Method and structure of die stacking using pre-applied underfill
Structures and processes for die stacking using an opaque or translucent pre-applied underfill material generally include selectively applying a low surface tension material to at least a portion of an alignment mark surface on a die; and applying the opaque or translucent underfill material to the die surface, wherein the underfill material does not wet or adhere to the low surface tension material such that the alignment mark surface is free of underfill material.
1. A process for pre-applying an opaque or translucent underfill material prior to coupling a die to a substrate, comprising:
selectively applying a low surface tension material of less than 35 dynes/cm to at least a portion of an alignment mark surface on a die; and
applying the opaque or translucent underfill material to the die surface, wherein the underfill material does not wet or adhere to the low surface tension material such that the alignment mark surface is free of underfill material.
2. The process of claim 1 , wherein selectively applying the low surface tension material to at least the portion of the alignment mark surface comprises contacting a wafer comprising one or more of the dies formed thereon with a metal mask including openings exposing the alignment mark surface; and applying the low surface tension material through the openings and onto the alignment mark surface.
3. The process of claim 2 , wherein applying the low surface tension material through the openings and onto the alignment mark surface comprises depositing particles of the low surface tension material, and heating the die to a temperature effective to coalesce the particles to form a coating.
4. The process of claim 1 , wherein selectively applying the low surface tension material to at least the portion of the alignment mark surface comprises applying a photoresist onto a wafer comprising one or more of the dies formed thereon; lithographically processing the photoresist to form openings exposing the alignment mark surface; and applying a low surface tension material through the openings and onto the alignment mark surface.
5. The process of claim 4 , wherein applying the low surface tension material through the openings and onto the alignment mark surface comprises depositing a solution containing the low surface tension material.
6. The process of claim 1 , wherein the low surface tension material is a fluorinated polymer.
7. The process of claim 1 , further comprising dicing the wafer to form a plurality of dies with the pre-applied underfill material and coupling the dies to a substrate using a vision alignment system.
8. The process of claim 1 , wherein the alignment mark surface on the die are located in a central region of the die.
9. The process of claim 1 , wherein the alignment mark surface on the die are located in an off-central region of the die.
10. The process of claim 1 , wherein the alignment mark surface on the die are located in one or more corners of the die.
11. The process of claim 1 , wherein the pre-applied underfill material is an epoxy.
12. The process of claim 1 , wherein the pre-applied underfill material is a thermally reversible material.
13. A pre-applied underfill die structure, comprising:
a wafer comprising a plurality of dies, wherein each one of the dies includes at least one alignment mark;
a transparent low surface tension material of less than 35 dynes/cm deposited onto at least a portion of the at least one alignment mark; and
a pre-applied underfill material deposited onto the wafer at a thickness approximating a height of the bumps on the dies so as to define the pre-applied underfill die structure.
14. The pre-applied underfill structure of claim 13 , wherein the low surface tension material is a fluorinated polymer.
15. The pre-applied underfill structure of claim 13 , wherein the low surface tension material is a self-assembled monolayer.
16. The pre-applied underfill structure of claim 13 , wherein the at least one alignment mark is located in a central region of the die.
17. The pre-applied underfill structure of claim 13 , wherein the at least one alignment mark is located in an off-central region of the die.
18. The pre-applied underfill structure of claim 13 , wherein the at least one alignment mark is located in one or more corners of the die.
19. The pre-applied underfill structure of claim 13 , wherein the pre-applied underfill material is an epoxy.
20. The pre-applied underfill structure of claim 13 , wherein the pre-applied underfill material is a thermally reversible material.
21. A pre-applied underfill structure, comprising:
a wafer comprising a plurality of dies, wherein each one of the dies includes at least one alignment mark;
a transparent low surface tension material deposited onto at least a portion of the at least one alignment mark; and
a pre-applied underfill material deposited onto the wafer at a thickness approximating a height of the bumps on the dies, wherein the low surface tension material is selected to provide the pre-applied underfill material with a contact angle greater than 60 degrees, and wherein the at least portion of the at least one alignment mark including the transparent low surface tension material deposited thereon is free of the pre-applied underfill material.