Method and structure for wafer level packaging with large contact area
A method to provide a wafer level package with increasing contact pad area comprising the steps of forming a first packaging layer on wafer top surface, grinding the wafer back surface and etch through holes, depositing a metal to fill the through holes and covering wafer backside, cutting through the wafer from wafer backside forming a plurality of grooves separating each chip then depositing a second packaging layer filling the grooves and covering the wafer back metal, reducing the first packaging layer thickness to expose the second packaging layer filling the grooves and forming a plurality of contact pads overlaying the first packaging layer thereafter cutting through the second packaging layer in the grooves to form individual package.
1. A method for preparing a wafer level packaging structure with a large contact area, wherein a plurality of first metal bonding pads are formed at front surfaces of semiconductor chips formed in a wafer, the method comprising the steps of:
etching a respective front surface of each semiconductor chip to form at least a respective bottom through hole with a depth shorter than a thickness of the wafer and filling a conductive material into the respective bottom through hole to form a respective bottom metal interconnecting structure;
forming a respective second metal bonding pad at the respective front surface of each semiconductor chip, the respective second metal bonding pad being connected to the respective bottom metal interconnecting structure;
forming a plurality of top metal interconnecting structures on the plurality of first metal bonding pads and the second metal bonding pads;
forming a first packaging layer covering the plurality of first metal bonding pads, the second metal bonding pads, the plurality of top metal interconnecting structures and a front surface of the wafer;
thinning a back surface of the wafer until the bottom metal interconnecting structures are exposed;
forming a metal layer covering the back surface of the wafer, the metal layer being connected to the bottom metal interconnecting structures;
cutting through the wafer and the metal layer from the back surface of the wafer to form a plurality of cutting grooves, wherein the plurality of cutting grooves extend into the first packaging layer and separate the individual semiconductor chips from each other, wherein the metal layer is cut into a plurality bottom metal layers and wherein a respective bottom metal layer of the plurality of bottom metal layers is formed at a back surface of each semiconductor chip;
depositing a packaging material to form a second packaging layer covering the plurality of bottom metal layers and filling into the plurality of cutting grooves;
grinding at the first packaging layer until the packaging material filled in the plurality of cutting grooves and the plurality of top metal interconnecting structures are exposed, wherein the first packaging layer is cut into a plurality of top packaging layers and wherein a respective top packaging layer of the plurality of top packaging layers is formed at the front surface of each semiconductor chip;
forming a plurality of contact bonding pads on the plurality of top packaging layers, wherein each of the plurality of contact bonding pads is electrically connected to one first metal bonding pad of the plurality of first metal bonding pads or one second metal bonding pad of second metal bonding pads through at least one top metal interconnecting structure of the plurality of top metal interconnecting structures; and
cutting through the second packaging layer and the packaging material filled in the plurality of cutting grooves along the plurality of cutting grooves to separate individual wafer level packaging structures from each other, wherein the second packaging layer is cut into a plurality of bottom packaging layers and wherein a respective bottom packaging layer of the plurality of bottom packaging layers covers the bottom metal layer of each semiconductor chip.
2. The method of claim 1 , wherein the plurality of top metal interconnecting structures are solder tin balls or metal bumps.
3. The method of claim 1 , wherein after the bottom through hole is formed, an insulation layer is deposited to cover a side wall of the bottom through hole before the conductive material is filled into the bottom through hole to form the bottom metal interconnecting structure, and wherein the bottom metal interconnecting structure is electrically insulated from the conductive material of the semiconductor chip surrounding the bottom through hole through the insulation layer.
4. The method of claim 1 , wherein the back surface of the wafer is heavily doped with ions before the metal layer is formed at the back surface of the wafer.
5. The method of claim 1 , wherein the bottom through hole is formed in a non-effective circuit preparing area.
6. The method of claim 1 , wherein the semiconductor chip is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), wherein the plurality of first metal bonding pads comprise gate electrodes and source electrodes, and wherein drain electrodes are formed at the plurality of bottom metal layers.
7. The method of claim 1 , wherein a remaining of the packaging material filled in the plurality of cutting grooves, after cutting through the second packaging layer and the packaging material filled in the plurality of cutting grooves along the plurality of cutting grooves, form side packaging layers covering sides of the semiconductor chips.