a. Field of the Invention
The present invention is in the field of semiconductor die packaging.
b. Description of the Related Art
Electronic equipment that includes packaged semiconductor dies, such as portable telephones, personal computers, and digital cameras, are being developed with increased functionality. To meet this trend, companies that assemble semiconductor dies into packages are developing semiconductor packages that include a plurality of stacked semiconductor dies in a single package.
A conventional technique for stacking plural semiconductor dies in a single package is to couple an inactive (i.e., backside) surface of a first semiconductor die to a substrate, so that the active surface of the first semiconductor die faces away from the substrate, and then to attach the inactive surface of a second semiconductor die onto the active surface of the first semiconductor die using an electrically insulating adhesive layer. The first and second semiconductor dies are each electrically coupled to the substrate by bond wires that extend from bond pads on the active surface of the respective semiconductor dies to the substrate. In order that the upper second semiconductor die not interfere with the bond wires coupled to the lower first semiconductor die, the second semiconductor die is typically smaller than the first semiconductor die so that the second semiconductor die fits fully within the opposed parallel rows of bond pads on the active surface of the first semiconductor die. In a case where a die attach paste is used to couple the first and second semiconductor dies, the size of the second semiconductor die also is limited to account for the die-attach fillet that is formed during the die-attach process for the second semiconductor die. Unfortunately, this approach of stacking a smaller second semiconductor die on a larger first semiconductor die is not feasible where it is desired to stack two same-size semiconductor dies, or to stack a larger semiconductor die on top of a smaller semiconductor die.
An alternative approach for die stacking is to attach a first side of a rectangular prism of silicon or of a dielectric film, called a “spacer,” to the active surface of the first semiconductor die, and to attach the inactive surface of the second semiconductor die to an opposite second side of the spacer. The spacer has an upper and lower surface area that is smaller than the area of the active surface of the lower die, and is placed so as to be entirely within the bond pads and active surface edges of the lower semiconductor die. The spacer has a thickness sufficient to space the inactive surface of the second die above the bond wires that are coupled from the bond pads of the first semiconductor die to the substrate. Unfortunately, the spacer adds additional vertical height to the package, and thus is not optimal for certain applications.
Accordingly, a new approach to stacking a plurality of semiconductor dies is desirable.