Method for fabricating thin, strong, and flexible die for smart cards

• US 5,480,842 A
• Filed: 04/11/1994
• Issued: 01/02/1996
• Est. Priority Date: 04/11/1994
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Clifton, Mark B., Flynn, Richard M., Verdi, Fred W.
• Primary Examiner(s): Fourson, George
• Assistant Examiner(s): Pham, Long
• Application Number:
  US08/225,687
• Time in Patent Office: 631 Days
• Field of Search: 437/226, 437/225, 437/228, 437/974, 148/DIG. 28, 148/DIG. 51, 257/679
• US Class Current: 438/464
• CPC Class Codes: G06K 19/07745 Mounting details of integrated circuit chips
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• 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 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/10253 Silicon [Si]
• CPC Class Codes: H01L 2924/14 Integrated circuits
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding
• CPC Class Codes: Y10S 438/977 Thinning or removal of substrate

Abstract

Improved methods for fabricating smart cards are disclosed. Semiconductor die approximately 0.004 to 0.007 inches thick are fabricated using chemical stress relief processes and UV dicing tape. The die are positioned substantially on the neutral axis of a smart card, thereby providing smart cards having improved resistance to mechanical flexure.

Claims

1. A method for fabricating a plurality of smart card semiconductor die from a full thickness semiconductor wafer including the following steps:

(a) mapping the semiconductor wafer to identify, specific semiconductor die, thus permitting the locations of bad or defective die to be specified for future reference;

(b) taping a first surface of the semiconductor wafer with protective tape;

(c) grinding the semiconductor wafer to a thickness of approximately 155 um;

(d) allowing the protective tape to remain on the wafers for a period of time not to exceed 24 hours;

(e) during the period of time specified in step (d), chemically etching the semiconductor wafer to strengthen the wafer by removing crystal defects and by repairing crystal lattice damage;

the etching process including the step of immersing the wafer in an acid bath of approximately 7;

2;

1 Nitric Acid;

Hydrofluoric Acid;

Acetic Acid for approximately one minute at ambient room temperature;

(f) rinsing the wafer in a deionized water bath for a period of about 10 minutes to remove residual acid;

(g) blowing the wafer dry with a Nitrogen gun;

(h) positioning the wafer on a flat, porous ceramic wafer chuck;

the chuck equipped to apply a substantially uniform vacuum across the wafer surface to prevent water flexure during step (j);

(j) detaping the protective tape from the wafer;

(k) taping the wafer with dicing tape;

(l) dicing the wafer using a dicing saw;

(m) exposing the wafers to UV light to cure the UV dicing tape on the wafers and to reduce the adhesion of the tape to the die; and

(n) ejecting the die from the UV dicing tape using non-piercing ejector pins and soft rubber or plastic die pickup heads, thereby reducing or eliminating die damage.

2. A method for fabricating a plurality of smart card semiconductor die from a full thickness semiconductor wafer including the following steps:

(a) mapping the semiconductor wafer to identify specific semiconductor die, thus permitting the locations of bad or defective die to be specified for future reference;

(b) taping a first surface of the semiconductor wafer with protective tape;

(c) grinding the semiconductor wafer to a thickness of approximately 155 um;

(d) allowing the protective tape to remain on the wafers for a period of time not to exceed 24 hours;

(e) during the period of time specified in step (d), chemically etching the semiconductor water to strengthen the wafer by removing crystal defects and by repairing crystal lattice damage;

the etching process including the step of immersing the wafer in an acid bath of approximately 7;

2;

1 Nitric Acid;

Hydrofluoric Acid;

Acetic Acid for approximately one minute at ambient room temperature;

(f) rinsing the wafer in a deionized water bath for a period of about 10 minutes to remove residual acid;

(g) drying the wafer;

(h) positioning the wafer on a substantially flat surface equipped to apply a substantially uniform vacuum across the wafer surface to prevent wafer flexure during step (j);

(j) detaping the protective tape from the wafer;

(k) taping the wafer, with UV dicing tape, to a dicing frame;

(m) dicing the wafer using a dicing saw;

(n) exposing the wafers to UV light to cure the UV dicing tape on the wafers and to reduce the adhesion of the tape to the die; and

(p) ejecting the die from the UV dicing tape using non-piercing ejector pins and soft die pickup heads, thereby reducing or eliminating die damage.

3. A method for fabricating a plurality of smart card semiconductor die from a full thickness semiconductor wafer including the following steps:

(a) mapping the semiconductor wafer to identify specific semiconductor die, thus permitting the locations of bad or defective die to be specified for future reference;

(b) taping a first surface of the semiconductor wafer with protective tape;

(c) grinding the semiconductor wafer to a thickness of approximately 155 um;

(d) allowing the protective tape to remain on the wafers for a period of time not to exceed 24 hours;

(e) during the period of time specified in step (d), chemically etching the semiconductor wafer to strengthen the wafer by removing crystal defects and by repairing crystal lattice damage;

the etching process including the step of immersing the water in an acid bath;

(f) rinsing the wafer in a deionized water bath to remove residual acid;

(g) drying the wafer;

(h) positioning the wafer on a surface equipped to apply a substantially uniform vacuum across the wafer surface to prevent wafer flexure during step (j);

(j) detaping the protective tape from the wafer;

(k) taping the wafer, with UV dicing tape, to a dicing frame;

(m) dicing the wafer using a dicing saw;

(n) exposing the wafers to UV light to cure the UV dicing tape on the waters and to reduce the adhesion of the tape to the die; and

(p) ejecting the die from the UV dicing tape using non-piercing ejector pins and soft die pickup heads, thereby reducing or eliminating die damage.