Laser-assisted Direct Write for aerospace applications

Abstract

Particulate silver inks are finding increasing use in the direct manufacture of electronic circuitry, for example in Direct Write (DW). Laser curing of these inks as opposed to traditional oven-curing methods is advantageous for reasons of speed and the protection of nearby heatsensitive components, and particularly for the construction of circuitry on conformal surfaces and 'on the fly' modification or production.To fully appreciate the benefits provided by using a laser-based process, it is important that the final-cured component has electrical and physical properties that are comparable to, if not better than, those that are produced using the conventional technique. Currently, in some single pass curing techniques, cavities are formed in the track due to rapid boiling off of solvents that leads to a higher resistivity and surface roughness than that of oven-cured tracks. While mass loss is similar, overall density is decreased through porosity of the tracks. By going from a single pass curing process to a multiple pass process and controlling the power regime, it is possible to improve the track quality by allowing the gradual release of solvent vapour from the ink and achieve lower resistivities than that of oven-cured samples and a surface roughness that is comparable. This incremental process improves settling of the silver particulates leading to a resistance of the cured inks that is lower than that achievable through oven curing. This creates the possibility of fabricating a surface-mounted or -embedded damage sensor without thermally affecting the substrate.The effect of substrate type thermal conductivity on the laser curing speed of silver inks is investigated. It was found that a noticeable factor in determining the resulting resistance of the conductive track was the substrate thermal conductivity. Both CO 2 and Er:YAG laser radiation was investigated. Although CO 2 lasers are in widespread use, the increasing demand for portability and ease of integration into existing DW systems favours fibre delivered laser radiation such as that from an Er:YAG fibre laser. This source was also investigated here to determine if fibre delivered processing could be achieved.

A predictive thermal dynamic model for parameter generation in the laser assisted direct write process

“…Due to its computer controlled nature, different designs can be easily made with just a change in programming and no requirement for hard tooling [1][2][3][4][5][6][7][8]. With no single dominant process, it is likely that several will emerge as the process of choice for any single component manufacturing process [10][11][12][13][14][15][16][17].…”

“…The laser assisted curing method is an application that involves the integration of knowledge in physical chemistry, mathematical modelling, process automation and laser optics. Laser induced heat conduction has been well studied both theoretically and experimentally for applications of metal machining and surface treatments [14,[212][213][214][215][216]. However there is still a lack of formulised investigation of composite inks.…”

Investigation of Inline Curing System Using Halogen Lamp on PET Substrate

“…Overheating must be avoided as it will physically deform and damage the cheap and thin substrate, thus ruining any conducted experimentation. Laser, on the other hand, if used to cure the conductive ink, will yield a faster result [4] but is more expensive than other curing techniques. Another drawback of this method is that it requires advanced equipment and proper skills and knowledge to operate [8].…”

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

“…Laser direct write can also be used in the production of flexible electronic circuitry such as that used in flexible displays. Using a laser wavelength at 532 nm can prevent thermal damage to the flexible substrate owing to the high transparency at 532 nm [4,5]. A typical polymer substrate -Polyethylene terephthalate (PET), for example, enables PCB manufacturing development towards to a new market place with advantages in weight and flexibility.…”