Yangyang Zhuo1, V.N. Maslovsky2, K.M. Moiseev3

1–3 Bauman Moscow State Technical University, Moscow, Russia

Ceramic materials are widely used in the electronics and instrumentation industry, blanks from which are subjected to subsequent processing. One of the most promising materials is low-temperature co-fired ceramics (LTCC) [1]. The LTCC technology has many advantages [2], including reliability and cost-effectiveness in a wide range of microwave electronics applications [3, 4].

For processing ceramics, as a rule, mechanical or laser processing is used [5]. However, electron beam processing (EBP) due to its characteristics – high energy density, high efficiency, high stability, etc. [6] is also suitable for processing ceramic materials and can be considered as a promising method [7–10].

The main difficulties that arise in the ELP of dielectrics are associated with their low thermal conductivity. Together with the high-power density of the electron beam, this leads to the formation of high temperature drops over the volume of the material, which cause significant residual thermal stresses, leading to cracking of the substrate during or after processing [9].

In this paper, the process of hole formation in LTCC is simulated to determine the preliminary processing parameters, analyze the causes of ceramic cracking during processing, and evaluate the effect of various ELP parameters on the quality of processing.

According to the geometrical dimensions and characteristics of the material during the simulation, Ansys software performs heat transfer analysis of low-temperature ceramic materials processed by an electron beam to create a temperature model in a limited range.

Considering that the thickness of the LTCC substrates is no more than 5 mm and the electron beam is immobile during processing, the Gaussian surface source model is adopted in this work. Using this model, the distribution of the power density of the electron beam along its radius is determined depending on the accelerating voltage (60 kV), the minimum beam current (1 mA), and the minimum beam radius (100 μm) of the ELTA-60.15DP electron beam gun.

For a substrate with a size of 2×2×0.5 mm made of LTCC ceramics of the KEKO SK-47 brand, a mathematical model of the drilling process was built in the Ansys software.

ELP simulation considers the non-linear transient process of heat transfer from the heating zone to other areas of the material through thermal conduction. Since the machining takes place under vacuum conditions, convective heat transfer is not considered, so the cooling of the substrate is carried out mainly with the help of thermal radiation.

The temperature field was obtained after exposure to the first pulse of an electron beam with a duration of 5 ms at U = 60 kV, I = 1 mA. The diameter of the material region where the temperature reaches the evaporation point and the melting point in 1 pulse at different initial temperatures (20°C, 400°C, 800°C) was determined. In 30 µs, the temperature reaches the evaporation point of 3000°C.

It is shown that at different initial temperatures of 20°C, 400°C, 800°C after the first pulse, the cooling process takes 95 ms, the temperature returns to the initial one. Such a significant temperature drop after the first pulse is a source of stress formation and subsequent deformation and cracking of the material.

At 20°С, the stress reaches values of about 300 MPa, because of which the ceramic substrate is destroyed. With an increase in the initial temperature, the thermal stress of the material decreases by 3.5 times, and the internal deformation by 6 times.

For the electron-beam gun ELTA-60.15DP of the "Luch" vacuum EBP machine, the dependences of the diameter and depth of treatment after exposure to the first pulse of different duration at an initial substrate temperature of 20°C and a beam current of 1 mA were determined. In this case, the processing depth increases significantly in a smaller range (from 80 to 120 µm), while the diameter increases significantly (from 200 to 320 µm) in a short interval of pulse duration.

At an initial temperature of 20℃, within 30 µs, the temperature in the processing zone exceeds the ceramic evaporation temperature of 3000°C. During the pause between pulses, the temperature of the sample decreases due to the uniform distribution of heat throughout the entire volume of the sample.With an increase in the initial temperature to 800℃ due to a decrease in the temperature

difference, the thermal stress in the material decreases by 3.5 times, and the deformation by 6 times, but the values remain too significant.

Preheating remains one of the main way to solve the problem of ceramic cracking during processing, but it is difficult to achieve temperatures above 1000°C by standard methods (IR lamps or heaters). Therefore, a defocused electron beam can be used for preheating.

The pulse duration and the current of the electron beam affect the diameter of the formed hole much more strongly than the depth of processing. Therefore, a high-quality EBP requires a short pulse with a duration of less than 30 μs at a machining current of less than 1 mA to obtain the smallest possible hole diameter.

Yangyang Zhuo, Maslovsky V.N., Moiseev K.M. Numerical simulation of electron beam dimensional processing of ceramic substrates. Science Intensive Technologies. 2022. V. 23. № 4. P. 5−13. DOI: https://doi.org/10.18127/j19998465-202204-01 (in Russian)

1. Kondratyuk R. LTCC – nizkotemperaturnaya sovmestno obzhigaemaya keramika. Nanoindustriya, 2011 № 2. S. 26 (in Russian).
2. Percel' Ya.M., Yakovlev A.N. Preimushchestva ispol'zovaniya tekhnologii nizkotemperaturnoj keramiki dlya realizacii radioelektronnyh ustrojstv. Sovremennye tekhnologii. 2012. № 8. S. 16–17 (in Russian).
3. Simin A., Holodnyak D. Mnogoslojnye integral'nye skhemy SVCh na osnove keramiki s nizkoj temperaturoj obzhiga. Komponenty i tekhnologii. 2005. № 5 (in Russian).
4. Abramova E., Pahomov N., Percel' Ya. Issledovanie tekhnologii izgotovleniya mnogoslojnyh pechatnyh plat SVCh s primeneniem zhidkokristallicheskih polimerov. Sovremennaya elektronika. 2014. № 5. S. 16–18 (in Russian).
5. Khoong LE., Tan Y.M., Lam Y.C. Overview on fabrication of three-dimensional structures in multi-layer ceramic substrate. Journal of the European Ceramic Society. 2010. № 30(10). P. 1973–1987.
6. Zhuo Y., Liang M., Moiseev K. M., et al. Possibilities of the Electron-Beam Machine «LUCh» for Dimensional Microprocessing of Glass and Ceramic Materials. IOP Conference Series: Materials Science and Engineering. IOP Publishing. 2020. V. 781. № 1. P. 012014.
7. Burdovicin V.A., Klimov A.S., Oks E.M. O vozmozhnosti elektronno-luchevoj obrabotki dielektrikov plazmennym istochnikom elektronov v forvakuumnoj oblasti davlenij. Pis'ma v ZhTF. 2009. T. 35. № 11. S. 61–66 (in Russian).
8. Medovnik A.V., Burdovicin V.A., Klimov A.S. i dr. Elektronno-luchevaya obrabotka keramiki. Fizika i himiya obrabotki materialov. 2010. № 3. S. 39–44 (in Russian).
9. Klimov A.S., Medovnik A.V., Yushkov Yu.G. i dr. Primenenie forvakuumnyh plazmennyh istochnikov elektronov dlya obrabotki dielektrikov. 2017 (in Russian).
10. Koste W.W. Electron beam processing of interconnection structures in multi-layer ceramic modules. Metallurgical Transactions. 1971. № 2(3). P. 729–731.
11. Permyakov G.L., Trushnikov D.N., Belen'kij V.Ya. i dr. Chislennoe modelirovanie processa elektronno-luchevoj svarki s prodol'noj oscillyaciej lucha na osnove eksperimental'no opredelennoj formy kanala proplavleniya. Sibirskij zhurnal nauki i tekhnologij. 2015. № 16(4) (in Russian).
12. Rai R., Palmer T.A., Elmer J.W. et al. Heat transfer and fluid flow during electron beam welding of 304L stainless steel alloy. Weld. J. 2009. V. 88. № 3. P. 54–61.
13. Moarrefzadeh A. Finite-Element simulation of electron beam machining (EBM) Process. International Journal of Multidisciplinary Sciences and Engineering. 2011. № 2.
14. Galati M., Iuliano L. A literature review of powder-based electron beam melting focusing on numerical simulations. Additive Manufacturing. 2018. V. 19. P. 1–20.
15. Kuznecov G.D., Kushkhov A.R. Fizika vzaimodejstviya uskorennyh ionov, elektronov i atomov s veshchestvom: uskorennye elektrony: Ucheb. posobie. M.: Izd. Dom MISiS. 2012. 97 s. (in Russian).