Information on Military Specifications
for DC/DC Converters
Part Selection and Quality Level
The Defense Supply Center Columbus (DSCC) is the logistics center and manager for military specifications for electronic parts including hybrid DC/DC Converters. Hybrid packaged (several devices inside one large package) DC/DC Converters are controlled with a number of specifications, standards and test methods. The top level specification is MIL-PRF-38534, Hybrid Microcircuits, General Specification for, which is used for (nearly) all “hybridized” electronic parts. This specification is very complex and undergoes constant review and interpretation via the JEDEC 13.5 (Hybrid Manufacturers) and G12 (Component Users) groups within the Industry/Government Solid State Devices Committee.
MIL-PRF-38534 is based on a Qualified Manufacturer List (QML) approach which emphasizes capability and consistency of manufacturing processes and materials and a highly defined test flow. Proof that the processes and materials used by a manufacturer will result in the production of parts that can withstand rigorous environmental stresses and is electrically stable with long-term use is achieved through destructive and non-destructive qualification testing and an audit of the manufacturer’s quality systems, process controls, and testing capability by DSCC. A successful production line audit results in “line certification”. Successful qualification testing, of parts made on that certified line, results in a QML Listing of that part number (if it is defined by a DSCC standard microcircuit drawing) – it is now “qualified”. Process materials and methods can be changed over time however within the QML system the manufacturer must perform additional qualification testing and submit the test results to DSCC if the change is considered major (could impact the mechanical robustness of the parts).
The certification classes are based on the DSCC audit of specific testing flows performed by the manufacturer on production parts. The five classes are K, H, G, D and E. Class H requirements typically form the baseline. The K level is awarded by DSCC if the vendor has shown the capability of performing extra pre-build inspections of components used inside of the part, post-build inspections and testing in addition to meeting all of the baseline requirements of Class H. The extra requirements that define Class K are intended to provide more confidence to the buyer that their part lot is of high initial quality and that any defective parts have been removed from the lot. Class K requirements also address the special needs of space users. NASA GSFC policy holds that Class H and K are the only classes routinely used in flight hardware. Radiation hardness requires special DSCC approval and can be added to any class level. Neither Class H nor Class K requirements lead the user to a numeric value for part reliability (e.g. FITS, MTBF, % failure/1000 hrs, etc.).
Once DSCC has accepted successful qualification testing of the materials and processes and has certified the facility for Class K production, the vendor can take orders for Class K product. For the initial production lot, the manufacturer must complete all Class K requirements including, Screening and Groups A, B, C, and D testing prior to shipping the product as Class K. For subsequent lots only Screening, electrical parametric testing (Group A) and destructive, in-line sample inspections (Group B) are required on every lot. As stated above the internal elements used for Class K devices must be 100% tested and qualified before they are used inside of the hybrid device. Qualification type tests (thermal shock, mechanical shock, life, etc.) called Group C tests are only repeated on an as needed basis and Group D tests (special interest tests such as salt atmosphere, package isolation and lead integrity) are repeated at intervals of no more than 26 weeks. Conformance Inspection (CI) and Periodic Inspection (PI) are a requirements for Classes H and K regardless of the procurement vehicle (e.g., purchase order, source control drawing, DSCC SMD).
All classes of parts including K can be sold to DSCC controlled drawings (SMDs), SMD+ drawings called Selected item Description (which calls out the SMD and then adds some unique requirements), manufacturer’s data sheets, or customer supplied drawings (SCDs). SMD’s are component specifications published by DSCC that combine the datasheet information for a unique part (electrical parameters, block diagram, maximum operating conditions, etc.) with clear wording to impose MIL-PRF-38534 requirements (test conditions, pass/fail requirements, etc.) and class level. SMD’s are written by a user, manufacturer or by DSCC on an as needed basis and can be created, coordinated with the manufacturer and published in a matter of a couple months.
For each SMD device type, DSCC requires the manufacturer to provide a “Certificate of Compliance”, which DSCC keeps on file. The manufacturer is required to maintain the electrical tests data (Group A) from the initial lot manufactured for each SMD device type (whether it was made to Class H or Class K requirements). Though manufacturers are allowed to sell QML devices to non-SMD purchasing vehicles (SCD’s, datasheets, etc.), DSCC does not require submission of a C-of-C for those lots.
There are four suppliers who are listed on QML-38534 for DC/DC Converters, but only one is listed for Class K SMD part numbers. The DC/DC SMD parts currently listed are indicated to be radiation tolerant by the part numbering scheme. There is no DSCC published list of non-SMD part numbers which are being produced under the QML system.
DSCC performs on-site auditing of QML hybrid vendors every other year to update and maintain vendor line certification status. During these audits, DSCC does a sample check to make sure that lots being sold as QML products are being processed and tested in accordance with the requirements of MIL-PRF-38534 and the procurement documents. If the manufacturer fails to meet any requirement, they may be required to issue a GIDEP Alert or Problem Advisory, a product recall, be issued a stop-ship, or may lose their QML certification.
Buying Class H or K DC/DC Converters comes with a certain confidence level based on the DSCC verification of the manufacturer’s systems. However, if the user wants confirmation beyond that of the manufacturer’s that the part has met all MIL-PRF-38534 and special customer requirements, he or she must do their own verification. Consulting DSCC’s qualification team is recommended as part of this verification process.
Manufacturers sell parts that may be misinterpreted as being Class H or K QML product. “Class K”, “Class H” and “QML” are terms used within the context of DSCC’s military specification system and loose their meaning outside of that system. Phrases such as “/883 compliant” or “screened to MIL-PRF-38534, Class K” are marketing language and are not specifically defined for non-QML product. It can be very hard to know if the parts advertised using this language are QML, especially if they are not bought to an SMD part number. Using marketing language on the manufacturer’s website to determine whether the part is a QML product is not recommended because the terms “Class K”, “Qualification” and “Certification” are regularly used incorrectly. Users can contact Jonnie Schneider (614-692-0585, Jonnie.Schneider@dla.mil) at DSCC to verify whether or not the non-SMD parts that they intend to buy for space use are QML parts. Part numbers being bought for space programs under the QML system can be submitted to DSCC for inclusion in the sample audit as well.
Individual drawings created for particular devices in the MIL-PRF-38534 system are called Standard Microcircuit Drawings (SMD’s). The details of the individual converter, its package style, pin assignments, electrical performance specifications and ratings, temperature ratings, functional block diagrams, and specific application notes, are found at the SMD level. SMDs for DC/DC Converters can be found by using DSCC’s Standard Microcircuit Cross-Reference Tool. This tool has three main fields: left, middle and right. Set the left field to “Description”, leave the middle set to “Contains”, and set the right field to “DC/DC Converter” (about 60 listings are described as DC-DC Converters, so to find all listings you have to do a second search using “DC-DC Converter”). This results in a list of about 1200 individual part numbers for all of the DC/DC Converters (not counting EMI Filters which may be supplied separately). These part numbers are found in about 230 specifications. The MIL-PRF-38534/SMD system standardizes the part numbering system using the following format: Note: The format came into effect about 1987. SMDs prior to that date use a different part numbering scheme.)
5962-0052201HXC or 5962R9161402KXA
The suffix 5962 begins all SMDs and is the National Stock Class for microcircuits . The next digit identifies radiation tolerance (dash is “not rated” and letters are used for the various levels of tolerance for accumulated ionizing dose). The next five digits identify the SMD drawing number (00522 and 91614 in the example above). The next two digits identify device type when more than one is listed in one SMD. The letter following device type, K, H, G, D or E, identifies the device class. The last digits are associated with package style and other physical details of the part.
SMD drawings are generally initiated by the user or manufacturer and are coordinated with those users and manufacturers who have expressed an interest and have been added to a “Registered Users’ List” for that SMD. DSCC maintains an SMD template to streamline writing and editing. They have staff that can transpose a manufacturer’s datasheet into the SMD format and will work with users to coordinate the document with the manufacturers. No change can be made without the approval of everyone on the “Registered Users List.” DSCC encourages the use of SMD’s as they promote standardization (multiple users and multiple manufacturers, competition, and longer availability of the parts) and have a greater visibility in the DSCC system that non-SMD part numbers.
As noted above, the supply base for these parts is managed by DSCC through certification, qualification approval and auditing. A list of manufacturers, who are allowed to sell hybrid microcircuit parts within the QML system, whether using SMD part numbers or not is QML-38534. The QML is updated quarterly. This list includes all QML hybrid microcircuit manufacturers, not just DC/DC converter manufacturers. An April 2005 analysis of the list showed the following to be who can manufacture QML DC/DC Converters to existing SMD part numbers (cage code is provided to distinguish the factory location):
Advanced Analog/International Rectifier (CAGE Code 52467)
M.S. Kennedy Corporation (Cage Code 51651)
VPT Incorporated (CAGE Code 0ZBZ6)
QML manufacturers are audited every other year if no significant production line changes or problems have been encountered since the last audit. DSCC schedules, coordinates and conducts these audits. NASA is an invited guest on DSCC audits. Mr. Terry Dowdy of NAVSEA Crane Division acts as NASA’s official representative on DSCC audits of hybrid microcircuit vendors. (contact Mike Sampson as an alternate). DSCC posts a list of upcoming audits at http://www.dscc.dla.mil/downloads/VQGeneral/IHAuditReports070521.pdf. Customers are welcome to participate in the audit, as long as there is room. Contact information is also found at on the DSCC website (link).
Use of the components with the highest reliability or of the highest confidence level is always preferred for space systems where failure can be mission-ending and repair is not an option. The QML, MIL-PRF-38534 program provides the most standardized requirements and supply control for hybrids. Class K provides the highest reliability by including Life test and Scanning Electron Microscopy (SEM) on every lot of microcircuits going into the hybrid, additional process controls, and more production tests (screening) including twice the burn-in of Class H and a tighter percent defective allowable (PDA), 100% non-destructive bond-pull, tighter internal visual criteria than Class H, X-Ray, and particle impact noise detection (PIND).
NASA GSFC’s qualification and screening guideline EEE-INST-002 contains instructions for ordering and processing hybrid microcircuits for space use which may not be available under the mil-system (or the mil-part’s Class does not meet mission requirements). A special EEE-INST-002 section focused on DC/DC Converters in particular is in process.