Numerical modelling of electrodeposition process for printed circuit boards manufacturing
Printed circuit boards (PCBs) are used extensively in electronic products to connect assembled components within a system. The so-called vertical interconnect access (via) is a vertical hole or cavity in the PCB filled with metal to facilitate conductivity. The current trend, particularly for high technology products (e.g., 3D packaging), is to manufacture PCBs with high aspect ratio (AR) vias. Typically, the size of such a via is at the micrometer scale (this is why they are termed micro-vias).\ud \ud The most widely used technique for manufacturing micro-vias is electrodeposition of metal (e.g., copper), where the PCB is immersed into a plating cell filled with an electrolyte solution. Using standard conditions, electrodeposition usually does not produce micro-vias with the required quality. This is due to a lack of copper ion transport into the via. This has lead to studies of various ways of enhancing the ion transport. This thesis documents the results from a modelling study into the electrodeposition processes for fabricating high aspect ratio micro-vias. This includes basic electrodeposition and techniques that enhance ion transport such as forced convection (using a pump) and acoustic streaming (using transducers).\ud \ud In this work, a novel numerical method for explicitly tracking the interface between the deposited metal and the electrolyte is implemented and validated under the conditions of basic electrodeposition using experimental data. Results from a parametric study have established a set of design rules for micro-vias fabrication.\ud \ud When ion transport is enhanced by forced convection (e.g., pumping) in the plating cell, we apply a multi-scale modelling methodology that provides interaction between models at the macro level (the plating cell) and the micro level (the interior of a via). Numerical simulations can then be used to verify how ion transport into the micro-via is improved. These results can then be used to identify process conditions for the plating cell which will result in the required flow behaviour at the micro-via. \ud \ud Megasonic agitation can also be used to enhance electrolyte convection in the plating cell. This is achieved by placing megasonic transducers into the plating cell. This leads to several phenomena, one of which is known as the acoustic streaming. Models have been developed for predicting megasonic agitation both at the macro and micro-scales, and a number of designs have been investigated for both open and blind micro-vias.