Study and Evaluation of Multilayer PCB Manufacturing Inaccuracies on Malfunctioning of Circui
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Date
2018-06
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Addis Ababa University
Abstract
The PCB is a mechanical base used for interconnection of electronic components. In PCB manufacturing industry, the quality and reliability of circuits is highly dependent upon the accuracy of the manufacturing processes. Because of the different factors affecting the processes to function imperfectly, manufacturing processes inaccuracies like photolithography inaccuracy, etching inaccuracy, drilling inaccuracies and inaccuracies in other processes may be encountered. These inaccuracies cause severe problems that may result in degradation of circuit performance and malfunctioning of circuits.
In this research the levels of effects of the manufacturing inaccuracies on the malfunctioning of PCB circuits is investigated and analyzed. The effects of each process inaccuracies on circuits as well as how the processes are related with the affecting parameters are addressed in this thesis.
A four-layer multilayer board is considered and the software selected to study the effects of manufacturing inaccuracies is OrCAD PCB designer. The major PCB manufacturing processes considered are Photolithography, Etching, and Drilling. Schematic development, PSpice simulation and layout design are made for selected circuits to study the effects of inaccuracies.
According to the results obtained, drum speed, resolution and ratio of track to track spacing are the affecting parameters in Photo plotting while depth of focus, dose and mask bias variations are the factors affecting photolithography.
In addition, inaccurate etching results in either larger or smaller width of traces, leaves unwanted conductive materials, creates unnecessary holes or open circuits and short circuits. In the case of drilling, when there is wrongly or inappropriately drilled, the top and bottom layers may not be connected and creates open circuit.
In the over etching case simulation, 64 % of the output voltage reduction occurred for a 69% increase in resistance. This simply considering only one simple scenario the effect will be even worsened when similar individual effects are added to it. For capacitive effects, the output becomes unstable and oscillating.
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Keywords
PCB, Inaccuracies, photolithography, etching, drilling, OrCAD