Universal Bond Tester for Hi-Rel Wire Bond & Die Attach Applications
Posted by Jessica Sylvester on Mon, Oct 10, 2011
Once wire bonding or die bonding is complete, the next step in the microelectronics assembly process is to test the quality of the bonds, known as bond testing.
What is Bond Testing Used For?
Whether a new product is undergoing development, or a tried and true product is heading out the door to the customer, bond testing can provide valuable process feedback.
In production environments, bond testing can provide a means of quality control, verifying that a sampling of bonds is consistent with established process expectations. Non-destruct wire pull testing is even used in high reliability applications to ensure each wire on the product complies with the set standard (without damaging the wire or bond).
In research and development environments, bond testing can help optimize a new or existing bond/assembly process.
What Information Can a Bond Test Provide?
The main data collected by a bond tester is the force at which the bond breaks. A strain gauge measures the force the bond exerts on the tool. The force increases as the displacement increases (commonly shown on a force profile plot). As the bond yields, the measured force will reach a peak. Bond test systems capture and record this peak force as the break force. A baseline force for a “good” bond can be established, and used to verify that all future bonds are adequately strong. The image to the right is a Force Profile Plot - Force (g) vs. Displacement (um), as generated by Royce Instruments, Inc. System 650.
Additionally, the operator can use a microscope to visually observe the test in-progress and then view the bond site after a destructive test failure to determine how the bond failed. This information can be stored with the quantitative data in the form of a grade code. A grading scheme establishes a number code for each type of possible bond failure. For example, MIL-STD-883H, Method 2011.8 establishes a grading scheme for wire pull testing. In this scheme, a grade code of (1) is defined as “wire break at neckdown point (reduction of cross section due to bonding process).” Different grade codes can expose different failures in the upstream bonding and/or assembly process.
What Types of Bond Tests are Available?
The most common bond test is the wire pull test. In this test, a wire is pulled upward (perpendicular to the substrate) by a hook until there is a failure (either a bond failure or the wire breaks). Wire pull hooks are selected to be twice the diameter of the wire and should be positioned in the same location under the wire for repeatable results.
To check an individual ball bond, a bond shear test can be performed. This tests the interface between the bond pad and a ball bond by applying force to the ball bond in the lateral direction (parallel to the substrate). For ball shear, the tool height with respect to the substrate is critical and should be the same for each test. A shear test can also be used to check die bonds, most commonly eutectic or epoxy. For the bests results a shear tool should be selected with a width larger than the diameter of the ball bond or longest die side. Other bond tests include tweezer or ball pull, stud pull, and die strength (three point bend).
The above images show several bond testing options (from left to right): Bond Shear, Die Shear, Tweezer Pull, Wire Pull.
What Next?
Royce Instruments, Inc., offers the System 650 Universal Bond Tester, 
with quick change modules for each different type of bond test. An image capture options allows the operator to take photos of the bond site. An industry standard Windows® 7 PC is included within the system, allowing for rich statistical reporting and network reporting.
Recommended reading:
Harman, George G. “Chapter 4: Wire Bond Testing.” Wire Bonding in Microelectronics: Materials, Processes, Reliability, and Yield. 2nd ed. New York: McGraw-Hill, 1997.
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Palomar Technologies would like to thank the Royce Instruments, Inc. team for guest blogging this week. Together, Palomar and Royce offer customers a complete view of the reliability and quality of wire bond and die attach applications.
For more information on the Royce Instruments, Inc. product line of US designed and manufactured bond testers and die sorters, please contact Sarah Kinzli, Sales Applications Engineer, at skinzli@royceinstruments.com or (707)255-9078 x142; or visit Royce online at www.royceinstruments.com
