10% of nominal thickness is normal , but I guess you are more interested in impedance so 10% of impedance is normal, and some
fabs will stretch to 5% if it's a stackup/materials that they are use to.
Just beware that many fabs are only capable of measuring impedance at 1MHz, so you may need to scale your demanded target
accordingly (which will be hard if you have no control over the actual materials).


Best Regards
 
David Greig
______________________________
GigaDyne Ltd
5 Albany Business Centre
Gardeners Street
Dunfermline KY12 0RN
United Kingdom
t: +44 (0)1383 624 975
www.gigadyne.co.uk
______________________________

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Babcock John
Sent: 26 June 2007 16:21
To: [log in to unmask]
Subject: [DC] Board Thickness Tolerance

Fellow Designers,

 

Long time lurker, first time poster.  I've had a few posts over the years, just not very many.

 

Ok here goes.

 

What is a good overall thickness tolerance to put on your dwg for a 0.125" thick board?  This board is impedance controlled and
should stay pretty close to the 0.125" to meet our required impedance values.

 

I am kind of in a unique situation where we deal directly with an assembly house and that assembly house farms out the board fab
to whoever gives them the best quote.  So I never know which board house will get the board.  Hence I never know the
capabilities of the board house where the board gets sent to be made.

 

With that being said, XYZ board house wants to loosen up the tolerance to +/- 0.012" on the overall board thickness.  This would
throw our impedance calculations off.

 

Just kind of curious what everyone would expect as a good tolerance on a 0.125" board.

 

 

John Babcock, C.I.D.
PCB Designer III



 


---------------------------------------------------------------------------------
DesignerCouncil 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 DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL) Search previous postings at:
www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
---------------------------------------------------------------------------------
--
Virus scanned by Lumison.

---------------------------------------------------------------------------------
DesignerCouncil 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 DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------