THERMALLY INDUCED OUT OF PLANE DEFORMATION ANALYSIS FOR A FLIP CHIP ON FLEX 35MM TBGAAuthor: Jennifer Muncy et al.
Company: Georgia Institute of Tech.
Date Published: 9/21/2003 Conference: SMTA International
There are several reasons for PWB or substrate warpage: the inherent CTE mismatches of the substrate building blocks, the transient temperature difference in the laminated substrate materials, and the rigidity of the substrate. Warpage from all of the above causes could affect flip chip attachment yield for first level interconnects. Warpage could cause misalignment between the die and the substrate and/or prevent the solder balls from making contact with the substrate flip chip pads during reflow, therefore the deflection of the substrate at reflow temperatures should be well understood for proper reflow process characterization.
This out of plane deformation experienced in the reflow soldering process was investigated experimentally and studied via moiré techniques. The output from the moiré analysis gave real time flatness measurements of the substrates and aided in the development of a robust reflow process that resulted in yields of 98% or greater for a wide range of fluxes.
Key words: thermal warpage, shadow moiré, phase stepping, flip chip, ball grid array (BGA), and flex substrate.
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