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Reliability of Micro-vias in Flex Based Materials James Keating, Robert Larmouth Teledyne Electronic Technologies 110 Lowell Road Hudson, NH 03051 Phone (603) 889-6191 FAX (603) 882-4457...

Space limitations are forcing electronic packages to have increasingly higher densities. Packaging options such as MCM-L are gaining in popularity as lower costs are required for consumer products. With these increases in circuit density come the need for smaller feature sizes on the substrate. One solution to the circuit density requirement is to reduce the diameter of the via and the associated pad at the design phase, but still maintain producibility at board fabrication. This paper will describe and compare two methods of producing micro-vias in laminate based materials. Data collected to date that compares the two methods will be presented to try to determine if there is a difference in the reliability of the laser versus plasma formed micro-via. An actual application for a tactical missile electronics module that incorporates micro-vias on flex based materials will be discussed along with how the micro-via approach helped accomplish the needed wiring density. Design rules for via diameter and pad diameter will be presented. Thermal cycling and thermal shock tests will be performed on a double-sided polyimide film based high density decal that represents wiring densities and techniques that will be employed in production. Test conditions and conclusions will be presented. INTRODUCTION The use of flexible circuitry has been steadily increasing in response to advances in the infrastructure and supplier chain. This type of circuitry, long used as a simple interconnect between electronic modules or rigid PC cards, is quickly becoming an industry unto itself. Many applications are being designed that require SMT on flex as well as Chip-on-flex (COF) and Flip Chip on Flex (FCOF). These types of electronic devices require increased density when compared to traditional pin in hole type components and rely heavily upon vias to create the electrical path to the inner layers. When compared to FR 4 epoxy resin laminates flex based materials offer factors such as improved electrical characteristics, the ability to more reliably create fine features, and they are amenable to a wider range of processing techniques. 1 Traditionally the size of a small diameter drilled via is 0.012" (0.30mm) diameter through an 0.020" (0.50mm) diameter pad. Using these types of circuit den...

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Reliability of Micro - Vias in Flex Based Materials pdffiles reliability of micro via in flex

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