The Microelectronic Wire Bond Pull Test-How to use It, How to Abuse It

The wire bond pull test is the most universally accepted method for controlling the quality of the wire bonding operation, and thereby offering added assurance that semiconductor devices will not fail in the field due to weak wire bonds. Specific test procedures and pull-force values are called out in military and other device purchase specifications, and yet there has never been a carefully controlled interlaboratory comparison of this important test. All of the variables that are known to affect the bond pull test are examined including ones that cannot be treated theoretically, such as bond peeling and tearing. Careless pulling methods and other abuses that affect test results are described and the results of an eight-organization interlaboratory pull test experiment are given. The conclusions are 1) attempts to cut costs during the test by following nonstandard procedures will generally result in pull-force values that are lower than those that would be obtained were the test conducted carefully in accordance with standard procedures; 2) Overdeformed bonds tend to show a larger percentage change in pull strength due to nonstandard pulling procedures than do less deformed bonds; 3) Although artificially inflated pull-force values can be obtained when one bond is significantly stronger than the other, the effort of intentionally exploiting this difference (cheating) in most cases is greater than any benefit derived.