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Ultrafine printing overview, printed LTCC-based mmWave RFFE, digital printing of screen pastes, 3D..

Ultrafine line screen printing: emerging application and competing technologies

TechBlick prepared this presentation for the Advanced Screen Printing Workshop organized by Asada Mesh (June 2022, Chicago). You can watch and read the full presentation here. You can also view the slides. The theme are

  • Existing and emerging applications for ever finer Screen Printing linewidths (sub-15 micron meters): Photovoltaic metallization | MicroLED wrap-around edge electrodes | Fan-out structure for flexible hybrid electronics | Transparent HMIs |Transparent Touch Displays | Edge Electrodes | MLCC | LTCC

  • Hybrid and direct (non-digital) printing technologies towards sub-micron linewidths: Hybrid screen printing (print + etch/ablate) | R2R flexo printing | R2R Gravure Offset Printing |S2S Offset Printing | S2S Reverse Offset Printing |R2R Reverse Offset Printing | R2R Imprinting + Filling | R2R Photolithgraphy

You can download the slides at the bottom of this blog. Simply scroll down

mmWave 5G RFFE based on LTCC and printed Ag metallization

LTCC with printed Ag metallization is an excellent choice for heterogeneous integration of electronics, especially for high-frequency (mmWave and 5G) and harsh environmental conditions. Indeed, it shows our printed electronics can play a role in the 5G/6G communications infrastructure. In this study, DuPont demonstrates an Antenna-in-Package (AiP) which integrates a beam steerable antenna array in a Radio Frequency Front-End module (RFFE) operating at 28 GHz and incorporating an Anokiwave IC with a 2 x 4 patch antenna array.

The ceramic dielectric (so-called GreenTape) shows excellent dielectric properties through 100 GHz while maintaining Dk of 7.1 and Df of <0.0010. It also shows stable properties throughout the extreme temperature range (-50°C to 150°C).

In this study, screen printed sintered Ag metallization was used for ground planes, via fills, signal lines and solderable pads. The data in this study shows the viability of LTCC for mmWave and 5G applications. It is an exciting solution with low moisture update, good temperature stability, etc.

As the density of parts in LTCC based heterogeneous systems rises, screen printing will also need to go to finer lines to support this densification, but that is a story for another day

Digital printing of screen printable pastes for rapid prototyping??!

Screen printing requires tooling which limits prototyping and rapid product iteration. Digital printing uses nanoinks which have a more limited menu of material options and are more expensive, and in any case are not always the ultimate material selected in final volume production. This leaves a gap in the market for digital printing of off-the-shelf screen printable materials and pastes.

Voltera is developing a prototyping benchtop machine aimed at solving this problem. This product will be launched at the TechBlick show in Eindhoven (12-13 OCT 2022). It allows users to rapidly digitally print using different screen pastes. The digital printing processes largely self caliberates, allowing uses to experiment with different materials and formulations without needing to go through the full learning curve/print optimizaiton process each time. The benchtype size also allows one to keep this in the lab, enabling rapid prototyping. The digital direct wire printing head allows printing on different substrate materials as well as over flat and 2.5D/3D shapes.

Applications demonstrated here: (1) soft insole pressure sensor on TPU | (2) wearable heater integrated into clothing (denim) | (3) thermally formed mug heater.

Digital Laser Processing of 3D Electronics

Combining digital printing (inkjet, aerosol, etc) with site-specific digital rapid laser-based sintering has many advantages. In the talk below, you will see various examples from Fraunhofer ILT in Aachen, Germany.

Multi-layer piezoelectric actuators: The structure is multi-layer [(PZT (140nm)-->LNO (30nm)--> PZT (140nm)-->LNO (30nm)--> PZT (140nm)-->LNO (30nm)]. Therefore, it is essential to have rapid sintering otherwise TACT time will be too long. Here, Fraunhofer ILT suggests that laser sintering (inkjet layer 1 --> laser sinter --> repeat) can be an excellent solution.

Strain sensors on and within 3D-printed bionic component: here, the insulating layer is first dispensed. The strain sensor materials are then digitally (inkjet) printed onto the surface of the 3D part and then digitally laser-sintered. The ability to digital print and sinter means that only the required parts will be metallized and subjected to heat treatment.

As such, it saves time, prints on non-flat shapes, and maintains integrity of the 3d printed mechanical parts. In another variation of the same device, they can stop the 3D printing process to digitally print (aerosol this time) and digital laser sinter the electronic components before resuming the 3D printing process. This way, the electronic functionality will become embedded in the structure itself.

3D Pad Printing on 3D Surfaces: 5G antenna for smart phones

Metallising 3D structure has many applications. The common technology approaches to LDS (laser direct structuring) or digital aerosol printing. The fomer is a multistage process with a relatively large machinery footprint, but offers high adhesion and bulk-level conductivity with ease of soldering. The latter is a two-step digital process with small compact machine. However, it offers ink-level conductivity, which can be low especially on low-T substrate.

Henkel has recently demonstrated pad printing - an old technique- for 3D electronics. This technology enables printing of inks onto 2.5 and 3D plastic structure, thus offering an alternative to LDS and aerosol. It is a simpler process than the other two. The process will not create fine structure but can print thicker (thus more conducting) lines using high viscosity pastes. It is also a robust and relatively low-tech process compared to LDS and aerosol.

As shown therein, in this process, a conformal silicone pad first pickes up the ink from a metallic plate. The ink formulation must ensure good adhesion to the silicone pad. The pad then stampls the 3D surface. Since the pad is conformal, it follows the shape of the target substrate, achieving non-flat or 3D coating.

Applicaiton examples demonstrated herein are developed with Henkel's Chinese partners:

  • printed 5G antenna on the outside polycarbonate frame of a mobile phone, achieving 10mOhm/sqr/mill

  • printed conductor on the inner side of the plastic to connect with mainboard

Fineline printing_Screen printing and beyond_TechBlick
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