These are processes where absorbing surfaces are machined using high intensity laser beams, but the depth of the mark is very shallow. In many cases, it is simply a slight discoloration of the surface, in others cases a thin groove is cut into the surface by vaporising material. The laser and its position can be very accurately controlled using PC. Advantages are as follows:

Speed

Accuracy

Quality

Repeatability

Non-contact method (curved surfaces can be accommodated)

Permanence

High Resolution

Flexibility (changes to a mark can easily be made)

Cost effective compared to other methods of marking or identification

Standard processes applied:

Barcodes and other 2-D codes

Variable information (i.e. serial numbers)

Logos

Icons & Symbols

During the laser engraving process, the target material is essentially vaporized by the laser beam. To achieve this result, the intensity of the laser beam is set to exceed a specific threshold value.

This threshold intensity is particularly high with materials that are electrically conductive, such as metals. The result is often a cone-shaped indentation influenced by the laser beam profile and the heat conductivity of the target material. The laser engraving technique is typically the fastest way of processing material.

Laser cutting is a technology which uses a laser to cut materials, and is usually used in industrial manufacturing. Laser cutting works by directing the output of a high power laser at the material to be cut. The material then either melts, burns or vaporizes away leaving an edge with a high quality surface finish.

Advantages of laser cutting over mechanical cutting: lack of physical contact, precision, speed, reduced chance of warping the material that is being cut as laser systems have a small heat affected zone. Some materials are also very difficult or impossible to cut mechanically and only the selected laser is used.

Laser drilling is the process of repeatedly pulsing focused laser energy at a material, vaporizing layer by layer until a thru-hole is created. This is what is called a “popped” or “percussion drilled” hole. Depending upon material and material thickness, a “popped” hole could be as small as 10μm in diameter.

If a larger hole is required, the laser, once through the material, is moved with respect to the work piece to contour the desired diameter. This is called “trepanning”. The end result is a fast, efficient way to create quality holes.

Laser ablation is the process of removing material from a solid surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates. At high laser intensity, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave laser beam if the laser intensity is high enough.

Normally, the ablation site is cleared by a pressurized inert gas, such as nitrogen or argon so the optical absorption and scattering of the incident laser beam can be reduced – including surface debris on the surrounding work surface and/or the laser beam delivery optics. The depth over which the laser energy is absorbed, and thus the amount of material removed by a single laser pulse, depends on the material's optical properties and the laser wavelength.

The laser annealing process is based on creating localised structural changes in the metal surface using heat that is generated by the laser beam focused on the target material. The localised structural changes are determined by the maximum temperature attained in the metal, the properties of the metal, and the parameters selected on the laser.

The annealing technique has a unique characteristic in that it produces a contrasting mark without disrupting the surface finish of the metal. The potential advantages of the laser annealing process with respect to conventional thermal process are:

Speed

Accuracy

Quality

Repeatability

Non-contact method (curved surfaces can be accommodated)

Permanence

High Resolution

Cost effective compared to other methods of marking or identification

When short-duration UV laser light pulses are tightly focused onto the wafer surface, each pulse is absorbed into a sub-micron thick surface layer, which then vaporizes. The vaporized material carries away the energy of the interaction, minimizing heat transfer to the surrounding material. This process is known as photoablation. In order to produce deep cuts, hundreds of successive laser pulses are required. Moving the wafer under a rapidly pulsed, focused laser beam produces an extremely narrow V-shaped cut, the depth of which is controlled by the scan speed.

Typically, these cuts terminate 30–50% into the thickness of the wafer. After laser scribing, the wafer is fractured using standard cleaving equipment. The V-shaped laser cuts act as stress concentrators, inducing well controlled fracturing with excellent die yield. Efficient photoablation is required for laser scribing and depends strongly on two properties of the UV laser light: wavelength and pulse duration. In general, photoablation benefits from a shorter laser wavelength and shorter pulse duration, for both optical and thermal reasons. The key benefits achieved by short laser pulse duration are increased irradiance on target, and reduced heat transfer to the substrate due to more rapid absorption and ablation. For short laser wavelengths, the main benefits are improved optical absorption, reduced absorption depth, lower irradiance required for ablation and reduced cut width. Shorter wavelengths impart more energy per photon.

For SiC, optical wavelengths below 370 nm have photon energies that exceed the bandgap of the material, resulting in direct photon absorption. However, sapphire has a bandgap that is higher than the photon energy of any commercially available UV laser. Multi-photon absorption is therefore required to induce efficient optical absorption. Typically, the necessary irradiance (W/cm2) for multi-photon absorption is very high. The efficiency of multi-photon absorption in sapphire is strongly wavelength dependent. Shorter wavelengths are absorbed more completely in sapphire, resulting in less heat input to the bulk material. The combination of short wavelength and short pulse duration provide complimentary benefits of improved absorption and ablation at lower irradiance, reduced heat transfer to the substrate, smaller cut width, and larger area coverage of the beam spot. These combined benefits serve to optimize cut speed and cut quality. Further, the smaller cut width helps to minimize surface debris.

Conventional saw dicing and mechanical scribing processes exhibit a number of problems when used with extremely hard SiC and sapphire substrates. Throughput is low, about one wafer per hour per system. Tool wear is also a significant issue; typically, dicing blades or diamond scribe tips are consumed at a rate of one per wafer. In addition, these processes are very sensitive to wafer flatness, and warped, crowned, or bowed wafers cannot be processed. Cut alignment is also a challenge. Streets between die must be large to avoid cutting into devices and this results in a lower die count per wafer, which drives up unit cost. Lastly, saw dicing and mechanical scribing are labor-intensive processes. Process yield is directly related to the skill of the equipment operator.

Laser milling involves applying laser energy to remove material through ablation in a layer-by-layer fashion. Computer numerical control (CNC) programs for laser milling are obtained directly from a three-dimensional computer aided design model of the workpiece.

Thus, apart from being a material removal rather than a material accretion system, a laser milling machine operates like any other layered manufacturing technology equipment.

Laser cleaning offers a highly selective, reliable and precise method of removing layers of corrosion, pollution, unwanted paint and other surface coatings due to the absorption of the laser energy.

Laser cleaning process involves laser beam at appropriate selected laser wavelength and energy but instead of having the target material positioned in the focal point of the laser beam, an offset is introduced to the extent that there is not enough of fluence for material removal.

Laser polishing is a viable technique to diminish the roughness of material surfaces. Here, the material properties can be matched by employing adequate laser wavelengths and pulse durations. Up to now, laser polishing was mainly applied to inorganic materials such as metals (Steel, Ti), semiconductors (Si, GaN), fused silica and diamond-like carbon coatings.

Laser polishing is a novel technique for improving the surface quality of laser milled surfaces. It employs the same working principles as laser milling, but instead of having the target material in the focal point of the laser beam, an offset is introduced to the extent that there is not enough of fluence for deep material removal.

Laser welding, occurs when the laser is used as an intense energy surce to selectively heat materials to a point between their melting and vaporizing temperatures. Once molten, the materials are allowed to alloy and then resolidify in a controlled atmosphere. The result is reliable, oxide-free weldment. The overall size and depth-to-width ratio of the weld can be custom tuned depending on materials and laser source selected. By adjusting various parameters such as the laser energy and focal point position, one can create weld ratio ranging from wide and shallow to narrow and deep. In most cases the welded part geometry dictates this ratio.

Laser welding offers a variety of benefits over other types of welding: deep penetration of precise narrow welds, small heat affected zone, low heat input, fast weld times, minimum part distortion, no secondary processing and high repeatability. Many metals can be welded including stainless steel, carbon steel, titanium, aluminum and dissimilar metals.

When defining a weld joint we refer to both the joint type and the weld type. There are two joint types: butt and lap. A butt joint is where two materials are to be welded at the seam that forms where the two materials are joined together. A lap joint is where two materials are to be joined by welding through one into the other. There are also two weld types: seam and spot. Seam welding is continuous while spot welding is intermittent. Glass sealing and glass-to-metal sealing is also accomplished with Nd:YAG lasers. Plastic welding with Nd:YAG lasers has been in development for some time and is now commercially viable with certain plastics.