The principles and characteristics of PCB laser coding

Laser marking is one of the most widely used areas in laser processing. Laser marking uses high-energy-density lasers to partially irradiate the workpiece, causing the material on the surface of the workpiece to evaporate or react chemically, leaving a permanent mark. It can carry out a variety of texts, symbols, patterns, etc. The character size can range from millimeters to micrometers, which is of special significance for product anti-counterfeiting.

Laser coding principle:

In the basic principle, a laser generator is used to generate a high-energy continuous laser beam, and the focused laser acts on the printing material, causing the surface material to melt and vaporize instantly, controlling the path of the laser on the surface of the material to form the necessary markings.

Feature 1

Non-contact processing, can be marked on any special-shaped surface, the workpiece will not be deformed, and no internal stress will be generated. It is suitable for metal, plastic, glass, ceramics, wood, leather, etc.

Feature 2

Almost all parts are marked, such as pistons, piston rings, valves, valve seats, hardware tools, sanitary ware, electronic components, etc.), and the marking is wear-resistant, easy to implement the production process, and the marked parts are less deformed.

Feature 3

The scanning method is used for marking, that is, the laser beam is placed in a double reflector, and the computer controls the scanning motor to rotate the XY axis respectively. After the laser beam is focused, it falls on the marked workpiece to form a trace of laser marking.

Advantages of laser coding:

1. The ultra-fine laser beam after laser focusing can be cleared point by point like a tool. Its advancedness lies in that marking is a non-contact processing, which does not produce mechanical extrusion or mechanical stress. Therefore, due to the small size of the workpiece after laser focusing, the heat affected range is small, and the processing accuracy is high, which cannot be achieved by traditional methods.

2. The "cutter" used for laser processing is the light spot after focusing. No other equipment and materials are needed. As long as the laser can work normally, it can be processed continuously for a long time. High-speed and low-cost laser processing; computer automatic control of laser processing is adopted, and there is no human intervention in the production process.

3. The information marked by the laser is only related to the content designed in the computer. As long as the graphic identification system designed in the marking system can recognize it, the marking machine can accurately restore the design information to the appropriate carrier. Therefore, the function of the software determines the function of the system to a large extent.

For the application of lasers in the SMT field, it is mainly used for coding tracking on PCBs, but the destructiveness of lasers of different wavelengths to PCB masks is not consistent.

The lasers currently used for laser coding are mainly fiber lasers, ultraviolet lasers, green lasers and CO2 lasers. The commonly used lasers in industry are UV lasers and CO2 lasers, while the application of fiber and green lasers is relatively small.

Fiber laser

A fiber pulse laser with a very rich luminous energy level is proposed. The pulse fiber laser has a wavelength of 1064 nanometers (the same as YAG, but the YAG action substance is neodymium) (QCW. The typical wavelength of continuous fiber laser is 1060-1080 nanometers, QCW is also a pulse laser, but its mechanism of generating pulses is completely different and the wavelength is different), and it belongs to near-infrared laser. It can be used for surface marking of metal and non-metal materials because it has high absorption.

The method is to use the thermal effect of laser on the material, or to make the material on the surface black by heating, exposing materials of different shades, or to make microscopic physical changes on the surface of the material (for example, some nano-scale micropores will produce a black body effect, very little light can be reflected, making the material appear dark black) to significantly change its reflective properties, or some chemical reactions when light energy is heated. And display the required graphics, characters, QR codes and other information.

Ultraviolet laser

UV laser is a short-wavelength laser, which usually uses frequency doubling technology to convert infrared light (1064nm) emitted by a solid laser into 355nm (tripled frequency) ultraviolet light. Its photon energy is huge, and it can match the chemical bonds (ionic bonds, covalent bonds, and metal bonds) of almost all substances in nature, directly interrupting the chemical bonds, and the material undergoes photochemical reactions without obvious thermal effects (certain energy levels of electrons in the nucleus can absorb ultraviolet photons, and then transfer the energy through lattice vibration. There is a thermal effect, but it is not obvious), which belongs to "cold processing". Without obvious thermal effects, ultraviolet lasers cannot be welded, and are generally used for marking and precision cutting.

UV marking is a process that uses ultraviolet rays to react with substances to cause color changes. The use of appropriate parameters can avoid obvious removal effects on the surface of the material, thereby marking graphics and characters without obvious touch.

Although ultraviolet lasers can mark metals and non-metals, due to cost factors, fiber lasers are usually used to mark metal materials, and ultraviolet laser marking requires high surface quality. Products that are difficult to achieve with CO2 form a high-low match with CO2.

Green Laser

Green laser is also a short-wave laser. Generally, frequency doubling technology is used to convert the infrared light (1064nm) emitted by the solid laser into 532nm (double frequency) green light. Green light is visible light, while ultraviolet laser is invisible light. The photon energy of green laser is very high, and its cold processing characteristics are very similar to ultraviolet light, which can form a variety of options with ultraviolet light.

Like ultraviolet laser, green light marking technology is also a method of using green light to react with materials to cause color changes. By using appropriate parameters, obvious removal effects on the surface of the material can be avoided. Thus, graphics and characters without obvious touch can be marked. The surface of the PCB board generally has a tin mask layer, which usually has many colors. The green laser responds well to it, and the marked graphics are very clear and delicate.

Carbon dioxide laser

CO2 is a commonly used gas laser with rich luminous energy levels. The typical laser wavelength is 9.3.10.6um. It is a far-infrared laser with a continuous output power of tens of kilowatts. Low-power CO2 lasers are usually used to complete the marking technology of non-metallic materials such as polymers. CO2 lasers are rarely used for metal marking because the absorption rate of metal is very low (metal can be cut and welded by high-energy CO2, but it is gradually replaced by fiber lasers due to factors such as absorption rate, electro-optical conversion rate, optical path and maintenance).

CO2 marking uses the thermal effect of laser on materials, or heats the material on the vaporized surface to expose different dark materials, or heats the surface of the material through microscopic physical changes caused by light energy, causing a significant change in its reflective properties, or a certain chemical reaction when light energy is heated. And display the required graphics, characters, QR codes and other information.

CO2 lasers are generally used in electronic components, instruments, clothing, leather, bags, shoes, buttons, glasses, medicine, food, beverages, cosmetics, packaging, electrical equipment and other fields that use polymer materials.