Strain release contact system for integrated circuits

• US 6,159,773 A
• Filed: 02/12/1999
• Issued: 12/12/2000
• Est. Priority Date: 02/12/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Mou-Shiung Lin
• Inventors: Lin, Mou-Shiung
• Primary Examiner(s): Bowers, Charles
• Assistant Examiner(s): JONES, JOSETTA I
• Application Number:
  US09/249,252
• Time in Patent Office: 669 Days
• Field of Search: 438/117, 438/612
• US Class Current: 438/117
• CPC Class Codes: H01L 2224/03462 Electroplating
• CPC Class Codes: H01L 2224/0347 using a lift-off mask
• CPC Class Codes: H01L 2224/0384 involving a mechanical process, e.g. planarising the bonding area
• CPC Class Codes: H01L 2224/0401 Bonding areas specifically adapted for bump connectors, e.g. under bump metallisation [UBM]
• CPC Class Codes: H01L 2224/05001 Internal layers
• CPC Class Codes: H01L 2224/05016 in side view
• CPC Class Codes: H01L 2224/05017 comprising protrusions or indentations
• CPC Class Codes: H01L 2224/05022 the internal layer being at least partially embedded in the surface
• CPC Class Codes: H01L 2224/05027 the internal layer extending out of an opening
• CPC Class Codes: H01L 2224/05099 Material
• CPC Class Codes: H01L 2224/05124 Aluminium [Al] as principal constituent
• CPC Class Codes: H01L 2224/05139 Silver [Ag] as principal constituent
• CPC Class Codes: H01L 2224/05144 Gold [Au] as principal constituent
• CPC Class Codes: H01L 2224/05147 Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2224/05558 conformal layer on a patterned surface
• CPC Class Codes: H01L 2224/05568 the whole external layer protruding from the surface
• CPC Class Codes: H01L 2224/05647 Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2224/05671 Chromium [Cr] as principal constituent
• CPC Class Codes: H01L 2224/1132 Screen printing, i.e. using a stencil
• CPC Class Codes: H01L 2224/11462 Electroplating
• CPC Class Codes: H01L 2224/13099 : Material
• CPC Class Codes: H01L 2224/131 : with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof
• CPC Class Codes: H01L 2224/13109 : Indium [In] as principal constituent
• CPC Class Codes: H01L 2224/13116 : Lead [Pb] as principal constituent
• CPC Class Codes: H01L 24/03 : Manufacturing methods
• CPC Class Codes: H01L 24/05 : of an individual bonding area
• CPC Class Codes: H01L 24/11 : Manufacturing methods for bumps on insulating substrates H01L21/4853
• CPC Class Codes: H01L 24/13 : of an individual bump connector
• CPC Class Codes: H01L 2924/0001 : Technical content checked by a classifier
• 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 2924/01005 : Boron [B]
• CPC Class Codes: H01L 2924/01006 : Carbon [C]
• CPC Class Codes: H01L 2924/01013 : Aluminum [Al]
• CPC Class Codes: H01L 2924/01019 : Potassium [K]
• CPC Class Codes: H01L 2924/01024 : Chromium [Cr]
• CPC Class Codes: H01L 2924/01029 : Copper [Cu]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/01047 : Silver [Ag]
• CPC Class Codes: H01L 2924/01049 : Indium [In]
• CPC Class Codes: H01L 2924/0105 : Tin [Sn]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/01082 : Lead [Pb]
• CPC Class Codes: H01L 2924/01322 : Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/014 : Solder alloys
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/19042 : being an inductor

Abstract

The problem of stress transmission from the outside of an integrated circuit package into the interior of the semiconductor has been significantly reduced by placing a micro-spring between the external solder ball and the interior tab. The process for manufacturing such a structure begins with a fully completed integrated circuit on whose surface freestanding metal posts are formed, each post being in contact with an I/O pad. Using a leveling plate at elevated temperature, the posts are given a permanent tilt relative to the surface and are then encapsulated in an elastomer. This subprocess may then be repeated as many times as desired with the direction in which the posts lean being changed by 90 degrees at each iteration. This results in the formation of an orthogonal spiral which acts as a coil spring to absorb stress originating at the solder ball.

Claims

1. A process for forming a stress release contacting system in an integrated circuit, comprising the sequential steps of:

(a) providing a silicon wafer containing a completed integrated circuit and having an upper surface on which are contact pads connected to said integrated circuit;

(b) forming first metal posts, attached one-on-one to the contact pads and extending vertically upwards from the contact pads;

(c) placing a leveling plate on said metal posts;

(d) through application of force to said leveling plate at an elevated temperature, causing the posts to tilt at an angle relative to said wafer upper surface and to point in a direction;

(e) filling all empty space between the leveling plate and the wafer surface with an elastomer while leaving all ends of the posts uncovered;

(f) removing the leveling plate;

(g) forming second metal posts that attach one-on-one to said uncovered ends;

(h placing a leveling plate on said metal posts;

(i) through application of force to said leveling plate at an elevated temperature, causing the posts to tilt at said angle relative to said wafer upper surface and to point in a direction that is orthogonal to the direction of the most recently formed posts;

(j) repeating steps (e) through (i) a number of times;

(k) filling all empty space between the leveling plate and the wafer surface with an elastomer while leaving all ends of the posts uncovered;

(l) removing the leveling plate;

(m) forming pads of underlayer barrier metal over all uncovered ends of said posts; and

(n) forming solder balls that extend upwards and are attached to the underlayer barrier metal pads.

2. The process of claim 1 wherein the step of forming the metal posts further comprises:

depositing a blanket layer of metal;

coating said metal layer with photoresist;

processing the photoresist to form a mask that is present everywhere except for holes over the contact pads;

by means of electroplating, filling said holes with the metal;

removing the photoresist, thereby leaving metal posts; and

removing the blanket layer.

3. The process of claim 1 wherein said elevated temperature is between about 100 and 400°

C.

4. The process of claim 1 wherein said tilt angle is between about 15 and 75 degrees.

5. The process of claim 1 wherein the step of filling with elastomer further comprises:

after the leveling plate has cooled down, placing the wafer in a vacuum having a pressure around 0.1 torr;

dispensing elastomer along all edges of the wafer; and

returning the pressure to atmospheric, thereby causing the elastomer to be sucked into said empty space.

6. The process of claim 1 wherein the posts have a diameter between about 5 and 100 microns.

7. The process of claim 1 wherein the posts have a length between about 5 and 200 microns.

8. The process of claim 1 wherein the number of times that steps (e) through (i) are repeated is between 0 and about 10 times.

9. The process of claim 1 wherein the elastomer is selected from the group consisting of silicone elastomer, polyimides and benzocyclobutene.

10. The process of claim 1 wherein the metal posts are selected from the group consisting of gold, silver, copper, solder, and aluminum.

11. The process of claim 1 further comprising, between steps (f) and (g):

depositing a layer of joint strengthening metal on the elastomer; and

patterning and etching said layer to form joint strengthening discs symmetrically disposed on and around said uncovered ends.