High precision component alignment sensor system

In a surface mount component placement machine having means for picking up a semiconductor component, a means for directly transporting the component to a work piece, a means for rotating the component and means for accurately placing the component on the work piece, the improvement comprising:

• a high precision high speed laser sensor comprising:
• a single laser light source;
• a collimating lens for directing the laser light past the component;
• a multi-element sensor array for collecting data points relating to the angular orientation and lateral position of the component;
• and
• processing means for determining the location of a plurality of data points which represent each edge of the shadow cast by the component on the sensor array, capturing only a plurality of data points which fall within or near the shadow of each edge of the component and analyzing the data from the sensor array relating only to a leading edge and trailing edge of the shadow cast by the component onto the sensor array to determine the angular orientation and lateral position of the component;
• and
• mounting means for mounting the sensor directly onto the means for transporting the component to the work piece.

A method for aligning a component carried by a surface mount component placement machine having a vacuum quill comprising:

• picking up the component with the vacuum quill;
• providing a stripe of collimated laser light;
• providing a photo element array in the path of the laser light;
• retracting the component into the stripe of collimated laser light so that it casts a shadow on the photo element array;
• rotating the component;
• detecting the leading edge and the trailing edge of the shadow cast upon the sensor array;
• capturing a plurality of data points which relate to each of the leading edge and the trailing edge of the shadow;
• calculating angular orientation based on the minimum shadow position using the captured leading edge and the trailing edge data;
• and
• comparing the lateral position of the leading edge and trailing edge of the shadow with the center of the quill to determine the lateral position of the component as carried by the quill.

A laser sensor comprising a laser light source and a sensor array for use in precisely placing a semiconductor component having various edges carried on a transport means, the transport means having control means connected to the transport means for causing the semiconductor component to be interposed between the laser light source and the sensor array and for incrementally rotating the semiconductor component to cause variation in the position of the shadow cast by at least one edge associated with the semiconductor component on the array as the semiconductor component is rotated, the sensor comprising:

• a monolithic multi-element sensor array;
• a single laser light source with a short coherence length directed toward the sensor array;
• collimating means interposed between the laser light source and the semiconductor component for providing a single, continuous, uninterrupted, collimated stripe of laser light;
• means for reading the voltages from each element of the sensor array caused by light striking each element of the multi-element sensor array;
• and
• means for determining the position of at least one edge associated with the semiconductor component as it is rotated under control of the control means by determining the location of a plurality of data points which represent at least one edge of the shadow cast by the component on the sensor array, capturing only a plurality of data points which fall within or near the shadow the one edge of the component and analyzing only the data representing the edge of the shadow cast by the component on the sensor array from the sensor array, said determining means comprising:
• means for generating a reference threshold voltage which is less than the voltage output from any element in the array upon which light falls and greater than the voltage output from any element falling fully within the shadow cast by the component on the array;
• means for comparing the voltages from each element of the multi-element sensor array with the reference threshold voltage after each incremental rotation;
• means for identifying the edge of the shadow when the voltage reading on any element equals the threshold voltage;
• means for determining after each incremental rotation whether the shadow is narrower by comparing the position of the edge of the shadow on the array as determined by the identifying means from successive readings of the voltages of each element as the component is rotated;
• means for capturing data which relates only to the edge of the shadow when the shadow is determined to be the narrowest shadow;
• and
• means for processing the captured data to precisely determine the location of the edge of the semiconductor component and for calculating the angular orientation and the lateral position of the semiconductor.

A method of orienting a semiconductor component carried on a transport means, the method comprising:

• providing a collimated stripe of laser light directed toward the component;
• providing a multi-element semiconductor array having a plurality of cell locations, the array being positioned on the side of the component opposite the laser light source so that the shadow of the component is cast upon the multi-element array;
• causing the component to be incrementally rotated;
• repetitively reading the voltages in multiple scans from each element of the sensor array and for each scan of the voltages;
• reading the voltages on each cell of the array;
• comparing the voltages to a threshold voltage;
• temporarily storing a plurality of voltage readings as data points which represent each edge of the shadow for purposes of determining each edge position of the component;
• and
• recording the cell locations where a transition occurs above and below the threshold voltage as the location of the leading edge and the trailing edge of the shadow;
• comparing the cell locations where each edge of the shadow was detected for each scan to determine the narrowest shadow width;
• capturing only data relating to the edge location when the shadow is the narrowest;
• and
• processing the captured data to determine the lateral position and angular orientation of the semiconductor component.

A method for determining the proper lateral and angular orientation of a component interposed between a laser light source and a multi-element photo detector array, each element comprising a pixel, comprising:

• providing a collimated stripe of laser light directed toward the component;
• establishing a reference voltage threshold which is less than the voltage ouput from any pixel in the array upon which light falls and greater than the voltage ouput from any pixel falling fully within the shadow;
• incrementally rotating the quill and the component about a vertical axis;
• reading voltages on each pixel of the array after each incremental rotation;
• comparing the voltages against the reference voltage threshold;
• storing the data voltage readings of a first edge pixel at a pixel count whose voltage first drops below the reference voltage threshold and of a second edge pixel at a higher pixel count whose voltage again rises above the reference voltage threshold;
• determining after each incremental rotation whether the first edge pixel is at a higher pixel count than the previously stored edge pixel thereby indicating that the shadow is still narrowing;
• capturing the data if the first edge pixel is at a lower pixel count than the immediately preceding stored first edge pixel which indicates that the shadow is the narrower;
• and
• processing the captured data when the shadow is narrowest to determine the lateral position and angular orientation of the component.