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24 The PCB Magazine • May 2014 Abstract This article describes the different tech- niques of via filling and their characteristics. It points out the advantages of reverse pulse plat- ing and how the technology was modified to ap- proach new market requirements such as thick- er core substrates and laser drilling of through holes. The current capability of the system for inclusion-free filling and the areas where devel- opment is ongoing is demonstrated. Introduction Laser drilling of blind microvias (BMVs) and subsequent copper filling has become the stan- dard manufacturing technique for high density interconnects. In order to reach the required interconnect density and to provide the nec- essary surface for reliable solder attachment in IC packaging, copper-filled BMVs are used. For smartphone production, the use of multiple lamination and typically 10 layers of stacked copper BMV filling is now the preferred tech- nology. This is also known as the "any layer" filling process. To maintain the development in circuit miniaturisation together with the reduc- tion in overall processing costs as expected by Moore's Law and to meet the demand for ever more filled BMVs on each plated layer, advances in filling processes are required. Via Filling Process Copper plating and filling can be described as shown in Figure 1. Capture pad is the connection area of a sur- face feature to the inner layer beneath. Recess describes the remaining non-copper filled area on top of a copper filled feature (trench, mi- crovia, through-hole) in relation to the copper plated on the board surface. Inclusions are non- copper filled voids within PCB features. The filling of blind microvias without ad- ditives (normal deposition) will usually lead to the formation of a void (Figure 2, a). Copper is by Henning Hübner, Ramona S. Mertens, and Dirk Rüß atotecH Germany Copper Filling of Blind Microvias and Through-Holes Using Reverse-Pulse Plating F e a t u r e

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