We're all aware of the serious battery problems which occurred with the recently introduced Samsung Galaxy Note 7 smartphone, leading to its recall followed by complete product withdrawal from the market. While there has been some of the usual sniping at engineers by people who have no idea what product design and release actually involve, I'm pleased to see that it has been relatively muted. Perhaps the critics and comedians have been distracted by the US election, which certainly has provided more “theater” and possibilities for humor and smarmy sarcasm than a smartphone?
At this point, we don’t know the cause or causes of the battery fires (or explosions?). It could be a latent defect in the battery cells which constitute the power pack, or the ICs which monitor and measure the cells in their pack, or the embedded firmware which manages charge and discharge based on those readings and control algorithms, or it could be some combination of the three (there's a good early diagnosis from The Wall Street Journal here). Perhaps it’s a strange thermal occurrence due to insufficient dissipation in some situations. It's certainly premature to come to any conclusion, and the deep-down root cause may actually be an unfortunate confluence of events, or the problem may even have different causes even though they have the same outward appearance—a very common reality in troubleshooting.
But the Samsung issue points to a major engineering challenge: how do you develop confidence in a design when the failure rate is so low? After all, the number of reported phone problems was actually quite low compared to the number of units sold. When you are at the tail end of that failure curve, how much longer and how do you test?
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