Research On The Reverse Additive Process Of Embedded Substrate

A new board level high density package and interconnection technology called embedded substrate reverse additive process was studied in this thesis. Electronic components were embedded into the substrate. The procedure of this process was as follows: electronic components were placed on the precise location of the substrate, followed by the encapsulation of electronic components with epoxy resin, after that, laser drilling was used to drill vias on the lead, finally, vias were filled and circuit pattern was formed. The advantage of embedded substrate reverse additive process is that products will be higher density package and interconnection, in addition, there is no need of reflow process, thus, high temperature process is avoided, and it's good for electronic components and substrate.The laser drilling process, vias filling process and circuit pattern manufacture process were studied in this thesis. Firstly, different process parameters of these processes were studied and those process parameters were optimized according to the experiment results, in addition, influencing factors of quality to these processes were also studied. Secondly, a model of multiplex waveform generator was made by embedded substrate reverse additive process. Finally, the thermal problem of the process was studied via the finite element software of electronic thermal design.According to the experiment result of laser drilling, the larger power or the smaller scanning speed, the worse shape of via and the more serious enlargement of via, while the smaller power or the larger scanning speed, the better shape of via and the fewer enlargement of via, but the resin above the lead or conductor can not be ablated. According to the experiment result of via filling, the smaller viscosity of the silver paste, the larger shrinkage of the vias, while the larger viscosity of the silver paste, the smaller shrinkage of the vias, but it will be resulted in more voids. In addition, step by step curing process of the silver paste should be taken to avoid the generation of cracks and voids. The experiment result shows that the larger or the smaller printing speed, scraping angle and space will result in more serious hackle of the wires. In order to get lower resistivity conductor, the curing temperature should be higher and the curing time should be more. It's interesting to find that there was no void in the conductor unless there was no gas void in the substrate.The procedure of the embedded substrate reverse additive process was determined by the layout design. The vias were drilled by laser drilling, and silver paste were used to fill the vias and print the wires, meanwhile, the coating of resin was used to fulfill the encapsulation of electronic components and the insulator layers of the substrate, at last, a high density package model was made.Finally, the finite element software was used to study the thermal problem of the embedded substrate reverse additive process. The influencing factors of thermal dissipation was studied, such as the chip layout, plastic encapsulation thickness and material selection, the numbers of substrate layers and material selection, ambient temperature and forced convection, the result was that the high power chip should be layout on the edge of the substrate and should be out of the heat-affected zone respectively in order to thermal dissipation, in addition, forced convection could be taken to strengthen the thermal dissipation.