Diodes and x-rays
An exclusive interview with a test engineer
Martin Rowe -- Test & Measurement World, 5/1/2007
Rob Stadelman is a project engineer with Central Semiconductor (Hauppauge, NY, www.centralsemi.com), a manufacturer of discrete semiconductors. The company’s products include transistors, diodes, bridge rectifiers, MOSFETs, and thyristors. Senior technical editor Martin Rowe recently asked Stadelman about the challenges he faces.
Q: What is your role in test?
A: Whenever we need a new test capability or need to improve a test capability for electrical or mechanical test (including inspection), that job falls to me. I recommend new test methods and research new equipment for purchase. I often develop bench testers from scratch, such as a zener-diode tester.
Q: How does the zener-diode tester work?
A: It’s quite simple, just a power supply to provide current and a digital mulitimeter (DMM) to measure voltage across the device. It lets us test using a continuous DC current as opposed to a pulsed current that most automated testers use.
We adjust the heating time so that the device is tested at its operating temperature. We get a more accurate Vz measurement because the device is at thermal equilibrium. Software lets operators enter min and max voltages, and the tester gives a pass/fail indication.
Q: What sort of mechanical inspection projects have you done?
A: We just completed investigating a new x-ray system for looking inside components to check for proper assembly. X-ray inspection systems have come a long way, especially in terms of automation and level of detail.
Q: How long did you spend investigating x-ray systems?
A: Six months to a year. The process involved our sending samples to manufacturers. We got photos back to see if the quality was what we expected. When we narrowed it down to three our four, we visited them. We’ve made our selection and are waiting for the budget allocation to purchase this system.
Q: How different are new systems from the system you currently have?
A: The existing system is analog. It uses a video-processing card, and it displays the image on the screen. New systems are digital and PC based. Our operators can run a system with a keyboard and a mouse as opposed to running an embedded system. That’s much easier to use, plus new systems deliver pictures with much better resolution. Our new system will also provide us with automation we don’t currently have.
Q: What automation features will you get with a new inspection system?
A: We sell many of our parts as individual die on trays. The new system will be able to identify missing die on a tray. We do that manually now. We’ll also be able to store digital images and share them over a network. We’ll be able to perform automatic die-voiding calculations, which is a huge advantage over our current system.
Q: What other automated test systems do you have?
A: We have an automated system that measures AC parameters such as Ton/Toff, switching time, diode reverse-voltage recovery, and gain-bandwidth product. Over the years, we’ve made some software changes. For example, we were able to program the system to better adjust an oscilloscope’s time base, thus providing a more accurate measurement.
Q: What other functions do you perform?
A: I spend about half of my time developing and specifying test systems and the rest evaluating new designs. I run environmental and stress testing on new devices. Sometimes, customers request specific tests for voltage, current, or temperature. I often handle those requests.
