Mil-PRF-38535 Standard

The Mil-PRF-38535 is a performance-based specification document that defines the general requirements, as well as the quality assurance and reliability requirements, for the manufacture of microelectronic or integrated circuits intended for use in military applications and related government microcircuit application programs.

Unlike the rigid military standards of the past, however, the Mil-PRF-38535 is designed to provide microcircuit manufacturers with maximum flexibility to employ the industry's best commercial manufacturing practices while still achieving the government's required quality and reliability levels.  To be granted such privilege, a manufacturer must first be certified to what is known as the Qualified Manufacturer Listing (QML), by complying with certain requirements of the Mil-PRF-38535.  Developed in 1995, the QML program aims to move the defense procurement process away from its erstwhile strict, regimented specifications to a newer system based on best commercial practices.

A non-QML-certified manufacturer must adhere to the stringent and non-flexible requirements of the military for the manufacture and repetitive testing of its military products.  Once a manufacturer is granted QML status, however, it is allowed to use best-known commercial practices to manufacture its products using its own process flows, as long as these are shown by data to produce products that meet military standards. Thus, a QML-certified manufacturer is free to pursue continuous improvements on its own, usually in the form of elimination of non-value-added process steps.

The first requirement of Mil-PRF-38535 is for the manufacturer to have a quality management (QM) program that is documented in its QM plan.  The manufacturer must subject its QM program to self-assessments, results of which shall be made available for review.

The manufacturer must also form a Technical Review Board (TRB), which shall be responsible for the following: 1) development of the QM plan; 2) control of process changes, which includes qualification and certification of all processes; 3) analysis of reliability data; 4)  failure analysis functions; 5) implementation of corrective action and recall procedures; etc.

The TRB shall maintain records of all its deliberations and decisions, which shall be made available for review.  The TRB shall ensure that the QM plan includes the following: 1) quality improvement plan; 2) failure analysis program; 3) statistical process control (SPC) plan; 4) corrective action plan; 5) change control program; 6) standard evaluation circuit (SEC) and technology characterization vehicle (TCV) program; and 7) certification and qualification plan.

The Mil-PRF-38535 also defines requirements for change control procedures.  All changes to any part of a QML manufacturer's line are to be governed by the manufacturer's TRB.  Any change shall be documented as to the reason for the change with relevant data taken to support the change, including reliability data as appropriate.  The criticality of the change shall be based on the effects of the change on quality, reliability, performance, and interchangeability of the resulting microcircuits. The next page shows examples of manufacturing process changes that require TRB evaluation and approval per Mil-PRF-38535.

The Mil-PRF-38535, as mentioned, defines the requirements for a manufacturer to be QML-certified. The generic QML certification process consists of: 1) quality management program documentation; 2) process capability demonstration; 3) qualifying activity management and technology validation; and 4) demonstration of the manufacturer's control of any off-shore operations.

Process capability demonstration consists of building actual devices and performing tests on them, as well as running software benchmarks necessary to demonstrate that the manufacturer has a good comprehension of how manufacturing process capability relates to quality, reliability, and manufacturability.

To demonstrate design process capability, the manufacturer shall provide evidence of the capability of its design methodologies for the following design areas: 1) model verification; 2) lay-out verification; 3) performance verification; and 4) testability and fault coverage verification.

To demonstrate wafer fab process capability, the manufacturer shall identify a specific technology or technologies for wafer fabrication. Wafer fab capability demonstration consists of showing data and documentation that support the qualification of the various materials and processes of the wafer fab steps (e.g., oxidation, metal deposition, diffusion, implant, photolithography, passivation/glassivation, etc.). Reliability test data, parametric monitor test data, wafer acceptance test data, mask inspection and defect density data, rework data, among others, must also be presented.

A Technology Characterization Vehicle (TCV) program must likewise be implemented by the manufacturer for every technology to be certified. This program must involve the development of test structures needed to characterize a technology's susceptibility to intrinsic reliability failure mechanisms such as electromigration, TDDB, and hot carrier effects. The manufacturer must also use a Standard Evaluation Circuit (SEC) to demonstrate the reliability of every wafer fab technology being considered for certification. The SEC must be designed solely for its role as a quality and reliability monitoring device.

To demonstrate assembly/packaging capability, the SEC  or  an actual product of the manufacturer must pass the required package qualification and certification process, which includes a variety of Mil-Std-883 test methods that depend on the assembly process step being qualified, and as per Tables I and II of paragraph 3.5.1.3.6 of Mil-PRF-38535.  Packages must likewise meet required thermal and electrical characterizations for QML-certification.

Initial QML qualification testing shall be performed on two microcircuit devices, referred to as 'demonstration vehicles', which were produced by the manufacturer on its actual manufacturing line.  The manufacturer shall present a qualification plan that details the qualification test flow, test limits, test data to be collected and analyzed, and test sampling techniques.  The qualification plan must likewise document the materials and manufacturing information as well as the traceability records for the demonstration vehicles.   

Once the qualification testing has been completed, the manufacturer must present a qualification test report, which details the analysis of the qualification data.  The analysis must show that the process or technology being certified is under control and repeatable. If failures are encountered during the qualification testing, failure analysis must be conducted on the failures so that corrective actions, if needed, may be undertaken.  After the corrective actions have been completed, the qualification testing must be restarted on new demonstration vehicles from the corrected process.

A certificate of qualification shall be issued to the manufacturer once all the requirements for QML certification have been completed.  To retain its qualification status on the QML, the manufacturer must perform regular qualification tests on selected SEC's and TCV's or perform alternative assessment procedures as documented in its QM plan.

See Also:  Mil-Std-883 Methods;  Mil QCI Group Tests;  Mil Lot Screen Tests

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