Wafer-level packaging

Wafer-level packaging (WLP) is a process where packaging components are attached to an integrated circuit (IC) 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 a conventional process, in which the wafer is sliced into individual circuits (dice) before the packaging components are attached. WLP is essentially a true chip-scale package (CSP) 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 (WL-CSP) is the smallest package currently available on the market and is produced by OSAT (Outsourced Semiconductor Assembly and Test) companies, such as Advanced Semiconductor Engineering (ASE). A WL-CSP or WLCSP package is just a bare die with a redistribution layer (RDL, interposer or I/O pitch) 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 (BGA) package. There are two kinds of wafer level packaging: fan-in and fan-out.