Spring Contact Probes In Wafer Level Test: Fundamentals And Advanced Concepts
Authors: Jon Diller and Frank Zhou Company: Interconnect Devices, Inc. Date Published: 11/5/2013
IWLPC (Wafer-Level Packaging)
Abstract: The use of spring contact probes in WLCSP vertical probe cards has grown steadily through the past several years. Spring contact probes have several advantages over other vertical probe technologies, including simple in-situ repair, a wide compliance range, and low relative cost. However, despite the maturity of spring probe technology, its benefits are not yet widely understood in this market. This paper will provide its audience with a detailed understanding of spring contact probe structures, key features, and the methods used to characterize their performance. Spring contact probe structures will be discussed in detail from a fundamental perspective. The number of moving parts in various spring contact probe designs creates various electrical and mechanical efficiencies, and influences the construction of the interposer; each design has advantages and liabilities in terms of cost, AC and DC signal integrity, and mechanical aspects such as longevity and accuracy. The comparison of these structures will be specific to the vertical probe card application space, with its unique requirements and environmental aspects. This will lead to a discussion of spring contact probe benefits in comparison to other vertical probe technologies. Compliance will be a primary focus; the paper will include a survey of best known methods to exploit the unusual compliance-to-length ratio of this technology. The AC signal integrity benefits of spring contact probes will also be explored in detail. The tools used to characterize DC, AC, and mechanical performance characteristics of spring contact probe based interposers will be examined. The relationship of laboratory characterization to real-world performance will be explored, and the audience will learn how to translate claimed specifications into realistic outcomes on the test floor. In summary, this paper will explore and link spring contact probe structures, benefits, and characterization tools clearly and succinctly.