How important is inserting DFT in ASIC design?

How important is DFT?

Dear all,

I just wanna know how important to insert DFT in ASIC design...

1. Do every ASIC design insert DFT?


2. What about Mix-signal design which contains minor digital circuit (say 100 gates), do we have to do DFT?


hope someone can solve my doubts....thanks


regards,
smart

How important is DFT?

For I know,
1. most but not everyone, must be for up then 1M gates.
2. DFT just for digital. Analog & mixed, I'm not sure.

Re: How important is DFT?

ok , i wanna hear from anyone who has done DFT b4...

What is the minimum gate size that you implement DFT b4?


regards,
smart

Re: How important is DFT?

Well, I'm not sure I'd bother doing full-scan insertion with a JTAG TAP and so on for 100 digital gates. That doesn't, however, mean that I'd not do DFT. DFT isn't just scan insertion, etc. It is making sure that your design makes testing easier.

Any chip being delivered in bulk to customers has to be testable, one way or another. Using ATPG tools and full-scan, etc. is a way to make the testing easier and faster: both to write the tests and to execute them. You do NOT want to send a bunch of chips to a customer and for the customer to find that 10% of them don't work: you will soon lose customers. DFT techniques also make it possible for you to find out WHY a chip doesn't work, which can be helpful in improving yields, etc.

So, if you don't use ATPG and standard DFT techniques, you're probably going to have to do manual test writing. This may be required for the analogue part anyway, and if the digital bit is simple, this may not be a big problem, but you must make sure the design makes this as easy as possible.

Re: How important is DFT?

hi guys,
to my knowledge, it's not just gate count that matters for the having DFT,
technology of the standard cell, i.e., whether u go for 180, 130, or 90nm technology

As the technology shrinks u need to have strict methods to assure that u have fabricated fault free CHIP,so the DFT helps in this regard,

there are various methods of DFT, it depends up on what kind of design ur are undertaking, and how critical is the design,
all these factors comes in to the picture in deciding the kind of TESTING METHOD employed for the design

Re: How important is DFT?

I think the DFT (design for testabilty) is so important.

In some design,it can reduce much time of CP(chip probe testing ) or FT .

" Time is money" , if reduce testing time mean cost down.

Re: How important is DFT?

thanks for all...

so far i have understood the important of the DFT. However still do not know what kind of DFT should be implemented for design say let's then 100 gates (which is used for mix-signal circuit)?anyone has done that b4?

hope to hear more from all of u..

regards,
smart

Re: How important is DFT?

For such a small design the DFT required would depend on the exact design: can you give any more details?

Re: How important is DFT?

DFT (Design for Testability) is very important in VLSI design ( > 1 Mgates). It is a method that facilities the testing of manufactured circuits.
Its usefulness can be listed as follows:
- Reduce testing times --> reduce time-to-market.
- Reduce ATE / testing tools --> saving money.
- Ease testing process --> it means reduce manpowers, saving money.
- Assure the tested circuits functions more correctly, more reliably.
- ...

DFT has many technique: BIST, Boundary Scan, Ad-hoc,...

For the question : "How many gates does DFT use? " ==> It depends on your design and your experiences, and also your testing technique.

Re: How important is DFT?

For such a small design, you can just write functional vector to test the digital portion, instead of using scan insertion of BIST.

Re: How important is DFT?

amaccormack said:

For such a small design the DFT required would depend on the exact design: can you give any more details?

Click to expand...

it's for PLL and ADC design, which have very little digital gate inside..

regards,
smart

How important is DFT?

It's all about cost and quality.
If the chip is tiny, and the yields are very high, and high quality is not very important for your product, then you can probably get away with no DFT.
If you need high quality, then you need more testing, so it is a balance between whether you need to use an expensive high end tester or you can add some DFT and use a cheaper tester.

Re: How important is DFT?

always@smart,

1. Do every ASIC design insert DFT?

Click to expand...

No. Not every ASIC but most ASICs usually require DFTs.
DFT is a not a hardware, so you don't insert. DFT is an engineering concept that is usually practised by engineers. Even mechanical engineering and aerospace engineering have DFTs.

2. What about Mix-signal design which contains minor digital circuit (say 100 gates), do we have to do DFT?

Click to expand...

Yes and no, it's you choice. If you think your test circuit is going to be so complex that will incur more area and power consumption, you might not want to have it. It really depends on the functionality and nature of your digital circuit. Simply saying it is less than 100 gates is not informative or helpful to anyone who can offer you a good advice. If it's asynchronous in nature, you might want to check for glitches. Most CAD tools can extract circuit parameters and generate patterns for you to spot glitches in your digital circuit. If it's synchronous in nature, you might want to check that the clock period is timed sufficiently for the signals to meet setup and hold times for other parts of the design that require these digital signals.

How important is DFT?

most case DFT is rely on tools provision such as DFT complier or Logic Vision

Re: How important is DFT?

DFT is crucial for mentaining your product's quality.

almost all of us use DFT for digital chips.

I think mix-signal chips with little digital logic need not inserting DFT.

these little digital logic must be treat as analog circuit.


best regards

always@smart said:

Dear all,

I just wanna know how important to insert DFT in ASIC design...

1. Do every ASIC design insert DFT?


2. What about Mix-signal design which contains minor digital circuit (say 100 gates), do we have to do DFT?


hope someone can solve my doubts....thanks


regards,
smart

Click to expand...

Re: How important is DFT?

it's obligatory in digital domain