In my last two blogs there has been a common underlying principle which is the advanced screening and testing that products must undergo to be qualified for space applications. It is imperative to perform sufficient testing and qualification to ensure that a product can withstand the harsh rigors of space. Prior to the last two blogs I spent a good bit of time discussing radiation testing for space products with an emphasis on single event effects for high speed ADCs. Now, I would like to turn the attention to the screening and qualification that space products undergo at Analog Devices. There are a few different screening flows for the different types of products that ADI offers. In this installment we will begin discussing screening for the standard space product offerings which include products such as ADCs, DACs, comparators, amplifiers, voltage references, switches, isolators, regulators, and attenuators.
The standard space product offerings are screened in accordance with the current issue of MIL-PRF-38535 QML level “V” which is summarized in Table 1 (see ADI Standard Space Products Program for the full table). The individual product data sheets for each device will contain the electrical parameters and end points for each space product. These are the parameters that are measured in tests 11, 13, 15, and 17 below.
ADI Standard Space Level Flow
As you can see there are quite a few steps involved in the space level screening for a standard space product. In this installment we will look at steps 1 through 17 to try to gain a better understanding of the purpose of each of these steps.
– The device must pass an initial ESD qualification to determine its class of operation. It is important to understand the ESD rating to know how to properly handle the device.
- Wafer Lot Acceptance
– Before the die is packaged a wafer lot acceptance test is performed to ensure that there is no improperly patterned metal, there is sufficient step coverage, metal and dielectric thickness are correct, etc.
- Non-destruct bond pull
– For devices that are offered in a package a non-destructive bond pull test is performed to gauge the bond strengths to ensure that the device will tolerate the harsh conditions in a space application including such things as thermal cycling, shock, and vibration.
- Internal Visual
– An internal visual inspection is performed to verify the die, device construction, wire bonds, materials, etc. are all correct and as specified for the device.
- Temperature Cycling
– Temperature cycling is exactly as it sounds. The device temperature is cycled to verify it will withstand the temperature variations seen in a typical space application.
- Constant Acceleration
– A constant acceleration test is performed to ensure that there are no structural weaknesses in the device. This ensures the device will stay intact during while undergoing the different forces exerted on the device during launch and while deployed in orbit (be it Earth or another planet).
- Visual Inspection
– Next, a visual inspection is performed to verify that the device has not been damaged from handling, assembly, or test thus far in the process.
– A PIND (Particle Impact Noise Detection) test is performed to detect the presence of any loose particles within the device package. Any particles inside the package could adversely affect performance of the device, i.e. a particle could short bond wires together or short two areas of the die together which could result in device failure.
– Device serialization is performed to be able to track the test and screening results on a per device basis for traceability.
– An X-ray inspection is performed as another means to verify the device construction and integrity.
- T1. Pre Burn-in Electrical
– A pre burn-in electrical test is performed to gather baseline data on the device to be used for comparison to electrical test data gathered in the subsequent steps of the screening process.
- Reverse Bias Burn-in
– In this test, the device has its internal transistors in an unbiased or non-conducting state and the device is subjected to high temperature. This test is used to help identify any excessive current leakage or voltage shifts. This is mainly for devices such as regulators, however, and is not performed on linear devices such as amplifiers and data converters.
- T2. Interim Electrical
– This is the second electrical test and is used to gather data on the performance of the device after the reverse bias burn-in. This data can be used in comparison to data collected later in the screening as well. These tests can identify the current leakage or voltage shifts from the reverse bias burn-in.
– At this step the device is subjected to high temperature in a normal operation mode which means the device is biased as it would be operated. This test is designed to eliminate devices that would have early life failures or, in common terms, have infant mortality.
- T3. Post Burn-in Electrical
– This electrical test is designed to ensure that the device performance does not shift beyond a specified amount after it has undergone the burn-in procedure.
– This parameter is the Percent Defect Allowable which establishes the percentage of devices that fail post burn-in electrical tests. A higher percentage of failing device could indicate that there are underlying reliability issues.
- Final Electrical
– The final electrical test is exactly as it sounds. It is the final electrical test performed where the device must meet the specifications set forth in the product data sheet.
If you would like to learn even more about these screenings and electrical tests I encourage you to visit EESEMI.com and look over all the great information that is available. There is a wealth of information available from the site including burn-in to electrical test and on to quality standards as well as much more. I would encourage you to bookmark the page for future reference. It has a lot of great information to keep in your engineering tool box.
Stay tuned for the next installment as we pick up the discussion with Group A testing. As is evidenced in our discussion thus far there is a lot of screening performed. This is important to ensure that devices can withstand the harsh environment that they will encounter in space applications. Analog Devices has over 45 years of history supplying components for space applications. If you would like to see the complete list of standard space product offerings I encourage you to take a look at the space qualified parts list here: Space Qualified Parts List July 2018. This illustrates the broad portfolio of standard space products that ADI has to offer and the company’s commitment to providing quality components for the space market.