金球推力国际标准Wire Bond Shear Test

EIA/JEDEC STANDARD

Wire Bond Shear Test Method EIA/JESD22-B116

JULY 1998

ELECTRONIC INDUSTRIES ALLIANCE

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JEDEC Standard 22-B116

Page 1

WIRE BOND SHEAR TEST

(From JEDEC Council Ballot JCB-97-64, formulated under the cognizance of the JC-14.1 Subcommittee on Reliability Test Methods for Packaged Devices.)

1 Scope

This test provides a means for determining the strength of the bond between a gold ball bond on a die bonding surface or an aluminum wedge or stitch bond on a package bonding surface, and may be performed on pre-encapsulation or post-encapsulation parts. This measure of bond strength is extremely important in determining two features:

1) the integrity of the metallurgical bond which has been formed.

2) the quality of gold and aluminum wire bonds to die or package bonding surfaces.

These test methods cover ball bonds made with small diameter (from 18 to 76 μm, or from 0.7 to 3 mil) wire and wedge bonds made with larger diameter (minimum of 3 mil) wire, of the type used in integrated circuits and hybrid microelectronic assemblies.

These test methods can be used only when the ball height (at least 10.16 μm or 0.4 mil) and diameter for ball bonds, or the wire height (at least 1.25 mils in height at the compressed bonded area) of the wedge bond, are large enough and adjacent interfering structures are far enough away to allow suitable placement and clearance (above the bonding pad or leadframe post and between adjacent bonds) of the shear test chisel. This test method may also apply to gold wedge or stitch bonds if the wire is thick enough to allow shearing of the wire from the bonding surface without smearing similar to a shearing skip.

The wire bond shear test is destructive. It is appropriate for use in process development, process control and/or quality assurance.

2 Terms and Definitions

The terms and definitions shall be in accordance with the following paragraphs.

2.1 Ball Bond

The adhesion or welding of a thin wire, usually gold, to a die pad metallization, usually an aluminum alloy, using a thermosonic wire bond process. The ball bond includes the enlarged spherical, or nail head, portion of the wire (provided by the flame-off and first bonding operation in the thermal compression and thermosonic process, or both), the underlying bonding pad and the ball bond-bonding pad intermetallic weld interface.

2.2 Bonding Surface

Either 1) the die pad metallization or 2) the package surface metallization to which the wire is ball, wedge or stitch bonded.

Test Method B116

JEDEC Standard 22-B116

Page 2

2 Terms and Definitions (cont’d)

2.3 Bond Shear

A process in which an instrument uses a chisel shaped tool to shear or push a ball or wedge bond off the bond pad (see Figure 1). The force required to cause this separation is recorded and is referred to as the bond shear force. The bond shear force of a gold ball bond, when correlated to the diameter of the ball bond, is an indicator of the quality of the metallurgical bond between the gold ball bond and the bond pad metallization. The bond shear force of an aluminum wedge bond, when compared to the manufacturer's tensile strength of the wire, is an indicator of the integrity of the weld between the aluminum wire and the bond pad or package surface metallization.

Figure 1 — Bond Shear set-up

2.4 Definition of Bond Shear Codes for Ball and Wedge Bonds (see Figure 2)

2.4.1 Type 1 - Bond Lift

A separation of the entire wire bond from the bonding surface with only an imprint being left on the bonding surface. There is very little evidence of intermetallic formation or welding, or disturbance of the bonding surface metallization.

2.4.2 Type 2 - Bond Shear

A separation of the wire bond where 1) A thin layer of the bonding surface metallization remains with the wire bond and an impression is left in the bonding surface, or 2) Intermetallics remain on the bonding surface and with the wire bond, or 3) A major portion of the wire bond remains on the bonding surface. Test Method B116

JEDEC Standard 22-B116

Page 3 2 Terms and Definitions (cont’d)

2.4 Definition of Bond Shear Codes for Ball and Wedge Bonds (see Figure 2) (cont’d)

2.4.3 Type 3 - Cratering

A condition under the die pad metallization in which the insulating layer (oxide or interlayer dielectric) and the bulk material (silicon) separate or chip out. Separation interfaces which show pits or depressions in the insulating layer (not extending into the bulk) are not considered craters. It should be noted that cratering can be caused by several factors including the wire bonding operation, the post-bonding processing, and even the act of shear testing itself. Cratering present prior to the shear test operation is unacceptable.

2.4.4 Type 4 - Arm Contacts Specimen (Bonding Surface Contact)

The shear tool contacts the bonding surface to produce an invalid shear value. This condition may be due to improper placement of the specimen, a low shear height or instrument malfunction. This bond shear type is not acceptable and shall be eliminated from the shear data.

2.4.5 Type 5 - Shearing Skip

The shear tool removes only the topmost portion of the ball or wedge bond. This condition may be due to improper placement of the specimen, a high shear height or instrument malfunction. This bond shear type is not acceptable and shall be eliminated from the shear data.

2.4.6 Type 6 - Bond Pad (or Bonding Surface) Lift

A separation between the bonding surface metallization and the underlying substrate or base material. There is evidence of bonding surface metallization remaining attached to the ball or wedge bond.

Test Method B116

JEDEC Standard 22-B116

Page 4

Test Method B116

2 Terms and Definitions (cont’d)

2.4 Definition of Bond Shear Codes for Ball and Wedge Bonds (see Figure 2) (cont’d)

TYPE 1: Bond Lift TYPE 2: Bond Shear - Gold/Aluminum

TYPE 4: Bonding Surface Contact

TYPE 3: Cratering TYPE 5: Shearing Skip TYPE 6: Bonding Surface Lift

Figure 2 — Bond Shear Codes

Examples shown here are for ball bonds. These same modes also apply to wedge and stitch bonds.

JEDEC Standard 22-B116

Page 5 2 Terms and Definitions (cont’d)

2.5 Shear Tool or Arm

A tungsten carbide, or equivalent, chisel with specific angles on the bottom and back of the tool to ensure a shearing action.

underlying bonding pad, and the ball bond-bonding pad intermetallic weld interface.

2.6 Wedge Bond

The adhesion or weld of a thin wire, usually aluminum, to a package bonding surface, usually a plated leadframe post or finger, using an ultrasonic wire bonding process. A wedge bond is sometimes also called a stitch bond. The wedge bond includes the compressed (ultrasonically bonded) area of the wire and the underlying bonding surface. For bonding to an aluminum alloy die bond pad, there is no wedge bond-bond pad intermetallic because the two materials are of the same composition, but the two materials are recrystallized together by the ultrasonic energy of the welding process.

3 Apparatus and material

The apparatus and materials required for bond shear shall be as follows:

3.1 Inspection Equipment

An optical microscope system or scanning electron microscope providing a minimum of 70X magnification.

3.2 Measurement Equipment

An optical microscope/measurement system capable of measuring the bond diameter to within ± 0.0001 inch (0.1 mil).

3.3 Workholder

Fixture used to hold the part being tested parallel to the shearing plane and perpendicular to the shear tool. The fixture shall also eliminate part movement during bond shear testing. If using a caliper controlled workholder, place the holder so that the shear motion is against the positive stop of the caliper. This is to ensure that the recoil movement of the caliper controlled workholder does not influence the bond shear test.

3.4 Bond Shear Equipment

The bond shear equipment must be capable of precision placement of the shearing tool (±2.54μm or ±0.10 mil) above the substrate. The specified distance (h) above the topmost part of the bonding surface shall ensure the shear tool does not contact the surface of the die and shall be less than the distance from the topmost part of the bonding surface to the center line (C L) of the ball or wedge bond.

Test Method B116

JEDEC Standard 22-B116

Page 6

3 Apparatus and material (cont’d)

3.5 Bond Shear Tool

Required shear tool parameters include but are not limited to: flat shear face, sharp shearing edge, shearing width of a minimum of 1.2X the bond diameter or bond length. The shearing tool should be designed so as to prevent ploughing and drag during testing. The tool should be clean and free of chips or other defects that will interfere with the shearing test.

4 Procedure

4.1 Calibration

Before performing the bond shear test, it must be determined that the equipment has been calibrated in accordance with manufacturer's specifications and is presently in calibration. Recalibration is required if the equipment is moved to another location.

4.2 Visual Examination of Bonds to be Tested After Decapsulation

If performing bond shear testing on a part which has been opened using wet chemical and/or dry etch techniques, the bond pads shall be examined to ensure there is no absence of metallization on the bonding surface area due to chemical etching, and wire bonds are attached to the bonding surface. Those ball or wedge bonds on bond pads with significant chemical attack or absence of metallization shall not be used for ball shear testing. It is possible that wire bonds on bonding surfaces without degradation from chemical attack may not be attached to the bonding surface due to other causes (e.g., package stress). These wire bonds are considered valid and shall be included in the shear data as a zero (0) gram value. Bonds must also be examined to determine if adjacent interfering structures are far enough away to allow suitable placement and clearance (above the bonding surface and between adjacent bonds) for the shear test tool. 4.3 Sample Sizes

Sample sizes shall be a minimum specified by SPC controls in effect for specific processes, or as specified in the applicable procurement document

4.4 Measurement of the Ball Bond Diameter to Determine the Ball Bond Shear Failure Criteria Once the bonding surfaces have been examined and before performing bond shear testing, the diameter of all ball bonds to be tested shall be measured and recorded. For asymmetrical bonds, determine the average using both the largest (d large) and the smallest (d small) diameter values (see Figure 3). These ball bond diameter measurements shall be used to determine the mean, or average, diameter value. The resulting mean, or average, ball bond diameter shall then be used to establish the failure criteria as defined in Figure 4 and Table 1. If process monitor data has established the nominal ball bond diameter, then that value may be used to determine the failure criteria as defined in Figure 4 and Table 1.

Test Method B116

JEDEC Standard 22-B116

Page 7

Test Method B116

4 Procedure (cont’d)

4.4 Measurement of the Ball Bond Diameter to Determine the Ball Bond Shear Failure Criteria

(cont’d)SYMMETRICAL ASYMMETRICAL

Figure 3 — Ball bond measurement (symmetrical vs. asymmetrical)

MINIMUM SHEAR VALUES

BALL BOND DIAMETER (mils)

S H E A R S T R E N G T H (g r a m s )0

10

20

30405060708090100

110

Figure 4 — Minimum recommended individual and average ball bond shear values

(see Table 1 for exact bond shear values)

JEDEC Standard 22-B116

Page 8

Test Method B116

4 Procedure (cont’d)Table 1 — Minimum recommended individual and sample average ball bond shear values

Diameter

(mils)

Minimum Shear Average (grams)Minimum Individual Shear Reading (grams)2.0

12.6 5.72.1

14.0 6.82.2

15.58.12.3

17.19.52.4

18.810.92.5

20.612.42.6

22.414.02.7

24.415.62.8

26.517.42.9

28.619.23.0

30.821.13.1

33.223.13.2

35.625.13.3

38.127.23.4

40.729.43.5

43.431.73.6

46.234.13.7

49.136.53.8

52.139.13.9

55.241.74.0

58.344.34.1

61.647.14.2

65.050.04.3

68.452.94.4

71.955.84.5

75.659.04.6

79.362.14.7

83.165.34.8

87.068.64.9

91.072.05.095.175.5

Note: These shear values are applicable to gold wire ball bonds on aluminum alloy bonding surfaces

JEDEC Standard 22-B116

Page 9 4.5 Performing the Bond Shear Test

The bond shear equipment shall pass all self diagnostic tests before beginning the test. The bond shear equipment and test area shall be free of excessive vibration or movement. Examine the shear tool to verify it is in good condition and is not bent or damaged. Check the shear tool to verify it is in the up position.

Adjust the workholder to match the part being tested. Secure the part to the workholder. Make sure the surface of the die is parallel to the shearing plane of the shear tool. It is important that the shear tool does not contact the surface of the die or adjacent structures during the shearing operation as this will give incorrect high readings.

Position the part so that the bond to be tested is located adjacent to the shear tool. Lower the shear tool, or raise the part depending upon shear equipment used, to approximately the surface from which the bond is to be sheared but not contacting the surface (approximately the thickness of the bond above the surface). Position the ball bond to be tested so that the shear motion will travel perpendicular to the surface edge. Position the wedge bond to be tested so that the shear motion will travel toward the long side of the wedge bond and is free of any interference (i.e. shear the outside bond first and then shear toward the sheared wedge bond). Position the shear tool within approximately one ball (for ball bonds) or wire diameter (for wedge/stitch bonds) of the bond to be shear tested and shear the bond.

4.6 Examination of Sheared Bonds

All bonds shall be sheared in a planned/defined sequence so that later visual examination can determine which shear values should be eliminated because of an improper shear. The bonds shall be examined using at least 70X magnification to determine if the shear tool skipped over the bond (type 5) or the tool scraped or plowed into the surface of the die (type 4). Readings in which either a type 4 or 5 defective shear condition occurred shall be eliminated from the shear data (see Figure 2).

Sheared bonds in which a type 3 cratering condition has occurred shall be investigated further to determine whether the cracking and/or cratering is due to the bonding process or the act of shear testing. Cratering caused prior to the shear test operation is unacceptable. Cratering resulting from the act of shear testing shall be considered acceptable and included in the shear data.

4.7 Footprint Inspection of Aluminum Wedge Bonds

All wire bonding processes to both the die bond pad and the leadframe post shall have a bond footprint inspection performed. For wires too small for bond shear testing (less than 1.25 mils in height at the compressed bonded area), the wire shall be removed at the bond location using a small sharp blade. The removal of the wire shall be sufficient such that the bond interface can be visually inspected and the metallurgical bond area determined. For larger wires after bond shear testing, all devices shall be inspected to examine the failure mode and to determine the bond footprint coverage.

Test Method B116

JEDEC Standard 22-B116

Page 10

4 Procedure (cont’d)

4.8 Bond Shear Data

Data shall be maintained for each bond sheared. The data shall identify the bond (location, bond diameter, wire material, method of bonding, and material bonded to), the shear strength, and the shear code number.

4.9 Shear Codes

For each bond sheared, a code as defined in Figure 2 shall be recorded.

5 Failure criteria

The following failure criteria are not valid for devices that have undergone environmental stress testing or have been desoldered from circuit boards.

5.1 Failure Criteria for Ball Bonds

The recommended minimum individual and sample average bond shear values are shown in Figure 4 and Table 1. This criteria is applicable to gold wire ball bonds on aluminum alloy bond pads. Other material combinations may require a new set of failure criteria.

Alternate minimum bond shear values may be proposed by the supplier if supporting data justifies the proposed minimum values.

5.2 Failure Criteria for Aluminum Wedge Bonds

The wedge bonds on a part shall be considered acceptable if the minimum shear values are equal to or greater than the manufacturer's tensile strength of the bond wire.

In addition, the percent of the bond footprint in which bonding should occur shall be no less than 50%. If it is necessary to control the wire bonding process using SPC for percent coverage, a Cpk value can be calculated to this limit.

6 Summary

The quality level and test conditions are contained within this document unless otherwise specified in the applicable Part Specification and/or Part Drawing.

Test Method B116