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Do flame retardants affect the reliability of molded plastic packages?

Microelectronics Reliability
Publication Date
DOI: 10.1016/0026-2714(81)90244-4
  • Chemistry


Abstract Epoxy based thermoset materials are widely used for molding of microelectronic devices. Accelerated aging of molded devices has led to increased failure rates when the molding compound contained a brominated flame retardant (FR). In this paper, we investigate the effect of a brominated FR on the failure rate of a device aged at elevated temperatures under bias. We also ask whether aging characteristics in the 200°C range can be extrapolated through the glass transition (Tg) to service temperatures. We chose an electrical/electronic, rather than semiconductor, grade novolac epoxy which previously exhibited the poorest bias aging results of a group of FR and non-FR molding compounds. Half FR and non-FR versions of the epoxy in question were also obtained for the present experiments. The test vehicle was a molded DIP with a TTL device and Tape Automated Bonding (TAB) technology. Devices were prepared with and without a silicone rubber junction coating. Devices were aged for times up to 10,000 h at 125, 150, and 200°C, with and without bias. The results from time to failure and failure mode analyses were complemented by X-ray fluorescence, and aqueous extraction performed on the cured molding compounds. Failure rate at elevated temperature was found to be independent of the presence of FR. This result is consistent with our finding of four times as much extractable Cl − as Br −, and with the identification of CH 3Cl as a major thermal degradation product below 200°C, in a companion study by Lum and Feinstein. The silicone rubber junction coating retarded failures by a factor of 5–10. Both electrolytic (operating bias) and chemical (no bias) corrosion mechanisms were operative. However, the failure rate was a factor of 5–10 lower for unbiased devices. Direct attack of the Cu beams did not appear to be a problem in this study, although leads may act as fuses after shorting of the chip metallization. Although a linear extrapolation of failure rates from 200°C to lower temperatures is not valid, the result will be conservative.

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