Author: Giovanni Di Salvo
The importance of EEE procurement: issues and solutions
The Procurement of Electrical, Electronic and Electromechanical Components (EEE) for Space hardware always creates troubles and doubts for many and many reasons. For example, for a chosen device (chosen by the engineering) you must match several parameters to perform the right procurement for the program.
In a nutshell, the main problems to solve are usually the following:
- the availability of the chosen device from one or more sources
- the applicable quality level. Sometimes you don’t find any qualified device (a typical case is the RF devices) while sometimes you can find the same component from more than one supplier, but you have to change the quality system (e.g. from ESCC to MIL or vice-versa). In some cases, program rules allow to use lower quality levels inside the same specification system. For instance, the possibility to use JANTXV level discrete devices (with the “MIL” system, MIL-PRF-19500) instead of the JANS level (the Top-quality level for discrete parts in the MIL system), as it is also a way to decrease the cost of the device;
- the cost of the device and its possible associated Non-Recurring Cost due to screening or LAT/QCI or DPA or Rad Test etc…(also depending on the device type, its source and Product-Assurance Program Requirements);
- the delivery time that should be in accordance with the program schedule.
There are two main authorities which maintain a “control” of the manufacturers of EEE Hi-Rel devices. And also QUALIFY the Hi-Rel devices:
- ESA (European Space Agency) thanks to the ESCC (European Space Coordination Centre) system in the Netherlands and the CNES (Centre National d’Etudes Spatiales) in France.
- NASA (National Aeronautics and Space Administration) with the DLA –Defense Logistics Agency in the United States of America, using the “MIL” system.
Both systems use a “similar” specification structure
On one hand, the ESCC specification system includes broadly Basic, Generic and Detail specifications.
The Basic specifications describe the test methods, the qualification methodology and the general requirements applicable to ESCC qualified components.
The Generic specifications define the general requirements for the qualification, qualification maintenance, procurement, and delivery for each individual family of components.
The Detail specifications describe the performance requirements (ratings and physical/electrical characteristics) and test/inspection for individual or ranges of components.
All specific test methods, used to perform each specific kind of tests, are coming from the NASA /MIL system (e.g.: MIL-STD-883 or MIL-STD-750 or MIL-STD-202 etc.)
On the other hand, the “MIL” system includes broadly:
- the “Basic” specifications, used to describe test methods and conditions on how to perform each specific test (e.g.: MIL-STD-883 or MIL-STD-750 or MIL-STD-202 etc.),
- the “General” performance specifications which includes the requirements for the screenings, for the periodic or specific Quality Conformance Inspection (QCI) and for the qualification testing for each individual family of components. (e.g.: MIL-PRF-19500 for Discrete devices or MIL-PRF-38535 for Microcircuits, etc.)
- the Standard Military/Microcircuit Drawing (SMD) which comprehends the performance requirements for individual or ranges of components.
Qualified Part Lists or Preferred Part Lists
It is important to know that both systems consider Lists of Qualified Devices: Qualified Part Lists or Preferred Part Lists.
To choose the best solution that fits the program requirements, anyone can usually select components from these lists. In fact, the Procurer should in any case try to fit the program requirements with the selectable devices.
Moreover, if the detail procurement specification does not exist, it must be prepared together with other documents, to test the reliability of the not-qualified device. In this instance a first preliminary feedback derives from the inheritance of the chosen device. It is really important to understand the intrinsic reliability of the device. In few cases a very expensive procedure called “Component Evaluation” has the purpose to test the reliability of a part’s technology. In certain cases, the component needs to perform additional tests such as up-screenings or particular selections.
You should take in consideration that the Procurement of EEE components does not end simply by selecting a part. At Dimac Red we have internal skills which are able to manage the procurement activities.
The Procurement of EEE components in details: steps and procedures
Another key point of EEE components procurement is the Part Approval Documents (PAD). It should be prepared to define exactly how to buy a single component or a family of components. In addition, it defines which inspections should be performed. The PAD is the Id-card of each component. Because it defines exactly the details of package, termination finish, manufacturer, procurement specification, part number, but also defines which activities need to be performed to procure each device (Pre-Cap inspection; Final source inspection; Lot Acceptance Test/Quality Conformance Inspection -including or not the Life Test; Destructive Physical Analysis; Radiation Tests etc…).
- The Pre-Cap inspection takes place at the manufacturer’s facility to check the parts prior to their encapsulation in the package.
- The Final Source Inspection is performed before authorizing the manufacturer to ship the parts; this inspection verifies that the manufacturer has properly carried out all the required tests.
- The Lot Acceptance Test or Quality Conformance Inspection consists of a series of tests divided in groups (Electrical Tests, Environmental Tests, Mechanical Tests, Endurance Tests). They work on a sample basis (defined by the system used- ESCC or MIL) to check the reliability of the manufactured lot.
- The Destructive Physical Analysis (DPA) usually consists of picking three pieces, used and destroyed to perform a series of analyses on the termination finish, on the hermeticity of the package, on the internal bonding of the die etc. It aims to demonstrate the good assembly of the device.
- The Radiation Tests are destructive tests to be performed on devices that are suspected to be not resistant or sensitive to the radiations. Requirements depend on the foreseen orbit and on the mission life of the satellite (these last two requirements define the mandatory minimum radiation level for the EEE). The radiation resistance of the parts depends mainly on the technology of the devices and partially on the production batch. We can truly say that it is intrinsic to the device technology.
An important phase of procurement: types of radiation tests
There are two main types of radiation tests:
- Total Ionization Dose test which, depending on the technology of the component, can be performed at:
- High Dose Rate (50÷300 Rad(Si)/sec.) means about 1KRad per Hour
- Low Dose Rate (0,1 Rad(Si)/sec.) means 360Rad per Hour
- Enhanced Low Dose Rate (0,01 Rad(Si)/sec.) means 36 Rad per Hour
These tests depends on the accumulated energy that the device can tolerate in the junction without a significant degradation of its electrical/physical performances.
- Single Event Effects test, which is destructive and the behaviour of the component depends only on its technology. These tests are not “sensitive” to the different manufacturing lots, and are more expensive than the TID test.
This test’s type is based on the possibility that a heavy Ion will hit the die and transfer energy to the junction, creating more energy than the required. In this way, the device changes permanently its electrical behaviour and risks the destruction. Depending on the die technology, we can observe many different problems. Firstly, Single Event Gate Rupture, in case of testing a mosfet. Secondly, Single Event Latch-Up in case of testing a Linear Ic. Then Single Event Transient, in case of a digital device, Single Event Upset etc.
The role of the procurer and the inspection
When it comes to the last check of EEE procurement phases, the Incoming Inspection of the “procurer” plays its role. In some cases the Final Inspection at manufacturer’s premises substitutes it. This could happen if electrical tests are not performed at the customer’s premises. The Incoming Inspection validates that the received components are fully in accordance to the requirement of the Purchase Order. And they are in the right quantity, visually acceptable and electrically within the foreseen specification limits. The Documentation (Data Package) should be in accordance to the requirements. Moreover, the inspection must check that during the various tests no failures exceeds the PDA (Percent Defective Allowable) limits.
Thanks to partners with a long heritage in Space segment, Dimac Red is able to perform a lot of activities. Form Electrical tests, up to DPA’s, Radiation tests, up-screenings and any required additional action.
To perform a good procurement all the program’s requirements must be clear and well known since the beginning. At the same time, the selection of devices must take into account the qualification or heritage they really accumulated. Many and many aspects are at stake in addition to the unit price…And a co-operation between “Procurement” and “Engineering” is extremely important.
Do you want to know more? Please do not hesitate to contact the experts at dimacred@dimacred.com
