We are proposing a method and system to mount and treat the surface of a fabricated micro-component to improve its tribological performance. By irradiating an infrared laser under ambient conditions, the heat will penetrate the micro-component's surface, causing it to melt and flow to reduce the amount of irregularity. This method can create a desired surface finishing with good repeatability on selected regions of the micro-components. It can also work on surfaces of various material types as well as internal surfaces of thin planar or circular structure. By changing the laser power, the repetition rate and the scanning speed, the process can deal with surfaces of different roughness. The final surface roughness can be improved from micro-meter level to sub-100nm level. The laser treated micro-components have improved tribological performance as the friction is reduced; the abrasion, heat and noise are also reduced. The improvement can enhance the lifetime of the micro-component when used in micro rotating or sliding mechanism.
A novel direct-write glass metallization based on laser induced plasma assisted ablation (LIPAA) was investigated. Laser is passed through a glass substrate and irradiated onto a metal target placed beneath the substrate. By tuning laser fluence above target ablation threshold, target ablation and plasma generation occur. The plasma flies towards the glass at a high speed and deposits metal materials onto glass backside surface. Metal films were fabricated and their sheet resistances were measured by a four-point probe. It was found that sheet resistances of the metal films vary with processing parameters. Experimental results reveal that low resistivity metal film (< 0.3 Ω/∠) can be obtained at an optimal laser scanning speed and pulse repetition rate. When target-to-substrate distance increases, film resistance also increases. Optimal design of overlap schemes among metal tracks provides a lower film resistance. Meanwhile, thin film and bulk metal targets were used to study their difference on film resistance. It was discovered that deposition using thin film target is more efficient. Laser annealing technique was also applied to activate the deposited metal materials to get higher quality glass surface metallization.
Precise laser microfabrication of glass is a high challenge task due to the stress-induced microcracks generated during laser ablation. In this paper, the results of high quality glass microfabrication by low energy Nd:YAG laser (355 nm, 30 ns) ablation and pocket scanning technique are presented. The pocket scanning is to scan the laser beam along parallel overlapped paths with the last path along the structure edge, while the conventional direct scanning is to scan the beam just along the structure edge. It is found that the cracks formed around the edges by pocket scanning are reduced significantly compared to that by direct scanning. Minimum crack sizes of less than 10 μm have been obtained at optimized parameters. The ablation depth is also enhanced greatly by pocket scanning to increase almost linearly with the laser fluence and scanning loop. There are no limitations of saturation as that observed in the cases of direct scanning.
A method for surface metallization on transparent substrate with laser induced plasma deposition was described. A laser beam goes through the transparent substrate first and then irradiates on a metal target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed to the substrate and induces metal materials deposition on its rear side surface and even doping into the substrate. The diffusion distribution of metallic particles was measured with Time of Flight Secondary Ion Mass Spectrometer (TOF-SIMS). Electrically conducting films are formed on the substrate with laser beam scanning. The near 1Ω/Square lower resistivity can be formed with precise control of the processing parameters. Laser fluence, pulse repetition rate and scanning speed, distance between the substrate and metal target and overlapping of the metal lines. This technology can be used to form electrodes, resistors, LCD or electronic circuits on the transparent substrates.
Laser-ablation-based microfabrication technology is applied to fabricate micro-electro-mechanical-systems (MEMS) devices on polymer substrates. A micromachining apparatus is designed and developed which includes a 355 nm laser, an uncoated focusing lens, computer-controlled precision x-y-z stages and in-situ process monitoring systems. Concentric rings microstructures are formed by efficiently changing the laser intensity distribution. Tiny via holes and micro-nozzles with different diameters have been obtained by low power laser direct drilling. Optical microscopy and scanning electron microscopy (SEM) are used to evaluate the processing results at different laser processing parameters. This method has the advantages of low-cost and time-saving in circle via holes fabrications. Potential applications of this novel MEMS fabrication technique are also briefed.
Fabrication of an object image inside glass material can be realized by laser direct writing with a programmable motion system. In the focus depth direction, namely Z-direction, the really formed dimension will have some difference from the distance moved by the motion system because of light refraction effect, which causes a deformation of the image from the object. Therefore, it is necessary to modify the object dimension in Z-direction in the executive program. The required amount of the dimension modification depends on the refractive index of the glass and the numerical aperture of the focus lens used. A formula for the dependence of the amount of dimension modification on the refractive index and the numerical aperture is presented based on Snell’s law. Experimental results show that the image created inside glass really reflects the dimension feature of the object with a programming dimension modification in Z-direction in terms of the formula presented. A comparison of a sphere and a cub images created inside glass with the dimension modification with that without the modification is produced for making sure the importance of the dimension modification.
Laser processing has large potential in the packaging of integrated circuits (IC). It can be used in many applications such as laser cleaning of IC mold tools, laser deflash to remove mold flash form heat sinks and lead wires of IC packages, laser singulation of BGA and CSP, laser reflow of solder ball on GBA, laser marking on packages and on SI wafers. During the implementation of all these applications, laser parameters, material issues, throughput, yield, reliability and monitoring techniques have to b taken into account. Monitoring of laser-induced plasma and laser induced acoustic wave has been used to understand and to control the processes involved in these applications.
The separation of IC packages from a BGA board is realized by means of laser multi-scan method. The laser used in the study is a double frequency Nd-YAG laser with wavelength of 532 nm. The big problem in the laser processing approach mainly arises from the multi-layer materials of BGA board with copper, polyethylene and epoxy glass fiber, because of their different absorption coefficient to the laser beam and their different absorption coefficient to the laser beam and their different heat conductivity. In the experiment approach, the effects of laser parameters, such as wavelength, on the dicing efficiency has been investigated for choosing laser. The influence of sample side for laser incidence on cut profile and, the influence of the focused extent of laser beam on singulation speed are discussed. The experimental results show that laser singulation of IC packages is efficient and reliable.
In this paper, we are reporting a new way to do marking on IC package. In this way, white ink is wrapped in microcapsules that are coated on a transparent tape. Laser is irradiated on the tape surface, the microcapsules are broken and the ink is released onto the IC package surface. After an UV light treatment, the ink will stick on the IC surface, forming a high contrast marking. It is found that the quality of the marking depends on tape configuration, tape-IC distance, laser peak power, scan speed of laser irradiation and other laser parameters.
In this report, a new way of wafer dicing is carried out by laser induced thermal shock process. This system consists of the use of a Nd:YAG laser to heat up the wafer surface following by a cooling fluid along the scanned line. The temperature gradient created by the laser heating and the gas cooling will cause a micro-crack on the wafer surface along the scanned line and the resulting crack propagation finally separate the silicon wafer into two pieces. As there is no material loss and removal during the separation process, the wafer dicing line width can be as small as sub-micron. The cross section of the wafer is smooth comparing with other separation methods and a high separation speed of 70 mm/s is achieved.
A laser cleaning model was established for removal of non- absorbing particles from an absorbing solid surface by taking adhesion force and cleaning force into account. The cleaning force per unit area due to laser-induced thermal expansion of a substrate surface is (gamma) E (Delta) T(0, t), where (gamma) , E, and (Delta) T(0, t) are the linear thermal expansion coefficient, the elastic modulus and temperature rise at the substrate surface, respectively. The cleaning condition and threshold fluence can be obtained by comparing the cleaning force and the adhesion force. The theoretical analysis shows that cleaning force increases with increasing laser fluence, deducing the pulse duration, or decreasing laser wavelength, which leads to a higher cleaning efficiency at higher laser fluence, smaller pulse duration or shorter laser wavelength. The experimental results show that the cleaning threshold fluence for laser removal of quartz particles from silicon surfaces is about 135 mJ/cm2, which is in good consistency with the theoretical threshold fluence of 120 mJ/cm2. With increasing laser fluence, the cleaning efficiency increases, which has been predicted by our theoretical analysis.