There are several different materials used in PCB fabrication. The type of material used depends on the end use. Materials widely used include the FR4, standard rigid FR4, CEM-3, prepreg, Kapton, and special materials for Microwave, RF and high speed applications.
The FR4 is among the most widely used materials; the FR stands for Fire Retardant. This material is made from fiber glass with epoxy laminate. Several layers of glass fiber are laminated together. In a 1.60-mm FR4 substrate, there are 8 layers of the material joined together.
Most manufacturers place their logo in the 4th layer during PCB fabrication. Two types of logo are used for the middle layer: red UL94-VO and blue UL94-HB. The red logo is used for newer, more modern materials. On the other hand, the blue logo means that the materials are from the older kinds such as phenolic (XPC) and glass epoxy (G10). Glass epoxy or G10 material mainly used for manufacturing thin watch circuits because holes are easily punched into it.
Standard rigid FR4
This material is specially designed for high density and multi-layered printed circuit boards. This is most suited for surface mounts, direct chip attach, MCM-Ls and for printed circuit boards that will be used for instruments and equipment in wireless communication and auto motives. The many beneficial characteristics of the FR4 is also very suitable in PCMCIA applications and in high volume fine line multi-layered pcbnet fabrication.
The behavior and function of this material is predictable and consistent, which makes processing tremendously easy. The mechanical and electrical characteristics make it user friendly for fabricators and designers of critical types of circuits.
The is an acronym for Composite Epoxy Material, which is very similar to FR4. However, instead of using glass fabric woven together, “flies” type is used. The CEM-3 is very smooth and milky white in color. The characteristics of this material can rival that of FR4. This is heavily preferred by Japanese manufacturers.
This material is made of glass fabric coated with epoxy. Prepreg has 2 main uses. One is as a dielectric in the manufacture of multi-layered PCBs. Another is as part of the raw materials used for FR4.
Materials used for Flex and Rigid-flex applications
Rigid-flex and flex circuit boards are increasingly becoming more popular in PCB fabrication because of the unique applications that these allow. These kinds of boards can be twisted and folded. These can even be wrapped around for tight packaging.
These boards are more popularly manufactured as Kapton, which was developed by the DuPont Corporation. The material is polyimide film-based and has several desirable characteristics. Kapton has great dimensional stability, is resistant to heat, and has a low dielectric constant of 3.6.
There are currently 3 variants of Kapton, namely: Pyralux LF (acrylic based and not flame retardant properties), Pyralux FR (acrylic-based and flame retardant), and Pyralux AP (adhesiveless and used for applications that demand high performance).
PCB materials for applications that involve Microwave, RF and High Speed
These materials were developed in response to the growing need for rapidly functioning circuits and for wireless communication. Typical materials include the following:
(from the Rogers Corporation)
• 5870/5880 series
• 3003/3006/3010 series
• 4003/4350 series
• DiClad and CuClad series Park Nelco
• Loss tangent= 0.012
• N4000 series/N5000 series/N6000 series/N7000 series/N8000 series Getek
Creating hybrids reduces the cost in PCB fabrication. Hybrid PCB materials are made by combining FR4 with other laminates designed for RF/high speed/microwave. This technology allow for more control in designing the layers while reducing the high cost of FR4.
Advancements in materials technology gave birth to printed circuit boards that are composed of multiple layers, with each layer having different copper strip patterns so more electronic components can be connected using a single board. For more detail information visit pcbnet.com .