Thanks for posting that Happy, it's a great history of the charts and how
they came to be where they are now...
 
Bill Brooks
PCB Design Engineer, C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
 
-----------------------
 I agree... and certainly my reason for saying anything at all is I didn't
want someone to doubt the recommendations of the charts... they are very
conservative. The charts have more than enough margin to prevent someone
from having a heating issue if they use them correctly within their given
ranges... and they have a long track record of successes... however they do
restrict the designer a great deal and the board is most likely over
designed when they are through... like you say many more times than need
be... 
  
I am very glad that Mike is doing what he is doing and we need to have
accurate design criteria to work with to be able to approach more difficult
design needs. 
  
 I really think you should have copied this to the DC forum for the benefit
of the other designers... it's a good history of the development of the
charts and how they got to be what they are.... And how they will be
improved for better design data. 
  
To say they are 4X is really a technical generalization... it's not a linear
relationship across the chart,  and it varies depending upon materials and
conditions and location and cross sectional area of the heated tracks...also
the presence of planes in the board stack up can greatly affect the
curves... What mike is creating is really a much better tool than the charts
could ever address... 
  
Best regards, 
Bill Brooks
PCB Design Engineer, C.I.D.+, C.I.I.

Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
 

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