TECHNET Archives

February 2001

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Steve Underwood <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 15 Feb 2001 19:27:14 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (124 lines)
Robert,

Do you know if your photoplots are made from your original supplied data
or from the post-CAM tooling?

When photoplot data is received by a PCB manufacturer.  They can
generate photoplots that match exactly what is contained in those files.
However, this is usually not the same photoplots that are used to make
the finished product.  The photoplot data is copied to make tooling for
production.  This tooling is made so that the finished product meets
your specifications within the tolerances that you specify (or that is
defaulted if you don't).  If you get a hold of this tooling and compare
it to the finished product, you will probably find that it is not
exactly the same.  The tooling that is used to make the board has to
have compensations added to it so that during processing, the board will
end up the way you specified in your original photoplot data.  For
instance, you may specify that a trace width of 0.005" is used.  In
order to get that 0.005" trace width on the final board, the tooling may
have anywhere from 0.005" to 0.007" traces on it depending on the etch
compensation factors used (if any).  (Etch compensation is how much of
the line width is lost during chemical removal of unwanted copper).
The final board should be compared to your original photoplot data and
it should match within tolerance.

I'm not trying to over-complicate this, but sometimes, a customer will
ask for photoplots and then not understand that the photoplots he
received is actually the tooling for production when what he wanted was
photoplots of his original data.

I hope this helps.  If you are in or near Ohio, I can show you this
process here.

Steve Underwood
Engineering Manager
Circuit Center, Inc.
4738 Gateway Circle
Kettering, Ohio 45440
937-435-2131 ext. 127
937-435-7698 fax
[log in to unmask]




:-) -----Original Message-----
:-) From: TechNet [mailto:[log in to unmask]]On Behalf Of Neel, Robert
:-) Sent: 15 February, 2001 2:18 PM
:-) To: [log in to unmask]
:-) Subject: [TN] design vs reality?
:-)
:-)
:-) Hi People,
:-)
:-) I've had technet streaming into my terminal for a couple of
:-) weeks now and
:-) thoroughly appreciate the background flow of information.
:-)
:-) I have a question for any interested participant: What
:-) causes a finished
:-) circuit board pattern/trace to deviate from the photoplot?
:-)
:-) I'm looking at the photoplot file of a critical section of
:-) a circuit board
:-) I'm trying to field.  The plot file shows a pad-to-ground
:-) clearance of 20
:-) mils.  And yet when I slap a finished board under the scope, the
:-) pad-to-ground clearance measures 15-mils from one supplier
:-) and 10-mils from
:-) another. (The component center-to-center patterns are
:-) correct, so it's not a
:-) matter of scaling.)
:-)
:-) What gives?
:-)
:-) The assembly people are pounding on me to open-up the
:-) clearance, but, for
:-) the application constraints, and, by the book, the design
:-) clearances are
:-) fine.
:-)
:-) Is this correct?  Will the finished PCB deviate so wildly
:-) from my plots?
:-) How much deviation can I expect?  How much compliance can I
:-) demand?  What's
:-) a reasonable difference between the photoplot file content
:-) and the finished
:-) board?
:-)
:-) (If you want to make my day, tell me they should match
:-) exactly. Then tell me
:-) why they might not match and by how much.)
:-)
:-) Thanks in advance.
:-)
:-) Robert
:-)
:-) ------------------------------------------------------------
:-) ---------------------
:-) Technet Mail List provided as a free service by IPC using
:-) LISTSERV 1.8d
:-) To unsubscribe, send a message to [log in to unmask] with
:-) following text in
:-) the BODY (NOT the subject field): SIGNOFF Technet
:-) To temporarily halt delivery of Technet send the following
:-) message: SET Technet NOMAIL
:-) Search previous postings at: www.ipc.org > On-Line
:-) Resources & Databases > E-mail Archives
:-) Please visit IPC web site
(http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
------------------------------------------------------------------------
---------

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------

ATOM RSS1 RSS2