Before the Dawn of IP Telephony - Part 28
Transistor destroyed for unknown reason (summer ~ October 2002)
These contents translated a serialization article carried by ITPro IP telephony ONLINE published by Nikkei Business Publications, Inc. Jump to the original (Japanese).
Shinji Usuba
General Manager
eSound Venture Unit
Oki Electric Industry Co., Ltd
We were at the final stage of line unit (LU) development. It was then discovered that the LSI, which had already entered mass production, did not perform sufficiently under certain conditions during software assessment. The situation seemed hopeless with no measures to be found.
At the end of July just immediately before summer break, we were almost near completion of tests, with seven types of noise measures finished and battling towards the completion of the full indoor device for telecommunication carriers. It was just when we were getting over the difficult part and plans for shipment becoming clear. Suddenly, bad news came out of the blue.
Prototypes that are manufactured for verification of the plant production line prior to the start of mass production are referred to as "mass-production prototypes." And we were notified that the mass-production prototype did not pass the electrostatic test (a test that artificially reproduces static electricity that may occur in a real environment by instantaneously applying high voltage).
Failure of a test after reaching the stage of mass-production prototype verification is not common. Design prototypes are manufactured using a process equivalent to mass production, and the verification of mass-production prototypes is considered as a "precautionary check" among the parties concerned.
However, the bad news did not end there. A test using a different mass-production prototype also failed for the same reason. And about the same time, the same phenomenon was reported by one of our customers provided with a mass production sample. We were completely lost. We were prepared for all-out war until the cause was found and a proper measure was taken. And from that day, our battle in the summer heat had started.
Destroyed transistor
Photo 1: Thermostatic chamber used for analysis
As a result of investigation, we discovered that the transistor was destroyed. But we did not know why. Through continuous investigation, we found that there was a slight change in output of the new device introduced in the previous episode at the time when the transistor became destroyed.
But we had no clue about why there was such change, and why such change led to the destruction of the transistor. From the outside, devices that operated normally and devices that led to destruction looked identical.
The design related to the characteristics of sound, which was realized by circuit design of hardware in the past, was built into the device and its settings were available using software. Part of the hardware design can be realized by setting parameters within the device. In other words, the design such as pattern design was simplified by conversion of hardware to software. This led to extreme difficulty in analyzing problems for those that did not understand the meaning and the relationship of registers within the device when a problem occurred. The temperature surrounding the thermostatic chamber after repeated verifications was hotter than the mid-summer heat (photo 1). And all the members working on this project were forced to spend days in the heat.
Continued to next page: Sharing the same ideal design concept
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