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Wafer-level packaging is a process where packaging components are attached to an integrated circuit before the wafer – on which the IC is fabricated – is diced. In WSP, the top and bottom layers of the packaging and the solder bumps are attached to the integrated circuits while they are still in the wafer. This process differs from more a conventional process, in which the wafer is sliced into individual circuits before the packaging components are attached.
WLP is essentially a true chip-scale package technology, since the resulting package is practically of the same size as the die. Wafer-level packaging allows integration of wafer fab, packaging, test, and burn-in at wafer level in order to streamline the manufacturing process undergone by a device from silicon start to customer shipment. There is no single industry-standard method of wafer-level packaging at present.
A major application area of WLPs are smartphones due to the size constraints. For example, the Apple iPhone 5 has at least eleven different WLPs, the Samsung Galaxy S3 has six WLPs and the HTC One X has seven. Functions provided WLPs in smartphones include sensors, power management, wireless, etc. In fact, it has recently been rumored that the iPhone 7 will use fan-out wafer-level packaging technology in order to achieve a thinner and lighter model.
Wafer-level chip scale packaging is the smallest package currently available on the market and is produced by OSAT companies, such as Advanced Semiconductor Engineering. A WL-CSP or WLCSP package is just a bare die with a redistribution layer to rearrange the pins or contacts on the die so that they can be big enough and have sufficient spacing so that they can be handled just like a ball grid array package.