[SI-LIST] Re: Power handling

Hi Lee,

Thanks for your response.

This is a power card with just 2oz layers - just for power (very few control
signals). There is only one connector for battery_in (BAT) and
battery_return (BATRTN). The connector has a row of eight 0.15"-diameter
pins, spaced 0.3" (center-to-center). 

Four pins are for BAT and are expected to carry 100A of current (in the
worstcase). The remaining four pins are for BATRTN. 3 planes are for BAT and
3 are for BATRTN. We planned to connect each pin to each of the allocated
planes through thermally relieved vias (thermal vias). In that case, we
expect around 33A to flow on each plane in a small pin area (approximately
1" wide). 

Each pin will carry 25A over 3 layers. Each thermal via will have to handle
around 8.3A. With 4 spokes on each thermal relief, each spoke will have to
carry around 2A. I used the PCB trace width calculator at:

http://www.geocities.com/CapeCanaveral/Lab/9643/TraceWidth.htm

and found that for 2A, 10 degrees temperature rise, and 0.5oz copper, the
trace width of each spoke has to be around 0.205". That was too wide. For
1oz, the spoke trace width has to be around 0.102" - still wide. That's why
I chose 2oz for trace width of around 0.051". Please let me know if this is
not the appropriate way to decide on the copper thickness. 

Thanks.

Hassan.



> -----Original Message-----
> From: Ritchey Lee [mailto:leeritchey@xxxxxxxxxxxxx]
> Sent: Tuesday, November 27, 2001 11:08 AM
> To: mnudelman@xxxxxxxxxxx
> Cc: 'hali@xxxxxxxxxxxxxx'; si-list@xxxxxxxxxxxxx
> Subject: Re: [SI-LIST] Re: Power handling
> 
> 
> Hassan,
> 
> Why are you using 2 ounce planes?  That complicates PCB 
> fabrication.  I use
> three 1/2 ounce planes for this very same purpose all the 
> time.  Make the power
> planes the same weight  as the signal layers to make 
> fabrication as easy as
> possible.
> 
> Also, I'd put a via in parallel with the plated through hole 
> for every 3 amps of
> current.  That is good redundancy and costs you little if 
> anything.  All you
> need is cracking at the barrel surface interface and you lose 
> the connection if
> you only have one plated hole.
> 
> Lee
> 
> Michael Nudelman wrote:
> 
> > It seems OK.
> >
> > BTW, SynQor (power supply mfr) wrote good paper on 
> pin-to-plane (including
> > thermals) temperature behaviour.         Check it out on their site.
> >
> > Mike.
> >
> > -----Original Message-----
> > From: Hassan Ali [mailto:hali@xxxxxxxxxxxxxx]
> > Sent: Monday, November 26, 2001 4:37 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Power handling
> >
> > This is a little off the signal integrity field, but it 
> concerns PCB design.
> >
> > Each pin of a power connector (diameter = 3.75mm) that is 
> to be mounted on a
> > PCB is expected to carry a current of up to 25A of the -48V 
> supply. I was
> > just wondering if  tapping off the power to three 2oz power 
> planes would be
> > sufficient. I would appreciate any comments on that. My 
> concern is the
> > effect of the small plane-pin contact area and the high 
> current (8A per
> > contact area).
> >
> > Thanks.
> >
> > Hassan.
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