Colour-Difference Measurement Method for Evaluation of Quality of Electrolessly Deposited Copper on Polymer after Laser-Induced Selective Activation

Abstract

In this work a novel colour-difference measurement method for the quality evaluation of copper deposited on a polymer is proposed. Laser-induced selective activation (LISA) was performed onto the surface of the polycarbonate/acrylonitrile butadiene styrene (PC/ABS) polymer by using nanosecond laser irradiation. The laser activated PC/ABS polymer was copper plated by using the electroless copper plating (ECP) procedure. The sheet resistance measured by using a four-point probe technique was found to decrease by the power law with the colour-difference of the sample images after LISA and ECP procedures. The percolation theory of the electrical conductivity of the insulator conductor mixture has been adopted in order to explain the experimental results. The new proposed method was used to determine an optimal set of the laser processing parameters for best plating conditions.Polymer-based electrical devices are used in different areas such as optical communications, biomedicine, and automotive industry 1,2 . Formation of the electrical circuits on polymers is important for these devices. There are many techniques called "selective metallization" to produce a circuit on the surface of polymers: direct chemical plating 3 , laser direct structuring (ablation and writing) 4,5 , laser direct imaging 6 and laser-induced selective activation (LISA) [7][8][9][10][11] .LISA was developed for selective metallization of polymers for three-dimensional moulded interconnecting devices. This method contains single step: laser structuring of the polymer surface. As a result of the laser structuring, sponge-like and nano-porous structures are created to improve the adhesion strength of the metal to the polymer. After LISA process the metal layer is deposited by the electroless copper plating (ECP) procedure. The ECP contains of three-steps: activation of the laser-structured surface with palladium colloidal activator; cleaning with distilled water; electroless deposition of copper layer on the activated sample. In the activation procedure, palladium atoms are trapped in a porous sponge like structures on the polymer surface. Cleaning with distilled water removes unwanted palladium from flat unstructured polymer and leaves it confined in the poriferous surface. The copper fills all the openings in the polymer and a porous, rough metal film is deposited during the final step of the ECP. Finally, after both, LISA and ECP procedures, the copper layer is deposited selectively only onto the laser structured areas while unstructured polymer is not coated with the metal deposition.The electrical and optical properties of the semi-transparent films were investigated in numerous works [12][13][14][15][16][17][18][19] . However, the analysis of the sheet resistance dependence on the optical transmittance can be applied only for films with the thicknesses smaller than the absorption depth. Such kind of measurements cannot be realized with a relatively thick metal layer on the porous opaque substrate.The characterization of the cross section of...

Glass Fiber Reinforced Polycarbonate Composites for Laser Direct Structuring and Electroless Copper Plating

“…The electrical resistance on the ablated surface by laser was higher than 10 6 Ω. While the value was lower than 0.5 Ω for the copper plating layer and in good agreement of metallized LDS polymers , indicating a good electrical conductivity.…”

“…The quality of metal plating layer is vital to use and it extremely depends on processing parameters. A colorimetric method proposed by Gedvilas et al based on digital image processing technique was proved to be effectively assessing the quantity and quality of metal deposition . According to percolation theory, sheet resistance of copper layers decayed by power law with color difference increasing.…”

Percolation effect of a Cu layer on a MWCNT/PP nanocomposite substrate after laser direct structuring and autocatalytic plating

“…The sample pictures at different amounts of Cu deposited on MWCNT/PP were taken by using an optical microscope and charge-coupled device camera with the experimental details given in ref. 10. The digital image processing procedure used for area fraction calculations of Cu layer on MWCNT/PP substrate is presented in Fig.…”

“…[1][2][3][4] Fabrication of the monolithic integrated electric circuits on plastics is necessary for those application areas. Several methods are usually applied to make an electric circuit on plastic surfaces: laser-direct-imaging, 5 laserinduced selective activation (LISA) [6][7][8][9][10] and laser-directstructuring (LDS). [11][12][13][14] The LDS method was invented for metal deposition selectively on plastic surfaces.…”

“…[31][32][33] Moreover, the percolation behavior of sheet resistance dependence on the color-difference between sample images aer LISA of precursor additive-free polymer and subsequent electroless Cu deposition procedures have been reported in our previous work. 10 However, there is not scientic work found in literature where percolation effect has been investigated for the Cu layer on nanocomposite material with precursor additives aer LDS and ACD treatment. The main idea presented in this paper is to investigate the percolation effect of a rough metal layer on the laser-patterned nanocomposite surface using digital image processing technique.…”