Big collaboration for a small problem

It turns out that a huge collaborative effort is required to detect nano-scale defects. The NanoMend project has been set up to do just that, and its findings could improve production of flexible electronics, ‘smart’ packaging and even holographic surfaces

Outdoor flexible electronics and paper packaging with inbuilt electronic displays both require high quality protective coatings to preserve their lifespan and performance. This is because even nano-sized defects within these coatings can reduce their ability to protect against weathering, UV degradation and the corroding effect of moisture permeating into the sensitive device structures. Furthermore, defects within the layers that make up these products can result in reduced efficiency, or a need to scrap them entirely, which in turn reduces yield and increases waste.

[caption id="attachment_36209" align="alignright" width="200"] Figure 1: Testing paper for pin holes at the Paper Converting and Packaging Technology unit in Tampere University of Technology[/caption]

Current defect detection systems need to make a trade-off between speed and resolution, which means that production must be slowed down in order to detect these tiny, but important defects. However, both the detection speed and detection resolution play an important role in increasing manufacturing yield. This is why 14 research organisations and small businesses have come together from across Europe to form the NanoMend project, which will pioneer novel, in-line, integrated defect detection and cleaning systems that are capable of detecting micro-scale defects within continuous production.

NanoMend, which has received €7.25M of funding from the EU’s Seventh Framework Programme (FP7), is developing three separate pilot lines in order to demonstrate the technology. Each demonstration will be tailored to the differing needs of manufacturing thin film flexible solar modules and coated paper packaging.

Studies conducted within NanoMend have found that micro-sized pin holes are the most damaging defect to paper packaging products. Therefore, NanoMend will develop a system that can work at the high speed of packaging manufacture, as well as having a resolution that can reach the micro-scale.

A similar system is needed to detect and remove the micro-sized defects in the nano-scale layers that make up as flexible thin film photovoltaics. Although the manufacturing processes for solar modules are slower than paper packaging, the inspection system still needs to work at relatively high speeds, where the resolution required for this system is higher.

[caption id="attachment_36210" align="alignleft" width="200"] Figure 2: The WSI instrument, which will be based at Centre for Process Innovation, part of the UK's high value Manufacturing Catapult[/caption]

The new inspection systems will be developed by increasing the detection resolution of the high speed systems currently available by using novel optical inspection methods. Once developed, they will comprise of a cleaning system to remove defects and a linear array of the latest high resolution cameras which will to detect any defects that remain. NanoMend will also develop the ability to process the large volume of data produced by these high resolution cameras, at a high speed.

Although these high speed systems will have a resolution that goes down to the micro-scale, a higher resolution still is required to detect the low contrast defects within nano-scale coatings that protect PV films from the degradation caused by water vapour.

The solution to this being pioneered by NanoMend is to use optical interferometry, which is able to produce a quantitative measurement of the film layer topographies in the form of a three-dimensional image.

Current industry standard interferometry systems generally work by mechanically scanning the position of a lens relative to the substrate being measured. Such a technique is too slow and too sensitive to environmental changes to perform the large number of in process measurements required to perform defect detection over large substrate areas.

The instrument being developed within NanoMend is a Wavelength Scanning Interferometer (WSI) that can make 3D measurements without mechanical movement as well as carrying out an analysis of the measured information in less than one second. This will allow these ‘hard-to-spot’ defects to be detected at a higher speed, and over a larger area than previously possible.

[caption id="attachment_36211" align="alignright" width="200"] Figure 3: The inspection systems at ISRA VISION[/caption]

Super resolution interferometers may be used to measure smooth and structured surfaces, such as the nano-scale ‘hills and valleys’ imprinted onto surfaces to produce holographic and iridescent effects on packaging material. Even micro-sized particles could alter this pattern, which would reduce the quality of the overall effect.

NanoMend will also investigate the potential of Atomic Layer Deposition (ALD), which is a coating deposition technology, to preserve and possibly strengthen these iridescent effects.

The project is also investigating how these new defect detection systems could be used to help preserve the electronic functions that will be integrated into the next generation of paper packaging. An example of this is Bluetooth devices integrated into medical packaging, which send information to a doctor concerning how regularly a patient takes medication. These ‘Smart Packaging’ products are much more sensitive to damage from water vapour than their standard counterparts. Therefore, they require ultra high quality protective coatings.

NanoMend will develop the technology to use continuous or roll-to-roll ALD to deposit protective coatings onto paper that are only a few nanometres thick, which provide protection by having a very low water vapour transmission rate.

[caption id="attachment_36212" align="alignleft" width="200"] Figure 4 The Roll-to-Roll ALD coater at Lappeenranta University of Technology[/caption]

Currently, ALD cannot be used on paper substrates because it is highly sensitive to defects in the substrate that it coats. Therefore, the defect detection and cleaning techniques developed by NanoMend are key to giving paper packaging the ability to utilise the benefits of ALD for products produced by roll-to-roll manufacturing processes. This could pave the way for Smart Packaging to be produced in larger volumes in the future.

From iridescent whisky labels to flexible solar modules, smart packaging and outdoor digital displays: the NanoMend technology will enable a broad range of products to last longer and be manufactured with a higher quality and in a more cost-effective way.

Author Holly Peacock manages the communications for a number of FP7 projects at the Centre for Process Innovation, part of the UK’s High Value Manufacturing Catapult Centre