Hi Roger,
IPC 2221 part 3.2 and 3.21 refer to the need to review and establish the
'end product requirements', of which the 'specifications' would be a part,
at the BEGINNING of any project or PRIOR to the Design phase. You do it
exactly right, of course.
Most of the designers I know that work on contractual basis provide a quote
based on 'first pass' and charge by the hour for ANY deviation from the
original design quote, including all changes thereafter. Sort of like the
Earl Scheib "I will paint your car for 29.95.. 'BUT, in the fine print...
if you want anything extra, you tack on the additional charges at the shop
labor rate of 60.00 an hour.' Etc.. etc.. Otherwise you have the unfortunate
experiences like the one you went through... I'm sure there are
testimonials to that effect out there...
I think as an engineer you are not so rare, there are other PCB Designers
that have engineering degrees and do their own boards, too.. Bravo! Now if
you can train someone to support you... there will be an increase your
throughput.. instead of just being an "Army of one" - :)
The Impedance question I'll leave to someone else.. I've been flapping by
virtual jaw too much today already.. :)
Bill Brooks
-----Original Message-----
From: Roger Gathright [mailto:[log in to unmask]]
Sent: Monday, June 09, 2003 1:29 PM
To: [log in to unmask]
Subject: [DC] When to request specifications? When not provided up front!
Hi everyone....
I was wondering at what point in the design cycle for a board layout
is it appropriate to request specifications?
AND: Should the specification for the Impedance to the Board house
be in stack data, or Impedance value?
To clarify the reason for the question:
A recent layout (done as a favor for a friend) with his firm resulted
in much rework due to several people making changes as work
progressed. It was a fixed Price and Should have been renegotiated
based on the changes, I know! I actually laid out the board
seven times, with an additional five sessions of major rework.
This board had a 14 pin equivalent density of 125 parts on 4 square
inches. Almost all surface mount, and was impedance controlled.
After much indecision the placement was approved and I did the first
of many layouts. After the third engineer was assigned to "Shepard
the board / circuit" into production reviewed it, and more major
changes were made, and a faraday shield was added, with much
rearrangement to connect it in place.
I realize now, that my "Friend" was only trying to get off the hook.
But the original questions remains!
Oh yes, I am an Electronic Engineer, with experience in Emissions and
virtually all phases of design and Fabrication and test. I also lay
out almost all my OWN boards, and occasionally (Rarely) for a
customer. For myself, I always have ALL requirements called out
BEFORE starting any layout!
Roger Gathright
Sr. Project Engineer
Astromation Company
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