A larger via is not always best, a number of smaller vias is always 
better. Make them as small as possible and still get internal plating.

You can fill vias with solder but solder is much less conductive. I 
recall that a 40 mil via is the point where the filled solder will have 
the same resistance as the wall. I recall that being .062 material with 
1/2 oz copper. You can calculate it yourself. The solder cross section 
increases with the square of the diameter, copper wall in the via is 
proportional.

Heat is similar in concept, look at what power LED folks suggest. A 
bunch of small vias gave me 1C/W on a DPAK, they were very effective but 
that was heat.

Bob K.


On 1/20/2018 5:14 PM, Yuan-chia Joyce Koo wrote:
> don't forget if it is ground plane, your allow the solder coverage 50% 
> (or 70%), you need take out one or two vias to ensure you have 
> sufficient connection to avoid local heat... (make sure the solder 
> coverage of 50% is not one sided under the components to avoid 
> overheating upon components operation - not just open/short test... if 
> it is split ground for MCM, you need to make sure EACH ground got 
> sufficient via/solder coverage at assembly level, not just PCB)...IMHO.
> jk
> On Jan 20, 2018, at 3:47 PM, Wayne Thayer wrote:
>
>> You simply take the length the via is carrying the current and divide 
>> that
>> by the circumference (pi * d). For power designs, you should insist on a
>> full ounce on the via wall. One ounce copper film is 0.7 
>> milliohms/square,
>> so you just take the calc above and multiply by 0.7 and now you have the
>> resistance of a single via. Multiply that by the current to get voltage
>> drop. If the voltage drop is too high, the via will get warm and someone
>> will complain about your lousy power distribution system. So add 
>> vias, or
>> make bigger vias until you're sure that won't happen!
>>
>> Wayne Thayer
>>
>> On Fri, Jan 19, 2018 at 11:00 AM, Nutting, Phil 
>> <[log in to unmask]>
>> wrote:
>>
>>> Many of our designs use 1, 2 or 4 ounce copper for our heavy current
>>> applications.  Vias and plated holes might have ½ or 1 ounce of copper
>>> plated in.  So, is there a design guide for the number and size of 
>>> holes to
>>> effectively transfer the current from one side of the board to the 
>>> other
>>> side of the board?
>>>
>>> Phil Nutting  |  HVP Senior Development Engineer   | Excelitas
>>> Technologies Corp
>>>
>>> Lab: +1 978.224.4332   |  Office: +1 978.224.4152
>>> 35 Congress St, Salem, MA  01970 USA
>>> [log in to unmask]<mailto:[log in to unmask]>
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>>>
>>>
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>