Hi Ioan,
While we have never tried star-shaped pads, we tried rectangular pads--and
found a small but significant increase in reliability, everything else being
nominally equal (oval may be better). We simply got less ball-shaped but more
column-shaped solder joints which give less of a stress-concentration near
the SJ interfaces. I would not dismiss star-shaped pads out of hand for
reliability reasons; the resulting SJ may actually have less of a stress
concentration than ball-shaped SJs due to the effect of the surface tension
of molten solder.

Werner Engelmaier

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