Current trends in assembly and packaging of electronic components encompass the establishment of additive manufacturing technologies [1] and the development of lead-free conductive materials in ink or paste form [2]. In addition, the miniaturization of electronic dies and the wide adoption of hybrid and complex integration schemes have introduced new challenges in the field of microelectronic component assembly. Alternative approaches have been developed to address these challenges such as drop-on-demand or direct printing fabrication technologies, enabling the digital deposition of die-attach materials and the assembly of ultra-fine pitch components. Laser-Induced Forward Transfer (LIFT) constitutes an excellent alternative for assembly of electronic components: it is fully compatible with lead-free soldering materials and offers flexibility in terms of geometry and form factor, as well as high throughput (up to 10000 pads/s) [3, 4].
    In this work, the laser printing of a commercially available solder paste (particle size 15-25 μm) on metallic pads was investigated to confirm the controllable transfer of solder paste micropatterns. The configuration employed for these experiments consisted of a side-view high-speed imaging setup coupled with a LIFT station (comprising a ns DPSS Nd:YAG laser, operating at a wavelength of 532 nm). The study of solder paste from two donor layer thicknesses set at 100 and 150 μm indicated that the increase in solder thickness on donor results in a shift of the threshold ejection fluence to higher fluences and towards lower average velocities of the travelling jet (Figure 1a). Furthermore, the laser printing of solder micro-patterns on metallic pads resulted in circular printed micro-patterns and square printed micro-patterns highlighting the digital tuning capability of LIFT in terms of form factors and geometrical characteristics. To demonstrate the bonding process enabled by LIFT, a commercial LED was interconnected to an all printed functional micro-circuit and its operation was validated (Figure 1b). Finally, the reported process will be applied in an industrial environment for the actual assembly of a 0.5 mm fine pitch BGA IC on FR4 type PCBs, resulting in functional demonstrators.

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[2] H.W. Tan, J. An, C.K. Chua, and T. Tran, Metallic Nanoparticle Inks for 3D Printing of Electronics, Adv. Electron. Mater., vol. 5, 1800831, (2019).
[3] F. Zacharatos, M. Makrygianni and I. Zergioti, Laser-Induced Forward Transfer (LIFT) Technique as an Alternative for Assembly and Packaging of Electronic Components, IEEE Journal of Selected Topics in Quantum Electronics, vol. 27, pp. 1-8, (2021).
[4] M. Makrygianni, F. Zacharatos, K. Andritsos, I. Theodorakos, D. Reppas, N. Oikonomidis, C. Spandonidis, I. Zergioti, Eco-Friendly Lead-Free Solder Paste Printing via Laser-Induced Forward Transfer for the Assembly of Ultra-Fine Pitch Electronic Components, Materials, vol. 14, 3353, (2021).