PCB base material – knowledge base

The base material of circuit boards can be divided into two categories: rigid PCB base materials and flexible PCB base materials.

Rigid material:

Generally, an important variety of rigid base materials is copper-clad laminates. It is made of reinforced material (Reinforcing Material), impregnated with resin adhesive, dried, cut, and laminated into a blank, then covered with copper foil, steel plate is used as a mold, and processed by high temperature and high pressure forming in a hot press Into. The prepreg used for general multi-layer boards is a semi-finished product in the production process of copper-clad laminates (mostly glass cloth is impregnated with resin and processed by drying). There are many ways to classify copper-clad laminates.

Generally, according to the different reinforcing materials of the board, it can be divided into five categories: paper base, glass fiber cloth base, composite base (CEM series), multi-layer laminate base, and special material base (ceramic, metal core base, etc.).

If classified according to the different resin adhesives used in the board, the common paper-based CCI. There is phenolic resin (XPc, XxxPC, FR-1, FR-2, etc.), epoxy resin (FE-3), polyester resin, and other types. Common glass fiber cloth base CCL has epoxy resin (FR-4, FR-5), which is currently the most widely used type of glass fiber cloth base.

In addition, there are other special resins (with glass fiber cloth, polyamide fiber, non-woven fabric, etc. as additional materials): bismaleimide modified triazine resin (BT), polyimide resin (PI), Diphenylene ether resin (PPO), maleic anhydride imine-styrene resin (MS), polycyanate resin, polyolefin resin, etc.

According to the classification of the flame retardant performance of CCL, it can be divided into two types of flame-retardant (UL94-VO, UL94-V1) and non-flame-retardant (UL94-HB). In the past one or two years, with more attention to environmental protection issues, a new type of non-bromine-free CCL has been divided into flame-retardant CCL, which can be called “green flame-retardant cCL”.

With the rapid development of electronic product technology, there are higher performance requirements for CCL. Therefore, from the performance classification of CCL, it is divided into general performance CCL, low dielectric constant CCL, high heat resistance CCL (normal board L is above 150 ℃), low thermal expansion coefficient CCL (usually used on package base material) ) And other types.

 

Flexible board material

In Flex PCB, the commonly used base materials are polyimide (PI) film and PET (polyester) film. In addition, polymer films such as PEN (polyethylene phthalate) can also be used. ), PTFE and aramid, etc.

Polyimide (PI) “thermosetting resin” is still the most commonly used material for Flex PCB. It has excellent tensile strength, is very stable in a wide operating temperature range of -200 O C to 300 O C, has chemical resistance, excellent electrical properties, high durability, and excellent heat resistance. Unlike other thermosetting resins, it can maintain its elasticity even after thermal polymerization.

However, the disadvantages of PI resin are poor tear strength and high moisture absorption rate. On the other hand, PET (polyester) resin has poor heat resistance, “making it unsuitable for direct welding”, but it has good electrical and mechanical properties. Another base material, PEN, has a better mid-level performance than PET, but not better than PI.

Liquid crystal polymer (LCP) base material:

LCP is a rapidly popular base material in Flex PCB. This is because it overcomes the shortcomings of PI base material while maintaining all the characteristics of PI. LCP has moisture resistance and moisture resistance of 0.04%, and a dielectric constant of 2.85 at 1 GHz. This makes it famous in high-speed digital circuits and high-frequency RF circuits. The molten form of LCP is called TLCP, which can be injection molded and pressed into a flexible PCB material, and can be easily recycled.

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