Effect of solder volume on joint shape with variable chip-to-board contact pad ratio
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Accepted Version
Date
2008
Authors
Jesudoss, Pio
Mathewson, Alan
Wright, William M. D.
O'Flynn, Brendan
Stam, Frank
Journal Title
Journal ISSN
Volume Title
Publisher
IEEE
Published Version
Abstract
The objective of this paper is to investigate the effect of the pad size ratio between the chip and
board end of a solder joint on the shape of that solder joint in combination with the solder volume available.
The shape of the solder joint is correlated to its reliability and thus of importance. For low density chip bond
pad applications Flip Chip (FC) manufacturing costs can be kept down by using larger size board
pads suitable for solder application. By using “Surface Evolver” software package the solder joint
shapes associated with different size/shape solder preforms and chip/board pad ratios are predicted.
In this case a so called Flip-Chip Over Hole (FCOH) assembly format has been used. Assembly trials
involved the deposition of lead-free 99.3Sn0.7Cu solder on the board side, followed by reflow, an
underfill process and back die encapsulation. During the assembly work pad off-sets occurred that
have been taken into account for the Surface Evolver solder joint shape prediction and accurately
matched the real assembly. Overall, good correlation was found between the simulated solder joint
shape and the actual fabricated solder joint shapes. Solder preforms were found to exhibit better
control over the solder volume. Reflow simulation of commercially available solder preform volumes
suggests that for a fixed stand-off height and chip-board pad ratio, the solder volume value and the
surface tension determines the shape of the joint.
Description
Keywords
Flip Chip Over Hole
Citation
Jesudoss, P., Mathewson, A., Wright, W., O'Flynn, B., Stam, F., 2008. Effect of solder volume on joint shape with variable chip-to-board contact pad ratio. In: IMAPS (International Microelectronics And Packaging Society)-CPMT(Components, Packaging and Manufacturing Technology) 32nd International Microelectronics and Packaging IMAPS-CPMT Poland Conference. Warszawa-Pułtusk, Poland 21-24 September 2008.
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