PCB Prepreg Specification

PCB Prepreg: The Invisible Backbone of Multilayer Circuit Boards

PCB Prepreg
In printed circuit board manufacturing materials, PCB Prepreg (pre-impregnated dielectric) is the critical adhesive bonding layers in multilayer circuit boards. Think of it as the “structural epoxy” – its resin flows under heat/pressure to fill copper gaps while forming the dielectric insulation between layers. Produced by impregnating glass fabric with partially cured resin (B-stage), prepreg’s specifications reveal its capabilities through a smart naming code: *The first two digits indicate glass style (e.g., “21”=2116 glass), the last two denote resin content percentage (e.g., “16”≈50% RC)*. Without this engineered interlayer, modern high-density boards simply couldn’t exist.
 

Some Common Prepreg Specifications

 
 
PP CodeGlass StyleResin Content (RC%)Thickness (mm)Key Characteristics
106106 (E-glass)68±3%0.050Ultra-thin for HDI microvias
10801080 (E-glass)62±4%0.070High flow for dense interconnects
21132113 (E-glass)54±4%0.100Balanced flow for impedance control
21162116 (E-glass)50±4%0.120Industry workhorse for general multilayer
76287628 (E-glass)42±4%0.200Structural stability for power boards
1017106 (E-glass)45±3%0.100Optimized for RF/high-speed signals
10277628 (E-glass)41±3%0.130Heavy copper support (3oz+)
10377628 (E-glass)35±3%0.170Backplanes & ultra-high layer counts
 
Get PP Selection Guide

3 Prepreg Selection Rules
Mastering Dielectric Control Through Copper Density & Resin Science

Selecting prepreg isn’t about picking codes – it’s about engineering dielectric behavior. As a top PCB manufacturer, we enforce three non-negotiable rules:

 

1. Copper Density Dictates Thickness

Post-lamination thickness ≠ Nominal thickness. Calculate reality:

Final Thickness = (Initial PP Thickness × (1 – Copper Area %)) + 0.025mm

Copper Area % = (Copper Surface Area / Layer Area) × 100

Copper Density2116 PP (0.12mm)1037 PP (0.17mm)
30% (Signals)0.109mm0.144mm
80% (Power)0.049mm0.059mm

Critical Insight: 80% copper crushes 2116 PP by 60% – risking impedance drift or delamination. 1037 PP preserves 20% more dielectric integrity.

2. Resin Content (RC%) Controls Flow vs. Speed

PP TypeRC%Flow CharacterTurnaround Impact
10668%High flow, slow cureUnsuitable for quick turns
211650%BalancedIdeal for 24hr prototypes
103735%Low flow, fast setPower board solution

Quick turn PCB pro tip: Use 2116 for designs under 70% copper density. Its 50% RC balances flow speed and void prevention during rapid lamination.

 

 

3. The Vicious Cycle: RC% ↔ Copper Density

High RC% PP (e.g., 106) flows better into dense copper – but demands slow ramp rates to avoid voids. Low RC% PP (e.g., 1037) cures faster but risks resin starvation on power planes. Solution:

                                                            Copper Density

Difference Between HDI & Standard Multilayer PP: Why Thinner ≠ Simpler

HDI PCB prepreg isn’t just “thin” – it’s precision-engineered dielectric surgery. While standard multilayer PP (like 2116/7628) prioritizes structural fill, HDI PP faces brutal constraints:

 

1. Thickness Tolerance War

ParameterStandard PPHDI PP
Thickness Range0.10-0.20mm0.05-0.07mm
Tolerance±10%±5%
Example2116 (0.12mm)106 (0.05mm)

Why it matters: 0.05mm HDI PP with ±0.0025mm control enables laser-drilled 75μm microvias. Standard PP’s ±0.012mm variation would ruin via depth.

2. Resin Chemistry Divergence

  • Standard PP: High RC% (50-68%) for copper gap filling

  • HDI PP: Low RC% (35-45%) with fast-flow resins – prevents resin smear during laser ablation

3. Glass Fabric Revolution

  • Standard: 2116/7628 glass (open weave)

  • HDI: 106/1080 glass (tighter weave) – smoother surface for 3/3μm trace/space

 

The Cost of HDI PP Mastery

top PCB manufacturers

 

Seek Tech’s Material Edge

The main Prepreg brands we adopt are SYST, NANYA, ITEQ and EMC.

Our PCB Prepreg library solves this calculus:

Pre-calculated Thickness Tables: For 20+ copper density scenarios

Lot-Specific RC% Data: QR codes on every PP roll

-15°C Storage: Preserves resin flow characteristics

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SEEK TECH: Multilayer Circuit Boards & Trusted Assembly
As one of the top PCB manufacturers, SEEK TECH excels in multilayer circuit board production. Our expertise spans complex stack-ups, ensuring precise layer alignment and reliable performance for diverse industries.

Beyond manufacturing, we operate as a trusted PCB assembly factory. From component sourcing to soldering, our assembly services handle multilayer boards with precision, matching the quality of our PCBs. Whether it’s a small batch or large production, we deliver integrated solutions that stand out in the industry.

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