[SI-LIST] Re: Standard for thermal relief on thru hole pins

Another way of stating thermal reliefs is to specify that the conductor area
shall not be decreased by more than n%.
The greater n is the more thermal relief occurs but the ampacity and
inductance go up.

The following table is instructions to the Photoplotter house on how to
detail thermals (th = through holes)

Definitions: 
   CIRCLE:  Round aperture for pads and/or line draws.
   SQUARE:  Square aperture for pads and/or line draws.
   THERMAL:  Thermal pads- Inside diameter is shown, airgap to outside
        diameter is .015.
        4 'X' ties of .020 thickness ea for Thermal call outs up to 75TH.
        4 'X' ties of .040 thickness ea for Thermal call outs from 80TH to
149TH.
        4 'X' ties of .070 thickness ea for Thermal call outs from 150TH to
199TH.
        4 'X' ties of .100 thickness ea for Thermal call outs from 200TH to
300TH.
Steven Salkow
Lockheed Martin
3200 Zanker Rd
San Jose, CA 95134
(408) 473-4058
steven.salkow@xxxxxxxx
Fax (408) 473-3044


> -----Original Message-----
> From: Jeff Seeger [SMTP:jseeger@xxxxxxxxxxxxxx]
> Sent: Tuesday, May 20, 2003 10:15 AM
> To:   si-list@xxxxxxxxxxxxx
> Subject:      [SI-LIST] Re: Standard for thermal relief on thru hole pins
> 
> 
> Gary Thompson wrote:
> > 
> > Sorry for the slightly off-topic post...
> > 
> > Anyone know if there is an IPC standard governing the composition of
> > thermal reliefs on plane layers for thru-hole components? 
> 
>       The rigid board design spec (IPC-2222) has most of a
>       page on "how to".  IMHO anyone doing physical design of
>       genuine product is really in need of this spec, or its
>       variants (for flex, PCMCIA, MCM, etc).
> 
>       The gist of the standard comes down to total web widths
>       don't exceed 60% of ideal land dia per layer, and is again
>       limited to a total of 4mm at 1oz Cu (maintain this ratio
>       for other copper weights).  If you need to violate this
>       to meet current carrying needs it must be noted, they say
>       to do so on the fab drawing but I personally belive it is
>       more pertinent on the assembly drawing.
> 
>       HTH,
> -- 
>  
>       Jeff Seeger                         Applied CAD Knowledge Inc
>       Chief Technical Officer                  Tyngsboro, MA  01879
>       jseeger "at" appliedcad "dot" com                978 649 9800
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