1. Field of the Invention
The invention relates to a method of manufacturing a package, and more particularly to a package, in which a metal heat slug is disposed below a bottom surface of a die, and a manufacturing method thereof.
2. Description of the Related Art
Since the electrical products are gradually miniaturized, the packages for protecting semiconductor dies and providing connections to external circuits also have to be miniaturized. Of course, the heat dissipation designs for the packages are also important considerations.
FIG. 1 is a cross-sectional view showing a conventional package having a metal heat slug ball grid array (HSBGA). Referring to FIG. 1, the package 100 includes a substrate 102, adhesive agents 104a and 104b, a die 106, a number of bond wires 108, a metal heat slug 110, an encapsulating mold compound 112, a number of bond pads 114, and a number of solder balls 116. The die 106 is disposed on the top surface of the substrate 102 through the adhesive agent 104a by way of die attaching. In addition, the bond wires 108 are formed, by way of wire bonding, between the top surface of the die 106 and the top surface of the substrate 102 outside the die 106 to electrically connect the die 106 to the substrate 102. Two pendent ends of the metal heat slug 110 are disposed on the top surface of the substrate 102 outside the bond wires 108 through the adhesive agent 104b. Thus, the middle, horizontal structure of the metal heat slug 110 is located above the top surface of the die 106. In addition, the encapsulating mold compound 112 covers a part of the metal heat slug 110, the die 106, the bond wires 108, and a part of the top surface of the substrate 102 with the middle, horizontal structure exposed out of the metal heat slug 110 by way of encapsulating. Furthermore, the bond pads 114 are formed on the bottom surface of the substrate 102 and are electrically connected to the bond wires 108 through internal traces of the substrate 102. A number of solder balls 116 flush with each other are formed on the bond pads 114 by way of ball mounting, and the package 100 is electrically connected to external circuits through the solder balls 116. It is to be noted that the thickness of the package 100 is defined as a distance from the bottom end of the solder ball 116 to the top end of the encapsulating mold compound 112.
When the package 100 is operating, the heat from the die 106 may be dissipated to the outside via the metal heat slug 110. However, because the thermal conductivity of the substrate 102 is not so good and a solder mask with low thermal conductivity is formed on the top surface of the substrate, the heat generated by the die 106 is blocked by the solder mask and is accumulated between the die 106 and the top surface of the substrate 102 and thus cannot be easily dissipated, thereby greatly influencing the operation of the package 100. In addition, the design of disposing the metal heat slug 110 above the top surface of the die 106 may increase the thickness of the package 100. On the other hand, based on the consideration of the arrangement of the bond wires, the pendent ends of the metal heat slug 110 have to be disposed on the top surface of the substrate 102 outside the bond wires 108, and the area of the top surface of the substrate 102 has to be enlarged accordingly. Consequently, the overall volume of the package 100 will be enlarged, and the manufacturing cost will be increased.