Method and apparatus for inspection of solder joints utilizing shape determination from shading

A method for inspecting a wall of a solder fillet, comprising the steps of:

• (a) storing an array of predetermined incremental solder surface height change values, each being a function of first and second predetermined reflected light intensity values resulting from illumination of a solder surface from first and second angles at predetermined incremental values of solder surface tilt and swing respectively;
• (b) optically scanning the solder fillet along a plurality of lines extending from a base of the wall to predetermined points on the wall while illuminating the fillet from the first angle, and sensing first reflected light intensity values at incremental points of said scan respectively;
• (c) optically scanning the solder fillet along said plurality of lines extending from the base of the wall to said predetermined points on the wall while illuminating the fillet from the second angle, and sensing second reflected light intensity values at incremental points of said scan respectively;
• (d) accessing the array to obtain incremental height change values corresponding to the sensed first and second reflected light intensity values at the incremental points of said scan respectively;
• (e) summing the accessed height change values along said plurality of lines to obtain the heights of the solder fillet at said predetermined points respectively;
• and
• (f) comparing said heights with a predetermined inspection criterion.

A method for determining the height of a predetermined point on a wall of an object having a substantially uniform value of albedo, comprising the steps of:

• (a) storing an array of predetermined incremental surface height change values, each being a function of first and second predetermined reflected light intensity values resulting from illumination of a surface having said substantially uniform value of albedo from first and second angles at predetermined incremental values of surface tilt and swing respectively;
• (b) optically scanning the wall from a base thereof to said predetermined point while illuminating the wall from the first angle, and sensing first reflected light intensity values at incremental points of said scan respectively;
• (c) optically scanning the wall from a base thereof to said predetermined point while illuminating the fillet from the second angle, and sensing second reflected light intensity values at the incremental points of said scan respectively;
• (d) accessing the array to obtain incremental height change values corresponding to the sensed first and second reflected light intensity values at the incremental points of said scan respectively;
• and
• (e) summing the accessed height change values to obtain the height of the wall at said predetermined point.

A method for determining the height of a predetermined point on a wall of an object having a substantially uniform value of albedo, comprising the steps of:

• (a) storing an array of predetermined incremental surface height change values, each being a function of predetermined reflected light intensity values resulting from illumination of a surface having said substantially uniform value of albedo from a predetermined angle at predetermined incremental values of surface tilt and swing respectively;
• (b) optically scanning the wall from a base thereof to said predetermined point while illuminating the wall from said predetermined angle, and sensing reflected light intensity values at incremental points of said scan respectively;
• (c) accessing the array to obtain incremental height change values corresponding to the sensed reflected light intensity values at the incremental points of said scan respectively;
• and
• (d) summing the accessed height change values to obtain the height of the wall at said predetermined point.

An apparatus for determining the height of a solder fillet at a predetermined point on a wall thereof, comprising:

• storage means for storing an array of predetermined incremental solder surface height change values, each being a function of first and second predetermined reflected light intensity values resulting from illumination of a solder surface from first and second angles at predetermined incremental values of solder surface tilt and swing respectively;
• scanning means for optically scanning the solder fillet from a base of the wall to said predetermined point while illuminating the fillet from the first angle, and sensing first reflected light intensity values at incremental points of said scan respectively;
• and optically scanning the fillet from the base of the wall to said predetermined point while illuminating the fillet from the second angle, and sensing second reflected light intensity values at the incremental points of said scan respectively;
• computing means for accessing the array stored in the storage means to obtain incremental height change values corresponding to the sensed first and second reflected light intensity values at the incremental points of said scan respectively;
• and summing the accessed height change values to obtain the height of the solder fillet at said predetermined point.

An apparatus for inspecting a wall of a solder fillet, comprising:

• storage means for storing an array of predetermined incremental solder surface height change values, each being a function of first and second predetermined reflected light intensity values resulting from illumination of a solder surface from first and second angles at predetermined incremental values of solder surface tilt and swing respectively;
• scanning means for optically scanning the solder fillet along a plurality of lines extending from a base of the wall to predetermined points on the wall while illuminating the fillet from the first angle, and sensing first reflected light intensity values at incremental points of said scan respectively;
• and optically scanning the fillet along said plurality of lines extending from the base of the wall to said predetermined points while illuminating the fillet from the second angle, and sensing second reflected light intensity values at the incremental points of said scan respectively;
• computing means for:
• accessing the array stored in the storage means to obtain incremental height change values corresponding to the sensed first and second reflected light intensity values at the incremental points of said scan respectively;
• summing the accessed height change values along said plurality of lines to obtain the height of the solder fillet at said predetermined points respectively;
• and
• comparing said heights with a predetermined inspection criterion.

A method for determining a height difference between two points on solder fillet, comprising the steps of:

• (a) optically scanning the fillet in a first scan between said two points while illuminating the fillet form a first angle;
• (b) sensing the reflected light intensity of the fillet at incremental points along said first scan;
• (c) optically scanning the fillet in a second scan between said two points along the same path as the first scan while illuminating the fillet from a second angle which lies in the same plane as said first angle;
• (d) sensing the reflected light intensity of the fillet at incremental points along said second scan;
• and
• (e) determining said height difference between said two points by computing said height difference as a predetermined function of said sensed reflected light intensities during the two scans.

A method for determining the height of a solder fillet at a predetermined point on a wall thereof, comprising the steps of:

• (a) storing an array of predetermined incremental solder surface height change values, each being a function of first and second predetermined reflected light intensity values resulting from illumination of a solder surface from first and second angles at predetermined incremental values of solder surface tilt and swing respectively;
• (b) optically scanning the solder fillet from the base of the wall to said predetermined point while illuminating the fillet from the first angle, and sensing first reflected light intensity values at incremental points of said scan respectively;
• (c) optically scanning the fillet from a base of the wall to said predetermined point while illuminating the fillet from the second angle, and sensing second reflected light intensity values at the incremental points of said scan respectively;
• (d) accessing the array to obtain incremental height change values corresponding to the sensed first and second reflected light intensity values at the incremental points of said scan respectively;
• and
• (e) summing the accessed height change values to obtain the height of the solder fillet at said predetermined point;
• steps (b) and (c) being performed simultaneously and including, in combination, providing a single optical scanning means capable of performing individual scans in response to light of first and second wavelengths respectively;
• and first and second light source means which emit light at the first and second wavelengths and are oriented at the first and second angles respectively relative to the scanning means.