Conversion of time
Let’s find out the conversion of time units first.
1ms (milliseconds) = 0.001 seconds = 10-3 seconds
1μs (microsecond) = 0.00000 1 = 10-6 seconds
1ns (nanosecond) = 0.0000000001 seconds = 10-9 seconds
1ps (picosecond) = 0.0000000000001 second = 10-12 seconds
1fs (femtosecond) = 0.000000000000001 seconds = 10-15 seconds
Knowing the time unit, we know that femtosecond laser is an extremely ultrashort pulse laser processing.
In recent ten years, ultrashort pulse laser processing technology has made rapid development.
Significance of ultrashort pulse laser
People have long tried to use laser for micromachining.
However, due to the long pulse width and low laser intensity of the laser, the material melts and evaporates continuously.
Although the laser beam can be focused into a small spot, the thermal impact on the material is still great, which limits the machining accuracy.
Only by reducing the heat effect can the processing quality be improved.
When the laser pulse time of picosecond magnitude acts on the material, the processing effect will change significantly.
With the sharp increase of pulse energy, the high power density is enough to peel off the outer electrons.
Because the interaction time between laser and material is very short, ions have been ablated from the material surface before transferring energy to the surrounding materials, which will not bring thermal impact to the surrounding materials.
Therefore, it is also called “cold working”. With the advantages of cold working, short and ultrashort pulse lasers have entered industrial production and application.
Laser processing: long pulse vs ultrashort pulse
Ultrashort pulse processing energy is injected into a small action area very quickly.
The instantaneous high energy density deposition changes the electron absorption and movement mode, avoids the effects of laser linear absorption, energy transfer and diffusion, and fundamentally changes the interaction mechanism between laser and matter.
Position after long pulse laser processing
Position after ultrafast laser pulse processing
Wide application of laser processing
Laser processing includes high-power cutting and welding;
The main uses of various laser processing methods for drilling, scribing, cutting, texturing, stripping, isolation, etc. of micro machining include:
|Output form||Continuous output||Millisecond-Microsecond
|Nanosecond (ns)||Picosecond ~ Femtosecond
Laser medical treatment
Laser rapid prototyping
|Micro nano machining
Fine laser medical
1. Drill hole
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 holes on the board μm small holes of class M.
Therefore, it is very important to ensure that the stability of the substrate will not be affected by the heat input during the drilling process. Picosecond laser is an ideal tool for this application.
Picosecond laser can complete the hole processing by impact drilling and ensure the uniformity of the hole.
In addition to circuit boards, picosecond lasers can also drill high-quality holes in materials such as plastic films, semiconductors, metal films and sapphires.
100μm stainless steel sheet, drilling, 3.3ns vs 200fs, 10000 pulses, near the ablation threshold:
2. Scribing, cutting
Lines can be formed by superimposing laser pulses by scanning.
Usually through a large number of scans, you can go deep into the interior of the ceramic 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 using ultrashort pulse laser ablation cutting, also known as ablation cutting.
The laser ablates the material and removes the material until it is cut through.
The advantage of this technology is that the shape and size of the machined 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.
4. Line ablation (removal of coating)
Another application often seen as micromachining is the precise removal of coatings without or slight damage to the base material.
Ablation can be either a few microns wide line or a large area of several square centimeters.
Since the thickness of the coating is usually much less than the width of the ablation, heat cannot be conducted on the side. Therefore, a nanosecond pulse width laser can be used.
The combination of high average power laser, square or rectangular conducting fiber and flat top light intensity distribution makes laser surface ablation applied in industrial field.
For example, the trumicro 7060 laser of Trumpf company is used to remove the coating on the glass of thin-film solar cell.
The same laser can also be used in the automotive industry to remove the anti-corrosion coating and prepare for subsequent welding.
Engraving is to create three-dimensional shapes by ablating materials.
Although the size of ablation may exceed the scope of micromachining in the traditional sense, its required accuracy still makes it divided into this kind of laser application field.
Picosecond laser can be used to process the edge of polycrystalline diamond tool of milling machine.
Laser is an ideal tool for machining polycrystalline diamond.
Polycrystalline diamond is an extremely hard material for making milling cutter edges.
In this case, the advantage of laser is non-contact and high machining accuracy.
Micromachining has a very broad application prospect. More and more daily necessities are entering our field of vision through laser micromachining.
Laser processing belongs to non-contact processing, which has the significant advantages of less 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 to improve product quality, labor productivity, automation Reducing material consumption plays an increasingly important role.