Basics - Where Do I Start?
I know you have many choices for DFT blogs, and I’d like to thank you for choosing DFT Digest. Welcome back!
Anyway, we have a cursory “why” discussion behind us for now. But where do we start? Do we make a plan? Have you ever heard of a DFT plan? Google “dft plan”. I found 282 matches. Now google “test plan” - over a million matches. Does that sound right to you? It does to me.
One thing we must remember: the test function is the customer of the DFT function. The Test Plan is our PRD (Product Requirements Document). The ultimate goal of design for test is to facilitate the efficient execution of that document. Right? We could do nothing to our IC design, and we can still test it. But not efficiently - and maybe not completely.
To continue the analogy, I suppose a DFT plan could be considered the reponse to the test plan. The test plan says the fault coverage will be 99%+; the DFT plan offers a way to accomplish that. The test plan says that each digital output must be tested for proper levels; The DFT plan specifies JTAG/boundary scan as the way to do that.
So therein lies the answer to “where do I start?” - the test plan. There are, of course, the obvious cornerstones of design for test features, such as scan, BIST and JTAG, whenever and wherever each are applicable. But to have a complete implementation, look to the test plan, and figure out what could be done to make it easier!
More to come on this later…
November 16th, 2006 at 1:57 pm
Hey John,
Good to see you @ ITC and thanks for hosting this site.
Just thought I’d drop by and see what’s up. Meanwhile I was intrigued by your recent topic and had to add my $0.02
Be good,
Craig
~~~
In view a testability plan can be defined as follows:
The Testability Plan specifies the flow to be used, the tester constraints, the DFT strategy that is being adopted, the fault coverage & DPPM requirements, and contacts for design and test engineers responsible for implementation of DFT on a design. This is a high level plan of the complete Design-for-Test strategy.
The Testability Plan is owned by a group of people and is developed with inputs from several team members with outside help as necessary. The Design Team Manager is ultimately responsible for the validity of the document. He also holds responsibility of ensuring that the steps are followed during the development phase of the product.
Once the Testability Plan is complete, the next step is to customize the generic DFT Guidelines and ensure that all the concerns of the design team are documented in the guidelines. This document will act as a guide to all DFT related issues that have to be implemented in the design.
Before a Testability Plan is generated a Customer/Product Profile is useful to determine physical, economical, technological, and marketing/timing constraints and targets as well as cost/coverage metrology.
November 16th, 2006 at 11:17 pm
Hey Craig!
It was good to see you too at ITC - it’d been way too long since I’ve seen you, and many of my old colleagues. Time passes, technology changes, but good people seeem to be pretty much a constant as far as I’m concerned.
Thanks for signing up and leaving your comments on this li’l ol’ blog. My ultimate goal is to have many people commenting and discussing whatever topics interest them.
You brought up some very good points with respect to the ‘Testability Plan’, which I’ll assume is interchangeable with ‘DFT Plan’. Forgive the cook in me if I boil them down to: ownership, reponsibility, and requirements.
I’m totally on board with multiple ownership, and may I add cross-functional ownership. Design, test, product engineers, as well as marketing folk inform and implement the Plan (information and implementation vary according to job title).
The requirements come from all sides: customers, tester limitations, packaging, quality/reliability, etc. There are bound to be conflicts. Trade-offs.
My question is, in your experience, where are the most battles fought? And how has that changed over the years?
December 4th, 2006 at 11:14 pm
[...] I started this thread a ccouple of weeks ago, a post - something about writing a DFT plan. My contention was that a testability plan is an outgrowth of the test plan, adding efficiency and coverage. [...]
December 4th, 2006 at 11:16 pm
[...] One comment (thanks, Craig!) on that post got us off to a good start by defining some of the goals and ownership of the DFT plan. [...]