Standard Test Methods for Measuring Pull Strength of Microelectronic Wire Bonds - PDF

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ASTM F459 specifies standardized procedures for measuring the pull strength of wire bonds in microelectronic devices.
This testing is critical in semiconductor packaging, electronics assembly, and microelectronic device reliability assurance, ensuring that bonded wires can withstand mechanical stresses during manufacturing, shipping, and operation.

This overview explains ASTM F459’s purpose, required equipment, the test procedure, and other related standards.

Purpose of ASTM F459

The goals of ASTM F459 are to:

• Measure the mechanical strength of wire bonds by applying a tensile force until failure occurs.

• Assess the quality and reliability of wire bonding processes (e.g., ultrasonic bonding, thermosonic bonding, thermocompression bonding).

• Help detect defects such as weak bonds, improper bonding parameters, contamination, or material degradation.

• Provide data for process validation, quality control, reliability studies, and failure analysis.

Wire bonds are often the most fragile part of a microelectronic assembly, and poor bond strength can lead to early device failure.

Equipment Required

Testing according to ASTM F459 generally requires:

• Bond Pull Tester Machine:

  • A highly sensitive device capable of applying precise tensile forces to micro-scale wires.

  • Typically equipped with motorized stages and fine control of displacement.

• Pincer Grips or Hook Grips

  • A specialized fine hook or loop attachment that engages the wire without damaging it prior to pulling.

• Microscope or Visual System:

  • Needed to accurately position the pull tool and inspect the bond before and after testing.

• Data Acquisition System:

  • For recording the peak pull force and capturing force-displacement curves.

• Environmental Control (Optional):

  • For tests requiring specific humidity, temperature, or atmospheric conditions (e.g., testing bonds exposed to accelerated aging).

Test Specimens

• Test specimens are typically microelectronic components with bonded wires connecting:

  • Pads to leads

  • Pads to pads

  • Pads to die surfaces

• Wire materials commonly include gold, aluminum, or copper.

• Wire diameters can range from very fine (e.g., 15–75 microns) to thicker wire bonds for power devices.

Test Procedure for ASTM F459

1. Specimen Preparation:

   • Mount the device securely onto the bond pull tester’s fixture.

   • Ensure the specimen is free of debris and contamination.

2. Test Setup:

   • Position the hook or loop under the wire at a designated height (typically close to midspan between bond points or according to specified requirements).

   • Care must be taken not to damage or pre-load the wire during engagement.

3. Pulling:

   • Apply a steady upward tensile force at a constant rate.

   • Recommended pull rates and positioning may vary depending on wire material and diameter.

   • Record the peak force required to break or detach the bond.

4. Observation of Failure:

   • After testing, inspect the failure mode under magnification.

   • Typical failure modes include:

     • Wire break

     • Heel break

     • Bond lift

     • Pad lift

     • Mixed failure

5. Data Recording:

   • Record maximum pull force (in grams-force [gf], Newtons [N], or other specified units).

   • Document failure mode and location.

Results and Reporting

A proper ASTM F459 test report should include:

• Wire material, diameter, and bond type.

• Environmental conditions during testing.

• Pull test method details (pull speed, hook placement).

• Maximum pull force values for each test.

• Statistical analysis (average, min, max, standard deviation).

• Failure mode categorization (heel break, bond lift, etc.).

• Visual documentation (optional) showing failure areas.

Consistent reporting enables manufacturers and engineers to monitor bonding processes, qualify devices, and support reliability requirements.

Related ASTM Standards

Several other ASTM and JEDEC standards relate to microelectronic wire bond evaluation:

• ASTM F1269 – Standard Test Methods for Evaluating Bond Strength for Microelectronic Wire Bonds by Destructive Pull Testing and Non-Destructive Pull Testing:
  Focuses on both destructive and non-destructive testing techniques for wire bonds.

• ASTM F72 – Standard Test Methods for Contact Pressure and Contact Resistance of Wire Bonded Connections:
  Measures the electrical contact performance, often evaluated alongside mechanical pull strength.

• ASTM F1871 – Standard Test Method for Measuring Pull Strength and Shear Strength of Wire Bonds for High Reliability Applications:
  Developed for more stringent reliability testing, often used for military and aerospace components.

• MIL-STD-883 Method 2011 – Bond Strength (Destructive Bond Pull Test):
  A military standard procedure for destructive bond pull testing of microelectronic devices.

• JEDEC JESD22-B116 – Test Method for Wire Bond Shear and Pull Test Methodologies:
  Semiconductor industry standard providing guidance on wire bond testing.

Each of these standards targets specific aspects of wire bonding, including mechanical, electrical, and reliability testing under varying conditions.

Applications of ASTM F459 Testing

ASTM F459 testing is widely applied in industries such as:

• Semiconductor manufacturing

• Medical device electronics

• Automotive electronics

• Consumer electronics

• Defense and aerospace systems

Testing ensures that delicate wire bonds are robust enough to endure production handling, mechanical stress, temperature cycling, and vibration.

Conclusion

ASTM F459 provides essential test methods for measuring the tensile pull strength of microelectronic wire bonds.
By applying controlled forces and observing failure modes, manufacturers can assess and improve the reliability of microelectronic assemblies.
While other standards like ASTM F1269, ASTM F1871, and MIL-STD-883 offer complementary methods, ASTM F459 remains a key reference for routine bond strength evaluation and quality assurance in microelectronics.