Via filling: Challenges for the plating process for conveyorised production

Copper filling of laser drilled blind micro vias (BMV's) is now the standard production method for high density interconnects. Copper filled BMV's are used as solder bump sites for IC packaging where the filling process enables the required interconnect density and provides the surface to ensure reliable solder attachment. For “smart phone” production use of multiple lamination and typically 10 layers of stacked copper BMV filling is now the preferred technology, this is also known as the “any layer” filling process. Advances in filling processes are required to maintain the development in circuit miniaturization together with the reduction in overall processing costs and to meet the demand for ever more filled BMV's on each plated layer. The required filling processes must provide void or inclusion free filling, a minimum of surface plated copper along with the capability to allow stacked filled structures. This paper describes the function and principles behind BMV filling processes together with methods for non destructive testing of the filled structures. Production processes for BMV filling in vertical and horizontal production equipment with both soluble and insoluble anodes are presented together with a discussion of the plating parameters currently used in volume production. A comparison in filling performance of DC plating with that achieved in reverse pulse plating is also made. Current production systems for BMV filling are usually conveyorized to meet the required production targets in terms of volume and uniformity. High relative electrolyte loading in such systems requires uniform processing parameters and tight control. Examples of fully automatic analysis and control systems for copper plating additives and inorganic components are shown.