A Manufacturing Method for High Thermal Conductivity PCB Substrate Materials

Thermal performance has always been a primary concern for PCB design and manufacturing engineers, and PCB substrate materials with high thermal conductivity play a crucial role in improving the thermal performance of PCBs. Based on this fundamental principle, this paper mainly introduces a manufacturing method for high thermal conductivity PCB substrate materials. Experiments prove that the thermal conductivity reaches at least 3 W/(m·K), with excellent insulation properties and reliable performance.

The manufacturing method for high thermal conductivity PCB substrate materials relies on alternately stacking prepregs with multiple voids and high thermal conductivity resin films before copper cladding. As shown in Figure 1, during the heating and pressing process, the voids on the prepreg are filled with the high thermal conductivity resin composite and solidified, thereby obtaining a high thermal conductivity PCB substrate material that features high insulation, reliable performance, and retained mechanical strength of the substrate. Refer to Figure 1 to Figure 3 below.

Figure 1 Prepreg with 

Multiple voids refer to the unoccupied spaces between warp and weft yarns that are not filled with impregnating resin, which is defined as voidage and conforms to Formula (1): X = Y / (s × t) Where: X = Voidage Y = Unfilled area formed by warp and weft yarns s, t = Side lengths

According to Formula (1) and Figure 1, it can be concluded that X should be increased to improve thermal conductivity. The value is usually 0.3 or higher, preferably 0.5 or higher, depending on the structure of the woven glass fiber cloth and related to the impregnation process.

Glass fiber cloth or organic fiber cloth can be used. For glass fiber cloth, the diameter of glass fiber is preferably in the range of 6–9 μm.

The resin used for impregnating glass fiber cloth is mainly epoxy resin, such as bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, etc. With improved heat resistance and electrical properties, novolac epoxy resin, bisphenol A novolac epoxy resin, and alicyclic epoxy resin can be used. Brominated flame-retardant epoxy resin is also applicable. These resins can be used alone or in combination of two or more.

Curing agents for epoxy resin are mainly phenolic compounds, amine compounds, and cyanate ester compounds, which can be used alone or in combination of two or more. The dosage is usually 0.1% to 5% of the total resin mass.

Curing catalysts used in the experiment are mainly 4-methyl-2-ethylimidazole, 2-ethyl-4-methyl-1H-imidazole-1-propanenitrile, etc., which can be used alone or in combination of two or more. The dosage is usually 0.001% to 0.01% of the total resin compound mass.

The resin solution is actually a mixture of epoxy resin, curing agent, catalyst, and organic solvent, used for impregnating glass fiber cloth. After impregnation, the glass fiber cloth is dried at 120 °C to 170 °C for 2 to 15 minutes to form a prepreg with multiple voids and a thickness of 0.04 mm to 0.3 mm. The resin content of this prepreg is usually above 30%.

This is a resin film in which inorganic fillers with high thermal conductivity are added to a thermosetting material. The resin system used is consistent with that of the prepreg with multiple voids (resin + curing agent).

There are various types and specifications of inorganic fillers. For example, alumina (Al₂O₃) powder, aluminum nitride (AlN) powder, silica (SiO₂) powder, silicon nitride (Si₃N₄) powder, and boron nitride (BN) powder have high thermal conductivity; organic fillers with excellent insulation properties are also applicable. Alumina (Al₂O₃) powder is highly suitable for this application. If used, the powder can be oxidized to form an oxide film on the particle surface, which helps improve the moisture resistance of the product.

To improve the bonding performance between inorganic fillers and organic resin, the fillers must be treated with a coupling agent.

The above-mentioned fillers can be used independently or in combination. The dosage of inorganic fillers in the resin compound ranges from 60% to 95%. Below 60%, the thermal conductivity improvement effect is insignificant; above 95%, film forming becomes difficult and the target performance cannot be achieved.

A mixer and a ball mill are usually used to achieve uniform mixing of multiple resin composites.

The high thermal conductivity resin film with a thickness of 0.04 mm to 0.3 mm is prepared by coating the resin mixture on metal foil or plastic film, followed by heating and drying.

According to Figure 2 and Figure 3, prepregs of glass fiber cloth substrate with multiple voids and high thermal conductivity resin films are stacked before copper cladding. The lamination process is carried out at 160 °C to 180 °C under a pressure of 2 to 4 MPa for 60 to 120 minutes.

Finally, based on the manufacturing technology of multi-layer PCBs, multi-layer PCBs with extremely high thermal conductivity can be fabricated using high thermal conductivity copper clad laminates, prepregs with multiple voids, high thermal conductivity resin films, and copper foils.

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