Everyone is no stranger to laser processing, but can you distinguish the nanosecond laser, picosecond laser, femtosecond laser, etc. that you often hear?
❑ Let's find out the time unit conversion first
1ms (ms)=0.001 seconds=10-3 seconds
one μ S (microseconds)=0.000001=10-6 seconds
1ns (nanosecond)=0000000001 seconds=10-9 seconds
1ps (picosecond)=0,000,000,000,001 seconds=10-12 seconds
1fs (femtosecond)=000000000000001 seconds=10-15 seconds
When we know the time unit clearly, we know that femtosecond laser is an extremely short pulse laser processing. In the past decade, the ultra short pulse laser processing technology has made rapid development.
Significance of ultrashort pulse laser
People have long tried to use laser for micromachining. However, the long pulse width and low laser intensity of the laser cause the material to melt and continuously evaporate. Although the laser beam can be focused into a small spot, the thermal shock to the material is still large, which limits the processing accuracy. Only by reducing the heat effect can the processing quality be improved.
When the laser is applied to the material in picosecond pulse time, the processing effect will change significantly. With the sharp rise of pulse energy, the high power density is enough to strip the outer electrons. Because the interaction time between the laser and the material is very short, the ions have been ablated from the material surface before transferring the energy to the surrounding materials, which will not bring thermal effects to the surrounding materials. Therefore, it is also called "cold processing". With the advantages of cold working, short and ultra short pulse lasers have entered into industrial production applications.
Laser processing: long pulse VS ultrashort pulse
The ultrashort pulse processing energy is injected into a very small area of action very quickly. Instantaneous high energy density deposition changes the electron absorption and motion mode, avoids the influence of laser linear absorption, energy transfer and diffusion, and fundamentally changes the interaction mechanism between laser and material.
Parts after long pulse laser processing
Parts after ultra fast laser pulse processing
 Widespread application of laser processing
Laser processing includes high power cutting and welding; Drilling, scribing, cutting, texture, stripping, isolation, etc. of micro machining. The main uses of various laser processing methods are:
1. Drilling
In circuit board design, people began to use ceramic substrate instead of conventional plastic substrate to achieve better thermal conductivity. In order to connect electronic components, it is generally necessary to drill hundreds of thousands of μ Class m small hole. Therefore, it is very important to ensure that the stability of the substrate will not be affected by the heat input during drilling. Picosecond laser is an ideal tool for this application.
Picosecond laser can process holes by means of impact drilling and ensure the uniformity of holes. In addition to circuit boards, picosecond lasers can also drill high-quality holes in plastic films, semiconductors, metal films and sapphires.
one hundred μ M stainless steel sheet, drilling, 3.3ns vs 200fs, 10000 pulses, near ablation threshold:
2. Scoring and cutting
Lines can be formed by superimposing laser pulses by scanning. It is usually possible to penetrate into the interior of the ceramic through a large number of scans until the depth of the line reaches 1/6 of the material thickness. The individual modules are then separated from the ceramic substrate along these scribed lines. This separation method is called scribing.
Another separation method is to use ultrashort pulse laser ablation cutting, also known as ablation cutting. The laser ablates the material, removing it until it is cut through. The advantage of this technology is that the shape and size of the processed hole have greater flexibility. All process steps can be completed by a picosecond laser.
Different effects of picosecond laser and nanosecond laser on polycarbonate materials.
3. Wire ablation (removing coating)
Another application that is often regarded as micromachining is the precise removal of coatings without damaging or slightly damaging the substrate material. Ablation can be either a few microns wide line or a large area of several square centimeters.
The thickness of the coating is usually much less than the width of the ablation, so that the heat cannot be conducted on the side. Therefore, nanosecond pulse width lasers can be used.
The combination of high average power laser, square or rectangular conducting optical fiber and flat top light intensity distribution makes laser surface ablation applied in industrial field. For example, the TruMicro 7060 laser of Tongkuai Company is used to remove the coating on the thin film solar cell glass. The same laser can also be used in the automotive industry to remove the anti-corrosion coating, preparing for subsequent welding.
4. Surface structure
Structuring can change the physical properties of the material surface. According to the lotus effect, the hydrophobic surface structure allows water to flow away from the surface. This characteristic can be achieved by using ultrashort pulse laser to create submicron structure on the surface, and the structure to be created can be precisely controlled by changing the laser parameters.
The opposite effects, such as hydrophilic surfaces, can also be achieved, and micro machining can also create larger structures. These processes can be used for the fuel tank in the engine to manufacture some microstructures that reduce wear, or to structurally weld the metal surface with plastics.
5. Carving
Sculpture molding is to create three-dimensional shapes by ablating materials. Although the size of ablation may exceed the scope of micro machining in the traditional sense, its required accuracy still makes it classified into such laser applications. Picosecond laser can be used to machine the edge of polycrystalline diamond tool of milling machine.
Laser is an ideal tool for machining polycrystalline diamond, and polycrystalline diamond is a very hard material that can be used to make milling cutter edges. In this case, the advantage of laser is non-contact and high machining accuracy.
Micro machining has a very broad application prospect. More and more articles for daily use are coming into our vision through laser micro machining.
Laser processing belongs to non-contact processing. It has significant advantages such as few follow-up processes, good controllability, easy integration, high processing efficiency, low material loss, and low environmental pollution. It has been widely used in automobile, electronics, electrical appliances, aviation, metallurgy, machinery manufacturing and other industries, playing an increasingly important role in improving product quality, labor productivity, automation, reducing material consumption, etc.