Plastic Encapsulated Microcircuits (PEMs)

Alexander Teverovsky, QSS Group Inc, CODE 562, NASA/GSFC

The quality assurance system employed by most plastic encapsulated microcircuit (PEM) manufacturers is targeted to commercial applications and is significantly different from the system used in production of military and space-grade parts.  For this reason, part engineers have to subject these devices to thorough screening and qualification procedures required to utilize the benefits of using advance technology and high-performance COTS PEMs for space applications.

This section describes GSFC’s policy of PEM applications and requirements for the three major elements of the quality assurance system: screening, qualification, and destructive physical analysis (DPA).  This system is based partly on the standard test practices for military and aerospace components, experience accumulated by the parts engineering community, and guidelines established by the high-reliability electronics industry.

Major issues

• All PEMs intended for space applications independent on the required quality level should be screened, qualified and subjected to DPA.  Qualification by history is not allowed.
• Screening is the only element of the quality assurance system, which is applied to the flight parts and affects reliability of the lot.  The purpose of screening is to reduce infant mortality failures; however, improper testing and handling of the parts can introduce more defects than it reveals during screening.  For this reason, extreme cautions should be undertaken to reduce the possibility of ESD/EOS and mechanical damage to the parts.
• PEMs are typically rated for a relatively low temperature range, that is below the temperatures used for stress testing of military-grade parts.  For this reason, screening and qualification of PEMs require a thorough analysis of testing conditions to avoid damage to the parts and the possibility of introducing new failure mechanisms.
• All results of DPA, screening, and qualification should be logged onto the GSFC PEMs database to gain more experience in application of PEMs for space projects and to analyze the effectiveness of the existing quality assurance procedures.
• Every standard and/or instruction for qualification of microelectronic components is getting obsolete with time.  This timeframe is probably especially short for PEMs because of ongoing changes in the design and materials used and the lack of experience in qualifying commercial parts for high-reliability applications.  A significant amount of information regarding screening and qualification of PEMs is permanently generated by GSFC space projects.  Analysis of this information and additional testing will allow optimizing stress test conditions, evaluating the importance of characterization of molding compounds, and assessing the value of different testing techniques.  Based on the results of this analysis, necessary corrections in the qualification and screening test flows will be made to reduce the cost and improve the system of quality assurance of PEMs for space applications.

Reference document

“Instructions for Plastic Encapsulated Microcircuits (PEM) Selection, Screening, and Qualification”, PEM-INST-001, May 2003.

This document describes a system of quality assurance for PEMs intended for space applications and provides detailed guidelines for three major elements of the quality assurance system: screening, qualification, and destructive physical analysis.  It also contains requirements for derating and handling of PEMs and recommendations for additional design evaluation and assessment of history of the parts.

Upcoming Events

• Commercialization of Military and Space Electronics Conference & Exhibition, February 9 - 12, 2004, Los Angeles, CA.
• 2nd Advanced Technology Workshop on Military, Aerospace, Space and Homeland Security:  Packaging Issues and Applications,  Baltimore, Maryland, March 28 - 30, 2004
• 2004 International Reliability Physics Symposium, April 25-29, 2004, Phoenix, AZ.
• EMPS 2004, June 16-18, 2004, Prague, Czech Republic.
• 16^th Annual International Military & Aerospace / Avionics COTS Conference, Exhibition & Seminar, August 3 - 5, 2004, Seattle, WA.
• IMAPS 2004, 37th International Symposium on Microelectronics, November 14-18, 2004, Long Beach, CA