Leadless plastic chip carrier with etch back pad singulation
View Patent ↗A leadless plastic chip carrier is constructed by half etching one or both sides of the package design onto a leadframe strip so as to create unique design features such as power and/or ground ring surrounding the die attach pad, interlocking rivet head construction for the contact pads, and an interlocking pattern for the die attach pad. After wire bonding and molding, a further etching is performed to isolate and expose contact pads. Singulation of individual chip packages from the leadframe strip is then performed by saw singulation or die punching.
1. A process for fabricating a leadless plastic chip carrier, comprising the steps of:
depositing a mask on a first surface of a leadframe strip to define at least one row of contact pads and a die attach pad of said leadless plastic chip carrier;
depositing a plurality of layers on portions of said first surface exposed by said mask for creating said at least one row of contact pads and said die attach pad;
dissolving away said mask;
mounting a semiconductor die to said die attach pad on said first surface and wire bonding said semiconductor die to said at least one row of contact pads;
encapsulating said first surface of said leadframe strip in a molded material; and
etching back a bottom surface of said leadframe strip for exposing said contact pads and said die attach pad.
2. The process of claim 1 , wherein said step of depositing said plurality of layers includes an initial deposition of flash Cu which is etched away during step of etching back said bottom surface to create a cavity.
3. The process of claim 2 , wherein said initial deposition of flash Cu is followed by depositing layers of Au, Ni, Cu, Ni and Au.
4. The process of claim 2 , wherein said initial deposition of flash Cu is followed by depositing layers of Au, Ni, Cu and Ag.
5. The process of claim 2 , wherein, further including a step of attaching solder balls to said contact pads exposed as a result of said step of etching back said bottom surface of said leadframe strip.
6. The process of claim 1 , wherein said step of depositing said plurality of layers includes depositing successive layers of Au, Ni, Cu, Ni and Au.
7. The process of claim 1 , wherein said step of depositing said plurality of layers includes depositing successive layers of Au, Ni, Cu, and Ag.
8. The process of claim 1 , wherein said step of depositing said plurality of layers includes depositing successive layers of Tin, Cu, Ni and Au.
9. The process of claim 1 , wherein said step of depositing said plurality of layers includes depositing successive layers of Tin, Cu, and Ag.
10. The process of claim 1 , further comprising the step of singulating said leadless plastic chip carrier from said leadframe strip.
11. A process for fabricating a leadless plastic chip carrier, comprising the steps of:
depositing a mask on a first surface of a leadframe strip to define at least one row of contact pads and a die attach pad of said leadless plastic chip carrier;
depositing a plurality of layers on portions of said first surface exposed by said mask for creating said at least one row of contact pads and said die attach pad;
dissolving away said mask;
mounting a semiconductor die to said die attach pad on said first surface and wire bonding said semiconductor die to said at least one row of contact pads;
encapsulating said first surface of said leadframe strip in a molded material; and
etching back a bottom surface of said leadframe strip for exposing said contact pads and said die attach pad; wherein
the step of depositing a plurality of layers includes forming a mushroom cap shaped portion at an upper portion of the contact pads.
12. The process of claim 11 , wherein said step of depositing said plurality of layers includes an initial deposition of flash Cu which is etched away during step of etching back said bottom surface to create a cavity.
13. The process of claim 12 , further including a step of attaching solder balls to said contact pads exposed as a result of said step of etching back said bottom surface of said leadframe strip.
14. The process of claim 12 , wherein said initial deposition of flash Cu is followed by depositing layers of Au, Ni, Cu, Ni and Au.
15. The process of claim 12 , wherein said initial deposition of flash Cu is followed by depositing layers of Au, Ni, Cu and Ag.
16. The process of claim 11 , wherein said step of depositing said plurality of layers includes depositing successive layers of Au, Ni, Cu, Ni and Au.
17. The process of claim 11 , wherein said step of depositing said plurality of layers includes depositing successive layers of Au, Ni, Cu, and Ag.
18. The process of claim 11 , wherein said step of depositing said plurality of layers includes depositing successive layers of Tin, Cu, Ni and Au.
19. The process of claim 11 , wherein said step of depositing said plurality of layers includes depositing successive layers of Tin, Cu, and Ag.
20. The process of claim 11 , wherein the step of depositing a plurality of layers includes creating a power/ground ring.
21. The process of claim 20 , wherein the power/ground ring is disposed between the die attach pad and the at least one row of contact pads so as to substantially surround the die attach pad.
22. A process for fabricating a leadless plastic chip carrier, comprising the steps of:
depositing a mask on a first surface of a leadframe strip to define at least one row of contact pads and a die attach pad of said leadless plastic chip carrier;
depositing a flash Cu layer on portions of said first surface exposed by said mask;
depositing a plurality of layers on said flash Cu layer for creating said at least one row of contact pads and said die attach pad;
dissolving away said mask;
mounting a semiconductor die to said die attach pad on said first surface and wire bonding said semiconductor die to said at least one row of contact pads;
encapsulating said first surface of said leadframe strip in a molded material; and
etching back a bottom surface of said leadframe strip and said flash Cu layer for exposing said contact pads and said die attach pad.
23. The process of claim 22 , further comprising the step of attaching solder balls to said contact pads exposed as a result of said step of etching back said bottom surface of said leadframe strip and said flash Cu layer.
24. The process of claim 22 , wherein said initial deposition of flash Cu is followed by depositing layers of Au, Ni, Cu, Ni and Au.
25. The process of claim 22 , wherein said initial deposition of flash Cu is followed by depositing layers of Au, Ni, Cu and Ag.
26. The process of claim 22 , wherein said step of depositing said plurality of layers includes depositing successive layers of Tin, Cu, Ni and Au.
27. The process of claim 22 , wherein said step of depositing said plurality of layers includes depositing successive layers of Tin, Cu, and Ag.
28. The process of claim 22 , wherein the step of depositing a plurality of layers includes creating a power/ground ring.
29. The process of claim 28 , wherein the power/ground ring is disposed between the die attach pad and the at least one row of contact pads so as to substantially surround the die attach pad.