Eco-Friendly Lead-Free Solder Paste Printing via Laser-Induced Forward Transfer for the Assembly of Ultra-Fine Pitch Electronic Components

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.

Printing via Laser-Induced Forward Transfer and the Future of Digital Manufacturing

“…The same principles for printing are used with the LIFT technique. There are numerous publications where the printing of solids, pastes, and liquid containing conductive materials have been used for the fabrication of conductive paths [ 25 , 26 , 27 ], light-emitting diodes [ 28 ], solar cells [ 29 ], and materials used for microsensors [ 30 ]. An important advantage over other printing techniques, such as ink-jet printing, relies on the fact that these systems are able to work with a wider viscosity range of inks with nanoparticle suspensions, which opens a wider variety of printable materials suitable for electronic applications, especially in the case of high-viscosity pastes made from particles with particle sizes in the microscale [ 1 ].…”

Hybrid structural electronics fabrication by combined SLA and metal printing

“…The conductive printing step is done by LIFT, a direct laser writing process that may be applied to large variety of materials, pure metals and alloys, high viscous metallic inks [18] and ceramics [19,20]. It is a high resolution, one step, process that can operate under ambient atmosphere.…”

Facile Modification of Flexible Electrodes via Laser Transfer

“…Each laser pulse allows the precise and well localized transfer of the donor layer as a pixel (with different shapes, areas and thicknesses) on a rigid or flexible substrate (receiver substrate) that is placed parallel, in contact to or at short distance from the donor. One of the advantages of LIFT is that it allows the transfer of materials in different phases (liquid [ 20 , 24 , 25 , 26 ] or solid [ 27 , 28 , 29 , 30 , 31 ]) with high resolution and without contamination, even if the process is carried out in air. This technique can be successfully applied for processing of sensors [ 31 ], organic light emitting diodes [ 32 ], flip-chip devices [ 33 ], etc.…”