FreeLists / pcdlist / [pcdlist] Re: Thru hole components

["Brooks,Bill" <BBrooks@xxxxxxxx>]

Hi William,

I would suggest you let the tolerance that the design can accommodate drive
the hole sizes. I try to pick nominal hole sizes that are from the old
standard drill chart we used when I was hand taping that are close to the
nominal size for the lead hole and tolerance, always driving the hole larger
rather than smaller because you make things worse if you reduce the
allowable tolerances unnecessarily. If you are using auto insertion in your
assembly process, that will drive the sizes too.
 Then I always do a review of the drill drawing finished hole chart before
sending out the board and try to consolidate hole sizes to reduce the number
of drills required to make the board. Usually there are holes that are
nominal to the design of the part that can be modified by a few mils (or
millimeters for those of you who are converting to the metric system and
hate all things that are related to inches...)and moved to the next largest
finished hole size to reduce the drill tool count. 
The way boards are quoted is by square in[or mm], number of layers, number
of holes and number of drill changes required and any additional setups or
process steps required....oh, and time to completion. 
The main thing being, number of tool changes can affect the cost of the
board in volume. Prototypes are hardly affected because its a one time
minimum setup fee that's the major part of the cost for small quantity
orders. Hope that helps start the conversation for you.. :) I'm sure the
others will have more to add from different points of view..


Bill Brooks 
PCB Design Engineer , C.I.D., C.I.I.
TITAN SYSTEMS CORPORATION
DATRON WORLD COMMUNICATIONS DIVISION
3030 Enterprise Court 
Vista, CA 92083 
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 
mailto:bbrooks@xxxxxxxx 
<http://www.dtwc.com/>
Member of: IPC Designers Council Executive Board, Steering Committee,
Education Committee, and San Diego Chapter Board of Directors
<http://www.ipc.org/SanDiego/>
<http://home.fda.net/bbrooks/pca/pca.htm
http://dc.ipc.org/
 




 



-----Original Message-----
From: Watt, William (sys) USX [mailto:wwatt@xxxxxxxx]
Sent: Thursday, May 09, 2002 10:16 AM
To: 'pcdlist@xxxxxxxxxxxxx'
Subject: [pcdlist] Thru hole components



Now that I know there are a few people out there, let me ask a question.  We
are having a discussion here in our design dept about standardizing hole
sizes.  The present method of determining finished hole size is to use the
IPC 2221 formula and pick the hole in the center of the range.  This is fine
except we end up with many holes that are within .001 of each other and our
mechanical checker or the fab house will ask to combine them into one common
size.  I recall from a past life that I used a hole chart with drill sizes
every .003 instead of every .001 and this worked fine.  I am having trouble
convincing some of my coworkers of the wisdom of this method.  I would like
to know if anyone else has an opinion on this. I would like to standardize
by using the formula, finding the median size and rounding up to the next
drill size.  How does the rest of the world do it?

Thanks for the help.  Maybe I can use an overwhelming opinion to convince my
department.

Bill Watt
Moog Inc
Jamison Rd
East Aurora, NY 14052
716-687-5596
wwatt@xxxxxxxx

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