Method for chip packaging
Provided is a method for chip packaging, including the steps of: providing a semi-packaged wafer which has a cutting trail and a metal bonding pad of the chip; forming a first protective layer on the cutting trail; forming on the metal bonding pad a sub-ball metal electrode; forming a solder ball on the sub-ball metal electrode; dicing the wafer along the cutting trail. The first protective layer according to the present invention can prevent the metal in the cutting trail from being separated by electroplating, and protect the lateral sides of a discrete chip after cutting. The process flow thereof is simple, and enhances the efficiency of the packaging as well as its yield.
1. A method for chip packaging, comprising:
providing a semi-packaged wafer, where the semi-packaged wafer comprises a semiconductor substrate with chips formed thereon and a protective mask on the semiconductor substrate to provide insulation and protection, the protective mask has openings exposing metal bonding pads of the chips, and the protective mask also has openings of slicing trails on the semiconductor substrate;
forming a first protective layer in the slicing trails;
forming sub-ball metal electrodes on the metal bonding pads;
forming a second protective layer on portions of the wafer without the sub-ball metal electrodes after the sub-ball metal electrodes are formed;
forming solder balls on the sub-ball metal electrodes; and
slicing the wafer along the slicing trails.
2. The method according to claim 1 , wherein the first protective layer has a width larger than that of the slicing trails.
3. The method according to claim 2 , wherein the width of the slicing trails ranges from about 30 μm to about 80 μm, and the width of the first protective layer ranges from about 50 μm to about 120 μm.
4. The method according to claim 1 , wherein the first protective layer comprises thermosetting epoxy resin and is formed using a screen printing process.
5. The method according to claim 1 , wherein the sub-ball metal electrodes are formed using an electrolyte less plating process.
6. The method according to claim 5 , wherein the electrolyte less plating process comprises: washing a surface of the wafer with zincate; and electrolyte less plating Ni and Au on the wafer successively.
7. The method according to claim 6 , wherein Ni has an electroplating thickness of about 3 μm, and Au has an electroplating thickness of about 0.05 μm.
8. The method according to claim 1 , wherein the sub-ball metal electrodes are formed using a selective vapor deposition process.
9. The method according to claim 8 , wherein the selective vapor deposition comprises:
disposing a mask plate on the wafer, where the mask plate exposes positions on the wafer where the sub-ball metal electrodes are to be formed; and depositing Ni and Cu successively on the wafer using a physical vapor deposition process with the mask plate as a mask.
10. The method according to claim 1 , wherein the second protective layer has a thickness ranging from about 5 μm to about 50 μm.
11. The method according to claim 1 , wherein the second protective layer comprises thermosetting epoxy resin and is formed using a screen printing process.
12. The method according to claim 1 , further comprising: after the second protective layer is formed, performing a polishing process to the wafer.
13. The method according to claim 12 , wherein the polishing process comprises:
placing the wafer on a fixed operating platform;
winding a non-woven softer than the wafer around a polishing head, and tightly attaching the non-woven onto the wafer; and
dipping the non-woven with a polishing solution and mechanically polishing the wafer.
14. The method according to claim 11 , further comprising: after the second protective layer is formed, removing the thermosetting epoxy resin on top of the sub-ball metal electrodes using a plasma etching process.
15. The method according to claim 11 , wherein the wafer is maintained at a temperature lower than a curing temperature of the thermosetting epoxy resin during the screen printing process.
16. The method according to claim 11 , wherein the curing temperature of the thermosetting epoxy resin is less than 200° C.
17. The method according to claim 16 , wherein the thermosetting epoxy resin comprises a solidified filler having particles with a particle diameter less than ⅓ of a printing thickness of the thermosetting epoxy resin.
18. The method according to claim 17 , wherein the printing thickness of the thermosetting epoxy resin is about 15 μm, the particle diameter of the solidified fillers is less than about 5 μm, and the second protective layer formed after the curing has an average thickness ranging from about 11 μm to about 12 μm.
19. The method according to claim 4 , wherein the wafer is subjected to a baking process or a plasma processing process to activate the surface of the wafer before the screen printing process.
20. The method according to claim 11 , wherein the wafer is subjected to a baking process or a plasma processing process to activate the surface of the wafer before the screen printing process.