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Method for coplanarity inspection of package or substrate warpage for ball grid arrays, column arrays, and similar structures

  • US 5,465,152 A
  • Filed: 06/03/1994
  • Issued: 11/07/1995
  • Est. Priority Date: 06/03/1994
  • Status: Expired due to Term
First Claim
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1. A method for determining coplanarity of substrates for ball grid array, column grid array, and similar surface mount integrated circuit chips, using 3-D optical sensing means, comprising the steps of:

  • providing opaque fiducials as index pads where the heights of said index pads are correlated with signal pad heights in a neighborhood about said index pads;

    said index pads being opaque to incident radiation from said 3-D optical sensing means;

    reflecting by said index pads sufficient radiation allow height measurement by said 3-D optical sensing means;

    disposing said index pads in a prearranged pattern over a domain of array signal pads;

    restricting said index pads to a predetermined range of heights;

    measuring the heights of each of at least three said index pads at said index pad coordinate locations;

    suitably fitting a preselected surface shape to the index pad height and coordinate location data; and

    calculating the difference in height between each index pad and the preselected surface shape evaluated at the index pad location.

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