Aluminum hydroxide is the main variety of inorganic flame retardants, with three major functions of flame retardancy, smoke reduction, and filling. It does not cause secondary pollution during combustion and accounts for more than 80% of the total amount of inorganic flame retardants used. Aluminum hydroxide is not only flame retardant but also reduces smoke emissions, making it affordable. It also has the effects of reducing the thermal expansion coefficient in the thickness direction of the board, improving the CTI performance of the substrate, and whitening the substrate. Widely used in the field of copper-clad laminates, especially with the increasing demand for "halogen-free" products, the application of aluminum hydroxide is becoming more and more widespread. Traditional aluminum hydroxide fillers, without surface treatment, when added in large amounts to the adhesive formula of copper-clad laminates, can cause difficulty in dispersion and settlement, leading to a decrease in the mechanical processing performance of the board; The problem of relatively poor alkali resistance is prone to occur during PCB reflow solder resist.
Silane coupling agent is a silicon-based chemical molecule that contains two types of reactivity - inorganic and organic - in the same molecule. Silanes containing three inorganic reactive groups on silicon atoms can effectively bind to the metal hydroxyl groups of most inorganic materials, especially those with structures containing silicon, aluminum, or heavy metals.
By reacting with added or residual water on inorganic surfaces, the alkoxyl groups on silicon atoms hydrolyze into silanol, which then reacts with the metal hydroxyl groups on the inorganic surface to form an alkoxyl structure and remove water.
Under the same conditions, different ratios of treated and untreated aluminum hydroxide fillers were added to test the rotational viscosity of the gel system. The addition of organosilane coupling agent can reduce the viscosity of the gel to a certain extent. This is due to the reduced agglomeration and high dispersion of modified aluminum hydroxide, resulting in reduced gaps between particles. The surface of aluminum hydroxide changes from polar to non-polar, with enhanced oleophilicity, reduced friction between particles, and improved lubrication performance.
The interlayer adhesion of untreated aluminum hydroxide sheet decreases with the increase of addition amount, but the decrease in interlayer adhesion slows down after organic silicon treatment. After treatment with coupling agent, the exposed filler is significantly reduced under external force, and there are also fewer voids that peel off from the resin and filler, indicating that the bonding force between the filler and resin is strengthened.
The combination between treated aluminum hydroxide and resin is good, and the filling material is well wrapped around it. However, untreated aluminum hydroxide shows more damage, indicating that the resin is easily peeled off from the filling particles under external forces, resulting in a significant decrease in adhesive strength.
After treatment with coupling agents, the affinity between the filler and the resin is strengthened, the interface is improved, and the dispersibility is enhanced. Organic silicon can form a silicon film on the surface of aluminum hydroxide, which can effectively prevent strong alkali from corroding aluminum hydroxide. The silicon film itself has alkali resistance, so it can improve the alkali resistance of the board. The use of silane to treat aluminum hydroxide improves the affinity between the filler and resin, and optimizes the interface; The interlayer adhesion of the produced copper-clad laminates has been improved, and their alkali resistance has also been significantly enhanced.
