Characterization and improvement of copper / glass adhesion

The development of glass substrates for use as an alternative to printed circuit boards (PCBs) attracts significant industrial attention, because of the potential for low cost but high performance interconnects and optical connection. Electroless plating is currently used to deposit conductive tracks on glass substrates and the quality of copper / glass adhesion is a key functional issue. Without adequate adhesive strength the copper plating will prematurely fail. Existing studies have covered the relationship between surface roughness and adhesion performance, but few of them have considered the detail of surface topography in any depth. This research is specifically considering the mechanical contribution of the glass surface texture to the copper / glass adhesive bond, and attempting to isolate new ISO 25178 areal surface texture parameters that can describe these surfaces. Excimer laser machining has been developed and used to create a range of micro pattern structured surfaces on CMG glass substrates. Excimer mask dimensions and laser operation parameters have been varied and optimized according to surface topography and adhesion performance of the samples. Non-contact surface measurement equipment (Zygo NewView 5000 coherence scanning interferometry) has been utilized to measure and parameterize (ISO 25178) the surface texture of the glass substrates before electroless copper metallization. Copper adhesion quality has been tested using quantitative scratch testing techniques, providing an identification of the critical load of failure for different plated substrates. This research is establishing the statistical quality of correlation between the critical load values and the associated areal parameters. In this thesis, the optimal laser processing parameter settings for CMG glass substrate machining and the topographic images of structured surfaces for achieving strong copper / glass plating adhesion are identified. The experimental relationships between critical load and areal surface parameters, as well as the discussions of a theoretical approach are presented. It is more significant to consider Sq, Sdq, Sdr, Sxp, Vv, Vmc and Vvc to describe glass substrate surface topography and the recommended data value ranges for each parameter have been identified to predict copper / plating adhesion performance

The assessment of areal surface texture parameters for characterizing the adhesive bond strength of copper plated micro-machined glass.

The micro-electronics industry is investigating glass as an alternative printed circuit board material and interposer. Electroless copper plating of glass is required for tracks and interconnects, but understanding of how the surface topography of the glass substrate affects the mechanics of the copper/glass bond quality is limited. Areal surface texture parameters provide the potential for characterizing key surface features associated with improving copper/glass bonding. Laser ablation techniques have been used to prepare glass surfaces with micro-scale structured features, and these features have been quantified using areal parameters. The copper/glass bond strength has been quantified using scratch testing techniques, with statistical analysis identifying strongly correlating areal parameters that may be used for predictive design of glass surfaces

The use of areal surface texture parameters to characterize the mechanical bond strength of copper on glass plating applications

This report describe research into the role that surface topography plays in influencing the mechanical bond strength of the electroless copper plating of novel glass substrates. The work considers bespoke laser machining of glass substrates, electroless plating chemistry, areal surface topography analysis using non-contact optical techniques, paramaterization of the surfaces using ISO 25178 areal parameters, and scratch testing of plated copper to measure the adhesive bond strength. By correlating bond strength to appropriate areal parameters, it is anticipated that better mechanical adhesive potential of machined glass surfaces can be achieved

Areal surface texture parameters for copper/glass plating adhesion characteristics

Glass as an alternative printed circuit board material and interposer has been investigated for use in the micro-electronics industry. Electroless copper plating is used to provide the conductive layer, but there is limited understanding of how the surface topography of the glass substrate affects the copper/glass bonding strength exhibited in the current literature. A laser ablation technique was used to prepare glass surfaces with micro-scale structured features in this study, and these features were characterized quantitatively using areal surface texture parameters. The copper/glass bonding adhesion strength was quantified using a scratch testing technique, and the relationships between the critical loads measured and the areal surface parameters, as well as discussion of the underlying mechanisms, are presented in this report. Statistical analysis was employed to identify the most relevant areal parameters that may be used for prediction of the copper/glass bonding strength and for design of adhesion promoting surface textures. The experimental results suggest that the most significant areal surface texture parameters to consider are Sq, Sdq, Sdr, Sxp, Vv, Vmc, and Vvc, and the recommended value range for each parameter for optimal plating adhesion performance is given

Improving copper plating adhesion on glass using laser machining techniques and areal surface texture parameters

Glass is a promising substitute substrate material being evaluated for electronic packaging technology. Improving the electroless copper plated layer adhesion of the glass is one of the most important considerations for development of the technology. An excimer laser (248 nm) was used for structured texturing of glass surfaces (to improve adhesion) by changing mask dimensions, laser operating parameters and overlapping pitch spacing, and therefore producing a range of micro-scale features. Electroless plated copper adhesion strength was assessed using quantitative scratch testing, demonstrating that micro-patterned structures can significantly improve copper/glass adhesion. New ISO 25178 Part 2 areal surface texture parameters were used to characterise the surface roughness of ablated glass surfaces, and correlated to the scratch testing results. Highly correlated parameters were identified that could be used as predictive surface design tools, directly linking surface topography to adhesion performance, without the need for destructive adhesion quantification via scratch testing