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Alignment Beam Splitter Cube

IP.com Disclosure Number: IPCOM000050303D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Gaston, CA: AUTHOR

Abstract

This article concerns an improved optical beamsplitter used for visually aligning multiple objects, for example, a semiconductor chip and a substrate, during chip mounting. The improved beamsplitter features a modified construction and beam path that avoids erroneous alignment caused by defects which may arise in the beamsplitter.

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Alignment Beam Splitter Cube

This article concerns an improved optical beamsplitter used for visually aligning multiple objects, for example, a semiconductor chip and a substrate, during chip mounting. The improved beamsplitter features a modified construction and beam path that avoids erroneous alignment caused by defects which may arise in the beamsplitter.

It is common in the precision assembly of opaque mating surfaces, for example, chip placement on a substrate, to use a modified beamsplitter cube for visual alignment. Such a cube, when properly positioned between the two mating surfaces, can produce optical superposition of the images to show when they are correctly aligned for assembly.

Fig. 1 shows a conventional beamsplitter cube 1. Cube 1 is formed by combining two triangular prism sections, designated I and II, to form the cube body. Cube 1, as assembled, is provided with a reflective diagonal 2 within the cube and a mirror on its rear face 3, while the top 4, front 5 and bottom 6 faces are left transparent. In use, light beam 7 from object A enters cube 1 at face 6 and is reflected from diagonal 2 and through front face 5 to the observer. Light beam 8 from object B enters cube 1 at face 4 and is reflected from diagonal 2 to the mirror at rear face 3 where it is again reflected back through diagonal 2 and front face 5 to the observer. In this way, an observer can simultaneously view and align objects A and B for assembly.

If the two prisms which form the beamsplitter cube are not assembled precisely, i.e., if top face 4 and bottom face 6 are not parallel, a deviation is produced between the upper and lower lines of sight. Such an angular deviation makes lateral alignment sensitive to vertical positioning and can result in erroneous alignment.

The improved beamsplitter of this article avoids this problem by using reflective surfaces which are common to a single prism of the two-prism construction. An improved beamsplitter is shown in Fig. 2. As in the case of the conventional beamsplitter cube, the improved cu...