In my previous blog in September, ADI Standard Space Products Screening, we began looking at the screening steps performed on standard space product offerings at Analog Devices. As we discussed last time this discussion there are many screening steps performed on space qualified components. It is imperative to perform these screening steps to ensure devices can withstand the rigors of the space environment. In the last installment we looked at steps 1 through 17 which are highlighted in green in the table below. In this installment we will pick up at step 18 with Group A screening (highlighted in yellow in the table below) and discuss the associated items for this particular group of testing.
ADI Standard Space Level Flow
Before we dive into the specifics of Group A testing lets first take a moment to set the stage with a high level look at Groups A, B, C, D, and E and understand the order and general criteria for these steps. In this blog we will focus in on Group A which is the first set of tests performed among these different groups. Only in the case where the use of electrical rejects is allowed can units be subjected to Groups B, D, D or E without previously passing all the electrical tests in Group A. Within the MIL-PRF-38535 specification there are tables that define the testing parameters for each group. The specification also calls out what units may be used for the test and how often the test needs to be performed as summarized in Table 2. It is required to perform Group A and Group B testing on each inspection lot. Group C testing is required every 3 months while Group D testing is required every 6 months. Group E testing must be performed on each wafer lot.
Groups A, B, C, D, and E Testing
Group A electrical testing is further subdivided down into four different categories: static, dynamic, functional, and switching. In each of these categories there are three subgroups which represent testing at minimum rated operating temperature, maximum rated operating temperature, and at +25°C. These different categories represent different types of electrical tests. These four different categories with three subgroups are given in Table 3.
Subgroups for Group A Electrical Testing
Once again, I’ll refer to a high speed ADC to provide examples of each category of Group A testing. I find it helpful to consider an example such as this so that the various subgroups in Group A testing can be better understood.
An example of a static electrical test would be a test for the power supply currents of the device. These would include information for each power supply domain. In addition, power supply currents are generally given for different operating modes of the ADC. There could be power-down and standby modes as well as different modes with various digital features enabled and/or disabled.
A dynamic electrical test parameter would be the test for the integral nonlinearity of the ADC. It would also include the SNR (Signal-to-Noise Ratio), SFDR (Spurious Free Dynamic Range), ENOB (Effective Number of Bits), and harmonics measurements among other similar items.
A functional test is more of a go or no-go test which is not something typically reference for an ADC since the specifications listed would have some sort of performance range associated with them over device operating temperature. An example of such a test could be something like checking to see if the ADC outputs data that can be used to generate an FFT. If an FFT can be produced, the test would be a go, and if no data is output resulting in no FFT it would be a no-go. This is not a test for which a specification can be listed in a data sheet for an ADC though.
Switching tests performed in Group A electrical testing cover items such as the parameters associated with the output data clock and bits of a high speed ADC. For a high speed ADC with digital outputs that use LVDS (Low Voltage Differential Signaling), these parameters would include setup and hold times associated with the output data clock and the output data. Switching tests would also include the propagation delay which gives the time between with the input clock edge and the converted data availability on the output of the ADC.
If you would like to continue reading for a deeper dive, and you have a lot of time on your hands, you can visit the DLA website to read more on the MIL-PRF-38535 specification here: MIL-PRF-38535 specification.
Stay tuned as we move beyond Group A testing into the other groups that are listed in Table 1. Next time we will move on to the leak tests and perhaps get as far as looking at Group B screening. We will work our way through each of the different groups over the coming months so we can better understand the different screenings that are performed for space products. I trust this has been insightful thus far and hope you will continue to join me in this discussion as we continue looking at the different space screening steps.