This adapter can be used for data recovery purposes by soldering a WFBGA eMMC chip and connecting to a standard microSD card reader for read/write operations or if you would like to build an inexpensive storage device using cheap memory chips obtained from Ebay/Aliexpress or salvaged from other devices. Image below shows the adapter assembled with a Toshiba 4GB eMMC chip.
Besides this custom designed PCB you will need a couple of bypass capacitors (0.1-1uF 10V or above in 0603 package) and the eMMC memory chip. eMMC chips in WFBGA153 package are available from every big distributor but if you would like to try your luck with some inexpensive options, check out this link.
Alternatively you can order this PCB adapter from my Tindie store.
More info about this project in Voltlog #351.