Electronics Assembly Knowledge, Vision & Wisdom
Via Filling: Challenges in the Plating Process
Via Filling: Challenges in the Plating Process
This paper describes the function and principles behind BMV filling processes together with methods for non destructive testing of the filled structures.
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Authored By:
Mike Palazzola
Nina Dambrowsky and Stephen Kenny
Atotech Deutschland GmbH, Germany

Summary
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. The impact of specific processing parameters on volume production systems is discussed and in particular the use of fully automatic process control and the advantages of such systems in achieving uniform and reliable product quality.

Conclusions
Copper BMV filling is a critical enabling process for the production of HDI panels and IC packages. The number of BMV's found on a typical substrate is increasing and the dimensions are decreasing which is pushing the limits for the production process and at the same time there is the ever present demand for cost down. Filling is required with a minimum of surface plated copper to allow etching of fine line structures in HDI applications in panel plate mode and to meet the demands for the smallest structures in pattern plating for IC packages.

Treatment of homogenous base materials as well as glass reinforced materials both with and without copper foil is required. Production is now being made in a wide range of equipment, vertical hoist and conveyorized systems as well as horizontal conveyorized systems. Integration of metallization together with electrolytic copper plating in a wet to wet horizontal plating system has gained market acceptance for HDI production particularly for hand held devices. Such conveyorized systems offer the high volume production capability together with reduced panel to panel variation enabling increased yields and reduced processing costs.


Initially Published in the IPC Proceedings

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