Bill:
That is all great advise and great guidelines to follow.
Thanks for your input and words of wisdom.
Dave
At 05:14 PM 5/8/2007, you wrote:
>Dave,
>
>In a word, 'No'. Not 'alright'. I can see that you were making a joke, of
>course.
>
>The personal risk in designing a board that is 'difficult to manufacture' is
>that the general effect will be that it causes someone out there to curse
>your name EVERY TIME they have to build your board... Day in and Day out...
>How many boards with they make? That could potentially be a lot of negative
>energy floating around there in the world... who knows what might happen
>from that? Risky... very risky... Do you want to be responsible for that? I
>prefer to play it safe if possible.
>
>Better to make the design more manufacturable, and easier to solder and have
>people curse 'someone else' for the thing 'they' designed that is hard to
>build... and not your board. Life is difficult enough as it is... let's
>keep it simple and the negative energy always pointing away from you.
>
>Here's a physical principle you can exploit... electrical current can be
>divided or 'shared'... If one wire can handle an amp... two wires of the
>same size together can handle 2 amps... and 4 of the same size can handle 4
>amps...etc.
>
>So... figure out what equivalent amount of copper in cross sectional mils or
>width of trace will handle the 30 AMPS... Make sure you keep the total
>copper quantity consistent all along the path where it must go. When you get
>to the point where you absolutely cannot avoid using vias... make them do
>'current sharing' as well.
>
>Calculate how much current a single via can handle with a 10 degree rise
>over ambient and then add enough extra vias to give yourself some margin...
>The vias do not need thermal spokes... nothing gets soldered to them... only
>leads in holes and surface mount parts are really a concern.
>
>You must look at the design and figure out if the parts can be soldered
>using a common manufacturing process... and not hand soldering if you can
>avoid it... that is the most expensive way to solder if you are making
>boards in quantity and a last resort when there is no alternative.
>
>I would consider that approach to be the 'safer way' to go with the
>application you are describing. Trust me... Your employer will love you for
>it, maybe even at bonus time. :)
>
>Best regards,
>
>Bill Brooks
>PCB Design Engineer, C.I.D.+
>Tel: (760)597-1500 Fax: (760)597-1510
>Datron World Communications, Inc.
>Vista, California
>
>
>-----Original Message-----
>From: David Baldwin [mailto:[log in to unmask]]
>Sent: Tuesday, May 08, 2007 4:04 PM
>To: [log in to unmask]
>Subject: Re: [DC] Current Capacity of Thermal Reliefs
>
>George:
>
>Nice calculator, good job. The via though is just a via,
>correct? It doesn't have anything for thermals. Like Bill said, I
>can add up the spokes and get the overall width and treat it like a
>trace. Or I could just forget about the thermals and let the
>assemblers deal with soldering the parts down, not the designers
>problem right;-)
>
>Thanks,
>
>Dave
>
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