1. The combustibility of a material, often referred to as flame retardancy, self-extinguishing properties, flame resistance, fire resistance, and flammability, is a measure of the material’s ability to withstand combustion.

2. A sample of the flammable material is ignited with a flame that meets specific criteria, and the flame is extinguished after a predetermined duration. The flammability rating is determined based on the extent of combustion observed in the sample.

3. There are three levels of flammability: the horizontal test method categorizes samples into FH1, FH2, and FH3, while the vertical test method classifies them into FV0, FV1, and FV2.

4. Solid PCB boards are categorized as HB boards and V0 boards.

5. HB boards exhibit low flame retardancy and are primarily utilized for single-sided applications.

6. V0 boards, on the other hand, have high flame retardancy and are mainly used in double-sided and multi-layer configurations.

7. PCBs that comply with V-1 fire rating requirements are classified as FR-4 PCBs.

8. The V-0, V-1, and V-2 classifications indicate varying levels of fireproofing.

9. A circuit board must be flame-resistant; it should not ignite at certain temperatures but may soften. This specific temperature is referred to as the glass transition temperature (Tg), which is critical for the dimensional stability of the PCB.

10. What defines a high Tg PCB circuit board, and what are its advantages?

11. When the temperature of a high Tg printed board reaches a certain threshold, the substrate transitions from a “glass state” to a “rubber state.” This transition temperature is known as the board’s glass transition temperature (Tg), marking the highest temperature at which the substrate retains its rigidity.

12. What are the specific types of PCB boards?

13. They can be categorized by grade level from lowest to highest as follows: 94HB, 94VO, 22F, CEM-1, CEM-3, and FR-4.

14. The details are as follows:


**94HB:** Ordinary cardboard, not fireproof (the lowest grade material, die punching, unsuitable for use as a power supply board).

**94V0:** Flame-retardant cardboard (die punching).

**22F:** Single-sided half glass fiber board (die punching).

**CEM-1:** Single-sided fiberglass board (requires computer drilling, not die punching).

**CEM-3:** Double-sided half glass fiber board (the lowest-end material for double-sided boards, aside from double-sided cardboard; it can be used for double panels and is 5-10 yuan/square meter cheaper than FR-4).

**FR-4:** Double-sided fiberglass board.

The circuit board must be flame-resistant, able to soften rather than burn at certain temperatures. This temperature is referred to as the glass transition temperature (Tg), which is linked to the dimensional stability of the PCB.

**What is a high Tg PCB circuit board, and what are its advantages?**

As temperature rises to a specific range, the substrate transitions from a “glass state” to a “rubber state.” The temperature at this point is known as the glass transition temperature (Tg) of the board. In essence, Tg is the highest temperature (°C) at which the base material retains its rigidity. Ordinary PCB substrate materials not only experience softening, deformation, and melting at elevated temperatures but also exhibit a significant decline in mechanical and electrical properties (which is not ideal for your products).

Typically, the Tg of a board is above 130 degrees, with high Tg generally exceeding 170 degrees and medium Tg around 150 degrees. PCBs with Tg ≥ 170 degrees Celsius are categorized as high Tg printed boards. As Tg increases, the thermal resistance, moisture resistance, chemical resistance, and overall stability of the printed board improve. Higher Tg values correlate with better temperature resistance, particularly in lead-free processes, where high Tg applications are increasingly common.

High Tg indicates enhanced heat resistance. With the rapid advancements in the electronics industry, particularly in computer technology, there is a growing demand for PCB substrate materials that can withstand higher temperatures. The rise of high-density mounting technologies such as SMT and CMT necessitates the use of substrates with superior heat resistance, especially concerning small apertures, fine wiring, and reduced thickness.

Therefore, the distinction between standard FR-4 and high Tg FR-4 lies in their performance under heat, especially after moisture absorption. Under thermal conditions, mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition, and expansion behavior vary. High Tg products perform significantly better than standard PCB substrate materials.

In recent years, the demand for high Tg printed boards has steadily increased. As electronic technology evolves, new requirements for printed circuit board substrate materials emerge, driving the ongoing development of copper clad laminate standards. Currently, the primary standards for substrate materials are as follows:

1. **National Standards:** China’s national standards for PCB materials classification include GB/T 4721-4722 (1992) and GB 4723-4725 (1992). Taiwan’s copper clad laminate standard is based on the Japanese JIS standard, issued in 1983.

2. **Other National Standards:** These include Japanese JIS standards, American ASTM, NEMA, MIL, IPC, ANSI, UL standards, British BS standards, German DIN and VDE standards, French NFC and UTE standards, Canadian CSA standards, Australia’s AS standard, the former Soviet Union’s FOCT standard, and the international IEC standard.

Common suppliers of PCB design materials include Shengyi, Jiantao, and International.

**Accepted Documents:** Protel, AutoCAD, PowerPCB, OrCAD, Gerber, or actual board copies.

**Sheet Types:** CEM-1, CEM-3, FR-4, high Tg materials.

**Maximum Board Size:** 600mm x 700mm (24000 mil x 27500 mil).

**Processing Board Thickness:** 0.4mm – 4.0mm (15.75 mil – 157.5 mil).

**Maximum Number of Processing Layers:** 16 layers.

**Copper Foil Layer Thickness:** 0.5 – 4.0 oz.

**Finished Board Thickness Tolerance:** ±0.1mm (4 mil).

**Forming Size Tolerance:** Computer milling: 0.15mm (6 mil); die punching: 0.10mm (4 mil).

**Minimum Line Width/Spacing:** 0.1mm (4 mil).

**Minimum Hole Diameter of Finished Product:** 0.25mm (10 mil).

**Minimum Punching Hole Diameter of Finished Product:** 0.9mm (35 mil).

**Finished Product Aperture Tolerance:** PTH: ±0.075mm (3 mil); NPTH: ±0.05mm (2 mil).

**Copper Thickness of Finished Hole Wall:** 18-25 μm (0.71-0.99 mil).

**Minimum SMT Patch Spacing:** 0.15mm (6 mil).

**Surface Coating:** Chemical immersion gold, spray tin, full plate nickel-plated gold (water/soft gold), and silk screen blue glue.

**Solder Mask Thickness on the Board:** 10-30 μm (0.4-1.2 mil).

**Peeling Strength:** 1.5 N/mm (59 N/mil).

**Hardness of Solder Mask:** >5H.

**Solder Resistance Plug Hole Capacity:** 0.3-0.8mm (12 mil-30 mil).

**Dielectric Constant:** ε = 2.1 – 10.0.

**Insulation Resistance:** 10KΩ – 20MΩ.

**Characteristic Impedance:** 60 ohm ±10%.

**Heat Shock:** 288 degrees Celsius for 10 seconds.

**Degree of Warpage of Finished Board:** <0.7%.
**Product Applications:** Communication equipment, automotive electronics, instrumentation, global positioning systems, computers, MP4 players, power supplies, home appliances, etc.

According to PCB reinforcement materials, they can be categorized as follows:

1. **Phenolic PCB Paper Substrate:**

This type of PCB board consists of paper pulp and wood pulp, which can sometimes result in cardboard, V0 boards, flame-retardant boards, and 94HB. The primary material is wood pulp fiber paper, synthesized by pressing phenolic resin. This paper substrate is not fireproof, can be punched, and is low-cost with a low relative density. Common examples include phenolic paper substrates like XPC, FR-1, FR-2, FE-3, etc. The 94V0 is classified as flame-retardant paperboard and is fireproof.

2. **Composite PCB Substrate:**

Often referred to as powder board, this substrate utilizes wood pulp fiber paper or cotton pulp fiber paper as the reinforcement material, complemented by glass fiber cloth for surface reinforcement. These materials are combined with flame-retardant epoxy resin. Examples include single-sided half-glass fiber 22F, CEM-1, and double-sided half-glass fiber board CEM-3, with CEM-1 and CEM-3 being the most common composite base copper clad laminates.

3. **Glass Fiber PCB Substrate:**

Also known as epoxy board or FR-4, this substrate employs epoxy resin as an adhesive and glass fiber cloth for reinforcement. These circuit boards can withstand high working temperatures and are not affected by environmental conditions. They are frequently used in double-sided PCBs but tend to be pricier than composite PCB substrates, typically with a thickness of 1.6mm. This substrate is suitable for various power supply boards and high-performance circuit boards, widely utilized in computers, peripheral devices, and communication equipment.

4. **Other Substrates:**

In addition to the three types mentioned above, there are metal substrates and multi-layer laminates.

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