You can help out your board fabricator quite a bit by tear-dropping the
pads at the trace entry point on the fine-line boards, especially if the
holes are not proportionately small along with the lines (for example: 5mil
spaces and 5mil lines, with 18mil holes- you're probably using
conventional means to drill the holes, in this case). Your CAD or CAM
system may well have a routine to tear-drop or "snow-man" the pads
such that opens do not occur if there is some mis-registration or drill
wobble. Its probably a good idea to use this feature. 

John Swinehart
BFGoodrich Avionics Systems, Inc.

>>> <[log in to unmask]> 07/21/97 02:37pm >>>
     Mike,
     
I would estimate that 75%, if not more, of all fabricators in the states
have 
the capability to fabricate .005 lines/spaces in a production mode.  The
problem
may be with your fabricator.  I'm not aware of of too many PCB shops
that can 
not fab .005/.005.  The game changes once you go beyond this point.  I
found 
most of my fabrication problems occured at .004/.004 and .003/.003
lines/spaces.
What has successfully worked is .004/.006 lines/spaces, respectively. 
The 
spacing is the driving force behind getting good conductor walls and
minimizing 
overetching.  The additional spacing allows for the etch chemistries to 
sufficiently etch copper in the tracks (valleys) and be replinished
efficiently.
The chemistries used to etch are isotropic, meaning they etch in all
directions 
proportionally.  What I observed on .003/.003 and .004/.004 lines/spaces
is 
severe undercut, conductor slivers and bridges.

This is not to say .003/.003 and .004/.004 lines/spaces can not be
obtained.  
The fabricator must have the necessary equipments, chemistries and
process 
controls in place to do so.  I know of several in the inductry that are
fab'ing 
.003 and .004 lines and spaces in volume, but at a premium.  If you need 
assistance, I can probably recommend several fab houses in your region
for your 
current .005/.005 requirement.  Hope this helps.


John Gulley 
Inet Inc 
1255 W. 15th St 
Plano, TX 75075-7270


______________________________ Reply Separator
_________________________________
Subject: Standard PCB/PWB Trace Width's
Author:  "Michael Forrester"<[log in to unmask]> at Internet
Date:    7/18/97 5:38 PM


     
     
     
     
We currently design boards with 8 mil. traces.  We have recently tried to 
go to 6 mil. traces and found that we had reliability problems from batch 
to batch.  What is the smallest trace that is considered reliable by todays 
standards?  Is it just our PCB/PWB manufacturer that may have a
problem. 
Typically what we saw was over etching of the traces.  Thank you.
     
Best Regards,
     
Mike Forrester
LeCroy Corp.
[log in to unmask]
     
     
*************************************************************************** 
* TechNet mail list is provided as a service by IPC using SmartList v3.05 * 
*************************************************************************** 
* To subscribe/unsubscribe send a message <to:
[log in to unmask]>   * 
* with <subject: subscribe/unsubscribe> and no text in the body.          * 
*************************************************************************** 
* If you are having a problem with the IPC TechNet forum please contact  
* 
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *

***************************************************************************
     

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to:
[log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact  
*
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************


***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************