New copper electrolyte for blind microvia filling with low surface copper operated with direct current

HDI-PCBs (High Density Interconnect - Printed Circuit Boards) are essential for the production of powerful electronic handheld devices like smartphones and tablet PCs. Complete filling of blind microvias, which are used for electrical interconnection of different HDI-PCB layers, with electroplated copper enables an increased miniaturization of HDI-PCBs, but for enhanced miniaturization the use of fine lines is mandatory. In order to avoid or at least to reduce process steps like chemical or mechanical copper thinning prior to fine line etching, modern electrolytes for blind microvia filling should plate only a thin copper layer on the PCB surface. This leads to a more economical and ecological production process. A new electrolyte labelled SLOTOCOUP SF 30 which allows complete filling of blind microvias in combination with a low surface copper thickness is presented. This new electrolyte is operated with direct current in VCP (Vertical Continuous Plating) lines equipped with insoluble anodes. Plating tests and pilot-productions in a 7,200 liter VCP line produced excellent and stable plating results. In the meantime the process is running successfully and steadily in HDI-PCB mass production. The performance of the electrolyte is demonstrated by microsection images and reliability data. Moreover operating conditions, analysis and maintenance of the electrolyte are discussed.