Abstract:
A semiconductor chip mounting circuit board includes a substrate, a wiring circuit formed on a substrate, a conducting pad electrically connected to an electrode of a semiconductor chip which is to be mounted on the substrate. An insulating resist layer is formed on the substrate to cover the wiring circuit and the resist layer has an opening to expose therein the conducting pad. A conducting bump is formed on the conducting pad exposed in the opening. A resist layer has a measuring opening which exposes a reference surface. A height of the conducting bump can be measured by an optical means using the measuring opening.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit board for mounting a semiconductor chip (hereinafter referred to as a circuit board), wherein conductor bumps to be electrically connected to electrodes of the semiconductor carried on a substrate of the circuit board are formed on conductor pads formed on a surface of the substrate of the circuit board, and a method for inspecting the same. 
     2. Description of the Related Art 
     As examples of such a circuit board as described above, there are a first circuit board shown in FIGS. 14 to  16  and  17  to  19  and a second circuit board shown in FIGS. 20 to  22 . 
     In the first circuit board, a circuit pattern  20  is formed on a surface of a substrate  10  thereof. A conductor pad  30  of a disc shape or other is formed on the circuit pattern  20 . The substrate  10  is made of insulating material such as resin or ceramic. The circuit pattern  20  and the conductor pad  30  are formed by etching a copper foil adhered to the surface of the substrate  10  or by etching a metal skin applied to the surface of an insulating resin layer by a build-up system on the substrate  10 . 
     A resist layer  40  comprised of insulating resin or the like is broadly formed on the surface of the substrate  10  for the purpose of preventing solder from sticking to the surface of the substrate  10 . 
     The first circuit board shown in FIGS. 14 to  16  has an opening  50  in the resist layer  40 , in which are consecutively exposed the conductor pad  30 , the circuit pattern  20  adjacent thereto and a surface of a portion of the substrate  10  therearound. 
     The first circuit board shown in FIGS. 17 to  19  has an opening  50  in the resist layer  40 , in which is exposed a central portion of the conductor pad  30 . 
     A conductor bump  60  is formed on the conductor pad  30  exposed in the opening  50 , which is of a sermispherical shape and constituted by conductive resin plated with solder or Au or mixed with conductive filler. 
     On the other hand, a metallized conductor pad  30  of a disc shape is provided on the surface of the substrate  10  made of ceramic or the like in the second circuit board. The conductor pad  30  is connected to the upper end of a column-like metallized conductor via  22  pierced through the substrate  10  in the thickness direction. The conductor via  22  constitutes a circuit pattern. 
     A resist layer  40  formed of insulating resin or the like is broadly formed on the surface of the substrate  10  for the purpose of preventing solder from sticking thereto. A circular opening  50  is formed in the resist layer  40  so that a central portion of the conductor pad  30  is exposed therein. 
     A conductor bump  60  is formed on the conductor pad  30  exposed in the opening  50  and is of a semispherical shape and is constituted by conductive resin plated with solder or Au or mixed with conductive filler. 
     In the prior art, when the first circuit board and the second circuit board are inspected, as shown in FIG. 16,  19  or  22 , a height hl from the surface of the resist layer  40  to a top of the conductor bump  60  is measured by means of an optical detector using a laser beam or a visible ray (hereinafter referred merely to a “photometer”) or a CCD (which is an abridgement of Charge Coupled Device) camera. Then, based on this measured value, a height h 2  from the surface of the substrate  10  to the top of the conductor bump  60  or a height h 3  from the upper surface of the conductor pad  30  to the top of conductor bump  60  are estimated. Next, based on this estimated value, a variation of heights of the conductor bumps is determined. Finally, based on this variation, it is determined whether or not the above-mentioned first and second circuit boards are acceptable. 
     The determination of whether or not the first and second circuit boards are acceptable is important because, if a large variation exists in height of the respective conductor bump  60  formed on the conductor pad  30  exposed in each of a plurality of openings  50  formed in the resist layer  40  in a matrix manner as shown in FIGS. 23 and 24, there might be a risk in that when a plurality of conductor bumps  90  formed on electrodes arranged in correspondence to the conductor pads  30  on one side of a semiconductor chip  80  in a matrix manner are pressed onto the plurality of conductor bumps  60  at a predetermined pressure so that both the conductor bumps  60 ,  90  are at once welded or pressbonded together, all of the conductor bumps  60  and  90  may not be electrically connected to each other in a reliable manner. 
     According to the above-mentioned determination in the prior art wherein the height h 1  is first measured, then the heights h 2  and h 3  are estimated thereby, and finally the variation of the height of the conductor bump  60  is calculated from the estimated values, it is impossible to correctly obtain the actual variation of the height of the conductor bump  60 . 
     This reason therefor is as follows. 
     There are two methods for forming the resist layer  40 ; one method wherein a resist liquid is coated broadly on the surface of the substrate  10 , which is then dried at a high temperature, and another method wherein a dry film of resist formed in a sheet form is adhered onto the surface of the substrate  10 , which is then dried at a high temperature. 
     The surface of the resist layer  40  formed broadly on the surface of the substrate  10  by these methods is not evenly flat but tends to undulate up and down, causing a variation in height everywhere on the surface of the resist layer  40 . 
     Therefore, it impossible to use the surface of the resist layer  40  formed on the surface of the substrate  10  in the above-mentioned manner as a reference surface for the correct estimation of the height h 2  or h 3 . 
     To solve such a problem, two methods are proposed; a first one wherein the height h 2  is directly measured by an optical detector or a CCD camera while using, as a reference surface, the surface of the substrate  10  in the vicinity of the conductor bump  50  exposed in the opening  50 , and a second one wherein the height h 3  is directly measured by an optical detector or a CCD camera. 
     According to the first or second method, it is believed that the variation f a height of the conductor bump  60  formed on the substrate  10  is correctly determined. 
     The first and second methods, however, could not be applied to the above-mentioned first or second circuit board of the prior art. 
     The reason why the height h 2  from the surface of the substrate  10  to the top of the conductor bump  60  could not be measured by the first method is that a gap between the conductor bump  60  and the inner wall of the opening  50  is too narrow as shown in FIGS. 15 and 16, and therefore a width of the surface area of the substrate  10  exposed in the gap is also too small. When one wishes to directly measure the height h 2  from the surface of the substrate  10  in the vicinity of the bump  60  exposed in the opening  50  to the top of the conductor bump  60  by the first method while using the optical detector, it is necessary to emit a laser beam or a visible ray from the optical detector disposed above the resist layer  40  onto the surface of the substrate  10  and reflect or diffuse the same to be directed to the optical detector. Such a reflected or diffused ray, however, is difficult to make incident upon the optical detector due to the interference with the conductor bump  60  or the resist layer  40 . on the other hand, if a CCD camera is used to directly measure the height from the surface of the substrate  10  in the vicinity of the bump  60  exposed in the opening  50  to the top of the conductor bump  60  by the first method, it is also difficult to focus the CCD camera on the surface of the substrate  10  of a narrow width. 
     To enable the height h 2  to be directly measured by the first method while using an optical detector, a CCD camera or the like, it is suggested to provide a large opening  50  in the resist layer  40  so that the surface of the substrate  10  is broadly exposed in the vicinity of the conductor bump  60  within the opening  50 . 
     In such a case, however, there is a wide space between the conductor pad  30  exposed in the opening  50  and the inner side of the neighboring resist layer  40 , whereby it is impossible to properly form a generally semispherical conductor bump  60  having a predetermined height on the conductor pad  30  in the opening  50  while effectively using the neighboring resist layer  40 . Accordingly, the formation of large opening  50  in the resist layer  40  as described above could not be adopted. 
     The reason why the height h 3  could not be measured by the second method is that the laser beam or a visible ray cannot pass through the conductor bump  60  to reach the upper surface of the conductor pad  30  beneath the former. Also, the laser beam or the visible ray reflected or diffused on the conductor pad  30  cannot pass through the conductor bump  60  to reach the optical detector or the CCD camera disposed above the resist layer  40 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a circuit board for mounting a semiconductor chip (hereinafter referred to as a circuit board) wherein the variation of heights of conductor bumps formed on a substrate for the circuit board can be directly, easily and reliably measured by an optical detector or a CCD camera. 
     Another object of the present invention is to provide a circuit board for mounting a semiconductor chip which can solve the problems in the prior art mentioned above. 
     A further object of the present invention is to provide a method for inspecting or measuring the circuit board, particularly the heights of conductor bumps of such a circuit board. 
     To achieve the above object, according to the present invention, a first circuit board is provided, wherein conductor pads to be electrically connected to electrodes of a semiconductor chip mounted to the substrate are formed on a circuit pattern provided on a surface of a substrate, and a resist layer made of insulating resin or the like is broadly formed on the surface of the substrate on which the circuit pattern and the conductor pads are provided, and wherein openings are formed in the resist layer so that the conductor pads are exposed therein, respectively, and the conductor bump is formed on the conductor pad exposed in the opening, characterized in that measurement holes are provided in the resist layer, in each of which is exposed a reference surface having a predetermined size or more necessary for measuring a height of the conductor bump by using an optical detector or a CCD camera. 
     Also, a second circuit board of the present invention is provided, wherein conductor pads to be electrically connected to electrodes of a semiconductor chip mounted to a substrate are formed on a surface of the substrate and of conductor pad is connected to an upper end of a conductor-via formed vertically through the substrate, and a resist layer made of insulating resin or the like is broadly formed on the surface of the substrate on which the conductor pads are provided, and wherein openings are formed in the resist layer so that the conductor pads are exposed therein, respectively, and the conductor bump is formed on the conductor pad exposed in the opening, characterized in that measurement holes are provided in the resist layer, in each of which is exposed a reference surface having a predetermined size or more necessary for measuring a height of the conductor bump by using an optical detector or a CCD camera. 
     In the first or second circuit board, the measurement hole is broadly opened in the resist layer so that the reference surface having a predetermined size or more is exposed in the measurement hole. 
     Accordingly, it is possible to direct a laser beam or a visible ray emitted from the optical detector disposed above the resist layer to the substrate through the broad measurement hole without interference from the resist layer. The laser beam or visible ray is projected onto the reference surface having the predetermined size or more exposed in the measurement hole and is reflected or diffused thereon. The reflected or diffused ray is incident upon the optical detector disposed above the resist layer through the broadly opened measurement hole. 
     Together therewith, the laser beam or visible ray emitted from an optical detector disposed above the resist layer is incident upon a top of the conductor bump in the opening and reflects or diffuses thereon. Then, the reflected or diffused ray is incident upon the optical detector disposed above the resist layer. 
     It is possible to directly measure the height from the reference surface to the top of the conductor bump by means of the optical detector while using the reflected or diffused ray reflected or diffused on the reference surface and incident upon the optical detector and that reflected or diffused on the top of the conductor bump and incident upon the optical detector. Based on the measured value, it is possible to correctly determine the variation of the height of the conductor bump formed on the substrate. 
     Alternatively, it is possible to easily and correctly focus a CCD camera, disposed above the resist layer on the reference surface having a predetermined size or more exposed in the measurement hole formed in the resist layer, without interference from the resist layer. Then, a distance from the CCD camera to the reference surface is measured by the CCD camera. 
     Together therewith, it is possible to focus a CCD camera on the top of the conductor bump in the opening and measure a distance from the CCD camera to the top of the conductor bump by the CCD camera. 
     Based on the difference between the distances from these CCD cameras, the height from the reference surface to the top of the conductor bump can be directly measured. Then, based on the measured value, it is possible to correctly determine the variation of the height of the conductor bump formed on the substrate. 
     In the first circuit board of the present invention, the reference surface is preferably defined by the substrate surface, the upper surface of the circuit pattern or the upper surface of the reference pattern provided on the substrate surface. 
     In the second circuit board of the present invention, the reference surface is preferably defined by the substrate surface or the upper surface of the reference pattern formed on the substrate surface. 
     In the first or second circuit board, while defining a reference surface on the surface of the circuit pattern, the upper surface of the circuit pattern or the upper surface of the reference pattern, it is possible to directly measure the height h 2  from the surface of the substrate to the top of the conductor bump, or to directly measure the height h 4  from the upper surface of the circuit pattern to the top of the conductor bump, or to directly measure the height from the upper surface of the reference pattern to the top of the conductor bump. Based on the results of the measurements, the variation of the height of the conductor bump formed on the substrate is correctly determined. 
     When the circuit pattern defining the reference surface on its upper surface is formed to have the same thickness as the conductor pad, it is possible to correctly surmise that the height h 3  from the upper surface of the conductor pad to the top of the conductor bump is the above-mentioned height h 4 . Based on this estimated value, the variation of the height of the conductor bump formed on the substrate can be correctly determined. 
     When the circuit pattern defining the reference surface on its upper surface has a thickness different from that of the conductor pad, the height h 3  from the upper surface of the conductor pad to the top of the conductor bump can be correctly determined from the above-mentioned h 4  while taking the difference in thickness between the circuit pattern and the conductor pad into account. Based on this estimated value, it is possible to correctly determine the variation of the height of the height of the conductor bump formed on the substrate. 
     In the first or second circuit board according to the present invention, the measurement hole may be formed separately from the opening in the resist layer. 
     The measurement hole may be preferably formed in the resist layer in continuous with the opening. 
     According to the circuit board wherein the measurement hole is formed separately from the opening in the resist layer, it is possible to prevent part of the inner wall of the opening from being bored by the measurement hole. When the conductor bump is formed on the conductor pad exposed in the opening, it is possible to prevent the conductor bump from bulging to the bored inner wall of the opening, and to obtain a generally semispherical shape of the conductor bump. 
     According to the circuit board wherein the measurement hole is formed continuous with the opening in the resist layer, it is possible to provide a measurement hole formed in an implement for coating a resist resin for forming the resist layer over the surface of the substrate, continuous with an opening provided in the implement. Thereby the implement for coating the resist resin can be simplified. 
     According to the present invention, there is provided a method for measuring a height of the conducting bump comprising: the following steps of: 
     (1) irradiating a laser or visible beam from a position above the resist layer through said measuring opening toward the reference surface and receiving the laser or visible beam reflected or dispersed at the reference surface through the measuring opening, 
     (2) irradiating a laser or visible beam from the position above the resist layer through the opening toward a top of the conducting bump and receiving the laser or visible beam reflected or dispersed at said conducting bump through the opening; and 
     (3) comparing these reflected or dispersed beams to determine the height of the conducting bump. 
     In this connection, the order of these steps (1), (2) and (3) may either be step (1), step (2) and step (3), or step (2), step (1) and step (3). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to  6  are partially enlarged plan views of various aspects of a first circuit board of the present invention, respectively; 
     FIGS. 7 to  10  are partially enlarged plan views of various aspects of a second circuit board of the present invenion, respectively; 
     FIGS. 11 and 12 are partially enlarged plan views of a first circuit board of the present invention, respectively; 
     FIG. 13 is a partially enlarged plan view of a second circuit board of the present invention; 
     FIGS. 14 and 15 are a partially enlarged plan view and a sectional view of a first circuit board, respectively; 
     FIG. 16 is an enlarged front sectional view of the first circuit board in the vicinity of a conductor bump; 
     FIGS. 17 and 18 are a partially enlarged plan view and a sectional view of a first circuit board, respectively; 
     FIG. 19 is an enlarged front sectional view of another first circuit board in the vicinity of a conductor bump; 
     FIGS. 20 and 21 are a partially enlarged plan view and a sectional view of a second circuit board, respectively; 
     FIG. 22 is an enlarged front sectional view of another second circuit board in the vicinity of a conductor bump; and 
     FIGS. 23 and 24 are illustrations for explaining a semiconductor chip on a circuit board. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described in more detail with reference to the preferred embodiments illustrated in the attached drawings. 
     FIGS. 1,  2 ,  3  and  4  are partially enlarged plan views of preferred embodiments of a first circuit board according to the present invention, respectively. 
     A square-shaped measurement hole  100  is provided in a resist layer  40  in each of the first circuit boards shown in FIGS. 1 and 3 and the vicinity of an opening  50  but at a distance therefrom. A surface of a substrate  1 O on which a circuit pattern  20  is formed is exposed within the measurement hole  100 . 
     A circular-shaped measurement hole  102  is provided in a resist layer  40  in each of the first circuit boards shown in FIGS. 2 and 4, in the vicinity of an opening  50  at a distance therefrom. A surface of a substrate  10  on which a circuit pattern  20  is not formed is exposed within the measurement hole  102 . 
     The measurement hole  100  or  102  has a predetermined open size or more so that the surface of the substrate  10  or the upper surface of the circuit pattern  20  defining a reference surface of a predetermined size or more is exposed within the measurement hole  100  or  102 . Accordingly, a laser beam or a visible ray emitted from the above-mentioned optical detector (not shown) disposed above the resist layer  40  can be directed to the substrate  10  via the measurement hole  100  or  102 , and reflected or diffused on the surface of the substrate  10  or the upper surface of the circuit pattern  20  exposed in the measurement hole  100  or  102 . The reflected or diffused ray is incident upon the optical detector through the measurement hole  100  or  102  without interference from the resist layer  40  around the measurement hole  100  or  102 , Alternatively, the CCD camera disposed above the resist layer  40  can be easily and correctly focussed on the surface of the substrate  100  or the upper surface of the circuit pattern  20  of the predetermined size or more exposed in the measurement hole  100  or  102  without interference from the resist layer  40  around the measurement hole  100  or  102 . 
     Each of the first circuit boards shown in FIGS. 1,  2 ,  3  and  4  has the same structure, other than above, as that of the first circuit board described with reference to FIGS. 14 to  16  or  17  to  19 , whereby it is possible to project the reflected or diffused ray upon the optical detector disposed above the resist layer  40 . 
     By using the reflected or diffused ray reflected or diffused on the surface of the substrate  10  and incident upon the optical detector and the reflected or diffused ray reflected or diffused on the top of the conductor bump  60  and incident upon the optical detector, the height h 2  can be directly measured by the optical detector. Then, based on the measured value, the variation of the height of the conductor bump  60  can be correctly determined. 
     Alternatively, it is possible to easily and properly focus the CCD camera disposed above the resist layer  40  on the surface with a predetermined size or more of the substrate  10  exposed in the measurement hole  100  or  102 , without interference from the resist layer  40  and the distance from the CCD camera to the surface of the substrate  10  can be measured by the CCD camera. 
     Together therewith, it is possible to focus a CCD camera disposed above the resist layer  40  on the top of the conductor bump  60  in the opening  50  and the distance from the CCD camera to the top of the conductor bump  60  is measurable by the CCD camera. 
     Then, based on the difference between these distances from the CCD camera, the height h 2  is directly measurable. Thereafter, the height variation of the conductor bumps  60  can be correctly determined from the measured values. 
     It is possible to measure the height h 4  from the upper surface of the circuit pattern  20  defining the reference surface to the top of the conductor bump  60  measured by the optical detector while using the reflected or diffused ray reflected or diffused on the upper surface of the circuit pattern  20 , which then is incident upon the optical detector, and the reflected or diffused ray reflected or diffused on the top of the conductor bump  60 , which is then incident upon the optical detector. 
     Also, it is possible to measure the distance from a CCD camera to the upper surface of the circuit pattern  20  by the CCD camera. 
     Based on the difference between distances from these CCD cameras, the height h 4  from the upper surface of the circuit pattern  20  defining the reference surface to the top of the conductor bump  60  is directly measurable. 
     If the circuit pattern  20  is formed to have the same thickness as the conductor pad  30 , it is apparent that the height h 3  from the upper surface of the conductor pad  30  to the top of the conductor bump  60  is correctly the same as the above-mentioned height h 4 . Based on this estimated value, it is possible to correctly determine the variation of the height of the top of the conductor bump  60  formed on the substrate  10 . 
     If the circuit pattern  20  is formed to have a different thickness from the conductor pad  30 , it is possible to correctly estimate the height h 3  from the upper surface of the conductor pad  30  to the top of the conductor bump  60  while taking the difference in thickness between the circuit pattern  20  and the conductor pad  30  into account. Based on this estimated value, it is possible to correctly determine the variation of the height of the conductor bump  60  formed on the substrate  10 . 
     FIGS. 5 and 6 are partially enlarged plan views, respectively, of other preferable embodiments of a first circuit board of the present invention. 
     In the first circuit board shown in FIG. 5, an elongate measurement hole  104  extending outward from the opening  50  is formed in the resist layer  40 . 
     In the first circuit board shown in FIG. 6, an elongate measurement hole  106 , of a strip form, extending between two adjacent openings  50  is formed in the resist layer  40 . 
     Each of the measurement holes  104  and  106  has a predetermined size or more whereby a surface of the substrate  10  defining a reference surface of a predetermined size or more is exposed in the measurement hole  104 ,  106 . Thus, a laser beam or a visible ray emitted from the optical detector (not shown) disposed above the resist layer  40  is directed to the surface of the substrate  10  exposed in the measurement hole  104  or  106  through the measurement hole  104  or  106  without interference from the resist layer  40  therearound is and reflected or diffused on the substrate surface. Alternatively, the CCD camera disposed above the resist layer  40  is easily and properly focussed on the surface of the substrate  10  having the predetermined size or more and defining the reference surface exposed in the measurement holes  104  or  106 , without interference from the resist layer  40  around the measurement hole  104  or  106 . 
     The remainder of the circuit board other than described above is the same as that described with reference to FIGS. 14 to  16 . in this first circuit board, the measurement hole  104  or  106  formed in the resist layer  40  may be provided to be continuous to the opening  50  also formed in the resist layer  40 . Thereby, a tool for forming the measurement hole  104  or  106  and the opening  50  can be simplified and the process for forming the measurement hole  104  or  106  and the opening  50  becomes easy. operations other than the above are the same as those of the first circuit board described with reference to FIG.  2 . 
     In the first circuit board shown in FIG. 5 or  6 , it is better to avoid the exposure of the surface of the substrate  10 , on which the circuit pattern  20  is formed, in the measurement holes  104  or  106 . 
     This is because, in such a case, if the conductor bump  60  is formed on the conductor pad  30  exposed in the opening  50 , part of the conductor bump  60  flows to the circuit pattern  20  connected to the conductor pad  30  exposed in the opening  50 . Thereby, it is impossible to properly form the conductor bump  60  having a generally semispherical shape on the conductor pad  30  exposed in the opening  50 . 
     FIGS. 7 and 8 are partially enlarged plan views, respectively, of other preferable embodiments of a second circuit board of the present invention. 
     In the second circuit board shown in FIG. 7, a measurement hole  108  of a circular shape or the like is provided in the resist layer  40  in the vicinity of the opening  50  but separate therefrom. The surface of the substrate  10  defining the reference surface is exposed in the measurement hole  108 . 
     In the second circuit board shown in FIG. 8, an elongate measurement hole  110  is provided in the resist layer  40  in the vicinity of the opening  50 , while extending outward therefrom. The surface of the is substrate  10  defining the reference surface is exposed in the measurement hole  110 . 
     Each of the measurement holes  108  and  110  has a predetermined size or more so that the surface of the substrate  10  defining the reference surface having a predetermined size or more is exposed in the measurement hole  108  or  110 . Thus, a laser beam or a visible ray emitted from the optical detector disposed above the resist layer  40  as described before is directed to the substrate  10  through the measurement hole  108  or  110  and reflects or diffuses on the surface of the substrate  10  exposed in the measurement hole  108  or  110 . The reflected or diffused ray can be incident upon the optical detector through the measurement hole  108  or  110  without interference from the resist layer  40  around the measurement hole  108  or  110 . Alternatively, it is possible to easily and properly focus the CCD camera disposed above the resist layer  40  as described before, on the surface of the substrate  10  exposed in the measurement hole  108  or  110 , having the predetermined size or more defining the reference surface without the interference with the resist layer around the measurement hole  108  or  110 , 
     The remainder of the circuit board other than described above is the same as that described with reference to FIGS. 20 to  22 . 
     In the second circuit board shown in FIG. 7 or  8 , it is possible to direct a laser beam or a visible ray emitted from the optical detector disposed above the resist layer  40  to the substrate  10  through the widely opened measurement hole  108  or  110  without the interference with the resist layer  40  and it is possible to reflect or diffuse the laser beam or the visible ray on the surface of the substrate  10  having the predetermined size exposed in the measurement hole  108  or  110 . The reflected or diffused ray is incident upon the optical detector disposed above the resist layer  40  through the widely opened measurement hole  108  or  110  without interference from the resist layer. 
     Together therewith, it is possible to cause the laser beam or the visible ray emitted from the optical detector disposed above the resist layer  40  to be incident upon the top of the conductor bump  60  in the opening  50  and reflect or diffuse the same on the top of the bump  60 . The reflected or diffused ray is incident upon the optical detector disposed above the resist layer  40 . 
     The reflected or diffused ray reflected or diffused on the surface of the substrate  10  and incident upon the optical detector and the reflected or diffused ray reflected or diffused on the top of the conductor bump  60  are used to directly measure the height h 2  from the surface of the substrate  10  defining the reference surface to the top of the conductor bump  60 . Based on the measured value, it is possible to correctly determine the variation of the height of the conductor bump  60  formed on the substrate  10 . 
     Also, it is possible to easily and properly focus the CCD camera disposed above the resist layer  40  on the surface of the substrate  10  having the predetermined size or more, exposed in the measurement hole  108  or  110 , without interference from the resist layer  40 . A distance from the CCD camera to the surface of the substrate  10  is measurable by the CCD camera. 
     Together therewith, a CCD camera disposed above the resist layer  40  can be focussed on the top of the conductor bump  60  exposed in the conductor bump  60 , and a distance from the CCD camera to the top of the conductor bump  60  is measurable by the CCD camera. 
     It should be understood by those skilled in the art that the foregoing description relates to only some preferred embodiments of the disclosed invention, and that various changes and modifications may be made to the invention without departing from the spirit and scope thereof.