System in Package (SiP) Die Attach
System in Package (SiP) Assembly Contents
Die to die bonding
If a single die is to be interconnected to the substrate via wire bonds, the die is first picked from the shipping media, and attached with the backside to the substrate by a suitable adhesive. For stacked die, high die placement accuracy is essential to mount the upper chip accurately onto the lower one [Buhlmann]. If the error repeats, the stackup of rotational error could cause the wirebonds to cross, causing a short circuit.
If the stack is pyramidal, the die may be bonded directly to the one below it (or to the substrate, if it is the bottom die in the stack). In this architetcture, all die may be placed and bonded prior to wirebonding
For stacks of same sized die , an interposer is used to allow space for the loop height of the lower wirebonds under the upper die.Therefore, the thickness of interposer (combined with bond line of die) must provide clearance (>50µm) for loop height of the lower wirebond