1) Field of the Invention
The present invention relates to a metal plate and a method of shaping the same and, more particularly, a metal plate that is called a stiffener (a radiating plate and reinforcing plate) employed in a semiconductor device, in which semiconductor chips are packaged in its package, and a method of shaping the same.
2) Description of the Related Art
In recent years, development of the LSI technology as a key technology applied to implement multimedia devices is proceeding steadily toward the higher-speed and larger capacity data transmission. With this development, the higher-density packaging technology of the interface between the LSI and the electronic device is in progress.
As the package that is adapted for the high-density packaging, various packages have been developed. For example, there is the BGA (Ball Grid Array) package in which solder ball terminals are provided to the surface of the package like a grid array in place of lead terminals. Also, there is the TBGA (Tape Ball Grid Array) package that aims at the high performance and multiple pin by using a polyimide tape as the package base material. In some of the TBGA packages, the radiating plate and reinforcing plate, which is called the stiffener, is provided to the back side of the semiconductor chip.
FIG. 1 is a sectional view showing an example of the TBGA package having the stiffener. As shown in FIG. 1, in a TBGA package 116 of this package, a concave portion 100a is provided in the center portion of one surface of a stiffener 100 made of the metal plate and then a semiconductor chip 108 is fixed to a bottom portion of this concave portion 100a via an adhesive layer 110b. A polyimide film 102 having Cu wirings 104 thereon is adhered to one surface of the stiffener 100 except the concave portion 100a via an adhesive layer 110a. A solder resist film 105 having opening portions in its predetermined portions is formed on the Cu wirings 104, and then solder bumps 106 are connected to the Cu wirings 104 via the opening portions respectively. Then, electrode pads of the semiconductor chip 108 and bonding pads of the Cu wirings 104 are connected mutually via wires 112. Also, the semiconductor chip 108, the bonding pads of the Cu wirings 104, and the wires 112 are sealed with a molding resin 114.
Further, in case a radiation effect of the package must be enhanced, a plate-fin type heat sink, for example, is adhered/arranged onto an opposite surface to the surface of the stiffener 100, on which the semiconductor chip 108 is arranged. For this reason, it is preferable that the surface of the stiffener 100, on which the semiconductor chip 108 is not arranged, should be kept in the flat state.
FIGS. 2A to 2C are sectional views showing a stiffener shaping method in the prior art. FIGS. 3A and 3B are sectional views showing problems in the stiffener shaping method in the prior art. The stiffener shaping method in the prior art is set forth in Patent Application Publication (KOKAI) Hei 11-102998, for example. More particularly, as shown in FIG. 2A, first a die 128 having a metal punch 120, a clamping metal member 122, and a supporting table 124 is prepared, and then a metal plate 100x serving as the stiffener is positioned between the clamping metal member 122 and the supporting table 124.
Then, as shown in FIG. 2B, the predetermined concave portion 100a is formed by moving the metal punch 120 to push it against the metal plate 100x. At this time, a convex portion 100b that protrudes from the other surface of the metal plate 100x is formed simultaneously with the formation of the concave portion 100a. 
Then, as shown in FIG. 2C, the convex portion 100b is cut by sliding a cutting edge 126 laterally from a connected portion A at which a base portion of the metal plate 100x and the convex portion 100b are jointed.
In the prior art, the stiffener is formed by shaping the metal plate 100x by means of the shaping method described above.
However, in the metal plate shaping method in the prior art, vertical variation in position of the cutting edge 126 is caused during the cutting. Thus, in the case that the cutting edge 126 is deviated upwardly during the cutting, the cutting edge 126 is stuck in the base portion of the metal plate 100x, as shown in FIG. 3A, when the cutting of the convex portion 100b by the cutting edge 126 is completed. Therefore, a cut chip 101a is still left in the state that such chip is connected to the metal plate 100x. 
As the countermeasure to this, there is such a method that a cutting start position of the cutting edge 126 is set such that it is previously shifted downwardly and then the convex portion 100b is cut. However, in the case of this method, as shown in FIG. 3B, the cutting of the convex portion 100b by the cutting edge 126 is completed at a side surface portion of the convex portion 100b, which is positioned lower than the position of the connected portion A at which the base portion of the metal plate 100x and the convex portion 100b are jointed. Therefore, a step 101b is still left after the convex portion 100b is cut.
That is, so-called global step is still left on the cutting surface side of the metal plate 100x. Therefore, if the above plate-fin type heat sink is adhered/fixed onto the cutting surface, there is such a possible that disadvantages are caused.
As described above, since a height of the cutting edge 126 is varied vertically during the cutting, it is difficult in the extreme to cut the convex portion 100b such that the cut chip 101a or the step 101b is not left.
It is an object of the present invention to provide a metal plate shaping method capable of shaping a metal plate by forming a concave portion on one surface of the metal plate and then cutting a convex portion that is formed on the other surface by above formation to project therefrom in such a manner that a chip being connected to the metal plate is not left and also the other surface of the metal plate is formed in the substantially flat state, and the metal plate.
The present invention provides a metal plate shaping method which comprises the steps of forming a structure in which a first concave portion is formed in a predetermined portion on one surface of a metal plate, and also a convex portion that protrudes from other surface of the metal plate is formed by formation of the first concave portion, and a second concave portion is formed in a predetermined portion on an outside of a peripheral portion of the convex portion, by shaping a metal plate by means of stamping using a die; and cutting convex portion formed on the other surface of the metal plate.
In the present invention, as shown in FIGS. 4A and 4B, FIGS. 5A and 5B, and FIGS. 6A to 6C, first a first concave portion 10a is formed in a predetermined portion on one surface S1 of a metal plate 10 by stamping using a die, and also a convex portion 10b that protrudes from the other surface S2 is formed by the formation of the first concave portion 10a. At this time, simultaneously a second concave portion 10c is formed in a predetermined portion of the other surface S2 of the metal plate 10 on the outside of the peripheral portion of the convex portion 10b. 
Otherwise, a fine concave portion 10e that corresponds to the second concave portion 10c may be formed previously on the other surface S2 of the metal plate 10. Then, the first concave portion 10a may be formed on one surface S1 of the metal plate 10, and the convex portion 10b that protrudes from the other surface S2 may be formed.
Then, the convex portion 10b formed on the other surface S2 of the metal plate 10 is cut by a cutting means 26. At this time, preferably a cutting operation is started from a portion, which is at the same height as the other surface S2, of a side surface portion B of the convex portion 10b by the cutting means 26. Then, the cutting means 26 breaks through a side surface portion C on the opposite side, and thus the convex portion 10b is cut off and separated from the metal plate 10.
In this manner, even if the vertical variation of the cutting means 26 is caused during the cutting operation of the convex portion 10b, the cutting means 26 can break through the side surface portion C of the convex portion 10b to finish the cutting operation since a depth D of the second concave portion 10c is set larger than a vertical variation dimension of the cutting means 26.
As a result, such a disadvantage is not caused that the cut chip 11 is connected to the metal plate 10 and is still left, and a cut chip 11 can be cut off and separated perfectly from the metal plate 10. In addition, a cut surface S3 of the convex portion 10b is almost equal in height to the other surface S2 of the metal plate 10 and thus a substantially flat surface can be obtained. Therefore, even if a heat sink is further provided to the other surface S2, there is no possibility that any trouble is caused.
In the above metal plate shaping method, preferably the die 28 includes a clamping metal member 22 having a cavity portion in its center portion, a metal punch 20 arranged in the cavity portion of the clamping metal member 22 movably in the vertical direction, and a supporting table 24 arranged below the clamping metal member 22, the supporting table 24 having a cavity portion in a portion that corresponds to the metal punch 20 and a projected portion 24a in a predetermined portion that corresponds to an outside of a peripheral portion of the metal punch 20.
If such die 28 is employed, such a structure can be easily shaped that the first concave portion 10a is formed in the predetermined portion on one surface S1 of the above metal plate 10 and also the convex portion 10b that protrudes from other surface S2 by formation of the first concave portion 10a is formed and the second concave portion 10c is formed on the outside of the peripheral portion of the convex portion 10b. After this, the convex portion 10b of the metal plate 10 may be cut by the above method. In this manner, the above metal plate shaping method can be easily implemented by employing the above die.
In this case, above drawing numbers and reference symbols are quoted so as to make the understanding of the invention easy. Therefore, they should not be interpreted to limit the present invention.