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On Sunday, 4 August 2019 15:37:22 UTC+1, John Larkin wrote:
Either links of thick copper wire soldered in, or stamped sheet links. A set of spokes of that sort should shift a therm or 2. Even a bunch of light links eg staple-style metal resistors can at least help.
NT
On Sun, 4 Aug 2019 06:51:35 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:
On Saturday, August 3, 2019 at 11:22:29 AM UTC-4, John Larkin wrote:
On Fri, 2 Aug 2019 21:41:29 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:
Above I posted this estimate from basic principles:
->| |<- .030"
o o o o o
o o o o vias = 0.02", 25um Cu plated, 0.062" FR-4
o o o o o
o o o o
I estimated the above via field at 5.5K/W unfilled, 3.2K/W when
solder-filled.
Updating my spreadsheet, it's 0.5K/W when copper-filled.
~~~~~~~~~~~~~
This guy makes and swages in his own copper rivets from soft
copper wire:
https://paulwanamaker.wordpress.com/300-2/
It's pretty simple, actually, and might be handy for
a super-critical bleeding edge product.
.-- swaged surface is recessed, but contacts top trace.
/
/ copper trace
====.___/___.==== /
====|\ V /|====
| | | |
| | | | FR-4
| | | |
| | | |
| | | |
====' '---' '====
Might that block solder?
From the via? Oh definitely. But is that a problem? I don't see
why.
He makes his rivets tight-fitting. That maximizes copper cross
section, which seems fine to me.
I could build a corral around the dpak by soldering in three ribbon
cable headers, the ones with two rows of square pins on 50 mil
centers. We already use them as jtags. They would fill the holes with
copper+solder and add a tiny bit of additional heat sinking up into
the air themselves.
It would look pleasingly bizarre.
I think I suggested something like that last time this issue
came up -- inserting a number of copper-leaded dummy parts. That
would really confuse people .
My other option is the thermistor shutdown circuit, which is simple.
I'm trying to protect a pulse generator 50 ohm output resistor in the
case that the customer programs a big voltage and then shorts the
load.
After going though all of this again, I think my preferred move next
time will be a single large via under the thermal tab, filled with a
matching copper plug. A 0.150" copper plug would be simple and could
move a lot of heat (theta = 0.7K/W). Or possibly 4 x 0.100" vias, etc.
#10 wire is 0.102" and #16 is 0.0508", which might be convenient. Or
possibly punch or cut rounds from flat sheet...it's certainly doable.
Amazon and Ebay sell a wide range of punched copper disks, intended
for jewelry use. Probably not pure copper, but pretty good. One of
those could drop into a round hole on a PCB. But then, where would the
heat go?
Either links of thick copper wire soldered in, or stamped sheet links. A set of spokes of that sort should shift a therm or 2. Even a bunch of light links eg staple-style metal resistors can at least help.
NT