206 : 316-8511 4-12 - 1 Laser Sintering Characteristics of Silver Nanoparticle Paste for Electronics Packaging YAMASAKI Kazuhiko, MAEKAWA Katsuhiro (Received January 10, 2012) Ibaraki University, Faculty of Engineering, Department of Mechanical Engineering (4-12 - 1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan) In terms of electronics packaging with conservation of resources and energy as well as low environmental damage, we investigated laser - sintering technology followed by printing of metal nanoparticles: especially, minute wiring and wire - bonding - pad formation using silver nanoparticles. A line width of 100 mm, a specific resistance of 4.8 µω cm, and pull wire - bond strength similar to that of electroplating were achieved. A bulk - like functional - film structure can be obtained by sintering to be started from the substrate using a continuous - wave, near - infrared laser beam with low - absorbance of the paste, together with preheating to reduce solvents in the paste. Key words : metal nanoparticles, laser sintering, patterning, thin film, wire bonding, electronics packaging 1. SiP SoC 1 a TEM 5 nm b NPS - J 10 mpa s 65 wt% 2.2 PITorey/DuPont Kapton500H 0.125 mm Fig. 2 100 C 1 min X - Y 4 mm/s 2. 2.1 Fig. 1 Fig. 1 Ag - nanoparticle paste used in laser sintering.
Vol. 19, No. 3 (2012) 207 Fig. 2 Procedures for minute wiring onto polyimide substrate. Fig. 3 Ink - jet printing apparatus as part of laser sintering. Fig. 4 Optical properties of Ag - nanoparticle paste. Nd : YAG 1,064 nm 0.4 mm 140 W 980 nm 50 W532 nm 5 W Ar 488 nm 1.4 W JIS C1220P 0.1 mm 0.3 mm Fig. 3 φ 300 μm 128 11 pl 1,200 dpi 100 C 1 min X - Y Nd : YAG 4 mm/s X - Y 3 l/min Ar Ar 3% Fig. 4 20,000 600 nm 420 nm 100 C 1 min 70 % 220 C 60 min 2.3 FIB - SIM LSM FIB - SIM Ga 30 LSM PI 90-0.5R 2 mm/s 10 mm/s 4 φ 25 μm
208 : 150 C 500 h 1,000 h 3. Fig. 5 4 PI PI 100 μm 500 μm Fig. 6 LD Ar 1,000 rpm 0.50 μm Fig. 7 Comparison of FIBed cross - sections of sintered Ag on polyimide. PI 4.8 μω cm 3 2 Ar 8.0 μω cm Fig. 7 4 FIB - SIM FIB - SIM 30 2 Fig. 6 Fig. 5 Comparison of laser - sintered Ag on polyimide after bend - peel test. Fig. 6 Comparison of specific electric resistance of laser - sintered Ag on polyimide. 4. 2 μm 1 coffee stain Fig. 8 0.20 μm IJ
Vol. 19, No. 3 (2012) 209 Table 1 Pull strength and fracture modes of laser - sintered pads before/after heat soak tests. Soak time at 150 C 0 h 500 h 1,000 h Fig. 8 LSM image of surface profile of laser - sintered Ag pad with single - step printing. Pull strength Fracture modes Average 9.2 cn 8.8 cn 8.8 cn Maximum 10.7 cn 10.7 cn 10.9 cn Minimum 7.5 cn 7.8 cn 7.8 cn 1st bond 0 0 0 Wire 100% 100% 100% 2nd bond 0 0 0 Fig. 9 LSM images of surface profile of laser - sintered Ag pad on Cu lead tip. Fig. 11 Cross - sectional analysis of laser - sintered Ag pad at 150 C for 1000 h. Fig. 10 FIBed cross - sections of laser - sintered Ag pads on Cu lead tip. Nd : YAG 100 W 3 Fig. 9 Fig. 10 FIB SIM 30 3.0 μm 8.6 cn 3 150 C 0 h Table 1 0 h 8.6 cn 500 h 1,000 h 8.8 cn 1st 2nd EDX Fig. 11 1,000 h Ag/Cu Cu Ag/Au 5. 5.1 Fig. 5
210 : Fig. 13 TEM image at laser - sintered Ag/polyimide substrate interface. Fig. 12 Schematic of laser sintering process with different wavelengths or absorbance of light. Fig. 7 FIB - SIM Fig. 12 Fig. 4 Nd : YAG PI Fig. 12 a Ar Fig. 12 b 5.2 Fig. 13 Ag/PI TEM PI PI PI Fig. 14 Ag/Cu X XPS Nd : YAG 133 W Fig. 14 Atomic percent profiles of cross - section of sintered - Ag/Cu interface. 1 75 ms 500 C 600 C Ag/Cu 20 nm Ag Cu b 220 C 60 min Ag/Cu 5.3 100 nm 2 μm 100 nm Fig. 15 80 wt%
Vol. 19, No. 3 (2012) 211 Fig. 15 SEM image of φ100 - nm - sized Ag particles. WB 2 3 μm 150 C 1,000 h Fig. 16 FIBed cross - sections of laser - sintered φ 100 - nm - particle paste. 88 W Nd : YAG Fig. 16 FIB - SIM 2 μm a b Ag/Cu Cr 100 nm 4 JST 18 21 JST A - STEP M&M 1 Wong, W.S. and Salleo, A. eds : Flexible Electronics : Materials and Applications, Springer, New York, 2009. 2 Haynes, W.M. ed. : CRC Handbook of Chemistry and Physics 92 nd ed., CRC Press, 2011, 12-42. 3 Maekawa, K., Yamasaki, K., Niizeki, T., Mita, M., Matsuba, Y., Terada, N. and Saito, H. : High - Speed Laser Plating for Wire - Bonding Pad Formation, Trans. The Japan Institute of Electronics Packaging, 3-1, 2010, 7-13. 4 Tsutsui, Y., Yamasaki, K., Maekawa, K., Niizeki, T., Bucheeri, A., Mita, M., Matsuba, Y., Terada, N. and Saito, H. : Size Effect of Ag Nanoparticles on Laser Sintering and Wire Bondability, Proc. ECTC 2010, 2010, 1870-1876. 6. 5 nm