Hechong,

Your question is not easily answered - there are FAR too many variables for
a "one-size fits all" design rule. I am not a PCB designer, but just off the
top of my head you must consider the application, operating voltage, line
current, signal integrity, circuit density, etc. to choose the best solution
for your application.  Indeed, this is an area where people can and have
devoted their entire careers to.  I would recommend that you consider taking
some IPC offered courses in the subject of PCB design.  


Link: http://dc.ipc.org/

Certified Interconnect Designer (CID) 
This program assesses a designer's knowledge of how to transform a schematic
into a reliable rigid PCB design, which can be easily manufactured,
assembled and tested. The IPC Designers Council recognizes that the most
effective designers must have a solid foundation in PCB fabrication and
assembly. The certification test is based on several critical IPC documents
that link design principles to the end product use of the printed circuit
assembly. Designers may purchase study materials and prepare on their own or
enroll in a two-day IPC Designer Certification Preparation workshop. All
designer certification testing is done on-site at a workshop location the
day after a course concludes. Individuals who do not feel prepared to take
the test immediately after the training may choose to keep their exam
voucher and take the test at a later date. The workshop training provides an
in-depth view of the principles contained in the examination and is strongly
recommended for anyone interested in obtaining the certification. 



-----Original Message-----
From: Cong He [mailto:[log in to unmask]] 
Sent: Monday, February 16, 2009 9:08 PM
To: [log in to unmask]
Subject: [TN] PCB'S minimum line width

Hi all,

 I want to know that how much is the minimum  line with when you usually
designe the PCB? 
The surface and the inner sides?

And what does that affect except the process capability of the PCB factory?

Will 3.5mil be OK?


Hechong

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