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Browse Prior Art Database

Chip-Flexure Measurement Device

IP.com Disclosure Number: IPCOM000043772D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Gorgas, W: AUTHOR [+3]

Abstract

When subjected to thermal cycling, handling, etc., mounted integrated circuit chips may undergo substantial distortion. A simple optical device is proposed for quantifying flexure or tilt of surface-mounted chips. Thermal coefficient of expansion mismatches, improper bonding and mishandling are examples of processes which stress chips on rigid or flexible substrates. Flexure of the chip is thus a diagnostic of excessive stress, damage and failure, and is measured by specular scattering angles (r, d) of reflected laser light when a localized laser beam is stepped across the back of the chip. Excessive variations in r or d across the nominally planar chip indicate a defective or flexed chip. The system provides a contour map of chip flatness. The measurement device is depicted schematically in the figure.

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Chip-Flexure Measurement Device

When subjected to thermal cycling, handling, etc., mounted integrated circuit chips may undergo substantial distortion. A simple optical device is proposed for quantifying flexure or tilt of surface-mounted chips. Thermal coefficient of expansion mismatches, improper bonding and mishandling are examples of processes which stress chips on rigid or flexible substrates. Flexure of the chip is thus a diagnostic of excessive stress, damage and failure, and is measured by specular scattering angles (r, d) of reflected laser light when a localized laser beam is stepped across the back of the chip. Excessive variations in r or d across the nominally planar chip indicate a defective or flexed chip. The system provides a contour map of chip flatness. The measurement device is depicted schematically in the figure. Dotted lines represent electrical paths. A low-power continuous wave laser and an inverted telescope provide a narrow probe beam. A mirror directs the probe beam to the sample at fixed angles r', d' relative to the sample support stage. The program-controlled x,y stage positions the chip under test and steps it relative to the incident beam. For each sample position (x,y) the reflected beam intercepts a resolution element (X,Y) on the spatially-selective optical detector (e.g., 2D photodiode array). X(x,y) and Y(x,y) are used to derive the scattering angles r(x,y) and d(x,y) which are related to the chip surface slope (first derivat...