The Use of Acoustic Emission in a Test for Beam-Lead, TAB, and Hybrid Chip Capacitor Bond Integrity

The use of acoustic emission (AE) in a test for beam-lead bond and anchor integrity has been investigated. AE refers to the emission of broad-band stress waves when materials are broken, cracked, or deformed. A major problem in the present work was to develop means of nondestructively stressing the delicate, irregularly extending beam leads. The most promising of the methods developed are a silicone rubber (SR) pull test, a push down test on SR-encapsulated devices, and various probe methods of applying force to the beams without contacting the chip. AE bursts from weak bonds or beam anchors axe detected with a substrate detector operating at 375 kHz or a probe detector operating at 1.1 MHz or both. The study has revealed considerable difference in the mechanical integrity of beam-lead bond-anchor systems. General deterioration of the beam-anchor system begins at pull forces per beam of approximately 1.0-2.5 gramsforce (gf), depending on the manufacturer´s procedure. The forces applied to the beam-anchor system for all methods of stressing, except the pull test, are dependent upon the shape of the individual beams as they extend from the chip, as well as the uniformity of the bugging height. There are many other potential uses of AE in electronics, such as to insure the bonding integrity of flip chips, capacitor chips in hybrids, and bonds on tape automated bonded integrated circuits. The latter two uses were experimentally demonstrated in the present work. Thus it appears that AE will have an increasing role in assuring reliability in the microelectronics field.