KGD Myth #4: Difficulty with acquiring KGD has relegated bare die implementation to niche markets.
KGD Myths Contents
On the contrary, the past 3 years has seen an explosion of bare die used for System in Package (SiP) implementation, especially for stacked die modules. The impetus for stacking was the requirement for more and more functionality in handheld digital systems such as cellular phones, while reducing the size and weight. The requirement for both volatile and non-volatile memories in cell phones caused manufacturers to stack a flash memory and an SRAM in the same package. Today, almost every cell phone sold has at least one stacked package, and many phones have several multi chip packages in stacked configurations.
The assembly infrastructure has rapidly matured to the point where 8 die stacks have been announced. However, in order to maintain profitable yields, die stacks have been focused on memory stacks of 2 or 3 die only. However, the latest generations of cell phones are beginning to incorporate stacks of 4 and even 5 die, containing both memory and processors, and in some cases, power management. See figure 4.
Figure 4: Memory devices in cellular phones have been the leading edge of
volume 3D packaging for the consumer markets.
Source: Portelligent Product Profile Database.
This figure emphasizes the increasing percentage of stacked and single chip modules seen in cellular phones from the Portelligent Product Profile Database over the past 3 years, which includes data for 20 leading edge phones in 2002, 44 phones in 2003 and 46 phones in 2004. Note that there may be more than one module or stack in each phone. Single die memory modules, which comprised 75% of the memory packages in 2002, comprise only 35% in 2004. For the first time in 2004, a 5-die stack is noted. The multi-die stacks have a packaging efficiency of approximately 1.8 (die to package area ratio) where the single die packages have a packaging efficiency ranging from 0.5 to 0.55. The evolution to more die in a stack has also seen a more heterogenous mix of devices, with logic and analog included in the stack.