Wafer-level Packaging (WLP) Process Flow

What is wafer level packaging?
Wafer-level packaging (WLP) is a technology for packaging directly on the Wafer. Wafer-level packaging compared with traditional packaging technology, the use of semiconductor manufacturing processes. Unlike traditional packaging, wafer-level packaging is the process of packaging the entire wafer before cutting the wafer into a single chip.

The process flow of wafer level packaging?

As shown above, the basic process flow of WLP Fan in is as follows:
1. Fab-out Wafer
Wafer preparation, which is the initial step in the entire packaging process. First, there is a wafer that has been completed through the manufacturing process, on which the circuit structure has been formed. Passivation Layer (Passivation Layer) on the surface of the wafer, used to protect the circuit on the surface of the wafer from the influence of external moisture and chemicals.
2. Thin Film Deposition & Thick Photoresist (TPR) Coating
Thin film deposition: A layer of metal film, usually Ti, Cu, Cr, Au, etc. is deposited on top of the passivation layer as a metal seed layer for plating.
Thick photoresist coating: A thick photoresist is applied to a metal film and exposed for development. This step opens certain areas and some parts are covered by the photoresist.
3. Cu Electroplating
Copper plating: Plating a copper layer on a patterned photoresist by an electroplating process. This step is to form a thicker RDL that draws the signal from the PAD.
4. TPR Strip & Thin Film Etching
Photoresist removal: Remove the photoresist covering areas where plating is not required, exposing the underlying metal layer.
Film etching: etching away parts of the metal film that are not protected by the photoresist, usually by wet etching.
5. Dielectric Coating
Dielectric coating: Coating a layer of dielectric material such as silicon oxide or PI on the already formed metal structure to isolate the metal layers and protect them from the external environment.
6. Ball Mounting
Solder ball mounting: Install solder ball in open position on dielectric layer. The tin ball is used to realize the electrical connection of the chip to the circuit board.

At this point, the wafer-level packaging process is complete.