Kye-Si Kwon. Inkjet measurement issue in printed electronics applications

Transcription

1 03. Measurement and assessment method of inkjet jetting performance for printed electronics (Korean Agency for Tecnology and standards) Soonchunhyang university Kye-Si Kwon Inkjet measurement issue in printed electronics applications Jetting measurement Jetting control Inkjet Head Frequency: Up to 40kHz Drop volume:~00pl Ink Printing System Printing Algorithm Jettable fluid (head dependent) Viscosity: ~5cP Surface tension: 0~70 dyne/cm Contact angle, Drying characteristics morphology control Small droplet, black matrix Substrate Paper; glass; flexible plastic substrates; metals, silicon

2 Why inkjet measurement standardization? Various Inks Various Heads Jetting conditions (Waveform, temparture) Measurement Ink manufacturers Head manufacturers Head manufatures Fair comparison was impossible if there is no standardization. Is it reliable measurement results? - : 5m/s - Droplet volume: 30pL - Jetting frequency vs jetting speed? 40kHz? (Jettability) Droplet volume Jetting Frequency Effects Jet straightness 3 Current proposal: Vision based measurement (Inkjet) Drop watcher system Droplet volume Previous measurement. jetting speed. droplet volume t (a) (c) t (b) (d) speed.m/s.5m/s Without standardization, results will differ. Binary images are affected by threshold, Focus, lighting conditions Measured droplet volume has inaccuracy. 4

3 Vision measurement algorithm Binary image conversion It is difficult to measure droplet volume. Gray image -Size location Image value : Image value :0 Binary image Threshold Gray scale image Image value: 0-55 Binary image Image value: 0, Threshold value 5 Threshold value 75 5 measurement Two locations at t and t v Py t Py t F At t At t Pixel errors might be canceled out - Less affected by pixel - Resolution errors (due to binary Conversion) 6 3

4 Current problem of jetting speed measurement If the main drop has long tail (or statellite) in any of the two timings, it is very difficult to define the location of droplet. Therefore, a standard method is needed to define the droplet location. Time Time ( s) ( s) (m/s) * vary significantly according to the drop formation! 7 Issues: ligament/ satellite/drop formation - measurement issues : It is difficult to define jetting speed in presence of Ligament and satellite.. Two locations of droplet at t and t Location of droplet?. Relative jetting speed of satellite with respect to main droplet (Conventional method focuses only on jetting speed of main droplet) 3. Drop formation (jetting speed varies significantly during jetting) Standardization is needed Location Satellite and ligament Drop formation Bottom? Center? Top? Relative jetting speed Between Satellite and Main droplet. 8 Drop formation 4

5 One possible solution? Instantaneous jetting speed curve Fixed frequency. Sequential image. Image processing 3. Updating results How we can measure jetting frequency vs jetting speed curve? (standardization is needed) Variation during drop formation 9 Drop formation and jetting speed variation Pinch-off 60 s 90 s 0 s Long ligament Single droplet two droplets 50 s 80 s 90 s Main drop jetting speed Satellite jetting speed 0 Time ( s) 5

6 Video If it needs to be accurate, it will take more time. So, the measurement methods can be classified according to the precision required. Precise Measurement (Grade ) Engineering Measurement (Grade ) Measurement of jetting performance: Vision based method (inkjet jetting speed and droplet volume) Scope of this proposal Vision system requirements to measure the jet performance Measurement methods and test procedures to measure the jet performance Current problems The test results differ according to test procedure. Jet test results are not reliable. It is difficult to compare jet performance of different ink and different heads. As a results, the jet performance of ink and head needs to be tested again by the labs and test engineers. standardization Reliable test results for ink, head, jetting performance. Direct comparison of different ink, head and operating method. Fast development for inkjet process and widely accepted test results (Benefits: ink developer, head developer, inkjet process engineer, manufacturer using inkjet process etc. ) 6

7 Future activities: inkjet measurement Measurement Items What should we measure? 사업종료후일정 Equipment Requirements What is the equipment requirement? Measurement process How should we measure? Measurement conditions Measurement Accuracy Precise Measurement (Grade ) Engineering Measurement (Grade ) These standards will help to improve jetting testing for printed electronics application and allow for true comparisons of different inks, heads and equipment. 3 Thank you! 7