Geoff Dearden

A thermal investigation on conductive silver ink tracks cured on flexible substrates by repeating irradiations of Nd:YAG laser at the wavelength of 532 nm

The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing.This work presented in this paper is an investigation into the Nd:YAG laser curing process at the wavelength of 532 nm of particulate silver inks. A mathematical approximation of key physical properties has been developed based on the presented experimental research for use in a finite element model (FEM) simulation. 532 nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transparency of the wavelength through the substrate material. In this paper, liquid-phase particulate silver ink tracks deposited on flexible substrates were irradiated by laser along the track geometry. Repetition of the laser beam scanning was found to produce a smooth and fully cured sample and further reduced the track’s electrical resistivity.The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing.This work presented in this paper is an investigation into the Nd:YAG laser curing process at the wavelength of 532 nm of particulate silver inks. A mathematical approximation of key physical properties has been developed based on the presented experimental research for use in a finite element model (FEM) simulation. 532 nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transparency of the wavelength through the subst...

Laser peen forming for 2D shaping and micro adjustment

Laser peen forming has been carried out on 0.075mm thick steel samples, using relatively low power Nd:YAG lasers at 1064nm, 532nm and 355nm wavelengths. The process was found to produce a bend angle up to approximately 20 degrees, depending upon the amount of passes and laser parameters used. The results from these experiments have been compared to samples formed using continuous wave thermal forming. The results showed that laser peen forming could take place with a pulsed Nd:YAG laser, which uses less energy than a laser used for thermal forming, and that the laser peen formed samples do not have evidence of heat affected zones or changes to the bulk material, both seen with laser thermal forming. This indicates that the laser peen forming process is largely athermal or non-thermal, as there is very little heat input into the samples except for decolorisation of the surface due to the plasma generated in the process. A parameter window has been established for laser peen forming on 0.075mm thick steel using a 1064nm wavelength. The effect that the process has on the surface of the material is also being analysed using optical interferomety and scanning probe microscopy.Laser peen forming has been carried out on 0.075mm thick steel samples, using relatively low power Nd:YAG lasers at 1064nm, 532nm and 355nm wavelengths. The process was found to produce a bend angle up to approximately 20 degrees, depending upon the amount of passes and laser parameters used. The results from these experiments have been compared to samples formed using continuous wave thermal forming. The results showed that laser peen forming could take place with a pulsed Nd:YAG laser, which uses less energy than a laser used for thermal forming, and that the laser peen formed samples do not have evidence of heat affected zones or changes to the bulk material, both seen with laser thermal forming. This indicates that the laser peen forming process is largely athermal or non-thermal, as there is very little heat input into the samples except for decolorisation of the surface due to the plasma generated in the process. A parameter window has been established for laser peen forming on 0.075mm thick steel u...

Multiple NUV beam internal structuring of materials using a spatial light modulator

Liquid crystal Spatial Light Modulator (SLM) can suffer irreparable damage, when exposed at wavelengths shorter than 400 nm combined with high peak intensity, due to photodegradation of the liquid crystal or the polymer alignment layer. By placing a thin BBO nonlinear crystal immediately after an SLM addressed with Computer Generated Holograms (CGHs), the first order diffracted NIR components at 775 nm can be converted to parallel second harmonic NUV beams at 387 nm, avoiding the potential damage while simultaneously reducing the order of non-linear absorption for refractive index modification. This procedure requires attention to phase matching of multiple beams and opens up parallel processing at UV wavelengths. Multiple NUV femtosecond beam direct writing of volume Bragg gratings inside poly(methyl methacrylate) and fused silica is demonstrated. First order diffraction efficiency over 70% is observed. By changing CGH, grating parameters such as period and thickness can be easily adjusted. This technique provides good flexibility and shows great potentials in rapid fabrication of volume gratings. The limitations of this technique are also discussed.Liquid crystal Spatial Light Modulator (SLM) can suffer irreparable damage, when exposed at wavelengths shorter than 400 nm combined with high peak intensity, due to photodegradation of the liquid crystal or the polymer alignment layer. By placing a thin BBO nonlinear crystal immediately after an SLM addressed with Computer Generated Holograms (CGHs), the first order diffracted NIR components at 775 nm can be converted to parallel second harmonic NUV beams at 387 nm, avoiding the potential damage while simultaneously reducing the order of non-linear absorption for refractive index modification. This procedure requires attention to phase matching of multiple beams and opens up parallel processing at UV wavelengths. Multiple NUV femtosecond beam direct writing of volume Bragg gratings inside poly(methyl methacrylate) and fused silica is demonstrated. First order diffraction efficiency over 70% is observed. By changing CGH, grating parameters such as period and thickness can be easily adjusted. This techniqu...

Modelling of real temporally variant beam shapes in laser materials processing

The ability to incorporate real, temporally variant intensity distributions is key to improving the accuracy of Finite Element (FE) models of laser processes. The work presented in this paper uses Laser Forming as a process example. Laser forming (LF) offers the industrial promise of controlled shaping of metallic and non-metallic components for prototyping, correction of design shape or distortion and precision adjustment applications. In order to fulfill this promise in a manufacturing environment the process must have a high degree of controllability, which can be achieved through a better understanding of its underlying mechanisms. FE modeling can be used to gain this understanding.

Multiple beam ultrashort pulse laser microprocessing

A problem identified in the use of ultra short pulse lasers for the processing of materials has been that, to work close to the ablation threshold and hence avoid thermal damage, a large percentage of the available laser energy must be attenuated. The surface ablation of materials, using multiple diffracted beams generated by a Spatial Light Modulator (SLM), driven by Computer Generated Holograms (CGH) and synchronised with a scanning galvanometer system, has been shown here to result in flexible and high throughput parallel processing. By using multiple low energy beams, derived from a single higher energy beam, more efficient use of the available laser energy is made and process time is significantly reduced. The results demonstrate high precision microprocessing, showing the potential for ultra short pulse laser parallel processing in real industrial application. A review of the background of the use of SLMs in parallel processing is given, followed by examples of applications investigated.A problem identified in the use of ultra short pulse lasers for the processing of materials has been that, to work close to the ablation threshold and hence avoid thermal damage, a large percentage of the available laser energy must be attenuated. The surface ablation of materials, using multiple diffracted beams generated by a Spatial Light Modulator (SLM), driven by Computer Generated Holograms (CGH) and synchronised with a scanning galvanometer system, has been shown here to result in flexible and high throughput parallel processing. By using multiple low energy beams, derived from a single higher energy beam, more efficient use of the available laser energy is made and process time is significantly reduced. The results demonstrate high precision microprocessing, showing the potential for ultra short pulse laser parallel processing in real industrial application. A review of the background of the use of SLMs in parallel processing is given, followed by examples of applications investigated.