Technology Research On Submicrosecond Laser Drilling Of Al₂O₃ Ceramic

Alumina ceramic has become the main material of power electronic device circuit substrate in high-power LED lighting,5G communication,high-power semiconductor device,solar panel,automobile and aerospace.In the manufacturing process of the alumina ceramic circuit substrate,in order to realize the mutual conduction between the front and back sides of the substrate,a large number of micropores with a diameter of 100 um need to be prepared.Nowadays,the mature laser drilling technology of alumina ceramic in the market is:using pulse fiber laser with long pulse width(millisecond level),peak power of 1 to 2 k W and wavelength of 1 um,and assisting high-pressure gas drilling of the ceramic substrate.Alumina ceramic substrate with thickness of 0.5 mm is used to prepare micropores of 100?m diameter and the drilling speed is 15-20 holes per second.The demand for the drilling speed of ceramic circuit substrate manufacturer is 50-100 holes per second.The existing technology cannot meet the needs of ceramic circuit substrate enterprises,and the existing technology needs to coat the surface of ceramic substrate with laser absorbent before laser drilling,and also needs to clean the absorbent after drilling,which makes the production process of ceramic drilling complex.In this paper,the self-developed Yb:YAG disk laser with a pulse width of submicrosecond is used to process alumina ceramic with thickness of 0.5 mm by multi-pulse drilling,with single pulse energy of 10m J and peak power of 10k W.Focusing on optimizing laser parameters and improving the quality of drilling,process research has been carried out.The main research results are as follows:(1)The laser pulse ablation threshold for alumina ceramic is measured.The spot size is50.57?m,and the ablation threshold is 19.3J/cm~2,which provides reference for subsequent drilling experiments.(2)By using control variable method of a single factor,the effects of different laser processing parameters such as the pulse repetition frequency,drilling duration time,pump power,focal distance and spot size on the hole size,taper angle and surface morphology of micropores on alumina ceramic plate are analyzed.Experimental investigation shows that when other parameters are constant,choosing a repetition frequency of 20 k Hz and appropriate pumping power can obtain a better hole quality.Increasing the drilling duration time can stabilize the aperture.Better taper angle can be obtained by positive defocusing method,Changing the spot size confirms that the correspondence between hole dimension and spot size.By optimizing process parameters,micro-pores with low taper angle(0.006)were obtained under specific conditions.(3)In view of the problem of low laser absorption rate of alumina ceramic,the two-step drilling method of different frequency is proposed,which is different from conventional single frequency drilling.The comparison of the holes is discussed in terms of hole size,taper angle,stability,etc.The result shows that the pre-processed pits help to increase the laser absorption rate of the material and can reduce the hole taper angle under the certain conditions.