Multi-beam laser sensor for semiconductor lead measurements

A multi-beam sensor for determining the height of each element of a multiple element device of the type having each of its elements nominally disposed in a single horizontal plane, wherein the multiple element device is in relative motion so that each element has a leading edge and a trailing edge, the multi-beam sensor comprising:

• a leading edge detection system comprising:
• at least one leading edge light source;
• a means for focusing a pair of leading edge beams of light from the leading edge light source to intersect in the horizontal plane of the elements wherein the pair of leading edge beams is occluded by the leading edge of the element;
• and
• at least one leading edge detecting means for detecting leading edge shadows created by the occlusion of the pair of leading edge beams by the leading edge of the element;
• a trailing edge detection system comprising:
• at least one trailing edge light source;
• a means for focusing a pair of trailing edge beams of light from the trailing edge light source to intersect in the horizontal plane of the elements wherein the pair of trailing edge beams is occluded by the trailing edge of the element;
• and
• at least one trailing edge detecting means for detecting trailing edge shadows created by the occlusion of the pair of trailing edge beams by the trailing edge of the element;
• and
• logic means, connected to the leading edge detection system and connected to the trailing edge detection system, for determining the center height of the element above the horizontal plane, wherein the center height is the average of the leading edge height and the trailing edge height, the logic means comprising:
• means for calculating the height of the leading edge of the element based on data received from the leading edge detection means;
• and
• means for calculating the height of the trailing edge of the element based on data received from the trailing edge detection system.

A four beam sensor for determining the height of each element of a multiple element device of the type having each of its elements nominally disposed in a single horizontal plane, wherein the multiple element device is in motion relative to the four beam sensor, the four beam sensor comprising:

• first, second, third, and fourth light providing means;
• first focusing means for focusing light from the first light providing means into a first beam of light wherein a focal point of the first beam is at the intersection of the horizontal plane and a vertical reference plane and the first beam forms an angle beta of between 5 and 25 degrees with the vertical reference plane;
• second focusing means for focusing light from the second light providing means into a second beam of light wherein a focal point of the second beam is at the intersection of the horizontal plane and the vertical reference plane and the second light beam forms an angle with the vertical reference plane that is greater than the angle beta;
• third focusing means for focusing light from the third light providing means into a third beam of light wherein a focal point of the third beam is at the intersection of the horizontal plane and the vertical reference plane and the third beam forms an angle of negative beta with the vertical reference plane so that the third beam forms an angle of 2 beta with the first beam;
• fourth focusing means for focusing light from the fourth light providing means into a fourth beam wherein a focal point of the fourth beam is at the intersection of the horizontal plane and the vertical plane and the fourth beam forms an angle that is greater than two beta with the first beam;
• first detecting means, located in the path of the first and second beams, for detecting the shadow edges created by occlusion of the first beam by an element edge of the multiple element device and the shadow created by occlusion of the second beam by the element edge;
• second detecting means, located in the path of the third and fourth beams, for detecting the shadow created by unblocking of the third beam by an element edge of the multiple element device and the shadow created by unblocking of the fourth beam by the element edge;
• means for receiving data indicating the instantaneous lateral position of the multiple element device as each shadow edge created by the element edges of the multiple element device is detected by the first and second detecting means;
• and
• logic means, connected to the first and second detecting means and to the means for receiving data, for calculating the height of the element edge from the horizontal plane whereby the calculation of the height is based on the instantaneous lateral position of the multiple element device as each shadow edge is created by the element edges.

A method for determining the height, from a horizontal reference plane, of the lower surface of a lead on a multiple lead device and for determining whether the lead height is within an acceptable height deviation, the method comprising:

• defining a vertical reference plane;
• defining a horizontal reference plane;
• generating a first laser beam;
• focusing the first laser beam at the intersection of the horizontal and the vertical reference plane so that it forms an angle beta with the vertical reference plane which is between 5 degrees and 30 degrees;
• generating a second laser beam;
• focusing the second laser beam at the intersection of the horizontal and the vertical reference plane so that it forms an angle of beta plus alpha with the vertical reference plane where the angle alpha is between 7 degrees and 23 degrees;
• moving the multiple lead device in a horizontal direction so that each lead's lower surface passes through each of the two laser beams;
• detecting a first state change caused by occlusion of one of the two laser beam's by a lead edge;
• detecting a second state change caused by occlusion of the laser beam not involved in the first state change and caused by the lead edge;
• measuring the lateral distance the lead travels from the position in which the lead causes the first state change to the position in which the lead causes the second state change;
• calculating the height of the lead edge above or below the horizontal reference plane by multiplying the lateral distance traveled by cosine (beta) and cosine (beta+alpha), and dividing the total by sin (beta);
• determining an allowable height deviation;
• comparing the calculated lead edge height with the allowable height deviation;
• and
• creating an electrical rejection signal if lead edge height is greater than the allowable height deviation.

A method for determining the height of each element of a multiple element device of the type having each of its elements nominally disposed in a single horizontal plane, wherein the multiple element device is in relative motion and each element has a leading edge and a trailing edge, the method comprising:

• detecting the leading edge, comprising:
• generating a leading edge light;
• focusing a pair of leading edge beams of light from the leading edge light, in the horizontal plane of the elements wherein the pair of leading edge beams is occluded by the leading edge of the element;
• and
• ascertaining leading edge shadows created by the occlusion of the pair of leading edge beams by the leading edge of the element;
• detecting the trailing edge, comprising:
• generating a trailing edge light;
• focusing a pair of trailing edge beams of light from the trailing edge light, in the horizontal plane of the elements wherein the pair of trailing edge beams is occluded by the trailing edge of the element;
• and
• ascertaining trailing edge shadows created by the occlusion of the pair of trailing edge beams by the trailing edge of the element;
• and
• determining the center height of the element above the horizontal plane, with data received from detecting the leading edge and data received from detecting the trailing edge, wherein the center height is the average of the leading edge height and the trailing edge height, comprising:
• calculating the height of the leading edge of the element based on data received from detecting the leading edge;
• and
• calculating the height of the trailing edge of the element based on data received from detecting the trailing edge.