Journal of SMT Article


Author: Lavanya Gopalakrishnan
Company: Bay Networks
Date Published: 10/1/1999   Volume: 12-4

Abstract: The need for high density interconnect and improved electrical performance for OEMs has led to the development and availability of fine pitch Ball Grid Array (BGA) and Chip Scale Packages (CSPs) from packaging houses. Routing, aspect ratio and capture pad dimensions limit the use of these packages on conventional Printed Circuit Boards (PCBs).

Microvia technology with redistribution layers offers an alternative solution for high density packaging needs. However, the materials and process technologies used in the construction of microvias are not very mature and cost effective yet. Therefore, it is important for OEMs to understand the ability of their supply base to provide this technology. The primary objective of this research was to compare two different microvia fabrication methodologies and three types of redistribution layers that are currently available within our supply base. The impact of drill to pad tolerance for the conventional dog bone technology was also studied. Test vehicles were fabricated through laser ablated and photo-defined microvia technologies using FR-4, Surface Laminar Circuitry (SLC ®), and Resin Coated Copper (RCC®) as the redistribution layers. Dog bone routing strategy was used, wherever possible, as a standard for comparison. These test vehicles were assembled and reworked with a variety of 0.5, 0.8 and 1.0 mm pitch area array packages. They were then subjected to both thermal cycling and random vibration. Exhaustive cross-section analysis was performed to compare the structure and the reliability of the microvias formed in all the scenarios.

Key Words: Microvias, Routing, High Density Interconnect, Aspect Ratio

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