Flexible PCB Material Selection

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Flex PCB materials should be able to meet a variety of design and operational requirements, including support for straightforward manufacturing techniques with high yield, ability to go through normal assembly processes, and static or dynamic bending. Although flex and rigid-flex PCBs are produced in high volume using a relatively small material set, flex PCB materials may initially look unusual. This tutorial will look at some of the fundamental characteristics of flex PCB materials and how flex and rigid-flex PCBs are constructed using them.

1.The choice of Copper Clad Laminate

The CCL is composed of three layers of "copper foil + glue +substrate". In addition, there is also a non-adhesive material, that is a "copper foil + substrate" two-layer combination, which is high cost and is suitable for products requires more than 100,000 bending times.

a.Copper foil

There are two types Copper foil: Rolled Anneal Copper Foil and Electrodeposited Copper Foil. The rolled copper has better bending performance than electrolytic copper. The thickness is 1/3oz, 1/2OZ, 1OZ, 2OZ.

b.Substrate

Commonly used dielectric materials for flexible circuits are PI (Polyamide, glued and non-gel) and PET (Polyester). PI is more expensive, but its flame resistance is better. PET is cheaper but don't have heat resistant. Therefore, if there is welding demand, prefer to use PI material. Generally, there are several 1/2 mil, 1 mil, and 2 mil thicknesses.

c.Adhesive

Commonly used adhesives for flexible sheets are acrylic and epoxy. The most commonly used is epoxy. The thickness is from 0.4 to 2 mil, and generally 0.7 mil thick glue is used.

2.The choice of Cover Film

The cover film is composed of "substrate + glue", and the substrate is divided into PI and PET, and the thickness includes 0.5~1.4 mil.

3. Selection of Reinforcing Materials

Function: In the flex board area, in order to weld the components, the reinforcing material is added for installation, and the thickness of the flex board is compensated.

Material: PI/PET/FR4/SUS

Combination method: PSA (Pressure Sensitive Adhesive): pressure sensitive type (such as 3M series), Thermal Set: thermosetting type (high bonding strength, solvent resistance, heat resistance, resistance to creep)

Understanding the materials used in rigid-flex and flexible circuits is crucial. You should be mindful of the variables that can lead to a flex PCB failing in the field, even if you may typically allow a fabricator to choose the materials to assure yield. Understanding the characteristics of the material will also benefit your product's mechanical design, assessment, and testing. For example, when modeling heat, moisture, chemicals, shock, and vibration for automotive items, precise material properties must be included in order to assess the product's dependability and lowest permissible bending radius. Ironically, hard surroundings are frequently the driving necessities that lead you to select between flexible and rigid-flex. For instance, inexpensive consumer personal computers