One-piece interconnection package and process

• US 4,876,587 A
• Filed: 05/05/1987
• Issued: 10/24/1989
• Est. Priority Date: 05/05/1987
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation Santa Clara California
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Emamjomeh, Ali, Hilton, Robert, Belani, Jagdish
• Primary Examiner(s): James, Andrew J.
• Assistant Examiner(s): NGO, NGAN V
• Application Number:
  US07/046,988
• Time in Patent Office: 903 Days
• Field of Search: 357/70, 357/68, 357/72, 357/74
• US Class Current: 257/669
• CPC Class Codes: H01L 2224/16 of an individual bump connector
• CPC Class Codes: H01L 2224/16245 the item being metallic
• CPC Class Codes: H01L 23/49541 Geometry of the lead-frame
• CPC Class Codes: H01L 23/49548 Cross section geometry H01L23/49562 takes precedence
• CPC Class Codes: H01L 2924/3511 Warping

Abstract

A one-piece interconnection structure (10) for an SO package (60) is formed from a single sheet strip (12) of copper having a thickness of about 8 mils. Contact finger patterns (14) are formed from a plurality of contact fingers (22) which extend in cantilever fashion. The fingers (22) have tips (24) of a reduced thickness of between about 2-3 mils. Stress relief slots (26) having a depth of about 2 mils are formed in the underside of each finger (22) spaced back from the tips (24) to give the fingers increased flexibility for downward bending during assembly operations. Vertical slots (28) on opposing sides of the fingers behind the stress relief slots give increased lateral flexibility to the fingers. Steps (30) extend vertically along the lateral fingers (22) and have two surfaces (32 and 34) angularly disposed with respect to central surface (36) on the top and bottom fingers. In combination, the stress relief slots (26), vertical slots (28) and the different configuration of the steps (30) make the fingers (22) have the same flexing characteristics in response to bending forces on them, even though the fingers (22) have different shapes depending on their positions in the finger pattern (14). The contact fingers (22) and the reduced thickness tips (24) are formed by masking strip (12) with photoresist in patterns on the top and bottom of the strip to define the contact fingers, but leaving the strip exposed on its top surface where the reduced thickness tips are to be formed, and directing spray etchant at the top of the strip and at the bottom of the strip at different pressures.

Claims

1. A one-piece interconnection structure for an integrated circuit, which comprises a plurality of conductive metal leads having body portions with outwardly directed first ends and second ends directed inward to surround a centrally disposed area, a plurality of contact fingers attached to the second ends of said body portions, said contact fingers having tips extending unsupported into the centrally disposed area, said contact finger tips being arranged and positioned for bonding to contact pads of an integrated circuit, said body portions of said leads having a first thickness and said contact finger tips having a second thickness less than the first thickness, said body portions of said leads having a cross-section with upper sides and lower sides forming an intersection between a top surface and a bottom surface of said body portions of said leads, said intersection between said upper and lower sides of said body portions of said leads being closer to one of said top surface and said bottom surface of said body portions of said leads, said contact finger tips having a surface parallel to said top surface and said bottom surface of said body portions of said leads, said surface of said contact finger tips being aligned with said intersection.

2. The one-piece interconnection structure for an integrated circuit of claim 1 in which said upper and lower sides have an arcuate shape and different radii of curvature.

3. The one-piece interconnection structure for an integrated circuit of claim 1 in which the second thickness is less than half of the first thickness.

4. The one-piece interconnection structure for an integrated circuit of claim 1 in which said leads have horizontal stress relief grooves extending across one of said top surface and said bottom surface of said body portions facing away from said surface of said contact finger tips.

5. The one-piece interconnection for an integrated circuit of claim 4 in which said body portions of at least some of said leads have a pair of opposed, vertical grooves extending between the top surface and the bottom surface of said body portions.

6. The one-piece interconnection for an integrated circuit of claim 1 attached to an integrated circuit with a plurality of contact pads on said integrated circuit each bonded to one of said contact finger tips.

7. The one-piece interconnection for an integrated circuit of claim 6 enclosed in a sealed enclosure over said integrated circuit and said contact finger tips.

8. The one-piece interconnection for an integrated circuit of claim 8 in which said sealed enclosure comprises a plastic body and a plastic top bonded to said plastic body with the first ends of said leads extending from said sealed enclosure.