Additive technologies for the patterning of fine metal tracks onto flexible substrates

Transcription

1 Additive technologies for the patterning of fine metal tracks onto flexible substrates Marc P.Y. Desmulliez MIcroSystems Engineering Centre (MISEC) Institute of Integrated Systems (IIS) Heriot Watt University, Edinburgh, Scotland, EH14 4AS IeMRC Annual Conference 21 st September 2011 University of Loughborough 0

2 Outline Motivation for flexible substrates and rapid patterning techniques. Taxonomy of additive processes of metal track patterning. Two examples of additive processes of metal tracks patterning researched at Heriot-Watt University. Conclusions. 1

3 Outline Motivation for flexible substrates and rapid patterning techniques. Taxonomy of additive processes of metal track patterning. Two examples of additive processes of metal tracks patterning researched at Heriot-Watt University. Conclusions. 2

4 Motivation for flexible substrates 3

5 Motivation for rapid techniques Need for customization-able, low volume production processes with decreasing feature size for future high technology devices. Development of more economical, high throughput processes. Development of less material wasteful processes. Need for rapid prototyping of designs Potential for reel-to-reel manufacturing techniques A potential candidate: additive bottom-up manufacturing technique. 4

6 Outline Motivation for flexible substrates and rapid patterning techniques. Taxonomy of additive processes of metal tracks patterning. Two examples of additive processes of metal track patterning researched at Heriot-Watt University. Conclusions. 5

7 Taxonomy of additive processes Preferably, the additive processes for the patterning of metals tracks onto flexible substrates should have the following properties: Non vapour phase mode of operation Atmospheric pressure Ambient air operation Potential to reel-to-reel manufacturing 6

8 Taxonomy of additive processes Non vapour phase direct metallisation Thermally induced deposition using laser Surface modification for subsequent electroless deposition Thermally enhanced rate of electroplating Thermal decomposition of liquid precursors Thermal decomposition of coated films Surface activation by laser damage Polyelectrolytes self-assembly Ink-jet printing Reduction of embedded metal ions J. Ng, M.P.Y. Desmulliez et al. (2009) Circuit World, Vol. 35, N.2, pp

9 Taxonomy of additive processes Thermally induced deposition using laser Surface modification for subsequent electroless deposition Photocatalysis by TiO 2 Non vapour phase direct metallisation Photocatalysis mediated deposition Photocatalysis by porous Si Surface voltage generation Metal ions reduction via photochemical reactions Photo-dissociation of metal-organic mixtures Photo-precipitation of metastable colloids J. Ng, M.P.Y. Desmulliez et al. (2009) Circuit World, Vol. 35, N.2, pp

10 Taxonomy of additive processes Non vapour phase direct metallisation Thermally induced deposition using laser Surface modification for subsequent electroless deposition Thermally enhanced rate of electroplating Thermal decomposition of liquid precursors Thermal decomposition of coated films Surface activation by laser damage Polyelectrolytes self-assembly Ink-jet printing Reduction of embedded metal ions J. Ng, M.P.Y. Desmulliez et al. (2009) Circuit World, Vol. 35, N.2, pp

11 Outline Motivation for flexible substrates and rapid patterning techniques. Taxonomy of additive processes for metal track patterning. Two examples of additive processes of metal tracks patterning researched at Heriot-Watt University. Conclusions. 10

12 First fabrication process PMDA-ODA polyimide (PI) treatment to enable metallisation KOH solution hydrolyses PI into polyamic acid and electrostatic bonds are formed K + K + Akamatsu, K. et al (2004), JACS, Vol. 126 No. 35, pp

13 First fabrication process Ag + K + ion exchange Ag + (aq) + e - Ag (s) K + (aq) + e - K (s) 0.80 V V Ag + Ag + K + K + AgNO 3 solution 12

14 First fabrication process Methyoxy-(polyethylene glycol) (aka MPEG) dissolved in absolute ethanol and spray-coated onto substrate using an airbrush. Acts as electron donator to reduce the silver ions on the PI film to silver nanoparticles Dissolved at 60 o C with concentration of 100g per litre J. Hoyd-Gigg Ng, M. Desmulliez, K. Prior, D. Hand, DTIP Confer. Proc. (2008). 13

15 First fabrication process HeCd laser process at 325nm (12mW max. power) or diode laser of 375 nm (~6mW max. power) Speeds of up to 0.5 ms -1 have been used with both lasers. Patterning can also be easily achieved using flood exposure from a UV arc lamp through a photomask but maskless patterning is the goal 14

16 First fabrication process Substrate washed in dilute H 2 SO 4 to remove un-reduced silver ions (in areas not exposed to UV light source) Sample annealed at 300 o C to allow nanoparticles to coalesce / aggregate to form larger particles The larger particles are not yet conductive so electroless plating is necessary to form enough continuous metal tracks 15

17 First fabrication process 16

18 First fabrication process 17

19 First fabrication process Commercial electroless silver bath used for stability. ESM 100 from Polymer Kompositer, AB Sweden. Trade-off between larger silver agglomerations requiring longer annealing or exposure time, which degrades the polyimide substrate and easier initiation of electroless plating. 18

20 First fabrication process - Results Inductor coils of various linewidth/pitch, µm 19

21 3D laser writing 30 µm linewidth on contoured surfaces using liquid polyimide 20

22 First fabrication process - Results Photomask exposure J. Hoyd-Gidd Ng, M.P.Y. Desmulliez, K.A. Prior, D. Hand, IET Micro & Nano Letters, Vol.3, N.3, pp (2008) 21

23 Effect of varying anneal time 3 hour anneal Silver clusters ~35-55 nm diameter Same UV dose (690 Jcm -2 ) for all samples 5 & 10 hour anneals 5hr silver clusters ~80-100nm diameter Visible PI degradation after both times 22

24 Modification of polyimide (a) (b) (c) (d) (e) (f) J.H.-G. Ng, M.P.Y. Desmulliez, M. Lamponi, B.G. Moffat, Circuits World, Vol. 35, N.2, pp.3-17 (2009) 23

25 Substrate degradation Ng, J.; Watson, D., Desmulliez, M., Sigwarth, J.; Kay, R.; McCarthy, A.; Hand, D.; Prior, K.; Yu, W.; Liu, C.; Accepted for Nanotechnology, IEEE Transactions on, Doi: /TNANO

26 Conclusions of first process Optimal UV energy dose is approximately 690 Jcm -2. Optimal annealing time for silver growth is approximately 4 hours. However, this length of time causes degradation within the substrate. This degradation only occurs in ion-exchanged samples. Therefore the polymer-silver electrostatic bond has a negative effect on polymer stability at the molecular level. This degradation occurs under the silver, causing the silver to become embedded a few hundred nanometres into the polyimide. 25

27 Second process : chemical reduction Silver ions can be reduced using chemical processes at the cost of larger line widths. Chemical reduction is used here through a photomask for line patterning. LF55GN is a new photoresist that can be developed using a detergent spray or even just water Other resist developers attack the polyamic acid (PAA) on the substrate surface 26

28 Second process : chemical reduction D.E. Watson, J. H.-G. Ng, M.P.Y. Desmulliez, Proc. of the 18 th European Microelectronics and Packaging Conference 27

29 Results of second process Resistance higher than anticipated over 10mm path (1 Ohm). Attributed to low duration in electroless silver plating bath. 28

30 Results of second process Peel test removed plating but seed layer was still visible. Plated silver stuck on tape still conductive. Adjustments that improve adhesion are being investigated.

31 Outline Motivation for flexible substrates and rapid patterning techniques. Taxonomy of additive processes for metal track patterning. Two examples of additive processes of metal tracks patterning researched at Heriot-Watt University. Conclusions. 30

32 Conclusions Current L/S is around 50/50µm. Two techniques carried out at HWU required more research on adhesion, surface integrity and subsequent electroless plating. Additive patterning processes of metal track are credible techniques for metallization onto flexible substrates. 31