Package on package (PoP) is an integrated circuit packaging method to combine vertically discreet logic and memory ball grid array (BGA) packages. Two or more packages are installed atop each other, i.e. stacked, with a standard interface to route signals between them. This allows higher component density in devices, such as mobile phones, personal digital assistants (PDA), and digital cameras.
Advantages of PoP over chip stacking
There are several key differences between stacked-die and stacked-package products.
The main financial benefit of package on package is that the memory device is decoupled from the logic device. Thus: This gives PoP all the same advantages that traditional packaging has over stacked-die products:
The memory package can be tested separately from the logic package
Only "known good" packages are used in final assembly (if the memory is bad only the memory is discarded and so on). Compare this to stacked-die packages where the entire set is useless and rejected if either the memory or logic is bad.
The end user (such as makers of mobile phones or digital cameras) controls the logistics. This means memory from different suppliers can be used at different times without changing the logic. The memory becomes a commodity to be sourced from the lowest cost supplier. This trait is also a benefit compared to PiP (package in package) which requires a specific memory device to be designed in and sourced upstream of the end user.
Any mechanically mating top package can be used. For a low-end phone, a smaller memory configuration may be used on the top package. For a high-end phone, more memory could be used with the same bottom package. This simplifies inventory control by the OEM. For a stacked-die package or even PiP (package in package), the exact memory configuration must be known weeks or months in advance.
Because the memory only comes into the mix at final assembly, there is no reason for logic suppliers to source any memory. With a stacked-die device, the logic provider must buy wafers of memory from a memory supplier.
Prompt Assembly & Packaging Inc.