Product Engineering: The bridge between design and manufacturing
Product engineers fill what could otherwise be a chasm between design engineers and production test engineers. Indeed, my first work assignment after earning my engineering degree was in product engineering. That's why visiting the product-engineering lab at Maxim Integrated in San Jose, Calif. earlier this year was so familiar.
Product engineers at Maxim have several roles. They serve as impartial arbiters between design and manufacturing. While their first job in a product's life cycle is to verify that new analog and power IC designs meet specifications, they also make sure that production test engineers have what they need for production to commence. Should something go wrong in the field, it's product engineering's job to figure out why. Product Engineering Manager Sarvesh Miyan gave me an overview of his department followed by a tour of the lab.
On the front end, product engineers get "first silicon" from the fab, which means they need to begin testing as soon as the devices arrive. To achieve that goal, they work with design engineers to get the details of each new IC: functional specs, design specs, mechanical layout, pin layout, etc. While the devices are being fabricated, product engineers design test boards and develop the automation code needed for bench testing of the new devices.
Product engineers also interact with their internal customers: the test engineers that support production. When gearing up for production, product engineers provide test engineering with specs and support. Following initial product evaluation, product engineers send samples to test engineers for further testing on ATE systems. This additional testing lets engineers correlate production test results with bench test results. Correlation units such as LED drivers that require digital trimming can be bench trimmed, ATE trimmed, or both. Thus, engineers do cross-platform correlation. If the ATE measurements are consistent with those made in the lab, the production setup is ready for temperature and process characterization. If there are differences in measurements, product and test engineers must work to find out if there is an issue with test setups.
Product engineers may also get involved in problem solving should production yields drop. It's their job to determine if there's a process problem or a production test problem. Reasons include a change in IC packaging, changes in ATE setups, or changes in manufacturing processes.
On the back end, product engineers are responsible for evaluating field failures, which can range from a device not meeting specs to a complete failure. Product engineers begin by evaluating failed parts on the bench, receiving the parts and sometimes boards from the customer. Should a total failure occur, product engineers might call on reliability engineers to inspect the failed IC's layers.
Product engineers are also responsible for how products perform over time. They will often compare failed parts against "golden" parts. We'll see how they perform long-term drift (LTD) tests in the lab later in this article.
The product engineering lab consists of several automated test benches. Product engineers develop automated bench tests by designing test boards, writing test scripts, and using bench instruments such as DMMs, oscilloscopes, function generators, and power supplies.
"All test benches are fully automated," explained Miyan, "with each using an in-house developed LabVIEW code library." Using the code libraries, product engineers create test scripts using general purpose and reusable functions that include instrument controls, standard communication protocols such as SPI and I2C. The protocols let engineers program parts that have communication ports for control, data readback, and for some parts, digital trimming."We don't need to push buttons on our test equipment," said Miyan. "Everything is programmed from the computers. Test automation means we can run tests all day and night and minimize errors. Automation lets us guarantee repeatability and reproducibility of measurements, not just during first-silicon evaluation or correlation, but even after years of production." Figure 1 shows a diagram of a typical bench setup.
Figure 1. A bench board routes signals between the DUT and test equipment while under software control. The test-system controller PC compiles data and produces reports. Courtesy of Maxim Integrated.
Next, see a tour of the lab where you'll see a training board for new engineers followed by product engineers testing IC temperature sensors, analog-to-digital converters (ADCs), buck/boost converters, LED drivers, and how engineers perform LTD measurements.