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Surface Energy and Wettability Study of Flip Chip Packaging Materials
Keywords: Flip chip materials, wettability, surface engery
Most recently, we have done many wettability analyses for various materials in flip chip packages, including, underfills, substrates, fluxes, and lead free solders. Some of these analyses contributed in solving some critical problems in packaging development. We will highlight some of these results in this paper. The dynamic contact angle system is used to provide information on wetting, adhesion, and surface cleanliness via contact angle measurements and surface energy characterization. The measurements are used both for materials or process characterization as well as for failure analysis. In this paper, we will discuss some of the applications of a video contact angle system for contact angle and surface energy measurements of flip chip packages. The interfacial properties between the underfill and die and substrate are important to the integrity of the package. The consistency of substrate surface is critical for quality of the packages. The contamination of substrate surface can increase the contact angle and cause dewetting problem in chip attach and underfill process. The effect of cleanliness of substrate on the contact angle was investigated. The cleaned surface had much smaller contact angle than unclean surface. The difference in surface energy has a great impact on the underfill processing. Three probing liquids, DI water, methylene iodide, and glycerol were used in contact angle measurements and surface energy calculations for different substrates. The different surface energy calculation methods are reviewed. The advantage and limitation of each surface energy methods are discussed in details. Also, the contact angles of fluxes and underfills on substrates are also measured. The correlation between the surface energy and flux and underfill contact angle are also studied. Contact angle measurements were also used to analyze the impact of flux residue on the wetting of substrates. We will discuss how the contact angle and surface energy analysis helped in identifying and solving these problems. Our results showed that contact angle and surface energy measurements can provide useful information about interfacial tension and is a good tool for quality control and product development where interfacial properties are important.
Jinlin Wang, Sr. Engineer
Intel Corporation
Chandler, AZ

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