Apparatus and method for locating a plurality of placement positions on a carrier object

#This invention relates to an optical apparatus particularly, but not exclusively, for locating a plurality of placement positions on a carrier object, such as a lead frame on which semiconductor dies may be bonded. The invention also relates to a method of locating a plurality of placement positions on a carrier object, such as a lead frame.

#Panning and zooming functions are usually provided in a conventional imaging system in order to capture a desired region of interest. Panning of the imaging system may involve moving the imaging system on an XY-plane in order to capture different parts of the desired region of interest. On the other hand, zooming of the imaging system may involve adjusting the internal mechanical assembly of the imaging system to vary a distance between the imaging system and the region of interest and/or the overall focal length of the imaging system, to thereby enlarge an image of the region of interest.

#Invariably, the panning and zooming functions of the conventional imaging system require physical movement of either the whole or a part of the imaging system, or an object being inspected. However, the time required to move the whole of the imaging system also includes time for stabilising the imaging system or object at a resting positing, which may require tens of milliseconds, perhaps more. This might undesirably affect the overall throughput capacity among high-speed applications. Further, adjustment of the internal mechanical assembly of the imaging system may cause a shift of the optical centre of the imaging system, such that an allowable threshold—especially among high-accuracy applications—may be exceeded. In addition, the movement of the imaging system may also render the precise control of the imaging system's zooming capability hard to achieve among applications that require machine portability.

#Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

#FIG. 1 shows an optical apparatus according to a preferred embodiment of the invention arranged in relation to a semiconductor die carrier for imaging respective rows of placement positions thereon;

#FIGS. 2a to 2c show three modes of a zooming function of the optical apparatus of FIG. 1;

#FIG. 1 shows an optical apparatus 100 arranged with respect to a target object, which is shown as a semiconductor die carrier in the form of a lead frame 101 comprising a plurality of placement positions 101a, each for receiving a semiconductor die (not shown). In particular, the placement positions 101a of the lead frame 101 are arranged in an array defining rows and columns in an ordered fashion.

#Specifically, the optical apparatus 100 comprises: i) an imaging device 102; ii) a light box 104 attached to the imaging device 102; iii) a positioning device (shown as a Y-arm 106) to which the imaging device 102 and the light box 104 are connected; and iv) a processor 108 for processing the images taken by the imaging device 102 and for controlling the imaging device 102, the light box 104, and the Y-arm 106.

#The imaging device 102 and the light box 104 both define a common longitudinal axis 105, which extends perpendicularly with respect to an XY-plane on which the lead frame 101 is located. The imaging device 102 and the light box 104 are actuated by the Y-arm 106 to capture different regions of interest at the top of the lead frame 101. Moreover, the imaging device 102 comprises a plurality of imaging sensors 102a—in particular four imaging sensors 102a as shown in the embodiment illustrated in FIG. 1—to capture images of respective rows of placement positions 101a on the lead frame 101. More specifically, the imaging sensors 102a are aligned on the imaging device 102 such that the imaging sensors 102a defines a combined field of view that includes all of a selected row of the placement positions 101a. When the light box 104 is activated, light is directed towards the respective regions of interest to increase their brightness before the imaging sensors 102a are activated to capture the images. Preferably, each of the imaging sensors 102a has a resolution of at least 4.9 megapixels. This means that the imaging sensors 102a are capable of capturing images with an exemplary resolution of at least 2560 pixels by 1920 pixels (i.e. 2560×1920≈4.9 megapixels). Nevertheless, it should be appreciated that other imaging sensors having different resolutions (e.g. 1.9 megapixels or 7.2 megapixels) may also be used for the optical apparatus 100.