The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Automation and Systems Technology for public examination and debate in Auditorium AS1 at Helsinki University of Technology (Espoo, Finland) on the 17th of November, 2006, at 12 noon.
Dissertation in PDF format (ISBN 951-22-8441-3) [1702 KB]
Dissertation is also available in print (ISBN 951-22-8440-5)
Electroless nickel plating is a part of electroless nickel immersion gold (ENIG)-surface finish used in printed circuit board (PCB) manufacturing. In the ENIG-surface finish, the electroless nickel alloy prevents the oxidation of a circuitry by working as a diffusion barrier between the coppered circuitry and protective gold alloy and protecting the circuitry from mechanical tearing.
It is well-known that the thickness and phosphorous content of the electroless nickel alloy have a dramatic effect on the PCB's characteristics. Unfortunately, these parameters cannot be directly measured during the plating process which makes it impossible to control the parameters in traditional way.
In this thesis a new model for electroless nickel plating process is developed using electrochemical reaction mechanism and mixed potential theory. The model inputs are the standard online measurements of PCB plating line. From these the model produces accurate realtime estimates inter alia from alloy thickness, phosphorous content, by-product concentrations and current densities of partial reactions. The developed model has been tested against independent data gathered from three active and several passive experiments conducted in an industrial PCB manufacturing line. In all the experiments, the model shows good agreement with the data and correct response to the changes in plating conditions. The behavior of the model is in a good agreement with the literature and former research results.
It the thesis, the model is applied in model-based monitoring of an industrial plating process and it is shown to be capable of estimating online the unobservable product and electrical process parameters from standard measurements of PCB-industry.
Based on the model also a new sophisticated control algorithm is developed. The algorithm calculates the optimal nickel ion concentration and pH trajectories by which the desired alloy thickness and phosphorous content are reached. These trajectories are tracked by PI-controlled pumping of ammonia and nickel sulphate. The performance of the control algorithm is tested by simulation and it is shown to be effective.
Keywords: electroless nickel, printed circuit board manufacturing, modelling, estimation, process control
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© 2006 Helsinki University of Technology