Journal
MATERIALS LETTERS
Volume 163, Issue -, Pages 254-257Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.matlet.2015.10.108
Keywords
Laser soldering; Intermetallic alloys and compounds; ENIG; Lead-free; Diffusion
Funding
- National Science Foundation of China [51522503]
- Program for New Century Excellent Talents in University [NCET-13-0175]
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In three-dimensional (3D) packaging and assembly technology, Lead-free SnAgCu solder joints inevitably experience multiple reflows. The interfacial compounds of Sn3.0Ag0.5Cu (SAC305)/ Electroless Ni-P/Immersion Au (ENIG) solder bump after laser soldering and subsequent hot air reflows were observed by transmission electron microscopy (TEM), respectively. The initial laser soldering played a key role in interfacial compound evolution during the subsequent multiple reflows. After laser soldering, a thin P-rich layer and an ultrafine scallop-type (Ni, Cu)(3)Sn-4 layer formed at the interface of SAC305/ENIG. The valleys of ultrafine (Ni, Cu)(3)Sn-4 grains served as rapid channels for Ni diffusion, which contributed to the formation of dendritic eta-(Cu, Ni)(6)Sn-5+ (Ni, Cu)(3)Sn-2 intermetallic compounds after the first hot air reflow. However, with the number of reflow times increasing, the eta-(Cu, Ni)(6)Sn-5 totally transformed to noodle-like (Ni, Cu)(3)Sn-2 owing to their similarly hexagonal lattice structure and the limited Cu supply in solder. (C) 2015 Elsevier B.V. All rights reserved.
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