Home > Community > Forums > PCB Design > Problem with thermal relief size

Email

* Required Fields

Recipients email * (separate multiple addresses with commas)

Your name *

Your email *

Message *

Contact Us

* Required Fields
First Name *

Last Name *

Email *

Company / Institution *

Comments: *

 Problem with thermal relief size 

Last post Tue, Aug 24 2010 1:12 AM by djhutchi. 7 replies.
Started by CarloL 17 Aug 2010 12:52 PM. Topic has 7 replies and 5189 views
Page 1 of 1 (8 items)
Sort Posts:
  • Tue, Aug 17 2010 12:52 PM

    • CarloL
    • Not Ranked
    • Joined on Tue, Aug 17 2010
    • Posts 5
    • Points 85
    Problem with thermal relief size Reply

     Hi, I'm a newbie.

    I have some problems with Orcad PCB Designed and thermal relief.
    I have edited a pad and defined this pad for all the layers:

    regular pad: circle 60
    thermal relief: circle 80
    antipad: circle 80

    When I create a dynamic shape to create a copper pour region the ray of thermal relief area is always of 5 mills.
    The part of copper pour between the spokes is only 5mills instead of 10mills [10=(80-60)/2].

    I have done a lot of attempts, changing pad parameters in the pad designer, but it doesn't workn. The size of the void spaces between the spokes of the thermal relief generated on the positive planes or dynamic shape is always the same.


    Thanks a lot.

    Carlo  

    • Post Points: 20
  • Tue, Aug 17 2010 1:16 PM

    • Rik Lee
    • Top 50 Contributor
    • Joined on Tue, Dec 2 2008
    • HOME, SC
    • Posts 166
    • Points 2,730
    Re: Problem with thermal relief size Reply

    The thermal relief line width is taken from 1 of the following

    1. MIN_LINE_WIDTH property if one is set on the net. e.g. MIN_LINE_WIDTH    = 10 MIL.
    2. The Physical constraint for MIN LINE WIDTH for that net and layer assignment. Look in Constarint Manager under Physical Constraint >All Layers.
    3. The shape parameter, either an instance based entry or global. Select Shape>Global Dynamic params...

    Selct the 'Thermal relief connects' tab. You can enter a fixed thermal width or an oversize. If you enter an oversize thermal with it will be added to the min line width specifed by the Physical constraint (#2 above) that that net class uses for line width.

    If you have a MIN_LINE_WIDTH property it will take precedence over the constraint and shape parameters.

    The void is derived from the spacing constraint Shape to pin (or via). You more than likely have a 5 MIL spacing constraint for the shape to element spacing set.

    The thermal and antipad definitions are used when constructing negative layers.

    • Post Points: 80
  • Wed, Aug 18 2010 12:32 AM

    • CarloL
    • Not Ranked
    • Joined on Tue, Aug 17 2010
    • Posts 5
    • Points 85
    Re: Problem with thermal relief size Reply

    Thanks for your answare.

    The problem is about the width of the void space between the spokes.
    I have set all spacing constraint at 12.00mills for my test, shape to pin and shape to vias too. I have update the dynamic shape but the size is always 5 mills.

    I have found these on my book "Complete PCB Design Using OrCAD® Capture and PCB Editor":

    Thermal relief connections between plated through holes and copper areas on
    positive planes are automatically generated by PCB Editor so flash symbols
    need not be defined for positive layers. The inner diameter (ID) of the thermal
    relief is defined by the pad diameter while the outer diameter (OD) is defined
    by the diameter of the (thermal relief) circle in the padstack definition set in
    the Padstack Designer.

    If I set a clearance oversize in Shape->Global Dynamic shape Parameters->Clearances Tab, for thru pin at 7mills the width of void space become 12mills(5+7) but the oversize is applied to the other type of pin, without thermal relief.

    What is the way to set the size of thermal relief void space between the spokes, without changing the clearence between dynamic shape (copper pour) and the pin connected to the signal nets?

    Thanks

    Carlo

    • Post Points: 20
  • Wed, Aug 18 2010 6:18 AM

    • Rik Lee
    • Top 50 Contributor
    • Joined on Tue, Dec 2 2008
    • HOME, SC
    • Posts 166
    • Points 2,730
    Re: Problem with thermal relief size Reply

    The spacing between the shape and pin is determined by the value for the 'Thru Pin to Shape Same Net Spacing' in Constraint Manager under Same Net Spacing >All Layers >Shape to <element> in this case the element is Pin.

    • Post Points: 20
  • Wed, Aug 18 2010 7:49 AM

    • CarloL
    • Not Ranked
    • Joined on Tue, Aug 17 2010
    • Posts 5
    • Points 85
    Re: Problem with thermal relief size Reply

     Thank you very much

     Carlo

    • Post Points: 5
  • Thu, Aug 19 2010 4:32 AM

    • djhutchi
    • Top 100 Contributor
    • Joined on Fri, Nov 14 2008
    • Hillsboro, OR
    • Posts 70
    • Points 870
    RE: Problem with thermal relief size Reply
    Where does the pin property

    DYN_FIXED_THERM_WIDTH fall into this precedence list?
    • Post Points: 5
  • Tue, Aug 24 2010 1:12 AM

    • djhutchi
    • Top 100 Contributor
    • Joined on Fri, Nov 14 2008
    • Hillsboro, OR
    • Posts 70
    • Points 870
    RE: Problem with thermal relief size Reply
    Where does the pin property DYN_FIXED_THERM_WIDTH fall into this precedence list?
    • Post Points: 5
  • Tue, Aug 24 2010 1:12 AM

    • djhutchi
    • Top 100 Contributor
    • Joined on Fri, Nov 14 2008
    • Hillsboro, OR
    • Posts 70
    • Points 870
    RE: Problem with thermal relief size Reply
    Where does the pin property DYN_FIXED_THERM_WIDTH fall into this precedence list?
    • Post Points: 5
Page 1 of 1 (8 items)
Sort Posts:
Started by CarloL at 17 Aug 2010 12:52 PM. Topic has 7 replies.