FR4 must be known before PCB board

FR4 Glass Epoxy Cutting Board must be known before PCB board

When we place an order in a PCB board factory, there is often a FR-4 board type to choose from. Currently, there are three types of board types: FR-4, aluminum board, and thermoelectric separation copper board.

1. FR-4, also written as FR4, is both a name and a standard grade

Organic substrate materials used to make PCBs consist of 3 components: resin, reinforcement material, and conductive copper foil.

FR in the NEMA classification standard means Flame-Retardant (flame-retardant) or Fire-Resistant (fire-resistant), that is, the fire rating, so the FR-rated boards are all flame-retardant boards, and the number "4" means that the material To distinguish it from other materials of the same level, 4 means that the resin is epoxy resin, the reinforcement material is glass fiber cloth, and the flame retardant grade is UL94 V-0. The flame retardant grades of FR-1, FR-2, and FR-3 are UL 94V-1, and the resins and reinforcing materials used are also different.

2. Performance index of FR-4
The FR-4 substrate is an epoxy resin system, so for a long time, Tg value is the most common index used to classify FR-4 substrates, and it is also one of the most important performance indicators in the IPC-4101 specification.

Glass transition temperature Tg

The Tg value of a resin system refers to the temperature transition point at which the material changes from a relatively rigid or "glassy" state to a deformable or softened state. This thermodynamic change is always reversible as long as the resin does not decompose. That is, when a material is heated from a normal temperature state to a temperature above the Tg value, and then cooled below the Tg value, it can change back to a rigid state with the same properties as before. However, when a material is heated to temperatures well above its Tg, irreversible phase changes can result. The effect of this temperature has a lot to do with the type of material and also with the thermal decomposition of the resin.

Generally speaking, the higher the Tg of the substrate, the higher the reliability of the material. If the lead-free soldering process is adopted, the thermal decomposition temperature (Td) of the base material also needs to be considered.

Other important performance indicators include coefficient of thermal expansion (CTE), water absorption, adhesion properties of the material, and commonly used delamination time tests such as T260 and T288 tests. [1]

3. Diversity of FR-4

Glass fiber cloth is used as a reinforcing material, the resin system is epoxy resin and the base material with a flame retardant rating of UL 94V-0 is FR-4. Is there any specific distinction between such a large class of materials?

Divide according to Tg value


The most obvious difference between FR-4 materials is the Tg value. According to the Tg temperature, FR-4 sheets are generally divided into low Tg, medium Tg and high Tg sheets.

In the industry, FR-4 with a Tg of about 135°C is usually classified as a low Tg sheet; FR-4 with a Tg of about 150°C is a medium Tg sheet; and FR-4 with a Tg of about 170°C is classified as a high Tg sheet.

If there are many pressing times during PCB processing, or the number of PCB layers is large (more than 14 layers), or the soldering temperature is high (≥230°C), or the working temperature is high (over 100°C), or the welding thermal stress is large (such as wave soldering) , should choose high Tg plate.

Divide according to loss.

FR-4 can be divided into:

Ordinary loss plate (Df≥0.02)
Medium loss plate (0.01
Low loss plate (0.005
Ultra-low loss sheet (Df<0.005)

Any inquiry , please contact sales@honyplastic.com