FEMS EUROMAT 2023
Poster
Comparative study of LIFT-printed solder paste materials with different particle sizes for integrated photonic applications
KA

Kostas Andritsos

National Technical University of Athens

Andritsos, K. (Speaker)¹; Makrygianni, M.¹; Zacharatos, F.¹; Zergioti, I.¹
¹National Technical University of Athens

Nowadays, the wide adoption of hybrid and complex integration schemes have introduced new challenges in the field of microelectronic component assembly. The most challenging aspect of optoelectronics is the field of optoelectronic integrated circuits (OEICs), that will become sustainable if the level of integration increases so as to accommodate novel advanced materials and the foot-print decreases. To address most of the integration challenges, an integration scheme is introduced, where laser-based processes (LIFT and laser soldering) are utilized for the integration of optoelectronic components. Laser-Induced Forward Transfer (LIFT) process is fully compatible with lead-free soldering materials and offers flexibility in terms of geometry and form factor, as well as high throughput. In this work, two types of commercially available solder paste materials have been used in order to define the optimum process parameters for the laser printing of well-defined solder paste patterns on several receiver substrates. The LIFT station employed, comprises a ns DPSS Nd:YAG laser operating at a wavelength of 532 nm and a 2D galvanometer scanner with scanning speed up to 3 m/s. First, LIFT printing of a type 5 solder paste (particle size 15-25 μm) has been carried out, where the donor substrate comprises a coated solder paste layer (150 μm thick) on glass substrates for printing solder paste micropatterns on PCB pads and Ag pads. Experimental results showed that a bridging-based transfer is beneficial for the process due to the resulting more directional transfers, which occurs at specific donor/receiver distances (≤ 100 μm). Also, it has been observed that square micro-patterns with length of 1100 μm and 1300 μm have been successfully printed at a laser fluence of 2.0 J/cm2 on PCB pads and Ag pads, respectively, covering 90% of the metallic pad area, thus increasing the effective area available for bonding. Second, the study of a type 6 solder paste (particle size 5-15 μm) on the receiver substrate will be investigated to also define the optimum donor/receiver distance. Donor substrates will be prepared with donor layer thicknesses ≤ 150 μm so as to determine the optimum thickness of the donor layer. Preliminary results of LIFT printed solder paste pixels, showed that for a wide range of laser fluences, the printed bumps keep a round shape while the flux is observed around the bumps. The diameter of the bumps increases from 70 μm to 400 μm with increasing laser fluence (from 1.5 to 4.0 J/cm2). The resulting information is expected to be used as feedback in order to achieve high throughput and controllable transfer of solder paste micropatterns (lateral size 50x50 μm2, or 100x100 μm2).

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