Additive FPCBs | Digital selective package-level EMI shielding | digitally dispensed PV metallization | EHD in microLEDs
Additively manufactured FPCBs with bulk-like conductivity and soldering?
Elepahntech (Japan) has spent more than $40M developing a technology based on inkjet printing (IJP) and plating to additively manufacture flexible PCBs (FPCBs) on PI as well as PET layers. The process is shown below.
Here, the additive nature of the process means that the production process is environmentally friendlier and does not involve etching chemicals. Furthermore, the digital nature of the patterning (inkjet printing) means that designs can be changed faster.
Here, inkjet printing is used to first print a thin silver nanoparticle track on the PET or PI substrate. Thi seed layer- which must adhere well to the substrate- is then thickened by copper (Cu) plating.
This hybrid approach ensures that (a) bulk-level conductivity similar to PCBs is achieved and (b) soldering can be deployed without the challenges faced by conductive inks. These are two important points enabling the technology to be positioned as an alternative to etched FPCBs without performance compromise and as a drop-in replacement.
The linewidth is currently limited by the resolution of inkjet printing. The L/S (linewidth over spacing) is now around 200um/200um. With laser scribing, this can be further reduced to 100/100um today. In the future, the development target is an L/S of 20/20. Furthermore, the technology currently is applied only on flat surfaces. In the future, however, the seed layer could be applied to a 3D layer, enabling 3D metallization too.
Selective-area additive package-level EMI metallization?
Sputtering remains the technology of choice for creating conformal package-level EMI shielding, which itself is a major trend in the electronics industry. For some years now, there have been attempts to replace the incumbent sputtering with spraying. The advantages are low Capex as well as non-vacuum operation, although these advantages may not be enough to overcome the momentum of incumbency.
However, there are now two approaches based on digital printing of conductive inks to create conformal package-level EMI shielding. The digital nature of the coating enables mask-less area-selective metallization, which is an important advantage compared to blanket sputtering when it comes to complex multi-chip heterogenous packaging or SiP package in which only a part of the package will need to be coated.
One approach has been developed by Heraeus. It combines multi-head on-wafer inkjet printing with their particle-free inks. Heraeus is offering a manufacturing-level turnkey printing machine optimized with its ink system, making it easy for customers to adopt its solution. Furthermore, the thin and smooth nature of the coating suggests it is effective even for mmWave frequencies and beyond, meaning that a single solution will suffice to cover sub-5G range, mmWave range, and many future frequency ranges.
Another currently-less-mature approach is being developed by Ntrium in Korea. Here, they deploy aerosol printing. The results below were disclosed at TechBlick in May 2021. It shows aarea selective metallization on a 8x12mm2 IC. The aerosol head moves at 10mm/s. The Ag nanoparticle coatings are 1.1- 1.3um thick, which is thinner than spray and in the same range as inkjet. Aerosol offers a focused jet, enabling high resolution, but it may at the same time limit coverage area per pass.
We do not know the latest developments but the plan in May 2021 was to achieve the following until late 2022/early 2023
UPH 1000 /system → 4000/system
Headspeed: 5mm/s → 15mm/s
Thickness: 1um/pass →3um/pass
Width: 500um/pass →1mm/pass
Digitally deposited interconnets as wirebond replacement for high frequency electronics
dditively deposited interconnects as wirebond replacement in electronic packaging can have many advantages.
They can reduce or eliminate the loop and the associated inductance, which is important in high frequency electronics. They can shorten the inteconnets, thus reducing loss. They can — depending on the printing technique- narrow the pitch and wire width down to 20 and 10um, respectively. They can enable custom shapes for the interconnects, enabling one to have custom resistance values. Finally, they can save space, as no bond pads will be required and can be more delicate as it is a non-contact deposition technique.
Here, we can see an example by Optomec. A microstrip is aerosol jet printed (AJP) with a width of 45um using silver nanoparticle (Ag NP) inks.
The data here suggests that wirebonds perform poorly at mmWave signals whereas AJP micrtrops can operate well upto 100 GHz. Of course, it is important to note that wire bonding is not as bad as this because often circuit compensation is built in. Furthermore, at such high frequencies, the competition is often not wire-bonding, but package-level integration.
Clearly, digital additive techniques like aerosol have many advantages. They still need to prove produciton at scale, reliability, etc. The conductivity of the printed lines- especially when the curing T is limited- needs to further improve as otherwise it becomes the dominant loss factor
For more information visit www.TechBlick.com
Digitally printed high viscosity metallization pastes on Si solar wafers with sub 20um resolution?
The standard metallization technology for Si solar cells is screen printing. Today, it can print 35um linewidths and is expected to evolve down in production to 20um linewidths. The productivity for a 182x182 mm2 wafer is today around 7000 wafers per hour, setting the industry benchmark for any alternative technology.
In the past, inkjet printing tried to offer an alternative, but could only handle low viscosity nanoparticle (expensive) inks with low aspect ratio. It was proposed to use inkjet as the technology to print seed layer, but inkjet — as a tool for PV metallization- has not yet gained significant traction, despite more a decade of development.
Fraunhofer ISE has developed a novel multi-head non-contact digital printing based on high-resolution dispensing. This technology — spun off into HighLine Technology GmbH — can digitally print high-aspect ratio (:1) ultra narrow linewidth (17–19um) metallization lines using high viscosity solar Ag pastes. This technique may improve upon the linewidth capability of screen printing whilst being inline and non-contact, which can lead to lower breakage/reject rate especially for ultrathin wafers.
For more information visit www.TechBlick.com
Digitally print ultrafine micropads and bumps for microLEDs?
As microLED’s inevitably shrink in size, the question of how to bond and contact them to the substrate becomes ever more important. This need will drive innovation both in terms of material development and deposition technology.
An interesting additive approach is based on electrohydrodynamic printing (EHD), which can digitally print inks with few-micron resolution and over a spectrum of viscosities (can handle far more viscous than inkjet can). The image below by Enjet presented at a previous TechBlick conference, shows how conductive bond pads and adhesives in the scale of 15–20um were digitally (EDH) printed. Currently, the EHD is generally somewhat slow, but the recent development of multi-head printers may change this. This is an important technology area to watch.
For more information visit www.TechBlick.com
