Material Characteristics of a Rigid-Flex Board

Typical Rigid-Flex PCB Material Feature

Material Description Specification Flexible Laminate Polyimide (adhesive-less or adhesive) Rigid Laminate FR-4 or glass-polyimide C-stage laminateCoverlay and Bond PlyAdhesive coated polyimide film Prepreg No-flow FR-4 or polyimide prepreg Build-up Material Resin costed copper foil or build up dielectrics

Rigid-flex material selection

Rigid PCB Flex PCB
Base substrate




Metal Core



Adhesive layer







ED Copper

High ductility


RA copper

High Ductility


ED copper

Introduction to Flexible PCB Materials

Introduction to Flexible PCB Materials

Base Raw Material

1). FCCL ( Flexible Copper Clad laminate)

  • Polyimide: KaptonÔ (12.5 mm/20 mm/25mm/50mm/75mm)
  • High flex life, good thermal management, high moisture absorption, and good tear-resistant
  • Polyester (25mm/50mm/75mm)
  • Most cost-effective, good flex life, low thermal resistivity, low moisture absorption, and tear-resistant

2).For FPC Material Status 2L FCCL

FPC Material Status 2L FCCL
Suppliers   Material Characteristics Current Status
Taiflex 2lps High Flexibility HVM
Rogers 2 series High Flexibility HVM
Nippon steel MC Low Dimension HVM
Dupont AC High Flexibility HVM

3).For FPC Material Status 3L FCCL

FPC Material Status 3L FCCL 
Supplier   Material Characteristics Current Status
Taiflex I X N High Flexibility HVM
Rogers 7 series Low Dimension HVM
Microcosm PSBR Low Dimension HVM
Arisawa LASW High Flexibility HVM

1.Dielectric Substrates dielectric film: polyimide (PI), polyester (PET)

Characteristics of PI:

  1. Good heat resistance: The long-term use temperature is 260℃.In the short term, it can withstand high temperatures above 400℃.
  2. Good electrical and mechanical properties.
  3. Good weather resistance and chemical resistance.
  4. Good flame retardancy.
  5. The water absorption rate is high, and the size changes after moisture absorption. (Defect)

IQC must regard the dimensional change rate as an important acceptance index for PI incoming materials. The environmental control requirements of the production process are also stricter than rigid boards.

Polyester film PET has good mechanical and electrical properties such as tensile strength, water resistance, and dimensional stability after moisture absorption. However, it has a large shrinkage rate when heated and has poor heat resistance. It is not suitable for high-temperature soldering (Now the lead-free soldering temperature is 235+/-10 ℃), and its melting point is 250 ℃. Less used

Polyimide (PI) is the most widely used, and 80%  is made by DuPont in the United States.

2.Cover Layer

Function: Protect circuit, insulation, electrical demand, and board deflection.

Features: 1. Good electrical characteristics, 2. Good processability, 3. Excellent flexibility

Cover Layer from ½ mil to 5 mils (12.7 to 127µm)

Polyimide: (12.5 mm/15 mm/25mm/50mm/75mm/125mm)

High flex life and high thermal resistivity.

Cover Layer

1) Other protective films and covering film materials

2) Flexible solder mask

The most cost-effective, lower flex life, and better for registration.

3) PIC—Photo Imaging covercoat

Lower flex life, better for registration.

3.Adhesive Sheet

Bond-ply insulation combination layer with bonding effect.

Cover layer Glue overflow

Cover layer Glue overflow

Pressing conditions: 190℃/85(kg/cm2) gauge pressure/forming pressure 60sec

4.Conductive Layer

Rolled Annealed Copper (9mm/12mm/17.5mm/35mm/70mm)

  • High flex life, good forming characteristics.
  • Electrodeposited Copper (17.5mm/35mm/70mm)
  • More cost-
  • Silver In
  • Most cost-effective, poor electrical characteristics. Most often used as shielding or to make connections between copper layers.

5.SF-PC5000 Electromagnetic Wave Protective Film Thickness Characteristics

1) Ultra-thin – Total thickness is only 22 microns.

The hot-melt process is used for compound processing between the two insulating films.

The inner insulating layer is extremely flexible, and the outer insulating layer has excellent wear resistance.

2) The sliding performance and flexural performance greatly improved.

Since it has a better sliding performance than silver paste, it further promotes the thinning of the slide-type mobile phone.

3) Adapt to moisture-resistant reflow soldering.

Due to the improved insulating resin, the thinning is realized, and the gas penetration ability is greatly improved.

It is fully suitable for lead-free reflow soldering.

4) Good dimensional stability.

Compared with previous materials, the thermal shrinkage rate of the insulating resin in this product is less than one-tenth of the original.

As a single-sided shielding material for thin FPC and COF, it can significantly reduce the warping problem caused by material shrinkage.

6 .Additional Material & Stiffeners

The hard material is additionally pressed on the local area of the soft board for welding parts or adding reinforcement for installation.

Stiffeners types: FR4, Aluminum, PI

7. No / Low Flow PP

TYPE (usually very thin PP) is used for lamination of rigid and flexible boards.

  • 106(2mil)
  • 1080(3.0mil / 3.5mil)
  • 2116(5.6mil) w/o micro-via

Flow PP Manufacturers: TUC, Panasonic, Arlon, Hitachi, Doosan

No / Low Flow PP

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