X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-06-14
2003-02-18
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S058000
Reexamination Certificate
active
06522719
ABSTRACT:
DETECTING BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for advantageously measuring heights of bumps, such as connecting terminals provided on a semiconductor package, such as BGA (ball grid array) package, or flip-chip connection bumps by which a semiconductor chip is mounted on a substrate.
2. Description of the Related Art
A surface-mount type semiconductor device, such as a BGA substrate, is commonly provided on a surface of the substrate with semi-spherical bumps formed as external connecting terminals. These bumps can be formed by adhering solder balls to lands provided on the surface of the substrate. However, in the production of such a semiconductor device, when the dimension in the radial direction of the bumps is small and when the bumps are densely arranged, the bumps are generally formed as follows. That is to say, a solder paste is supplied onto the lands by a printing method to reflow the solder paste so as to form the bumps on the substrate. In this case, however, if the amount of solder paste to be supplied onto the lands fluctuates, the height or size of the bumps will not uniform.
Therefore, in a semiconductor device in which bumps are formed on a surface of the substrate as external connecting terminals, the height of the bumps must be measured by a suitable measuring device after the bumps are formed on the substrate. In a measuring device known in the prior art, an optical method is generally used to detect the height of the bumps.
FIG. 6
schematically shows a method for optically detecting the height of the bumps
12
formed on a substrate
10
. The height of the bumps
12
is measured by a suitable measuring device after the bumps are formed on the substrate. One of the methods for optically detecting the height of the bumps is a method in which a surface of protective film
14
, such as solder resist film, covering the surface of the substrate
10
is defined as a reference surface and a distance from this reference surface to the top of the bumps
12
is then optically detected. Otherwise, also known is a method in which the shape of the top of bumps is flattened by a coining process and then the flattened top portion of the bump is optically detected to measure the height of bumps.
However, in the prior art method for optically detecting the height of the bumps, the optical reflection rate is significantly different case by case and greatly depends on a gloss of the bumps and, therefore, the accuracy of the measured results may fluctuate due to a fluctuation of the state of the bumps. In the case that the height of bumps are measured on the basis of a surface of the protective film
14
, as the reference surface, the measuring accuracy is lowered since the height of bumps from the referenced surface fluctuates because the thickness of the solder resist as the protective film fluctuates. In addition, if there is any warp on the surface, the optical focus is deviated and therefore an accurate measurements cannot be expected.
In addition, since the number of terminals has been gradually increased in recent semiconductor devices having fine connecting terminals, a high accuracy in the measuring results of the height of bumps has been more and more required. As mentioned above, the deviations of the height of bumps are caused by the fact that the amount of solder paste which should be supplied to the individual lands fluctuates or the amount of flux contained in the solder paste fluctuates. In the case of bumps having a height of several hundred &mgr;m, a deviation in the amount of solder paste is not a significant problem. However, if the bumps have a lower height, such as the heights of bumps being several tens of &mgr;m, the height and size of the bumps are greatly affected by even small deviations in the amount of solder paste.
Also, in the case of the size of bumps being small, if a surface which might easily deviate, such as the surface of the protective film of the solder resist or the like, is used as the reference surface, the accuracy will be reduced and, also, even a small warp in the substrate causes reduced accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and an apparatus for accurately measuring the height of bumps formed on a semiconductor package or substrate.
Another object of the present invention is to provide a method and an apparatus for measuring the height of bumps in which the above-mentioned drawbacks in the prior art can be overcome.
According to the present invention, there is provided a method for measuring a height of a bump formed on a work of substrate, said method comprising: irradiating X-rays having a predetermined wavelength and incident intensity toward a first work of substrate which is the same as the above-mentioned work of substrate, but no bump is formed thereon, and detecting a first X-ray transmitted intensity at a position on which the bump is to be formed; irradiating X-rays having the same wavelength and incident intensity toward a material constituting the bumps and detecting a linear absorption coefficient of the X-rays; memorizing the first X-ray transmitted intensity and the linear absorption coefficient as known data; and irradiating X-rays having the same wavelength and the same incident intensity toward a second work of substrate which is the same as the above-mentioned work of substrate, but a bump is formed thereon, and detecting a second X-ray transmitted intensity at a position on which the bump is formed; and determining the height of the bump from the second X-ray transmitted intensity on the basis of the known data.
According to another aspect of the present invention, there is provided a method for measuring heights of first and second bumps formed on first and second surfaces, respectively, of a work of substrate in which materials of the first and second bumps are different from each other, a planar arrangement of the first bumps is the same as that of the second bumps, said method comprising: irradiating at least two kinds of X-rays having different wavelengths toward the materials constituting the first and second bumps, respectively, and detecting first and second linear absorption coefficients of the X-ray; memorizing the first and second linear absorption coefficients of the X-rays as known data; and irradiating the two kinds of X-ray toward the first and second works respectively, and detecting the first and second X-ray transmitted intensities at a position on which the first and second bumps are formed; and determining the heights of the first and second bumps from the first and second X-ray transmitted intensities on the basis of the known data.
According to still another aspect of the present invention, there is provided an apparatus for detecting a height of bumps, said apparatus comprising: a stage on which a work of substrate having a plurality of bumps formed thereon is disposed; a X-ray generating unit for generating X-rays incident to the work; and a detecting unit for detecting an intensity of X-rays transmitted through the work at a position where the bump is located.
The detecting unit may comprise a CCD camera for detecting the intensity of X-rays transmitted through the work, and an analyzing unit for analyzing an image data output from the CCD camera to detect the intensity of X-rays transmitted through the bump.
Otherwise, the detecting unit may comprise an image intensifier for detecting the intensity of X-rays transmitted through the work, and an analyzing unit for analyzing an image data output from the image intensifier to detect the intensity of X-rays transmitted through the bump.
Alternatively, the detecting unit may comprise a photomultiplier tube for detecting the intensity of X-ray transmitted through the work, and an analyzing unit for analyzing an image data output from the photomultiplier tube to detect the intensity of X-rays transmitted through the bump.
REFERENCES:
patent: 4607380 (1986-08-01), Oliver
Higashi Mitsutoshi
Murayama Kei
Church Craig E.
Paul & Paul
Shinko Electric Industries Co. Ltd.
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