Underfill coating for LOC package

• US 6,090,644 A
• Filed: 05/11/1999
• Issued: 07/18/2000
• Est. Priority Date: 05/21/1996
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Moden, Walter L.
• Primary Examiner(s): Picardat, Kevin M.
• Application Number:
  US09/309,347
• Time in Patent Office: 434 Days
• Field of Search: 438/118, 438/123, 438/124, 438/126, 438/127
• US Class Current: 438/127
• CPC Class Codes: H01L 2224/04042 Bonding areas specifically adapted for wire connectors, e.g. wirebond pads
• CPC Class Codes: H01L 2224/05647 Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2224/06136 Covering only the central area of the surface to be connected, i.e. central arrangements
• CPC Class Codes: H01L 2224/32014 the layer connector being smaller than the bonding area, e.g. bond pad
• CPC Class Codes: H01L 2224/32245 the item being metallic
• CPC Class Codes: H01L 2224/45124 Aluminium (Al) as principal constituent
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/4826 Connecting between the body and an opposite side of the item with respect to the body
• CPC Class Codes: H01L 2224/48647 Copper (Cu) as principal constituent
• CPC Class Codes: H01L 2224/48747 Copper (Cu) as principal constituent
• CPC Class Codes: H01L 2224/49171 Fan-out arrangements
• CPC Class Codes: H01L 2224/73215 Layer and wire connectors
• CPC Class Codes: H01L 23/4951 Chip-on-leads or leads-on-chip techniques, i.e. inner lead fingers being used as die pad
• CPC Class Codes: H01L 24/06 of a plurality of bonding areas
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 24/49 of a plurality of wire connectors
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00012 : Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 : the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01006 : Carbon [C]
• CPC Class Codes: H01L 2924/01013 : Aluminum [Al]
• CPC Class Codes: H01L 2924/01014 : Silicon [Si]
• CPC Class Codes: H01L 2924/0102 : Calcium [Ca]
• CPC Class Codes: H01L 2924/01029 : Copper [Cu]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/01073 : Tantalum [Ta]
• CPC Class Codes: H01L 2924/01075 : Rhenium [Re]
• CPC Class Codes: H01L 2924/01078 : Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/01082 : Lead [Pb]
• CPC Class Codes: H01L 2924/014 : Solder alloys
• CPC Class Codes: H01L 2924/181 : Encapsulation
• CPC Class Codes: H01L 2924/1815 : Shape
• CPC Class Codes: Y10T 29/49121 : Beam lead frame or beam lead device
• CPC Class Codes: Y10T 428/24165 : Hexagonally shaped cavities
• CPC Class Codes: Y10T 428/24207 : with strand[s] or strand-portion[s] between layers [e.g., upholstery trim, etc.]

Abstract

An LOC die assembly is disclosed including a die dielectrically adhered to the underside of a lead frame. An underfill material is introduced between each lead finger and semiconductor die, extending from the bonding location of the die and the edge of the die, in order to prevent filler particles from lodging between the leads and the active surface of the die during transfer molding of a plastic encapsulant. The seal created by the underfill material reduces point stresses on the active surface of the die usually caused by the filler particles. The decreased flexure in the leads further enhances the locking of the leads in position with respect to the die.

Claims

1. A method of assembling a semiconductor die to a lead frame, said method comprising the steps of:

providing a lead frame having a plurality of lead members, at least one lead member of said plurality of lead members having a plurality of longitudinal edges, having a top surface, having a bottom surface, having a lead end portion connected to a portion of the lead frame, having a length, having a thickness, and having a free end portion;

providing a die having an active surface, having at least one bond pad thereon, and having at least one outer edge;

superimposing a portion of one of the top surface and the bottom surface of the at least one lead member of the plurality of lead members of said lead frame on said die, the portion of the one of the top surface and bottom surface of the at least one lead member of the plurality of lead members extending over a portion of the active surface of said die forming a gap therebetween; and

applying an underfill material around at least a portion of said at least one lead member of said plurality of lead members, the underfill material flowing by capillary action into the gap between the portion of one of the top surface and the bottom surface of said at least one lead member of said plurality of lead members and the portion of the active surface of said die.

2. The method of claim 1, further comprising the step of:

curing said underfill material.

3. The method of claim 1, further comprising the step of:

drying said underfill material.

4. The method of claim 1, further comprising the step of:

adhering said at least one lead member of said plurality of lead members to said active surface of said die.

5. The method of claim 1, further comprising the step of:

adhering each lead member of said plurality of lead members to said active surface of said die.

6. The method of claim 1, wherein the step of applying an underfill material includes:

applying said underfill material substantially between each lead member of said plurality of lead members and said active surface of said die.

7. The method of claim 1, wherein the step of applying an underfill material includes:

applying said underfill material at a location substantially adjacent to at least one edge of said plurality of longitudinal edges of said at least one lead member of said plurality of lead members.

8. The method of claim 1, wherein the step of applying an underfill material includes:

applying said underfill material substantially over said top surface of said at least one lead member.

9. The method of claim 1, wherein the step of applying an underfill material includes:

applying said underfill material substantially on a portion of said active surface of said die.

10. The method of claim 9, wherein a sufficient quantity of the underfill material is applied to substantially cover said active surface of said die.

11. The method of claim 1, wherein said underfill material is applied with an underfill dispenser.

12. The method of claim 11, wherein said underfill dispenser is a syringe.

13. The method of claim 1, wherein said underfill material is sprinkled on said die.

14. The method of claim 1, wherein said underfill material is dripped on said die.

15. The method of claim 1, wherein said underfill material is sprayed on said die.

16. The method of claim 1, wherein said underfill material is write dispensed on said die.

17. The method of claim 1, wherein the step of applying an underfill material includes:

applying said underfill material substantially over a portion of said top surface of said at least one lead member and over a portion of said active surface of said die.

18. The method of claim 1, wherein the method further comprising the step of:

bonding at least one wire to a portion of said at least one lead member and said at least one bond pad on said active surface of said die.

19. The method of claim 18, wherein the step of applying an underfill material includes:

applying said underfill material substantially on a portion of said at least one lead member, a portion of said active surface of said die, and a portion of said at least one wire.

20. The method of claim 18, wherein a sufficient quantity of underfill material is applied to substantially cover a portion of said active surface of said die and a portion of said at least one wire.

21. A method of transfer molding a plastic package about a die assembly using a molding compound including filler particles, said method of transfer molding comprising the steps of:

providing a lead frame having a plurality of lead members, at least one lead member of said plurality of lead members having longitudinal edges, having a top surface, having a bottom surface, having a lead end portion connected to a portion of the lead frame, having a length, having a thickness, and having a free end portion;

providing a die having an active surface having at least one bond pad thereon and having at least one outer edge;

superimposing said lead frame on said die with said active surface lying adjacent said lead frame and a portion of the free end portion of said at least one lead member of the plurality of lead members extending over the at least one outer edge of said die and over a portion of the active surface of said die forming a gap therebetween;

applying an underfill material between the portion of the free end portion of said at least one lead member of said plurality of lead members and said active surface of said die;

disposing the lead frame having the underfill material disposed between the portion of the free end portion of the at least one lead member of the plurality of lead members and the active surface of the die, said die being secured by its active surface to the portion of the free end portion of said at least one lead member of the plurality of lead members, in a lead over chip configuration in a mold cavity;

introducing a softened molding compound including filler particles therein into said mold cavity to form a plastic package around a portion of the lead frame and said die; and

preventing flow of the softened molding compound into the gap between the portion of the free end portion of the at least one lead member of the plurality of lead members and the active surface of said die, thereby preventing the filler particles in the softened molding compound from flowing between said active surface of said die and said at least one lead member of the plurality of lead members during said transfer molding.

22. The method of claim 21, wherein said filler particles are prevented from flowing between said active surface of said die and said at least one lead member of the plurality of lead members by underfill material.

23. The method of claim 22, wherein said underfill material is substantially located between said active surface of said die and said at least one lead member of the plurality of lead members.

24. The method of claim 23, wherein said underfill material is substantially located between said active surface of said die and said plurality of lead members.