Method of Detecting Floated Lead of Electrical Component

1. Field of the Invention

This invention relates to a method of detecting a floated lead of an electrical component and, more particularly, to means for detecting a floated lead of an electrical component by radiating a laser light from a laser device toward the leads of the electrical component, calculating a virtual plane including the leads, and obtaining a height difference of the leads with respect to the virtual plane.

2. Description of the Prior Art

When a lead is floated in a case where an electrical component having a plurality of leads such as a QFP is placed on a substrate, the lead cannot be bonded to the electrode of the substrate. For this reason, heretofore, as shown in FIG. 5, there has been known means for radiating a laser light from a laser device 103 toward the leads 102 of an electrical component 101 sucked to a nozzle 100 and obtaining heights Z1, Z2,.. of the leads 102 from a reference surface S to detect the float of the lead 102.

There are as causes of the floating of the lead of an electrical component, in addition to bending, deforming of a lead, an inclination error .DELTA..theta.1 of axial center of a nozzle, an inclination error .DELTA..theta.2 of the lower surface of a nozzle for sucking an electrical component, an inclination error of the upper surface of a mold of an electrical component, a positional error of a XY table for moving a pick and place head in X-Y directions, etc. If there is such a mechanical error or a constant error, the electrical component 101 is inclined just .DELTA..theta. with respect to a horizontal plane L to cause an error .DELTA.Z therebetween. Therefore, there is a problem of erroneously judging the floating of the lead 102.

Accordingly, an object of this invention is to provide a method of accurately detecting a floated lead of an electrical component by eliminating the above-described error.

In order to achieve this and other objects according to the present invention, there is provided a method of detecting a floated lead of an electrical component comprising the steps of positioning the electrical component above a laser device on the way of feeding the electrical component to a substrate by sucking the electrical component to a nozzle of a pick and place head; radiating a laser light from the laser device toward the leads of the electrical component thereby to detect the heights of three points of the leads; and then calculating a virtual plane including the three points of the leads to obtain a height difference of the respective leads with respect to the virtual plane.

With the arrangement described above, the method obtains the virtual plane including the leads and obtains a height difference of the respective leads with respect to the virtual plane. Therefore, the above-described error can be eliminated to accurately detect the floated lead of the electrical component.

These and other objects and features of the present invention will become apparent from the following detailed description in conjunction with the attached drawings.

FIG. 1 is a side view of an arrangement for measuring a positional deviation of a lead in a predetermined direction according to the present invention;

FIG. 2 is a perspective view of the arrangement in FIG. 1;

FIG. 3 is a plan view of an electrical component placing apparatus for executing a method of detecting a floated lead of an electrical component according to an embodiment of the present invention;

FIG. 4 is a plan view of another embodiment of the invention; and

FIG. 5 is a side view of conventional means for detecting a floated lead of an electrical component.

An embodiment of the present invention will now be described with reference to the accompanying drawings.

FIG. 3 is a plan view of an electrical component placing apparatus for executing a method of detecting a floated lead of an electrical component according to the embodiment of the present invention. The apparatus has a tray 1 as a supplying unit for supplying an electrical component 2, and a substrate 3 positioned at clamping means 4. This apparatus picks and places the electrical component 2 of the tray 1 on a table 6 by a sub pick and place head 5, recognizes and roughly corrects the positional deviation of the electrical component 2 on the table 6, and then sucks to pick up the electrical component to a nozzle 8 of a pick and place head 7. Then, the apparatus feeds the electrical component 2 above a laser device 9, radiates a laser light toward the leads 2a of the electrical component 2 while moving the pick and place head 7 in X-Y directions, and detects the positional deviations of the leads 2a in X-Y-.theta. directions. Thereafter, the apparatus corrects the stroke of the pick and place head 7 in the X-Y directions, and/or rotates the nozzle 8 at .theta. with the axial center as a center thereby to correct the detected positional deviations in the X-Y-.theta. directions, and then pick and place the electrical component 2 on the substrate 3.

FIGS. 1 and 2 show the means for detecting the positional deviations of the lead 2a in the X-Y-.theta. directions and measuring the floating of the lead 2a (an error in a Z direction). The means has a mold 2b, and a number of leads 2a are extended radially from the mold 2b in four directions. The laser device 9 has photodetectors 11 and 12 at both sides of a light emitting unit 10 to raise measuring accuracy by averaging the measured values of both the photodetectors 11 and 12. The leads 2a are formed by punching a lead-frame or a film carrier.

The electrical component 2 is disposed above the laser device 9, which radiates a laser light to the leads 2a while horizontally moving the pick and place head 7 in the X-Y directions, and photodetects the reflected lights of the laser light from the leads 2a to the photodetectors 11 and 12 thereby to detect a height Zi from the reference surface S of the leads 2a.

Then, three leads 2a are suitably selected, and the height Z0 of a virtual plane K including the reflected points P1, P2 and P3 of the three leads 2a are calculated from the heights Z1, Z2 and Z3 of the reflected points P1, P2 and P3 of the three leads 2a. The height Z0 of the virtual plane K can be simply calculated from the following plane equation:

Then, the height difference .DELTA.Z between the height Zi of each lead 2a detected in advance as described above and the height Z0 of the virtual plane K is obtained by the following equation:

Thus, the floating of each lead 2 is detected.

Since the above-described method obtains the height Z0 of the virtual plane K including the three leads 2a and obtains the height difference .DELTA.Z of each lead 2a with respect to thee height Z0 of the virtual plane K as described above, it can accurately detect the floating of the lead 2a by eliminating the above-described error. Virtual plane determining means may be variously considered. For example, as shown in FIG. 4, average values P1m, P2m and P3m of the heights of a plurality of leads 2al to 2an projected from the three sides of a mold 2b are calculated, and a plane including these three average values P1m, P2m and P3m may be employed as a virtual plane. If a height difference .DELTA.Z more than an allowable value is detected at the lead 2a of the electrical component 2, the placing of the electrical component 2 on the substrate 3 is ceased.

As described above, the present invention provides the method of detecting a floated lead of an electrical component comprising the steps of positioning the electrical component above a laser device on the way of feeding the electrical component to a substrate by sucking the electrical component to a nozzle of a pick and place head; radiating a laser light from the laser device toward the leads of the electrical component thereby to detect the heights of three points of the leads; and then calculating a virtual plane including the three points of the leads to obtain a height difference of the respective leads with respect to the virtual plane. Therefore, the method of the invention can accurately obtain the floated lead of the electrical component.