The toughest among the toughest of light-curing resins

In the photocuring industry, phenolic epoxy acrylate is an indispensable raw material in printed circuit boards. As a photocuring resin manufacturer, Bossin will talk about phenolic epoxy acrylate today.

Novolac epoxy acrylate is prepared by the reaction of novolac epoxy resin and acrylic acid, wherein the novolac epoxy resin is prepared by the polycondensation reaction of phenol and formaldehyde to obtain a linear low-polymerization phenolic resin, which is then reacted with epichlorohydrin to obtain the corresponding epoxide. Due to the high viscosity of the novolac epoxy acrylate obtained from the final esterification reaction, a diluent is typically added during the early stages of the synthesis to reduce viscosity. Novolac epoxy acrylate is a multifunctional acrylate, so it has higher reactivity and greater crosslinking density than bisphenol A epoxy acrylate; it has a large benzene ring density, high rigidity, and better heat resistance. Its cured film also has the advantages of high hardness, high gloss, excellent chemical resistance, and good electrical properties.

At present, it is mainly used in PCB solder mask ink. PCB, Chinese name is printed circuit board, also known as printed circuit board, is an important electronic component, the support of electronic components, and the carrier for the electrical connection of electronic components. Because it is made by electronic printing, it is called "printed" circuit board.

PCB classification: 1. Classification by number of layers : single-sided board, double-sided board, multi-sided board. 2. Classification by product structure: rigid printed circuit board (RPCB), flexible printed circuit board (FPC/FPCB), rigid-flexible printed circuit board (R-FPCB), high-density interconnect board (HDI).

For a bare board with circuits made, the insulating materials that need to be covered on its surface and holes are solder mask ink, plugging ink, and text ink. Solder mask ink covers the circuit and substrate surface, plugging ink fills the necessary vias, and text ink is printed around the pad on the solder mask layer..

Today we mainly introduce solder resist ink, also known as solder resist ink or green oil, which is a permanent insulating protective coating covering the printed circuit board. According to the curing method, solder resist ink can be divided into thermal curing type and light curing type.

PCB solder mask ink can be displayed in different colors, including green, white, blue, black, red, yellow, matte color, purple, chrysanthemum, bright green, matte black, matte green, etc.  Typically, white is used for LED lighting products, while other colors serve product grading systems. For instance, some companies use red for experimental boards, blue for critical boards, and black for internal computer boards. Green is the most common color, hence the term "green oil."

So why is green oil used extensively in PCB solder mask ink ?

1. Functional Perspective: The formulation of green ink is well-established, making it easy to develop and less prone to falling off

2. Inspection Convenience: The contrast between green ink and the copper surface (yellow) is stark, facilitating the detection of defects like scratches and deviations.

3. Cost Efficiency: Green ink is relatively cheaper due to its mainstream status, mature and straightforward production process, and larger purchase volumes, which drive down costs.

4. Processing Advantages: In the yellow light room, green PCBs offer the best visual effect and are more amenable to instrument recognition during optical positioning calibration.

5. Safety and Quality Control: Other colors like blue and black, which incorporate cobalt and carbon respectively, pose a risk of short circuits due to their weak conductivity. Dark colors like black, purple, and blue complicate inspection and maintenance, making process control more challenging.

Why do PCB circuit boards need solder mask?

There are copper layers on both sides of the PCB board. PCB boards without solder mask are easily oxidized when exposed to the air, and become defective products, which also affects the electrical performance of the PCB board. Therefore, there must be a protective coating on the surface of the PCB circuit board that can block the oxidation reaction between the PCB and the air, and this coating is the solder mask covered with solder mask paint. The main function of the solder mask on the PCB board is to protect the circuit, prevent conductors from being tinned; prevent electrical short circuits between conductors caused by moisture or chemicals; prevent circuit breaks caused by poor handling in the later process of PCB production and electrical equipment; and various harsh environments from invading the PCB board.

The oligomers of UV solder resist ink mainly select resins with good heat resistance, good insulation and good adhesion to copper, such as bisphenol A-epoxy acrylate, novolac epoxy acrylate and polyurethane acrylate. Currently, novolac epoxy acrylate is commonly used. The active diluent is a multifunctional acrylate with a monofunctional hydroxy ester, and the photoinitiator is mainly 651 or 2-ethylquinone. The pigment is mainly phthalocyanine green, and the dosage is generally not more than 1%. Fillers are added to enhance heat resistance and reduce volume shrinkage. Adhesion promoters, such as methacrylate phosphite monoester or diester, are also included at 1%-2% to improve ink adhesion to copper.

As a photocuring manufacturer, BOSSIN' products in PCB solder mask ink include phenolic epoxy acrylate B-191A, high-functional monomer dipentaerythritol hexaacrylate BM6263 (DPHA), phosphate acrylate monomer B-05, etc. Feel free to request samples for testing.