Diffusion and absorption of corrosive gases in electronic encapsulants C. Hillman * , B. Castillo, M. Pecht CALCEElectronicProductsandSystemsCenter,1103,Building89,UniversityofMaryland,CollegePark,MD20742,USA Received 28 August 2002; received in revised form 25 September 2002 Abstract Plastic encapsulated microcircuits with aluminum triple track structures were exposed to mixed flowing gas con- ditions to simulate and accelerate possible environments during long-term storage. No increase in resistance was measured and no corrosion products were observed after 800 h of accelerated exposure. Further experimentation in- dicated that chloride gas reacts with surface moisture in microscale and macroscale voids within the encapsulant, creating chloride ions. These ions become strongly bound to ion getters present in the epoxy molding compound, trapping the chloride ions within the bulk encapsulant and effectively retarding the diffusion process, which could lead to corrosion at the surface of the die. Ó 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction In the age of consumer electronics, industries that use components in niche applications requiring long-term life in harsh environments, such as military, aerospace, oil drilling and automotive, purchase a miniscule frac- tion of the microelectronic components that are pro- duced. As a result, there is little marketplace demand for hermetically sealed packages, especially since they are generally orders of magnitude more expensive than their plastic counterparts [1]. The proliferation of affordable, leading-edge plastic encapsulated microcircuits (PEMs) has introduced questions about their reliability in long-term storage applications [2–4]. Because of extended periods of dor- mancy, there is concern that exposure to elevated tem- perature/humidity will produce more corrosion in stored devices than in operating devices. Stored devices lack the power dissipation that helps keep condensed moisture off the surface of the die [5]. The diffusion behavior of moisture through electronic encapsulants and the resulting presence of monolayers of water at the die surface have been well documented [6,7]. However, previous research has shown that for corrosion to occur at the die surface within a reasonable amount of time, ionic contaminants must be present [8]. Over the years, sources of mobile ions from the manu- facturing process have been identified and removed [9]. This may result in the operating environment becoming a primary source of ionic contamination [10]. The epoxy molding compounds (EMCs) are gas permeable and it is possible that ionic contamination could penetrate into the plastic encapsulated microcir- cuit in the form of a corrosive gas, such as Cl 2 ,H 2 S, or SO 2 . The purpose of this paper was to investigate the diffusion behavior of corrosive gases through encapsu- lants and to document the possible occurrence of ion- induced corrosion in PEMs after long-term exposure to corrosive gases. 1.1.Encapsulants Predicting gas transport behavior through electronic encapsulants is problematic due to the complex nature of EMCs. Molding compounds consist of an encapsu- lating resin, typically epoxy cresol-novolac (ECN) or Microelectronics Reliability 43 (2003) 635–643 www.elsevier.com/locate/microrel * Corresponding author. Tel.: +1-301-405-5323; fax: +1-301- 314-9269. E-mailaddress: chillman@calce.umd.edu (C. Hillman). 0026-2714/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0026-2714(02)00315-3