High-speed drilling of alumina ceramic by sub-microsecond pulsed thin disk laser.

The rapid development of optoelectronic components has demanded high-speed drilling for alumina ceramic substrate. However, the existing drilling speed cannot meet the demand due to the limitation of conventional laser system and drilling method. In this paper, by adopting a sub-microsecond pulsed thin disk laser that based on a multi-pass pumping module, a laser system with a pulse energy of 37.4 mJ and a peak power of 103.8 kW is developed, which helps us to achieve high processing efficiency. In addition, experimental and theoretical analysis suggest the positive defocusing method can be used to control the hole taper angle, and micro-holes with a hole diameter difference less than 6% is realized, which helps us to achieve high processing quality. Ultimately, it is reported that the drilling speed for micro-holes with a diameter of ∼150 µm reaches 30 holes per second, and for micro-holes with a diameter of ∼100 µm reaches as high as 66 holes per second. The performance of the sub-microsecond pulsed thin disk laser presented in this paper provides a reference in the field of high-speed laser processing.

Laser processing of alumina ceramic by spatially and temporally superposing the millisecond pulse and nanosecond pulse train.

A novel combined laser pulses (CLPs) consisting of a millisecond (ms) pulse and an assisted nanosecond (ns) pulse train was proposed for drilling alumina ceramic. The processing efficiency and quality were well improved by spatially and temporally superposing the ms and ns laser beams. As a result, due to the multi-reflection of keyhole and ejection of melt, the temporally superposed CLPs could decrease the energy consumption of the drilling by an order of magnitude compared with the conventional ms pulse. On the other hand, the spatial distribution of the ns laser on the focal plane was elliptical due to the off-axis distortion of the optical system. However, since the reflection of the laser in the keyhole was non-uniform, the spatially superposed CLPs showed no dependence on the shape of the focused elliptical ns laser spot in terms of the drilling quality. The research results have an important guiding for improving the efficiency and quality of laser processing, especially for the alumina ceramic laser processing.

Nanosecond-millisecond combined pulse laser drilling of alumina ceramic.

A nanosecond-millisecond combined pulse laser (CPL) drilling method was proposed for drilling alumina ceramic. The total energy consumption of the CPL drilling was 1/7 of that of a conventional millisecond laser, and the drilling quality was better. The simulation results demonstrated that, due to the nonuniform reflection of the millisecond laser in the keyhole, the ellipse keyhole ablated by the off-axis incident nanosecond pulses had no effect on the circularity of the through hole. In addition, the multireflection of the laser in the keyhole enhanced the absorption, so the keyhole ablated by the nanosecond pulses could be used as a target for limiting the absorption of the subsequent millisecond pulses. In this context, the keyhole could be used to reduce the hole diameter if the subsequent millisecond laser had a bigger spot size, and this CPL drilling method could be used as an effective group hole drilling method.

Characterization of micro-holes drilled in alumina ceramic by the combined pulse laser technique.

Nowadays, combined pulse laser (CPL) technology has shown obvious advantages in alumina ceramic drilling. However, the characterization of micro-holes drilled by the CPL is not clear. In this paper, micro-holes drilled by ns-ms and ns/ms CPLs are systematically compared from the aspects of hole diameter, cracks, spatter deposition, recast layer, re-solidified particles, grain size, and chemical composition. The results show that due to the synchronous output of the nanosecond laser, the ns/ms CPL can eject more melt through expelling of the plasma shock wave; thus, the recast layer, re-solidified particles, and oxygen vacancies are decreased, while the spatter deposition is increased. On the other hand, due to the higher temperature and larger temperature gradient introduced by the nanosecond laser, the hole diameter, cracks, and grain size are increased. Therefore, an ideal CPL method to optimize the drilling performance is proposed. The research results have important guidance for improving the processing quality of the CPL, especially for alumina ceramic laser processing.

Laser processing of alumina ceramic by a spatially superposing millisecond laser and a nanosecond laser with different beam shapes.

Advanced combined pulse laser (CPL) processing technology with high processing efficiency is of interest for both academic and engineering prospects. However, the influence of the spatial superposition of the CPL on the processing quality is unclear. Here, we use a CPL composed of a nanosecond and millisecond laser with different beam shapes to drill alumina ceramic. Experimental and simulation results suggest that the CPL drilling process actively homogenizes the laser in the hole through multi-reflection of the laser, and thus holes with high circularity are obtained without the influence of the beam shape of the nanosecond laser. The research shows this to be a novel processing method, and that the processing quality is independent of the laser beam shape.

Experimental study on the optimum matching of CW-nanosecond combined pulse laser drilling.

A combined pulse laser (CPL) drilling method that consisted of a continuous wave (CW) laser and an assisted nanosecond laser was used for drilling the Q235B steel. The influence of the repetition rate of the nanosecond laser on the CPL drilling efficiency was analyzed. The results show that the plasma screening threshold during the CPL drilling was about ${1.40} \times {{10}^9}\,\,{\rm W}/{{\rm cm}^2}$1.40×109W/cm2. When the peak power density of the nanosecond laser exceeded the plasma screening threshold, it still could not compensate for the energy loss caused by the plasma screening, even though the high-pressure shock wave introduced by the plasma could improve the drilling efficiency. On the other hand, when the peak power density of the nanosecond laser was lower than the plasma screening threshold, it was shown that the optimum matching between the CW laser and nanosecond laser could be obtained when the repetition rate of the nanosecond laser was between 10 and 25 kHz. Finally, the results show that the CPL drilling method had a better drilling efficiency and quality than conventional millisecond laser drilling.

Reflow soldering method with gradient energy band generated by optical system.

Laser reflow soldering is an important technology in electronic components processing. In this paper, we presented a simple but efficient method to achieve reflow soldering process with gradient energy band created by just two parallel mirrors. The detailed influence of the variety of optical parameters on the soldering process has been analyzed by using the finite element method. And the modulation of the optical parameters on reflow soldering parameters also has been demonstrated. In our experiment, one HR mirror and one-mirror with transmissivity of 10% have been used to create a gradient energy band with an incident laser power of 50W. In summary, both the simulations and the experiments show that the typical reflow soldering profile has been acquired by the optical system. The high quality joints on both the front and rear surface of the capacitor can be acquired by just one surface radiation of the optical system.

The Plastic Deformation Mechanism in Nano-Polycrystalline Al/Mg Layered Composites: A Molecular Dynamics Study.

Understanding plastic deformation behaviour is key to optimising the mechanical properties of nano-polycrystalline layered composites. This study employs the molecular dynamics (MD) simulation to comprehensively investigate the effects of various factors, such as grain sizes, strain rates, and the interlayer thicknesses of the intermetallic compounds (IMCs), on the plastic deformation behaviour of nano-polycrystalline Al/Mg layered composites. Our findings reveal that the influence of grain size on deformation behaviour is governed by the strain rate, and an increase in grain size is inversely proportional to yield stress at low strain rates, whereas it is positively proportional to tensile stress at high strain rates. Moreover, an optimal thickness of the intermediate layer contributes to enhanced composite strength, whereas an excessive thickness leads to reduced tensile strength due to the fewer grain boundaries (GBs) available for accommodating dislocations. The reinforcing impact of the intermediate IMCs layer diminishes at excessive strain rates, as the grains struggle to accommodate substantial large strains within a limited timeframe encountered at high strain rates. The insights into grain sizes, strain rates, and interlayer thicknesses obtained from this study enable the tailored development of nanocomposites with optimal mechanical characteristics.

Advances in Laser Drilling of Structural Ceramics.

The high-quality, high-efficiency micro-hole drilling of structural ceramics to improve the thermal conductivity of hot-end parts or achieve high-density electronic packaging is still a technical challenge for conventional processing techniques. Recently, the laser drilling method (LDM) has become the preferred processing tool for structural ceramics, and it plays an irreplaceable role in the industrialized processing of group holes on structural ceramic surfaces. A variety of LDMs such as long pulsed laser drilling, short pulsed laser drilling, ultrafast pulsed laser drilling, liquid-assisted laser drilling, combined pulse laser drilling have been developed to achieved high-quality and high-efficiency micro-hole drilling through controlling the laser-matter interaction. This article reviews the characteristics of different LDMs and systematically compares the morphology, diameter, circularity, taper angle, cross-section, heat affect zone, recast layer, cracks, roughness, micro-nano structure, photothermal effect and photochemical reaction of the drilling. Additionally, exactly what processing parameters and ambient environments are optimal for precise and efficient laser drilling and their recent advancements were analyzed. Finally, a summary and outlook of the LDM technology are also highlighted.