Abstract

Copper Wrap Plate, as specified in IPC 6012B Table 3-2, is a requirement developed to enhance reliability for PCBs designed with via structures that require planarization and surface capping. PCBs built without wrap plating are more prone to failures associated with separation between the interconnection of the barrel copper to the surface copper. The improvement in reliability is a function of the copper wrap thickness, which supports the difference in IPC requirements for Class II and Class III programs. The general rule is "the thicker the wrap plating the better the reliability." The increase in copper thickness, associated with wrap plating, however competes with the ability for PCB fabricators to manufacture products with high density and fine features. The general rule for manufacturing fine features is "the thinner the copper the better the manufacturability."

The technology developed by DDI Corporation, called FLAT-WRAP™, offers a copper wrap solution that does not require build-up of copper on the external surface of a filled plated hole. This allows the improvement in reliability without sacrificing the ability to manufacture designs with high density and/or fine features. This technology also facilitates, in process non-destructive copper thickness measurements and ensures consistency of copper wrap thickness across the entire board surface. In this technology, the external surface copper thickness of filled plated holes will control the copper wrap thickness. In PCB designs requiring multiple copper wraps, the benefits of this technology are even more evident.

This article examines the current process problems with copper wrap plate and discusses the benefits provided by the new technology with respect to manufacturing and reliability.

Introduction

Multilayer PCB production is a constantly evolving, increasingly complex interplay of, processing techniques, customer demands, design rules and product specifications. Many times new processes will be added to meet certain demands, but are not easily and fully integrated into the existing process web. There is always a search for better ways to improve and simplify manufacturing processes. IPC added Copper Wrap Plate requirement to IPC 6012B specification, requiring copper plating from the filled plated hole to continue around the knee of the hole and onto the surface. This requirement was introduced to improve reliability for failures due to separation between surface features/caps and the plated hole-wall. The increased surface copper thickness due to copper wrap plate posed additional challenges for manufacturers to manufacture and designers to design the PCBs. This article highlights the current issues for dealing with the copper wrap requirements specified in IPC 6012B and the benefits of the new technology called FLAT-WRAP™.