	Optimized for compact RF module designs
100% Electrical Testing	Guaranteed quality and performance
IPC-Class-2	Meets industry-standard quality requirements

 

 

Typical Applications

This 6-layer hybrid PCB is ideal for a wide range of high-performance applications:

1. RF/Microwave Modules: Phased array antennas, beamforming networks, and transceiver modules.
2. Automotive Radar: 24 GHz and 77 GHz radar modules for ADAS.
3. 5G/6G Infrastructure: Massive MIMO antennas and mmWave base stations.
4. Satellite Communications: Spaceborne and ground-based satellite equipment.
5. Test & Measurement Equipment: Vector network analyzers and high-frequency test fixtures.
6. Small-to-Medium RF Modules: Cost-sensitive applications requiring high-frequency performance.

 

 

Conclusion

As a specialized supplier of custom high-frequency circuit boards, we combine the proven performance of Rogers RO3003 (low loss, stable Dk, excellent dimensional stability) and Isola 370HR (high Tg, excellent thermal reliability, best-in-class sequential lamination) with our precision manufacturing capabilities to deliver world-class hybrid PCB solutions.

 

The 6-layer hybrid offering fully leverages RO3003’s low-loss high-frequency performance and 370HR’s thermal reliability and processing advantages, while incorporating advanced features such as blind vias (L1–L2) and conductive copper paste vias (0.15mm) to ensure optimal signal integrity and reliability in a compact 0.82mm form factor.

 

Whether you are developing automotive radar modules, phased array antennas, or 5G mmWave infrastructure, our engineering team is ready to support your project. For technical consultations, samples, or volume orders, please contact us today.