Abstract
Current challenges in printed circuit board (PCB) assembly require high-resolution deposition of ultra-fine pitch components (<0.3 mm and <60 μm respectively), high throughput and compatibility with flexible substrates, which are poorly met by the conventional deposition techniques (e.g., stencil printing). 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 high-resolution printing of solder paste bumps (<60 μm) and throughput (up to 10,000 pads/s). In this work, the laser-process conditions which allow control over the transfer of solder paste bumps and arrays, with form factors in line with the features of fine pitch PCBs, are investigated. The study of solder paste as a function of donor/receiver gap confirmed that controllable printing of bumps containing many microparticles is feasible for a gap < 100 μm from a donor layer thickness set at 100 and 150 μm. The transfer of solder bumps with resolution < 100 μm and solder micropatterns on different substrates, including PCB and silver pads, have been achieved. Finally, the successful operation of a LED interconnected to a pin connector bonded to a laser-printed solder micro-pattern was demonstrated.
Highlights
Published: 17 June 2021The broad field of microelectronics has rapidly grown over recent decades, owing to novel materials and advanced fabrication technologies, which offer key-solutions to specific challenges
The methodology is structured to facilitate the solder paste bonding enabled by Laser-Induced Forward Transfer (LIFT): (i) the donor’s thickness is sufficiently high to ensure that the volume of the transferred solder paste is comparable to the volumes deposited by conventional processes. (ii) The selected receiver substrates are actual gold (Au)/nickel (Ni)/copper (Cu) printed circuit board (PCB) pads, validating the compatibility with the PCB-assembly technology. (iii) We demonstrate the versatility offered by LIFT, in terms of form factors, by printing micropatterns consisting of many solder paste bumps, to achieve controllable coverage of the effective area of the PCB pads. (iv) Using LIFT
The compatibility of LIFT with the selected solder paste material and their performance in key-challenges related to the PCB-assembly technology were investigated by conducting three different experimental studies: (i) the influence of the donor layer’s thickness on the jet dynamics, (ii) the influence of the donor/receiver’s gap on the printing quality and (iii) the contributions of the substrate
Summary
The broad field of microelectronics has rapidly grown over recent decades, owing to novel materials and advanced fabrication technologies, which offer key-solutions to specific challenges. These technologies have fostered the advancement of die-attach and chip-bonding techniques, which are essential for the packaging and assembly of microelectronic components. Novel integration schemes and printable materials [5] have enabled innovative configurations, such as flexible and stretchable devices, aligned with environmental concerns for greener approaches [6] These integration schemes, incorporating heterostructures and 3D architectures in many cases [7], have laid the foundations for a novel paradigm in interconnection technology: the digital and drop-on-demand fabrication techniques [8]. The inkjet printing of high-resolution bumps with 2.5 Ω/bump resistance [9] and micro-dispensing with high
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