Fabrication of Optimally Micro-Textured Copper Substrates by Plasma Printing for Plastic Mold Packaging
Tatsuhiko Aizawa*,, Yasuo Saito**, Hideharu Hasegawa**, and Kenji Wasa***
*Surface Engineering Design Laboratory
3-15-10 Minami-rokugo, Ota, Tokyo 144-0045, Japan
**Chuo Denshi Kogyo, Co., Ltd., Uki, Japan
***MicroTeX Labs, LLC, Tokyo, Japan
Micro-embossing using plasma printed micro-punch was proposed to form micro-groove textures into the copper substrate for plastic packaging of hollowed GaN HEMT-chips. In particular, the micro-groove network on the copper substrate was optimized to attain uniform stress distribution with maximum stress level being as low as possible. Three-dimensional finite element analysis was employed to investigate the optimum micro-grooving texture-topology and to attain the uniform stress distribution on the joined interface between the plastic mold and the textured copper substrate. Thereafter, plasma printing was utilized to fabricate the micro-punch for micro-embossing of the micro-grooving network into the copper substrate as a designed optimum micro-texture. This plasma printing mainly consisted of three steps. Two-dimensional micro-pattern was screen-printed onto the AISI316 die surface as a negative pattern of the optimum CAD data. The screen-printed die was plasma nitrided at 673 K for 14.4 ks at 70 Pa under the hydrogen-nitrogen mixture for selective nitrogen supersaturation onto the unprinted die surfaces. A micro-punch was developed by mechanically removing the printed parts of die material. Then, fine computer numerical control (CNC) stamping was used to yield the micro-embossed copper substrate specimens. Twelve micro-textured substrates were molded into packaged specimens by plastic molding. Finally, gross leak testing was employed to evaluate the integrity of the joined interface. The takt time required to yield the micro-grooved copper substrate by the present method was compared to the picosecond laser micro-grooving; the former showed high productivity based on this parameter.
-  A. Prejs, S. Wood, R. Pengelly, and W. Pribble, “Thermal analysis and its application to high power GaN HEMT amplifiers,” Proc. IMS-2009, pp. 917-922, 2009.
-  D. Doughetty, M. Mahalingam, V. Viswanathan, and M. Zimmerman, “Multi-lead Organic Air-Cavity Package for High Power High Frequency RFICs,” Proc. IMS-2009, pp. 473-476, 2009.
-  A. Longford, J. Matlis, and J. Lynch, “Advanced of Using LCP-Based Pre-Molded Leadframe Packages for RF and MEMS Applications,” Advancing Microelectronics, Vol.39, No.5, pp. 8-12, 2012.
-  A. Kobayashi, T. Hishinuma, and K. Satoh, “Microtexturing of copper substrates by nanosecond laser processing,” Japan Patent 4020957, 2007.
-  T. Aizawa and T. Inohara, “Pico- and femto-second laser micromachining for surface texturing,” Z. Stanimirović and I. Stanimirović (Eds.), “Micromachining,” IntechOpen, 2019.
-  Y. Saito, T. Aizawa, K. Wasa, and Y. Nogami, “Leak-proof packaging for GaN chip with controlled thermal spreading and transients,” Proc. BCICTS2018, pp. 243-246, 2019.
-  T. Aizawa, “Plasma Printing: An Innovation Toward Micro- and Nano-Manufacturing,” 3rd ISAST Conf. (Bali, Indonesia), CD-ROM, 2015.
-  T. Aizawa, “Micro-manufacturing by controlled plasma technologies,” Automobile Engineering, Vol.72, No.6, pp. 35-41, 2018.
-  T. Aizawa and K. Wasa, “Plasma printing of micro-nozzles with complex shaped outlets into stainless steel sheets,” J. Micro Nano-Manuf., Vol.7, No.3, 034502, 2019.
-  T. Aizawa and S. Yoshihara, “Microtexturing into AISI420 dies for fine piercing of micropatterns into metallic sheets,” J. JSTP, Vol.60, pp. 53-57, 2019.
-  T. Shiratori, T. Aizawa, Y. Saito, and K. Wasa, “Plasma printing of AISI316 multi-punch die micro-embossing into copper plates,” J. Metals, Vol.9, p. 396, 2019.
-  Y. Saito, T. Aizawa, K. Wasa, and Y. Nogami, “Hollow packaging structure, its manufacturing, semi-conductor chip utility system and its manufacturing,” Japan Patent 6625774, 2019.
-  T. Aizawa, Y. Saitoh, and H. Hasegawa, “Leak-free plastic mold packaging into micro-textured copper substrate by plasma printing,” Proc. 3rd WCMNM2019, TuAT3.1, 2019.
-  T. Aizawa, T. Shiratori, and K. Wasa, “Plasma-printed AISI316L multi-punch array for fabrication of aluminum heatsink with micro-pillar fins,” Proc. 3rd WCMNM2019, WeBT1.2, 2019.
-  http://www.quint.co.jp/ [Accessed June 27, 2019]