h40 IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, zyxwvutsrqp AND MANUFACTURING TECHNOLOGY, VOL. 15, NO. 5, OCTOBER 1992 Comparison of Plastic and Hermetic Microcircuits Under Temperature Cycling and Temperature Humidity Bias Lloyd Condra, zyxwvutsrq Senior zyxwvutsrqp Member, IEEE, Steve O’Rear, Tim Freedman, Leo Flancia, Michael Pecht, Fellow, IEEE, and Donald Barker Abstract- Plastic and hermetic integrated circuits (IC’s), as discrete packages and as assembled on circuit card assemblies, were temperature cycled between zyxwvutsrqp - 55 and +85”C through 1000 cycles, and 26 parametric values were observed in terms of failure rates or shifts. The circuit card assemblies were then tested for up to 650 h in 85”C-85%relative humidity zyxwvuts (RH). Circuit cards were also assembled using both plastic and hermetic versions of a custom IC, for comparison against each other as well as against an older discrete version of the card, which had a history of reliable operation for over 20 years. The IC version of the cards were coated with either,urethane or parylene, and along with unassembled IC’s, were tested for 1000 h in 85”C-85% RH with intermittent bias temperature, humidity, bias (THB). Conservative lifetime estimates, for both the plastic and the ceramic IC’s, for avionics applications, were determined to be well over 20 years. It is concluded that, in this and similar applications, there is no reliability advantage between plastic and ceramic IC’s. Keywords: Reliability, plastic, hermetic, humidity, temperature, Weibull, moisture. I. INTRODUCTION LASTIC packaged integrated circuits (IC’s) are widely P used in commercial and industrial electronics, because they are less expensive, smaller, lighter, and more widely available than their hermetic-packaged counterparts [ 11. De- spite these benefits, plastic IC’s are generally not used in commercial and military avionics applications because of their perceived lower reliability. Over the past two decades, significant improvements have been made in plastic IC reliability, and there is much interest in using them in applications which have been previously re- served for hermetic packages [2], [3]. The authors consider the use of plastic IC’s in products both necessary and inevitable. While the use of plastic encapsulated microcircuits is be- coming a realistic option in “high reliability” applications and the benefits in reducing size, weight, and cost, as well as the wider availability of designs in plastic are well documented [4], [5], the perceptions of lower reliability for plastic parts present a barrier to their widespread use. Manuscript received July 8, 1991. L. Condra, S. O’Rear, T. Freedman, and L. Flancia are with the ELDEC Corporation, Bothell, WA 98041-3006. M. Pecht and D. Barker are with the CALCE Electronic Packaging Research Center, University of Maryland, College Park, MD 20742. IEEE Log Number 9202705. Many manufacturers and users of plastic IC’s have pre- sented data showing the high reliability of plastic parts. Most of the data presented has been in the form of standard reliability tests, such as high temperature operating life, which usually measures failure rates during 1000 h of operation at 125OC; or 1000 temperature cycles between -55OC and +125”C; or 1000 h at 85OC-85% relative humidity (RH). In general, these data have been less than persuasive to manufacturers and users in the avionics markets, because of difficulties in relating them to expected performance in real products and operating environments. On the other hand, over the last two decades, many investigators have conducted temperature cycling and temperature humidity bias (THB) tests and proposed models for component failures in these environments. A few of the most recent are listed in Reference Temperature cycling and moisture are perhaps the environ- mental factors of greatest concern in plastic part reliability and are typically tested using the methods of MIL-STD-883, Method 101 0 and JESD-22, Method A104. These environmen- tal factors are discussed in the following. Temperature cycling occurs due to a thermal cycling envi- ronment or due to device power cycling. Under these condi- tions, sufficiently large tensile and shear stresses can arise in the molding compound, the lead frame, and the die to cause package cracking, passivation layer cracking, wire bond lift- off, die cracking, and metallization deformation. The test, as per the MIL-STD 833, Method 1010, is carried out in an environmental chamber equipped with a temperature control, so that the sample can be heated and cooled within 15 min in dry, flowing air. The time used for changing the sample temperature from one limit of the specified test temperature to the other is to be less than 1 min. Equipment and media for heating and cooling, as per JESD-22, Method A104, are the same as above. For plastic encapsulated devices, the high temperature limit is to be kept below the glass transition temperature of the molding compound. The minimum number of cycles is 10 for screening and 1000 for qualification. More than 10 cycles are considered partial use of duty cycle. Post- stress examination includes parametric and functional tests and tests for mechanical damage. In terms of moisture, the plastic molding materials them- selves are permeable to moisture. The mold line can contain cracks, and microcracks can be generated which admit mois- 171-1141. 0148-6411/92$03.00 zyxwvutsrq 0 1992 IEEE