Hey! A question in my field for a change!
Bob, the folks are correct about JTAG/BoundaryScan. For this testing
technology to be even applicable, the designers must utilize components with
BoundaryScan capability in them, and then connect them in a certain fashion.
Typically you will only see this utilized on boards with large, active
components.
As for "Board Level Testability Analysis" this is another way of saying
"Design for Testability" (DFT).
DFT includes:
- Mechanical considerations
(ex: test pad sizing/spacing, tooling pin sizing/clearances)
- Electrical considerations
(ex: control line availability for ICT Testers, BIST control)
This stuff revolves around two arenas, 1) the ability for In-Circuit testers
to make connection to the assembly (fixturing) and manipulate it (circuit
design), and 2) how well the assembly is designed to be tested in a
functional fashion (functional test, diagnostics, Built in Self Test, etc.)
Typically your Test Engineer (or outside test house) should be compiling a
set of DFT guidelines based on their test capabilities.
Unless I've been asleep or blind (both entirely possible) most of the folks
setting up guidelines for design (IPC, SMTA, etc.) don't have much to say on
the subject of DFT although I would love to be proven wrong. The result is
alot of us have developed our own DFT Guidelines in self defense.
Now that your head is spinning, send me an e-mail directly with a bit more
info on your role in this and what you make, and I can elucidate you to death
on this subject! <lol>
-------------------------------------------------------------
Robert D. Green - Supervisor, Test Engineering
Hadco - Value Added Manufacturing
e-mail [log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Re: [TN] JTAG.??
Author: "Stephen R. Gregory" <[log in to unmask]> at smtplink-hadco
Date: 5/24/99 2:18 PM
In a message dated 5/24/99 10:56:13 AM Pacific Daylight Time,
[log in to unmask] writes:
<< To all...
I attemted to send this out Fri., but I don't
think it went. I'll try again. My boss asked me
if I knew anything about a "Board level testability
analysis including the role of and use of JTAG"? I
responded with an very educational DUH!!! Help,
does anyone know what this is about??? Any help
would be appreciated and thanks in advance.
Regards,
Bob Vanech
Mango Computers
(203) 857-4008 x108 >>
Hi Bob!
JTAG is a sorta kinda trade name that came about from a joint effort by
certain companies, that's really talking about Boundry-scan testing. If you
go to: http://www.corelis.com/products/scanovrv.html there will be a real
good overview about Boundry-scan testing and what has to happen as far as
design and whatnot in order to able to accomplish it. Below I've pasted a
couple of paragraphs from that page that gives a general description about
it...
-Steve Gregory-
Boundary-Scan Standard Background
Boundary-scan, as defined by the IEEE-1149.1 standard, is an integrated
method for testing interconnects on printed circuit boards that is
implemented at the IC level. The inability to test highly complex and dense
printed circuit boards using traditional in-circuit testers and bed of nail
fixtures became evident in the mid eighties. Due to physical space
constraints, fixturing cost increased dramatically while fixture reliability
decreased at the same time. This problem has been further complicated by the
growing use of complex custom application specific IC's (ASIC's) that require
extensive test pattern sets. This not only increases test development cost,
it also increases test times and decreases test coverage.
In 1985, companies such as IBM, AT&T, Texas Instruments, Philips Electronics
NV, Siemens, Alcatel, and Ericsson, recognizing the need for a uniform
solution to these problems, took the initiative to overcome these issues and
founded the Joint Test Action Group (JTAG). This initiative quickly led to a
new boundary-scan testing (BST) method, adopted by the IEEE as Standard
1149.1 in 1990. Since that time, this standard has been adopted by major
electronics companies all over the world. Applications are found in high
volume, high-end consumer products, telecommunication products, defense
systems, computers, peripherals, and avionics. Now, due to its economic
advantages, smaller companies are starting to take advantage of BST.
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