( ESNUG 335 Item 5 ) ---------------------------------------------- [11/3/99]
Subject: ( ESNUG 300 #3 309 #8 ) The Politics Of Testing & Test Engineers
> With all the above good reasons, it is no surprise that test automation
> tools have always been undersold, under-utilized and have been considered
> unnecessary by most companies except the leading-edge, quality conscious
> companies, and companies that have been in areas that I have mentioned
> above where the liabilities can be substantial.
>
> So how has the EDA industry responded to such a low level of interest from
> customers? Like most insurance policies, manufacturing test tools have
> sold very well after disaster strikes. Without giving specific instances,
> it should suffice to say that most companies have used EDA tools for test
> only after they were desperately arm-twisted by their potential or current
> customers for lack of quality, lack of relaibilty, terrible defect rates,
> etc...
>
> - Shankar Hemmady
> Guru Technologies Cupertino, CA
From: Duncan Walker <walker@cs.tamu.edu>
John,
A few minor quibbles with Shankar's ESNUG post:
1. Everyone eventually gets burned, thus everyone eventually uses a better
test methodology. Even if the company burns up, the engineers will
still take that memory to the next company.
2. Those with tight schedules are the ones mostly likely to just say use
full scan, run ATPG, and take what we get. Even a no-brainer solution
can get much higher coverage than functional vectors, and take much
less time to generate (assuming you don't get some from the designer).
3. Test can play an important role in getting product to customers. If
some QA devices fail, the customer does not want that lot until the
fails are explained. That means you need to do diagnosis pronto.
Without DFT/DFdebug, this is impossible on a large chip. Then the
marketing guys must sing and dance and convince the customer those
fails are really random, and the customer should accept the product.
4. Design for debug. This is where the designers get burned and demand
more debug features on the next chip. Debug != test, but anything hat
increases observability is good for test.
5. The metrics are good, fast, and cheap. Test is really about goodness.
Obviously this is lower priority than fast and cheap in many
applications, but this has always been so. But there is an increasing
fraction of electronics used in safety or money-critical applications,
which in turn drives testing.
6. One thing you didn't mention for ASICs is that often the chip test can
be so-so, and then the customer can do the real test at board level.
This costs much more to repair, but if it the defect level is low
enough, it may cut the time to volume it may be worth it. So the chip
is getting tested, but not at chip test.
7. Some designs are simple enough with high enough volume that brute-force
functional test and customer feedback is enough. Do you know that MIPS
just hired its first DFT engineers last year? (A former student is of
mine is one of them.) Many controllers are relatively simple, cheap,
high-volume, and high quality. This is so because they are mature, and
the functional test sequence was iterated enough that the defect level
is acceptable.
8. If your yield is 100%, you don't need to test. I saw an SSI/MSI
assembly and test factory where the test was just a pins shorted/open
test. The chip manufacturing yields were high enough that no chip test
was necessary.
9. If you weight by dollar value/volume, the vast majority of chips havea
real test methodology applied. In many ways your discussion was from
the EDA seat-count point of view.
I think a lot of it is just ignorance. Look at the discussion of memory
testing in the very same ESNUG 309 #4 -- some participants seemed unaware
of the huge body of work on this topic. The distribution of DFT expertise
among companies is mirrored in many other ways. Too many companies are run
using a series of "get it out the door any way I can" hacks without ever
developing true expertise in the relevant technology areas. I suppose this
is why consultants can make a living, bailing out those who run into a
situation that hacks cannot overcome.
- Duncan Walker
Texas A&M University College Station, TX
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