Faulty Chips Might Just be 'Good Enough'

Ritalin16 writes "According to a Wired.com article, 'Consumer electronics could be a whole lot cheaper if chip manufacturers stopped throwing out all their defective chips, according to a researcher at the University of Southern California. Chip manufacturing is currently very wasteful. Between 20 percent and 50 percent of a manufacturer's total production is tossed or recycled because the chips contain minor imperfections. Defects in just one of the millions of tiny gates on a processor can doom the entire chip. But USC professor Melvin Breuer believes the imperfections are often too small for humans to even notice, especially when the chips are to be used in video and sound applications.' But just in case you do end up with a dead chip, here is a guide to making a CPU keychain."

Comments

No Thank You.

[Anonymous Coward]

I'd rather my chip works as advertised.

Nothing new

[Rosco P. Coltrane]

LCD manufacturers routinely put defective screens on the market, on the premise that a dead pixel here or there "won't be noticed". Too bad, because consumers do notice and do tend to return the product equipped with the dodgy screen, only to be told that it's "normal".

In short: computers suck...

Already being done (somewhat)

[SA Stevens]

The CPU vendors are already doing a 'sort and grade' operation, when they label processors. Have been for years. When the yield from the fab is lower-grade, the dies get packaged and labelled as lower-speed parts.

Then the Overclockers come in and ramp the speed back up, and claim 'the faster chips are a ripoff' and complain that 'Windows is always crashing.'

Re:Already being done (somewhat)

[taniwha]

(I'm a sometimes chip architect, so some background) - there's two sorts of tests that go on when you fab chips - functionality (do they do the right thing, are all the gates working, are all the wires connected) and speed (does it go fast enough).

For most chips, except ones like CPUs where you can charge a premium you don't speed bin (it costs lots of money), you pick a speed you think it should go at and toss the rest. Shipping chips that almost work is bad business - think about it, I make a $5 chip it gets put in a $100 product, if 10% of my chips don't work my customer loses $100 for every $50 he pays me, I have to get my failure rate down so it's in the noise as far as the customers are concerned, otherwise they'll go to the competition.

I think that the number of applications the original article's talking about where chip errors are tollerable are pretty small, suppose my CPU has a bit error in the LSB of the integer adder, the IRS may not care if my taxes are off by 1c, but the MSB is a different matter ("sir you appear to owe us 40M$"). On the other hand an LSB error is a big deal if the value you are dealing with is a memory pointer and breaks a program just as badly as if it is the MSB.

Finally a word about "metastability" - all chips with more than one clock (video cards are great examples" have to move signals between clock domains - this means that signals can be sampled wrongly (well designed logic should handle this) or in rare cases suffer metastability where the result causes unstable logic values to be latched into flops (usually these look like a value that swings wildly between 0 and 1 at a freq much higher the normal clock, a flop in a metastable state can 'pollute' other flops downstream from it turning a chip into a gibbering wreck. Now well designed logic doesn't do this very often, the flops chosen for crossing clock domains are often special anti-metastability flops used not for their speed or their size but their robustness - but the physics of the situation means that it's simply not possible to avoid - just possible to make it not happen very often. What you do need to do is figure out how often something will fail and pick a MTBF that is appropriate for your device ... I once found myself discussing this issue around a video chip we were designing and basically what it came down to was comparing the theoretical worst case failure rate (chip people tend to be very conservative, keeps us on the right side of Murphy) of our chip with Windows - our chip might fail once a year (and even then there was a pretty good chance you wouldn't notice it) while back then windows blue screen every day - would anyone notice? nope

they don't waste finished chips

[seanadams.com]

Many of the chips fail inspection prior to going into the package, and then some more fail functional test after that. Probably more than half the price of a chip is the factory itself and the R&D work which is amortized over so many zillions of parts, and much of the rest is all the handling, packaging, shipping, and middlemen. I'd guess less than 10% is per-part materials and labor.

Therefor throwing away a $2 chip during production doesn't cost $2. It's only worth $2 by the time the customer pays for it.

Sure you could sell the defects at some discount, but it's only worth the trouble for some high volume part like RAM where defects are easily useable, and definitely NOT a part where the impact of some particular defect in the end user's application could be really hard to characterize (like a CPU).

Re:I'm not so sure...

[mjh49746]

I'll have to agree. I've just RMA'd a DVD burner a day after I got it back from the last RMA. Not to mention having to RMA a stick of RAM not three months ago. QA seems to be a really sad joke, these days.

We've already got enough bad components floating around. We surely don't need any more.

This is completely bogus.

[david.given]

And anybody who actually knew anything about computers would know this. TFA doesn't mention what this guy is a professor of --- I bet it's not electronics.

Basically, the problem is this. With mechanical and analogue devices, most of the time you know that if you change the inputs a small amount, the outputs will change a small amount.

But digital devices are chaotic. Change one bit in the input, and the output is likely to be radically different. One bit in the wrong place on a Windows system can make the difference between Counterstrike and a BSOD.

You can use substandard devices for some applications; dodgy RAM, for example, can be used to store audio on, and it would work just as well for video framebuffers. But you could never put anything programmatic on it; that has to be perfect.

(IIRC, they do recycle faulty wafers. One of the ways is to scrape the doped layer off and turn them into solar cells. I don't know if they can use them again for ICs, though.)

Re:Stories

[bbrack]

If you go and buy a handful of 5% resistors, you will find ~0 that are within 2% of their value - if you buy 2%, none w/in 1%, etc...

Manufacturers are VERY aware they can charge a larger premium for better parts

This is also a problem in medicine

[Glowing Fish]

If you look at what the "big ticket" items are in the US economy, electronics and medicine are up at the top of the list.
And the reason for this is, as you get closer to perfection, it takes more and more of an economic cost, in terms of money or resources or time or effort. For a computer or a medicine to go from 90 percent to 99 percent utility means a ten fold increase in price.
Thats why the constant quest to have "perfect" electronics and medicine is driving up the prices of these things to the point where normal people can't afford them. If we could accept that we didn't always need new, perfect, shiny medicines and electronics, it would put them in a sane price range.