Several types of lasers have been used for cutting, drilling, welding, and changing the surface of relatively thick metals. These technologies are widely used in various industries, including automotive, shipbuilding, and medical device industries. However, many recent emerging applications require the use of very thin metal films for laser processing and require high precision and smooth edges. In recent years, many new laser technologies have been proposed for laser micromachining. These lasers have good pattern quality and focusability. These two factors are important for obtaining small feature sizes and very smooth edges.

In this study, we compared the results obtained using several different types of low-power lasers: 355 nm, 532 nm, 1064 nm, and 1.085 μm. This article focuses on cutting metal films with different thicknesses and complex shapes into multiple parts.

Laser advantage

Although there are many different technologies used to process metals, they all have some drawbacks, especially when compared to lasers. For example, you can use EDM (Electrical Discharge Machining) to machine metal very efficiently, but this process has limitations on the smallest feature size of the object being processed. In addition, electrodes with smaller EDM are more expensive and more prone to failure than lasers, and frequent replacements increase costs.

Etching techniques are also used to process metals, which may be economical in some cases, but this processing method also has some serious drawbacks. First, the etching process requires a lot of processing steps, and the laser processing can be completed in one step. Second, people have to deal with some of the corrosive chemicals and toxic waste products caused by etching. Finally, the aspect ratio is limited to 1:1, in which case undercuts or tapered sidewalls may even appear. At the same time, the mechanical drilling or groove feature diameter is limited to 250 μm. Although 100 μm drills are sold, these drills are not only expensive but also have a short life.

The use of lasers to cut metal into different shapes and styles brings a lot of convenience. After using the laser, there is no longer any need to consider the problems of bit breakage and tool wear. In addition, laser technology is used to limit the achievable hole diameter and feature size. Laser technology also makes it possible to drill holes on angled or curved surfaces, and it is suitable whether the material is hard or soft. In addition, the programmable nature of the laser device also makes it possible to perform thousands of such high-speed punching and conventional applications at high speed in a short cycle time.

In this study, we evaluated many difficult-to-process thin film metals including copper (Cu), beryllium copper (BeCu), phosphor bronze (Pbronze), molybdenum (Mo), stainless steel (SS), and nickel (Ni). Aluminum (Al), titanium (Ti), tempered steel (TS), and thin layer of indium tin oxide (ITO) with metal properties (on soft and hard material substrates) and other metals. The above-mentioned metals are currently used in mainstream and exotic processing applications requiring smooth edges and small feature sizes. Thin metal films are currently attracting attention. As the circuit becomes smaller and more integrated, the thickness of insulators and conductors is also becoming thinner. Some interesting applications in these areas, one of which is related to very thin (usually hundreds of angstroms) conductor materials such as Cu, Au, Ag, and ITO. These metals show very interesting properties in the form of thin films, and when they are exposed to laser light, they behave slightly differently than they do in bulk. For example, when ablation of "thick" metal (thickness greater than 1 micron) requires an energy density of the order of several to several tens of J/cm2, while the same metal uses only a fraction of 1 J/cm2 in the form of a thin film. One of them is enough to peel off the metal from the substrate. These films are used in many products, such as touch screens, flat panel displays, aircraft cockpits, and medical devices. These are just a few examples, and more applications are still under research and development.

In each case, we used low-power lasers (less than 100 W, and in most cases far less than this value). Therefore, we limit the thickness of the metal to less than 20 mils (500 microns). For the study, we used Coherent (A Santa Clara, CA) Avia 355nm, 3W laser, Photonics Industries (Bohemia, NY) 532nm, 7W laser, Spectra Physics (Mountain View, CA) 1064nm, 3W laser. In the study, we did not use a CO2 laser or an excimer laser. This is due to the reflection of CO2 lasers for the metals we studied, and the commercialization of excimer lasers is not enough to meet this kind of work.

We also used a 1.085 micron wavelength, 100W fiber laser for some experiments and discussed the results. Diode-pumped solid-state lasers have excellent beam quality at short wavelengths and can be focused to a spot size of 20 microns or less. Since this is much smaller than the feature size that we are going to study in our experiments, we need to make multiple holes or notches. We import the DXF file into the optical processing software and add laser parameters. In this way, we have obtained a processing file with all processing information, which is convenient for future reference and use. It should be pointed out that all the pictures attached here (except for the one specifically indicated), that is, the high-resolution photographs were taken directly after the laser processing with a 40-times magnification stereo camera equipment, and have not been processed. Cleaning. Therefore, the picture given here can be considered as the "worst" case. In addition, all of the drawings were obtained using a galvanometer scanning beam and did not utilize assist gas.

Figure 1a: Notch of 355 nm laser on 125 μm thick copper Figure 1b: Notch of 532 nm laser on 125 μm thick copper Figure 2a: Notch of 355 nm laser on 150 μm thick beryllium copper alloy Figure 2b: 532 nm laser at 150 μm thick Cuts on beryllium copper alloy Figure 3a: Notch of 355 nm laser on 50 μm thick molybdenum Figure 3b: Notch of 532 nm laser on 50 μm thick molybdenum Figure 4a: Notch of 355 nm laser on 100 μm thick stainless steel Figure 4b: 532 nm laser Cuts in 100 μm thick stainless steel Figure 5a: Notch of 355 nm laser on 125 μm thick tempered steel Figure 5b: Notch of 532 nm laser on 125 μm thick tempered steel Figure 6a: 355 nm laser on 330 μm thick nickel Notch Figure 6b: Cutting of 532 nm Laser on 330 μm Thick Nickel

Laser processing results

Here we show some of the results of laser processing, including the comparison of two different lasers: a 355 nm laser (all panels a) and 532 nm (all panels b). Figure 1 shows a typical cut that uses both lasers to cut a 125 micron thick copper; in all cases, the cuts are in the range of about 75 to 85 microns. Although the cutting results of the two lasers are very good, the 532 nm laser is coupled very well and the processing time is faster and smoother than the 355 nm laser. The 355nm laser is suitable for printed circuit board processing because the coupling of the 532nm laser to the dielectric is not as good as the 355nm UV laser.

Figure 2 shows the same two lasers acting on a 150 μm thick copper beryllium alloy. These results are in good contrast with the results of copper (the same is true for phosphor bronze, which is not given here). All of these metallic copper and metal alloys couple well with both lasers. What we need to point out here is that we cannot use the 1.085-micron fiber laser to get smooth copper processing. This is because the reflectivity is too high at the 1.085-micron wavelength.

Figure 3 shows the same pattern of laser cutting molybdenum. The coupling of 532nm laser with molybdenum is not as good as its coupling with copper, although this laser is still available. These results are compared with the results for 100 micron thick stainless steel (Figure 4), tempered steel (Figure 5), and nickel (Figure 6). It should be noted here that aluminum does not respond well to a 532 nm laser, whereas the 355 nm laser can be well cut on a 300 μm thick aluminum plate (Figure 7). For comparison, Figure 8 shows the same incision as in Figure 6a. It uses the 355nm laser to cut nickel, but in Figure 8 we also use the ultrasonic cleaning after laser processing under weak acid conditions. This gives a Very clean final product. Figure 9 shows a pattern obtained by cutting a 125 micron thick molybdenum laser at 355 nm. The "arm" in the figure extends to about 25 mm below the figure. Due to the slightly heated cutting port, we did not see unevenness on the surface, which is common when using many "hot" lasers.

Figure 7: Notch of 355 nm laser on 300 μm thick aluminum Figure 8: Result of ultrasonic cleaning of the sample shown in Figure 6a

Figure 9: Finger laser incision on molybdenum

We also observed the effect of using a 1.5 micron fiber laser. We cannot use it to etch any copper-based metal. However, for other metals such as stainless steel, tempered steel, and nickel, the processing speed is fast (relative), the etching quality is good, and the result is satisfactory. We noticed here that the laboratory equipment was under alkaline conditions, so we used a fixed beam transmission system and used a high degree of gas assistance. We also studied the use of 13ps, 1064nm lasers. We found that the cutting quality was very good. Although we did not further verify this laser for other metals, it is believed that this laser will be effective for a wide range of materials. Figure 10a shows a drawing of a stainless steel cut using a fiber laser and Figure 10b shows a 25 μm cut made on stainless steel using a picosecond laser. It is noticed that the results of fiber lasers are not evenly compared with other results, but this is due to the hurriedness of artificial settings, not due to the defect of the laser source itself.

Figure 10a: Cut-out of a 1.085 μm fiber laser on 100 μm thick stainless steel Figure 10b: Cut-out of a 1064 nm picosecond laser on stainless steel Figure 11: Composite pattern of gold coated on plastic

Finally, Figure 11 shows a composite pattern of gold etched on a polyester film. Using lasers, we can easily and cleanly peel very complex and dense pattern films. Using 355nm or 532nm lasers depends on the substrate and the required feature size. The galvanometer-based beam transmission can make the transmission simpler and achieve an accuracy of the order of 10 to 20 micrometers (fixed beam transmission accuracy can reach micrometers, but the processing speed is slower).

in conclusion

Here are our conclusions:

The Q-switched laser at 355 nm shows excellent processability in all of the metals we tested, with a small feature size (25 micron pitch). Any metal thinner than 125 microns can be processed quickly and cleanly. Machining results are very smooth on metals between 5 and 10 mils (250 microns) thick, but the processing of the bulk may be slower. There may also be nearly 20 mils (500 microns) thick metal in the processing, and these processing speeds will be reduced. Metals larger than 20 mils are not suitable for processing with Q-switched lasers. We believe that this conclusion will not change much for currently available lasers such as 10W or 15W.

The 532nm laser also gives very good results on many metals, especially for copper-containing metals. Because of its longer wavelength, the minimum spot size it can achieve for a given optical device is larger than a 355 nm laser. These lasers have a usable range of up to 15W with a small M2 value (larger lasers are also available, but M2 also increases). These lasers are less expensive to purchase and operate than 355nm lasers.

The 532nm and 355nm lasers exhibit excellent characteristics in peeling films from various substrates. A 532 nm laser can be used to pass through a transparent substrate such as glass. The 355 nm laser can peel off the top cover layer even when the substrate absorbs ultraviolet light, with little or no damage to the substrate.

The picosecond laser is also worth noting, and it provides very smooth processing results. However, due to the current relatively high cost, picosecond lasers can hardly be used except for some special occasions.
In short, fiber lasers seem to be another available option for metalworking. Their laser cutting is smooth and fast, even for a few millimeters thick metal. The intrinsic frequency cannot be applied to copper-containing metals, but the development of second- and third-frequency technologies in the future may make these lasers suitable for all metals.

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