The software is most of the work
An exclusive interview with a test engineer
By Martin Rowe, Senior Technical Editor -- Test & Measurement World, 3/1/2008
Todd Grey is a senior test engineer at Maxim Integrated Products in Dallas, TX. Though relatively new to Maxim, Grey has been a test engineer for more than 25 years. He supports production test in initial product runs on digital devices that contain simple microprocessors and EEPROM. The devices contain a one-wire communications interface and are used in printer cartridges and in ID devices. Senior technical editor Martin Rowe spoke to Grey by telephone.
Q: What are your major responsibilities?
A: I’m responsible for production test, which consists of helping designers understand how production test differs from simulation. I’m also responsible for reducing test costs and for supporting the production floor when problems arise.
Q: What do you teach designers about production test?
A: Our production ATE [automatic test equipment] forces us to operate devices using different clock speeds than the devices see in actual use. For example, suppose a device uses three clock domains. Each domain runs separately. But we test the devices with all clock domains generated from a single source. All domain clocks are multiples of the single clock source.
Our digital IC testers operate based on time slices. Simulations generate test vectors that tell you when to strobe a device or pin, and those times don’t always align with the tester’s clock. We often ask designers to run a simulation under the conditions the device will encounter while undergoing a test.
Q: How do you support production?
A: I develop the software for our ATE. I also design test fixtures that let us test devices both on the wafer and assembled into packages. I spend 95% of my test-development time writing code. The test code contains the test procedures and the tester’s user interface that walks a technician through each test. My job also requires that I minimize the cost of test. Our devices typically have between two and eight pins and cost between $1 and $2 each. To minimize test costs, we use 64-pin digital IC testers rather than 512-pin or 1024-pin testers. We also perform reduced pin-count testing on devices while they’re still on the wafer. We get about 60% to 80% test coverage while devices are still on the wafer. Then, we run a final test on packaged devices.
Q: How many devices are in a production run?
A: A typical initial production run in Dallas is about 5000 pieces. Full-scale production takes place in the Philippines. I spend about half of my time on the Dallas test floor. If a production test issue arises, I typically review the test procedure.
Q: What do you consider the most significant test challenges facing test engineers today?
A: Cultural differences in people around the world are a big challenge. At my previous employer, we had designers and test development in several countries. In other countries, Americans may be perceived as “pushy,” particularly when it comes to schedules. Sometimes, people will tell you that they can deliver according to your schedule because they don’t want to offend you by giving an honest answer. Americans need to explain to others that we appreciate an honest answer so that we can plan accordingly and be ready on schedule. Maxim keeps all test development in the US, so we don’t see these cultural differences during development. But production is in the Philippines, so we run into it there.
