Bleached Kraft Paper for PCB – High Purity & Insulation
Kraft paper for PCB covers the entire production chain, playing a key role from raw material synthesis to transportation packaging. At the raw material stage, bleached kraft paper, with its excellent insulation properties, serves for bare board insulation, lamination buffering, and auxiliary insulation in high-frequency PCBs. When PCBs enter the 220–230℃ high-temperature process, kraft paper provides thermal insulation for solder mask curing. During multi-layer core lamination, it acts as underlay paper to ensure even pressure transfer and to protect board surfaces from defects. In the transportation stage, kraft paper impregnated with paraffin or PE offers moisture resistance, anti-rust protection, and cushioning against impact. Moreover, this type of kraft paper can be precisely adapted to different PCB processes, including rigid PCBs (such as computer motherboards), flexible PCBs (such as circuit boards in smart wearables), and rigid-flex PCBs (such as complex circuits in smartphones), thereby meeting the needs of various PCB applications.
Bleached PCB Kraft: Key Functions (Purity & Insulation) in Production
PCB production involves a complex process. From raw material synthesis to final product transportation, kraft paper plays an irreplaceable role thanks to its properties of insulation, heat resistance, cushioning, and protection. The specific applications are as follows:
| Production Step | Kraft Paper Type / Property | Core Function | Value for PCB Production |
|---|---|---|---|
| Raw Material Synthesis | Bleached kraft paper (insulation ≥10¹²Ω) | (1) Bare board insulation: separates PCB bare boards from metal tools to prevent short circuits; (2) Lamination buffer layer: absorbs pressure impact during lamination, protecting circuits; (3) High-frequency PCB insulation: reduces signal interference and improves circuit stability | Bare board defect rate drops from 5% to 1%; high-frequency PCB signal efficiency increases by 8% |
| High-Temperature Processing (220–230℃) | Heat-resistant kraft paper (strength retention ≥90% at 150℃) | Solder mask curing insulation: isolates high temperature from the PCB substrate, prevents deformation, and ensures uniform curing | Solder mask curing pass rate rises to 99.5%, eliminating substrate warping |
| Multi-Layer Core Lamination | High-density kraft paper (thickness tolerance ≤±1μm) | (1) Even pressure transfer: as underlay paper, disperses lamination pressure (800–1200 psi) and ensures tight bonding; (2) Surface protection: isolates steel plate from PCB surface, avoiding scratches | Lamination bubble rate ≤0.3%, surface defect rate decreases by 70% |
| Transportation Packaging | Paraffin / PE impregnated kraft paper (moisture resistance ≤3g/㎡·24h) | (1) Moisture and rust protection: blocks humidity during transport, preventing copper foil oxidation; (2) Cushioning and impact resistance: absorbs vibration, protecting edges and solder joints | PCB transport damage rate drops from 3% to 0.5%, copper foil oxidation ≤0.1% |
Bleached Kraft: Adaptation for Rigid/Flexible PCB (Insulation Fit)
Different PCB processes—rigid, flexible, and rigid-flex—require specific auxiliary material properties. Kraft paper for PCB can be adjusted accordingly to provide precise adaptation for diverse production needs:
Rigid PCB: Meeting “High Rigidity & High Insulation” Demands
PCB Features: Rigid structure, widely used in fixed applications (such as computer motherboards, server boards, and home appliance control boards), requiring resistance to high-pressure lamination and high-temperature soldering.
Kraft Paper Solution: Bleached, heat-resistant kraft paper (insulation resistance ≥10¹²Ω, heat insulation ≥80% at 220℃).
Key Adaptation Points: Acts as a buffer layer during lamination to prevent board cracking caused by uneven pressure; serves as insulation under high-temperature soldering to protect nearby components.
Typical Applications: Computer motherboards, refrigerator control boards, industrial drive boards.
Flexible PCB: Meeting “Flexibility & Bend Resistance” Demands
PCB Features: Bendable and foldable, widely used in compact or dynamic applications (such as smartwatch straps, foldable phone connectors, and medical equipment wiring). Production requires both cushioning and flexibility.
Kraft Paper Solution: Low-grammage, high-flexibility kraft paper (60–80g/㎡, longitudinal elongation ≥5%).
Key Adaptation Points: Works as flexible underlay paper during lamination without affecting PCB bendability; functions as cushioning packaging during transport to prevent solder joint breakage at folding points.
Typical Applications: Smart band circuits, foldable phone hinge connectors, ECG device wiring boards.
Rigid-Flex PCB: Meeting “Rigidity & Flexibility Combined” Demands
PCB Features: Partly rigid (e.g., component soldering areas) and partly flexible (e.g., connection cables), used in complex circuits such as smartphone motherboards, automotive dashboards, and drone flight control boards, requiring the most complex production.
Kraft Paper Solution: Segmented adaptation—rigid areas use heat-resistant insulating kraft paper, while flexible areas use high-flexibility modified kraft paper.
Key Adaptation Points: Ensures insulation and heat resistance in rigid areas, maintains bendability in flexible areas, and provides consistent moisture and rust resistance through unified impregnation treatment.
Typical Applications: Smartphone motherboards, automotive infotainment circuits, drone navigation control boards.