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Technique for Measuring C4 Height

IP.com Disclosure Number: IPCOM000035951D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 146K

Publishing Venue

IBM

Related People

Hsiao, R: AUTHOR [+3]

Abstract

In a controlled collapse chip connection (C4) process, joining is achieved by reflowing the solder bumps (C4 joints) on a chip placed on tinned or untinned Cu pads on a substrate. The height of the C4 joints has an important impact on the thermal fatigue life of C4 joints because it is inversely proportional to the thermal strain during a thermal cycle. However, once a chip is joined to a substrate, it is difficult to measure the height of the C4s accurately and conveniently. This disclosure describes a new technique for measuring the height of C4s joined to ceramic cards.

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Technique for Measuring C4 Height

In a controlled collapse chip connection (C4) process, joining is achieved by reflowing the solder bumps (C4 joints) on a chip placed on tinned or untinned Cu pads on a substrate. The height of the C4 joints has an important impact on the thermal fatigue life of C4 joints because it is inversely proportional to the thermal strain during a thermal cycle. However, once a chip is joined to a substrate, it is difficult to measure the height of the C4s accurately and conveniently. This disclosure describes a new technique for measuring the height of C4s joined to ceramic cards.

The technique uses an Alpha-step profilometer obtained from Tencor Instruments, which has the capability to measure extremely thin film. The technique is both accurate and convenient. The vertical resolution of the profilometer is in the order of a few hundred angstroms, and the results of the measurement can be displayed on a screen or printed out. Each measurement can be done in less than 30 seconds. The measurement is illustrated in Fig. 1. A chip is joined to a ceramic card, and a second chip is placed upside down as a reference. An example of the measurement is shown in Fig. 2. The small dip in the figure near the interface is due to the gap between the two chips. The distance, a, as marked in Fig. 1, measured by running the probe of the profilimeter through the interface between the two chips, is then the height of the C4 joints. By repeating the same experiment at different spots of the chip, the tilt of the chip could also be determined.

This technique was used to measure the...