The microfail project is focused on understanding the effect of microfailures and defects on issues observed on product level, that can influence the lens performance and/or reliability. The first year of the project was particularly focused on problems in drop test. We have observed that components might experience accelerations of up to 50000 times the gravitational acceleration (50000G). These are extreme impacts, and they also tend to be very chaotic and the reliability requirement for mobile phone with respect to drop test and chock impact seems to increase over years, moved from 5000G (0.8m free fall in bulky and soft old fashion mobile phone in the 2000 to today supet slim and stiff mobile phone free fall drop from 1.5m 50KG and future new requirement could go up to 2m free fall drop test. Early in the project, we identified a method to drastically improve the drop test resistance of the lenses. A patent application has been filed, and the method is implemented in the production line for all TLens products. During the year, we have also completed a full product qualification, including an extensive reliability test program. The realization that correct and controlled mounting of lenses in drop test jigs has been an important finding. This was accomplished by extensive experimental work, statistical analysis and theoretical simulations, and led to a deeper understanding of the complex correlations between conditions in the drop test jig and drop test performance. By controlling/reducing the possibility for the lenses/cameras to move inside the drop jigs, the failure rate in drop test was reduced from 20% to below 5%, which is considered to be sufficient to claim that the issues we have faced with drop test over the past 2-3 years have been resolved.
During the product qualification, a new phenomenon was discovered. The component used for the patent pending drop test solution, a epoxy glue and the method to apply it, has shown to interact with the moisture in the surrounding air. When the relative humidity is lower than 30%, mechanical stresses occur in the epoxy film, which causes a non-ideal deformation of the membrane, that again causes images with poorer quality in a camera phone. The changes in the membrane deformation is in the sub-micron range, and are difficult to detect. Experimental designs with controlled ambient humidity during optical characterization have been important to understand the phenomenon, and we have contained the problem to a pure yield issue. The temporary solution has been to adjust control limits during production to avoid shipping lenses with this issue to customers. This comes on the expense of lower yield, which must be resolved. We have the need for extensive R&D work during next year to reduce failures due to this phenomenon, both within material and process development.
During the last few months, we have also discovered a new kind of defect in the piezo actuator stack, that increases the risk for lenses to fail during real life operation. This defect is not possible to detect using automatic visual inspection, which is part of the production process today. This work has maximum priority in the company, since the defect is present on material ready to be shipped in high volumes to customers. Pre-studies has been carried out internally, and the conclusion is that the problem has been dealt with indirectly for new wafers to be prodcued, but we need to implement advanced image processing and analysis to be able to detect the defects during automatic inspection in production. We see the need for development of algorithms that can be implemented in the production line, in order to be able to automatically process 1000s of lenses every day the coming months.
2020 has been a very positive year for the company. Our first product is qualified and put into production for use in smart watches. In the same period we have identified some new effects that may reduce functionality and life time. We have already found solutions that are implemented.
The post-doc student has had good progress. An application for synchrotron beam time (high energy X-ray diffraction) has been filed, where the plan is to do high resolution stress and property mapping of TLens actuators. It has also been planned to carry out X-ray diffraction measurements while lenses are exposed to mechanical or electrical stress. While waiting for synchrotron beam time, pre-studies using SAXS has been carried out at NTNU, to investigate whether changes in amorphous structures are detectable, carried out on lenses with different biasing history and performance.
The post-doc student have had a challenging year due to "corona". We had a slot at the Synchrotron in march that was postponed to october this year. Later it was postponed until notice is given. We will most likely not be able to carry out these analysis within the time frame of this project.
poLight as has developed their Tlens technology through the last years and the first product (Silver) is now entering in to mass-production. The next step will be development of new products such as AF-lenses with larger apertures as well as Optical Image Stabiliser (OIS) and an integrated OIS-AF. This require a range of new knowledge which will be aquired through R&D project together with SINTEF, NTNU, HSN and a number of sub-suppliers. Parts of this work i organized in projects partly funded by Forskningsrådet (BTHE, HybridMEMS, HiFPac and this new project Microfail)
Microfail is devoted to understanding the effect of micro fails and defects on any observed issue like cracks, delamination, corrosion, moisture absorption and haziness. Larger, more complex structures like OIS are most likely more sensitive to these defects and it is important that we are able to control them.
Samples are selected from our product test programs (Not a part of this project) and made in controlled experiments due to time temperature and environment.
All selected samples are analysed by SINTEF and NTNU and evaluated in cooperation with poLight scientists. A number analytical techniques will be used including destructive and non-destructive tests described in the project description. We may also need analytical instruments not available in Norway. Through our partners we may use facilities in SNRF, CERN and som other laboratories.
Finally we will tune and adjust wafer processing parameters and assembly process to avoid or reduce the number of defects.