System in Package (SiP) Wirebond
System in Package (SiP) Assembly Contents
Stacked Package
Successful implementation of stacked packages requires a fresh look at mature technologies. This is especially true for wirebonding. Even though the die bond pad pitch is not considered leading edge, it is still a challenge to produce. This is exacerbated by the need to bond several die in the same vertical space, with strict control of the loop height on all bonds levels. While standard wirebonding might have a loop height of 150 to 175 µm, die stacking could require loop heights under 100 µm. Today, 125µm loop with 25µm wire is achievable.
One way to acheive even lower loop heights if to use reverse bonding as shown in the Intel quad stack photo below. This technique puts the ball bond on the substrate, and then the stitch bond is made to the die pads. If there is concern about damaging the die glassivation with the bonding tool, a stud bump can be bonded to the die prior to the reverse bonding, and the stitch bond can be made to the stud bump.
Bonding on cantilevered edge of thinned die
Wirebonding the upper die in a stack can be challenging because of the need for very thin die. The specifications for the entire stack height require that each die be as thin as possible, which can result in the need to wirebond to a cantilevered edge of a very thin die.
Stitch-through bonding
Stitch-through or multiple stitch bond can enhance throughput and lower material costs for the stacked package.
Wire Bonder Requirements
The bonder must have the accuracy and sufficient optical depth of field to bond to die with a 100µm die bond pad pitch typical with a 750 µm height differential from the top die to the substrate. The bonding cycle may need multiple passes if magnification requirements can't be met.