2. Understanding Back Drilling Technology

 

Back drilling, also known as controlled-depth drilling, is a specialized PCB manufacturing process used to remove the unused portion of a plated through-hole via that extends beyond the required interconnection layers . In high-frequency applications, these unused via stubs act as antennas, causing signal reflections, impedance discontinuities, and insertion loss that degrade signal integrity .

 

2.1 How Back Drilling Works

 

The process involves drilling out the non-functional stub portion of a via to a precisely controlled depth, removing the excess copper barrel that would otherwise cause signal degradation . For this PCB design, back drilling is implemented for L1-L3 and L1-L5 transitions, ensuring that signal paths remain clean and uninterrupted through the critical upper layers where high-frequency signals travel.

 

2.2 Benefits of Back Drilling

Benefit	Description	Impact on Performance
Stub Elimination	Removes excess via barrel length beyond signal layers	Reduces signal reflections by eliminating resonant structures
Impedance Control	Maintains consistent characteristic impedance	Improves signal integrity for >10 GHz designs
Insertion Loss Reduction	Minimizes energy loss in transmission paths	Enhances overall circuit efficiency
EMI Reduction	Decreases electromagnetic interference from via stubs	Improves system noise performance

 

 

3. PCB Specifications Overview

 

RO4003C 6-layer high-frequency PCB is manufactured to precise specifications, ensuring consistent performance for critical RF and microwave applications.

 

Feature	Specification	Technical Note
Layer Count	6 Layers	Optimized for complex RF routing and power distribution
Core Material	Rogers RO4003C™ (0.203mm each layer)	Glass-reinforced hydrocarbon/ceramic laminate
Prepreg Material	Rogers RO4450F™ (2 sheets between cores)	Compatible bonding material for multilayer construction
Total Thickness	1.174 mm (finished)	Precision-controlled lamination
Copper Weight (Outer)	1 oz (35 µm) finished	Optimized for outer layer signal transmission
Copper Weight (Inner)	0.5 oz (17.5 µm) finished	Balanced for inner layer routing requirements
Surface Finish	Immersion Gold (ENIG)	Excellent solderability and corrosion resistance
Solder Mask & Legend	Green Mask, White Legend (Top & Bottom)	High contrast for automated optical inspection
Board Dimensions	92.5 x 77.3 mm (per piece)	Compact form factor for integrated assemblies
Special Process	Back Drilling L1-L3, L1-L5	Stub elimination for critical signal paths

 

 

4. In-Depth: Rogers RO4003C Material Technology

 

Rogers RO4003C represents a breakthrough in high-frequency laminate technology, offering electrical properties approaching those of PTFE/glass materials while maintaining the processability of standard epoxy/glass systems .

 

4.1 Key Material Properties

Property	Value	Conditions
Dielectric Constant (Dk)	3.38 ± 0.05	@10 GHz, process control value
Design Dk	3.55	@10 GHz, for impedance calculations
Dissipation Factor (Df)	0.0027	@10 GHz, 23°C
Thermal Coefficient of Dk	+40 ppm/°C	-50°C to 150°C
Volume Resistivity	1.7 x 10¹⁰ Mohm	Typical
Surface Resistivity	4.2 x 10⁹ Mohm	Typical
Water Absorption	0.04%	D48/50%
Thermal Conductivity	0.71 W/m/°K	50°C, ASTM D5470
CTE (X-axis)	11 ppm/°C	-55°C to 288°C
CTE (Y-axis)	14 ppm/°C	-55°C to 288°C
CTE (Z-axis)	46 ppm/°C	-55°C to 288°C
Peel Strength (1 oz ED)	6.0 lbs/in (1.05 N/mm)	Typical
Density	1.8 g/cm³	Typical
Flammability Rating	NON FR (UL94)	Note: Not UL 94 V-0 rated

 

4.2 Key Advantages of RO4003C

 

Exceptional Electrical Performance: Tightly controlled dielectric constant (Dk 3.38 ± 0.05) and low dissipation factor (0.0027 at 10 GHz) ensure minimal signal loss and phase stability across frequency .

 

FR-4 Compatible Processing: Unlike PTFE-based microwave materials, RO4003C requires no special via treatments or handling procedures, allowing fabrication using standard epoxy/glass processes at significantly lower cost .

 

Ideal for Multilayer Constructions: The material's mechanical properties and compatibility with standard lamination processes make it excellent for complex multilayer board (MLB) designs .

 

Dimensional Stability: Low Z-axis expansion (46 ppm/°C) and CTE matching with copper ensure reliability through thermal cycling .

 

Low Moisture Absorption: At just 0.04%, the material maintains stable electrical performance even in humid environments .

 

Thermal Performance: Glass transition temperature exceeding 280°C and decomposition temperature above 425°C support lead-free assembly processes .

 

4.3 Typical Applications

 

Rogers RO4003C finds widespread use in demanding high-frequency applications :

 

Wireless Communications: 5G base station antennas, power amplifiers, filters, and combiners

 

Automotive Radar: 77 GHz millimeter-wave radar systems for ADAS and autonomous vehicles

 

Aerospace & Defense: Satellite communication systems, radar arrays, and avionics

 

Test & Measurement: Microwave test equipment and precision measurement instruments

 

RF Identification: High-performance RFID readers and tags

 

Point-to-Point Microwave: Backhaul communication systems

 

Broadcast Systems: LNBs for satellite television reception

 

5. Design Considerations for Optimal Performance

 

5.1 Impedance Control

The stable Dk of RO4003C (3.38 ± 0.05) enables precise impedance control for 50-ohm and 100-ohm differential transmission lines. For microstrip structures on 0.203mm core material with 1 oz copper, typical 50-ohm line widths range from 0.35mm to 0.40mm, depending on final stack-up configuration .

 

5.2 Back Drilling Precision

For L1-L3 and L1-L5 back drilling, depth control tolerance of ±0.05mm is maintained to ensure complete stub removal without compromising the target layer connections. This precision is essential for maintaining signal integrity in multi-gigahertz designs .

 

5.3 Thermal Management

While RO4003C offers thermal conductivity of 0.71 W/m/°K, high-power applications benefit from thermal via arrays and consideration of copper plane distribution for effective heat spreading .

 

5.4 Hybrid Stack-Up Possibilities

For cost-optimized designs, RO4003C can be combined with FR-4 inner layers, though careful stack-up design and process control are required to manage CTE differences and prevent warpage .

 

6. Conclusion

 

This 6-layer high-frequency PCB, constructed with Rogers RO4003C cores and RO4450F prepreg, represents an optimal balance of electrical performance and manufacturing efficiency. The material's tightly controlled dielectric constant (3.38 ± 0.05) and low dissipation factor (0.0027) ensure minimal signal loss through 10 GHz and beyond, while its compatibility with standard FR-4 processing eliminates the cost premiums associated with traditional microwave laminates . The implementation of precision back drilling for L1-L3 and L1-L5 transitions eliminates via stub effects that would otherwise degrade signal integrity at high frequencies. With immersion gold finish, green solder mask, and controlled impedance capabilities, this PCB is engineered to meet the demanding requirements of 5G infrastructure, automotive radar systems, aerospace communications, and advanced test equipment where signal purity and reliability are non-negotiable.

 

Founded in 2003, Shenzhen Bicheng Electronics Technology Co., Ltd is an established high frequency PCB supplier and exporter in Shenzhen, China, serving customers worldwide.

 

We are devoted to delivering high-frequency PCB products and solutions of the highest quality, along with customized service. Get in touch with us to start your project !

Visit https://www.bicheng-enterprise.com to learn more.