After final assembly, the first inspection that we perform on 100% of NI modular instruments is AOI. This inspection checks for gross defects on a product. We first inspect a few known good products and the machine creates a sketch of these products and saves it to memory. Every other product inspected is compared to the sketch and checked for part orientation errors or missing parts. Once product passes AOI it moves on to ICT.
Figure 1. Automated Optical Inspection System
ICT, also known as “bed of nails” test, consists of a fixture with a top and bottom plate outfitted with several probes. The plates close down on the unit under test, contacting each test point and checking the resistance between points. This test allows us to check for shorts, opens, or backwards components. After ICT, NI modular instruments move on to IFT.
Figure 2. In-Circuit Test, “Bed of Nails”, Station
IFT tests the basic functionality of the product. We make sure that it powers up before we perform any more tests. Once the product passes IFT, it moves on to ESS.
Figure 3. Initial Functional Test Stations
ESS includes burn, thermal conditioning test (TCT), and highly accelerated stress screening (HASS). This screening can take anywhere from a several hours to several days to complete. There are two different types of burn we perform. One is static burn, which is where we place the modular instrument in a PXI chassis, bring it to a certain temperature and hold it there. We do not provide any stimulation to the instrument. The second type of burn is dynamic. For dynamic burn we provide stimulation to the instrument while it is at an elevated temperature and monitor how it responds.
We also perform TCT on some of our products. TCT consist of cycling the temperature from 0 – 55 degrees C over a period of several hour or days while we check for latent failures. During TCT we ramp the heat chamber up to a certain temperature, wait for the unit under test to stabilize and then we perform a test. After that, we ramp the heat chamber down to a specified temperature, wait for the UUT to stabilize and then test again.
Figure 4. Temperature Chamber for Burn and Thermal Conditioning Test at National Instruments
Finally, certain products go through our in-house HASS chamber as part of ESS. The final test once a product goes through ESS is FVT.
At this point in the product verification we should have found all of the latent failures. During FVT we calibrate all of our modular instruments and test to make sure that they meet all of the specifications.
As an example of how critically we treat this final step of unit verification, we calibrate the FVT calibration stations for our RF products on a weekly basis to ensure that our RF products are accurate and meet all of our specifications. We measure the loss from cables, splitters, adapters, and fixtures and store those values in our test executive so we can compensate for those when we calibrate our RF instruments.
Figure 5. Functional Verification Test Station at National Instruments
The final step after FVT is quality assurance (QA). This is a visual inspection where we check to see if there are any scratches or imperfections on the product that could impair the performance. Once the product passes this step it is checked into stock and ready to ship to our customers.
To ensure the quality of our modular instruments, the design team meets six months after a product is released to review the health of product. They look at return rates, failure rates, data from performance testing, and more. Any changes that need to be made to improve the quality of the product are identified during the meeting. NI continues to monitor the health of the product on a monthly basis.