Preparation of Halogen-free Copper Clad Laminate

Halogen-free copper clad laminates prepared with benzoxazine resin with a broad molecular weight distribution and high nitrogen content modified phenolic resins have good heat resistance (Td 5%>350°C, T288>60 min), hygroscopic heat resistance and Good bending strength; good toughness of the plate, less cracks when cutting the plate.

Keywords: molecular weight broadly distributed benzoxazine resin, high nitrogen content modified phenolic resin, copper clad laminate performance

I. Introduction

The EU's two directives have promoted the development of the halogen-free and lead-free copper clad laminate market. The non-halogenated copper clad laminates have good heat resistance, CAF resistance resistance and low dielectric loss tangent, especially made from benzoxazine resin systems. Halogen-free copper clad laminates are popular with users due to their good moisture absorption and heat resistance. However, regardless of the kind of non-halogen-coated copper plate, due to the structural rigidity of the resin material used and the addition of the inorganic filler, the halogen-free clad copper plate prepared therefrom is relatively brittle, and processing and drilling are difficult. The purpose of this paper is to develop a high-toughness halogen-free copper-clad laminate that can maintain the toughness of the copper-clad laminate while maintaining the advantages of good heat resistance, CAF resistance, and low dielectric loss tangent of the halogen-free copper-clad laminate. To overcome the brittleness, it has a better processing performance.

Second, development ideas

Benzo-fazine is a new type of phenolic resin. Because of its rich nitrogen content and excellent properties of cured products after curing together with other materials, benzofluorazine resins are widely used in the preparation of halogen-free clad laminates. In this study, we used a broad molecular weight distribution of benzoxazine resin. This kind of resin can make the glue have a better sizing and pressing process; second, it can make the cured product of the glue have a more perfect cross-linked network structure, so as to obtain a better overall performance of the copper-clad board. Phenolic resin as a curing agent makes the copper clad laminate greatly improved in heat resistance and achieves lead-free requirements. We take full advantage of the phenolic resin as a curing agent and modify it to a nitrogen-containing phenolic resin with a higher nitrogen content. In this way, while maintaining the good heat resistance of the copper clad laminate, it also increases the flame retardancy, reduces the addition of inorganic fillers, and provides a copper clad laminate with good processability and toughness.

Third, the experimental process

Raw materials: Benzofluorine resin, trade name: WL-0910, Huashuo Science and Technology Co., Ltd. (Hubei Chemical Research Institute) produces nitrogen-containing phenolic resin, trade name: WL-0812, Huashuo Technology Co., Ltd. (Hubei Provincial Institute of Chemistry) Production of benzoxazine resin, nitrogen-containing phenolic resin, epoxy resin, surface-treated inorganic fillers, curing accelerators, and solvents are added to the vessel in a certain proportion, and the mixture is stirred until it is uniformly mixed. Fiberglass cloth, baked and laminated a certain number of adhesive sheet, copper foil at a certain temperature after the press forming and gradually warming, and finally heat treatment temperature of 190 °C 90min, and then cooled out of board detection.

IV. Results and Discussion

1. Adhesive glue, pressing process

1.1 glue water glue craft

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1.2 Semi-cured resin rheological curve

Figure 1 shows the rheological profile of the resin removed from the prepreg. As can be seen from Figure 1, the glue has a wider processing window and better viscosity after baking, indicating that the glue will have a better pressing process and leveling after baking.

1.3 Post-processing conditions of pressed plate

Take a certain amount of adhesive sheet laminated neatly and covered with copper foil on both sides, press forming at a certain temperature and gradually warming, and finally heat treatment at 190 °C for 1.5 hours, cooling out of the board. The laminate surface has no dried flowers or lack of resin, and the overall performance of the copper clad laminate is good (Table 1), indicating that the resin system has mild post-treatment conditions.

2. CCL performance

2.1 PCT test

The copper clad plate after etching copper was cut into small pieces of a certain size and put in a pressure cooker. After being cooked at 105 kPa, 121° C., and 180 min, the PCT was tested (tin bath at 288° C.) for a time of >5 minutes without bubbling. Stratification shows the good water-resistant cooking performance of the CCL.

2.2 Thermogravimetric Analysis

The copper-etched copper clad plate is taken as a small amount to perform a thermal weight loss test (TGA analysis). The test result shows that the weight loss temperature of 5% wt is 371° C., and the surface of the copper clad plate has good heat resistance, which can achieve lead-free requirements.

2.3 Flexural strength and toughness

Because of the rigid structure of nitrogen-containing phosphorus resins and the addition of fillers, the halogen-free copper-clad laminates are generally relatively brittle and easily cracked during the processing of printed circuits. We indirectly observe the toughness of the board by shearing and testing the bending strength of the board. We found that when the 1.6mm board was cut, the edge of the board was almost free of cracks; the bending strength was measured to be 608 MPa in the longitudinal direction, 613 MPa in the transverse direction, and 532 MPa in the horizontal direction. 525MPa, its bending strength value is large. From the shear crack and bending strength values, it can be indirectly reflected that the copper-clad laminate has good toughness.

2.4 Alkalinity

After the plate was placed in a 10% NaOH solution at 80°C for 1 hour, the plate had a good appearance without delamination, no foaming, and no apparent change in appearance. Table 1, part of the performance of CCL

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