Precision optical sensor packaging

Abstract

Conventional packaging of optical sensors is of little assistance in determining the location and attitude of the focal place of the sensor 10, since package tolerances lack the requisite precision. Each sensor 10 must be separately focused to its optical assembly 40. Such focusing is expensive, as is the package itself. This invention instead mounts the sensor 10 directly onto one face 28 of a transparent plate 18. Radiation is focused through the plate 18 and onto the sensor 10. Precision alignment targets 12, 22 are formed separately on the sensor 10 (providing a known location of the active image area 14 with respect to the target 12) and on the plate 18 (providing a known location of the edges 24 of the plate 18 with respect to the target 22). The targets 12, 22 are aligned, and contact pads 16, 30 on the sensor 10 and on the plate 18 are joined by electronically conductive bumps 36 of known thickness. The plate 18 itself is of known thickness. The location and attitude of the edges 24 of the plate 18, and of the opposite side 46 of the plate 18, may readily be determined, yet these locations and attitudes are all that is required to determine the location and attitude of the active image area 14, and thus to place the active image area 14 precisely in the focal plane of the optics 40. Moreover, microlenses 52 may be formed in the plate 18, one for each sensor cell 48 in the active image area 14, thereby greatly enhancing the light-gathering capacity of the sensor 10.