6-Layer with Filled Via and 4-layer Isola FR408HR PCB with Blind Via ENIG
In today’s rapidly evolving electronics industry, demand for PCBs that deliver exceptional thermal stability, electrical performance, and long‑term reliability has never been higher.The FR408HR multilayer PCB series is engineered to address the most demanding industrial, communication, and high‑reliability applications, combining premium base material, precision manufacturing, and strict quality control. This product line includes two optimized constructions: a 6-layer high‑density PCB and a 4-layer PCB with blind via design, both built onIsola FR408HR high‑performance laminate. These boards are not only compatible with lead‑free assembly processes but also designed to withstand extreme thermal cycles, ensuring stable performance in challenging operating environments.
PCB Construction Details
PCB Case 1: 6-Layer FR408HR PCB
This is a 6-layer high-reliability PCB built on FR408HR material, featuring resin‑plugged vias, full electrical testing, and uniform cosmetic appearance.
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Item
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Specification
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Base material
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FR408HR
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Layer count
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6 layers
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Board dimensions
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79mm x 105mm, 1 piece
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Finished board thickness
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1.60mm
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Finished Cu weight
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1oz finished copper per layer
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Surface finish
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Immersion Gold (ENIG)
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Top Solder Mask
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Blue
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Top Silkscreen
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White
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Bottom Solder Mask
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Blue
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Bottom Silkscreen
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White
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Via processing
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Resin plug hole for 0.2mm–0.4mm vias
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Blind vias
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No blind vias
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Pre shipment test
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100% Electrical test
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PCB Case 2: 4-Layer FR408HR PCB
This is a 4-layer compact PCB using FR408HR substrate, equipped with L1-L3 blind vias for improved routing density and structural integrity.
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Item
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Specification
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Base material
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FR408HR
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Layer count
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4 layers
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Board dimensions
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96mm x 115mm, 1 piece
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Finished board thickness
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1.58mm
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Finished Cu weight
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1oz finished copper per layer
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Surface finish
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Immersion Gold (ENIG)
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Top Solder Mask
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Blue
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Top Silkscreen
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White
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Bottom Solder Mask
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Blue
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Bottom Silkscreen
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White
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Blind vias
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L1–L3
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Pre shipment test
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100% Electrical test
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PCB Stack-up
4-Layer FR408HR PCB Stackup
This stackup provides balanced electrical performance and thermal management for compact, high‑speed circuits.
6-Layer FR408HR PCB Stackup
This stackup supports increased routing density, improved impedance control, and better heat dissipation for complex circuits.
FR408HR Material Introduction
FR408HR is ahigh-performance FR-4 resin system with a 230°C (DMA) Tg, specifically developed formultilayer PCB applications that require maximum thermal performance and reliability. Manufactured using Isola’s patented high‑performance multifunctional resin system reinforced with electrical‑grade E‑glass fabric, FR408HR delivers a 30% improvement in Z‑axis expansion compared to standard materials. It also provides a 25% increase in electrical bandwidth with lower signal loss than competing products in the same class.
Combined with excellent moisture resistance during reflow, FR408HR effectively bridges performance gaps in both thermal and electrical behavior. The material supports laser fluorescence and UV blocking, ensuring excellent compatibility with automated optical inspection (AOI) systems, optical positioning equipment, and photo‑imagable solder mask imaging. This makes it highly suitable for automated, high‑precision manufacturing lines.
FR408HR Key Features
- RoHS Compliant, meeting global environmental standards
- CAF (Conductive Anodic Filament) resistant, preventing insulation failure in humid environments
- Lead-free assembly compatible, aligning with modern manufacturing requirements
- 0.8 mm pitch capable, supporting high-density component placement
- 6x 260°C reflow capable, withstanding repeated thermal stress
- 6x 288°C solder float capable, ensuring durability during assembly
- FR-4 process compatible, integrating seamlessly with standard PCB manufacturing workflows
- Via filling capability, supporting advanced via processing for enhanced reliability
- Multiple lamination cycles compatible, enabling complex multilayer designs
FR408HR Typical Values Table
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Property
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Typical Value
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Units
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Test Method
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Glass Transition Temperature (Tg) by DSC
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190
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°C
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2.4.25C
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Decomposition Temperature (Td) by TGA @ 5% weight loss
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360
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°C
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2.4.24.6
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Time to Delaminate by TMA (Copper removed)
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A. T260
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60
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Minutes
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2.4.24.1
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B. T288
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>30
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Z-Axis CTE
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A. Pre-Tg
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55
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ppm/°C
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2.4.24C
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B. Post-Tg
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230
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ppm/°C
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C. 50 to 260°C, (Total Expansion)
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2.8
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%
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X/Y-Axis CTE
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Pre-Tg
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16
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ppm/°C
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2.4.24C
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Thermal Conductivity
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0.4
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W/m·K
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ASTM E1952
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Thermal Stress 10 sec @ 288ºC (550.4ºF)
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A. Unetched
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Pass
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Pass Visual
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2.4.13.1
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B. Etched
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Dk, Permittivity
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A. @ 100 MHz
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3.72
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—
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2.5.5.3
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B. @ 1 GHz
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3.69
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2.5.5.9
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C. @ 2 GHz
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3.68
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Bereskin Stripline
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D. @ 5 GHz
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3.64
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Bereskin Stripline
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E. @ 10 GHz
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3.65
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Bereskin Stripline
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Df, Loss Tangent
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A. @ 100 MHz
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0.0072
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—
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2.5.5.3
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B. @ 1 GHz
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0.0091
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2.5.5.9
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C. @ 2 GHz
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0.0092
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Bereskin Stripline
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D. @ 5 GHz
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0.0098
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Bereskin Stripline
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E. @ 10 GHz
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0.0095
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Bereskin Stripline
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Volume Resistivity
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A. After moisture resistance
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4.4 x 107
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M阝-cm
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2.5.17.1
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B. At elevated temperature
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9.4 x 107
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Surface Resistivity
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A. After moisture resistance
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2.6 x 106
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M阝
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2.5.17.1
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B. At elevated temperature
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2.1 x 108
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Dielectric Breakdown
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>50
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kV
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2.5.6B
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Arc Resistance
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137
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Seconds
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2.5.1B
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Electric Strength (Laminate & laminated prepreg)
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70 (1741)
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kV/mm (V/mil)
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2.5.6.2A
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Comparative Tracking Index (CTI)
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2 (250-399)
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Class (Volts)
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UL 746A
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ASTM D3638
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Peel Strength
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A. Low profile copper foil and very low profile copper foil all copper foil >17阝m [0.669 mil]
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1.14 (6.5)
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N/mm (lb/inch)
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2.4.8C
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B. Standard profile copper
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1. After thermal stress
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0.96 (5.5)
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2.4.8.2A
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2. After process solutions
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0.90 (5.1)
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2.4.8.3
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Flexural Strength
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A. Length direction
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72.5
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ksi
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2.4.4B
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B. Cross direction
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58
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Tensile Strength
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A. Length direction
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54.5
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ksi
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ASTM D3039
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B. Cross direction
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38.7
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Young's Modulus
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A. Length direction
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3695
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ksi
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ASTM D790-15e2
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B. Cross direction
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3315
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Poisson's Ratio
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A. Length direction
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0.137
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—
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ASTM D3039
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B. Cross direction
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0.133
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Moisture Absorption
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0.061
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%
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2.6.2.1A
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Flammability (Laminate & laminated prepreg)
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V-0
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Rating
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UL 94
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Relative Thermal Index (RTI)
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130
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°C
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UL 796
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Typical Applications
FR408HR PCBs are widely used in high‑reliability sectors including industrial automation, automotive electronics, communication base stations, high‑speed data transmission equipment, power supplies, and medical devices.
They are ideal for products requiring stable signal transmission, excellent heat resistance, and long‑term operational reliability, especially in environments exposed to temperature fluctuations, high density, and high current loads.
Conclusion
The 4-layer and 6-layer FR408HR PCBs represent a premium solution for advanced electronic assemblies. By combining high‑performance base material, precise layer stackup, reliable surface finishing, and 100% electrical testing, these boards deliver outstanding thermal stability, electrical performance, and mechanical reliability. Whether used in compact designs with blind vias or complex multilayer layouts with resin‑plugged vias, this multilayer FR408HR PCB series ensures consistent quality, long service life, and excellent compatibility with modern assembly processes. For customers seeking high-reliability PCBs that perform under pressure, our FR408HR series is the ideal choice.
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