Package-on-Package or (PoP) memory was created as a way to reduce the physical size of the memory sub-system on a single board computer. The basic idea is to stack two BGA devices one on top of the other as shown above.
PoP Memory has Several Advantages Including:
- More reliable manufacture because the memory sub-system can be assembled separately from the final system.
- Higher memory cycle speeds due to shorter connection lengths.
- Small size
This type of memory is used in handsets and other types of portable devices and is also making it’s way into mid-level products as well.
BGA assemble issues, can only re-ball the part a limited number of times then it must be scrapped. So, for example, if the RAM portion fails, the FLASH could be de-soldered and re-soldered to a working RAM module, but only a limited number of times.
Test issues – BGA packages do not allow access to device pins once the device is soldered down. In the case of a PoP module, since the top module is soldered to the bottom, there is no way to access the pins. Typically JTAG boundary-Scan tools can be used to test in this configuration.
Examples of Boards with PoP Memory: