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John Larkin
Guest

Mon Feb 11, 2019 6:45 pm   



I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

John Larkin
Guest

Mon Feb 11, 2019 6:45 pm   



On Mon, 11 Feb 2019 09:07:49 -0800, John Larkin
<jjlarkin_at_highlandtechnology.com> wrote:

Quote:


I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.


It even has its own Youtube show.

https://www.youtube.com/watch?v=rS4TUQDpUsE




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Lasse Langwadt Christense
Guest

Mon Feb 11, 2019 7:45 pm   



mandag den 11. februar 2019 kl. 18.07.59 UTC+1 skrev John Larkin:
Quote:
I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



http://www.vishay.com/docs/31098/rcp.pdf

George Herold
Guest

Mon Feb 11, 2019 7:45 pm   



On Monday, February 11, 2019 at 12:07:59 PM UTC-5, John Larkin wrote:
Quote:
I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Yeah it's hard to know if a layer of 'insulation' would help.
I was once thinking that several layers of heat shrink tubing
around a through hole R's might allow for higher powers.
And though the 'insulator/ goop' is better than still air, is it better
than convection in air? Who knows, and may be orientation dependent.

I never tried the resistor + heat shrink tubing.

George H
Quote:

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics


John Larkin
Guest

Mon Feb 11, 2019 8:45 pm   



On Mon, 11 Feb 2019 10:18:51 -0800 (PST), Lasse Langwadt Christensen
<langwadt_at_fonz.dk> wrote:

Quote:
mandag den 11. februar 2019 kl. 18.07.59 UTC+1 skrev John Larkin:
I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



http://www.vishay.com/docs/31098/rcp.pdf


I've used them, but they are not stocked in the value I need (lots of
50 ohms available) and a 1206 would get awfully hot. They need lots of
copper to cool the end caps, and I don't have space for that, nor can
I afford the capacitance.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com


Guest

Mon Feb 11, 2019 8:45 pm   



On Monday, 11 February 2019 19:04:14 UTC, John Larkin wrote:
Quote:
On Mon, 11 Feb 2019 10:18:51 -0800 (PST), Lasse Langwadt Christensen
langwadt_at_fonz.dk> wrote:
mandag den 11. februar 2019 kl. 18.07.59 UTC+1 skrev John Larkin:

I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



http://www.vishay.com/docs/31098/rcp.pdf

I've used them, but they are not stocked in the value I need (lots of
50 ohms available) and a 1206 would get awfully hot. They need lots of
copper to cool the end caps, and I don't have space for that, nor can
I afford the capacitance.


FWLIW I once used electrolytic caps to cool some small germanium transistors. Just tied them together. It worked :)

Dunno if you can get some copper powder in that epoxy - not too much of course.


NT

John Larkin
Guest

Mon Feb 11, 2019 10:45 pm   



On Mon, 11 Feb 2019 13:14:08 -0800, John Larkin
<jjlarkin_at_highland_snip_technology.com> wrote:

Quote:
On Mon, 11 Feb 2019 15:59:28 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:

On 2/11/19 12:07 PM, John Larkin wrote:


I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



There are 1-W 0612 resistors. I'm using these ones:

R15-100H-00, RES,, FIXED, 100.0m, 1.0%, 1.0W, 100.0p, THICK, 200.0,,
Wide 1206 hi pwr , 0612 , ERJ-B2CFR10V ,
PANASONIC , $0.1174 , 1000.0 , @EACH, DIGIKEY

Cheers

Phil

That only comes in 0.1R. The 0612 orientation does allow better
conduction cooling, hot spot to end caps.

Susumu has a 1 watt 1206

https://www.digikey.com/product-detail/en/susumu/HRG3216Q-20R0-D-T1/408-1893-2-ND/5762557

but it looks like they just have more pad area. I can do that with any
1206.


There are some 0612s in my resistance range, rated 3/4 watts.

https://www.digikey.com/products/en/resistors/chip-resistor-surface-mount/52?k=&pkeyword=&sv=0&pv2085=u19.6+Ohms&pv2085=u20+Ohms&pv2085=u20.5+Ohms&pv2085=u21+Ohms&pv2085=u21.5+Ohms&pv2085=u22+Ohms&pv2085=u22.1+Ohms&pv2085=u22.6+Ohms&pv2085=u23.2+Ohms&pv2085=u23.7+Ohms&pv2085=u24+Ohms&sf=1&FV=ffe00034%2C142c199b%2C142c0367&quantity=&ColumnSort=0&page=1&pageSize=25


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

John Larkin
Guest

Mon Feb 11, 2019 10:45 pm   



On Mon, 11 Feb 2019 15:59:28 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
On 2/11/19 12:07 PM, John Larkin wrote:


I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



There are 1-W 0612 resistors. I'm using these ones:

R15-100H-00, RES,, FIXED, 100.0m, 1.0%, 1.0W, 100.0p, THICK, 200.0,,
Wide 1206 hi pwr , 0612 , ERJ-B2CFR10V ,
PANASONIC , $0.1174 , 1000.0 , @EACH, DIGIKEY

Cheers

Phil


That only comes in 0.1R. The 0612 orientation does allow better
conduction cooling, hot spot to end caps.

Susumu has a 1 watt 1206

https://www.digikey.com/product-detail/en/susumu/HRG3216Q-20R0-D-T1/408-1893-2-ND/5762557

but it looks like they just have more pad area. I can do that with any
1206.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Phil Hobbs
Guest

Mon Feb 11, 2019 10:45 pm   



On 2/11/19 12:07 PM, John Larkin wrote:
Quote:


I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



There are 1-W 0612 resistors. I'm using these ones:


R15-100H-00, RES,, FIXED, 100.0m, 1.0%, 1.0W, 100.0p, THICK, 200.0,,
Wide 1206 hi pwr , 0612 , ERJ-B2CFR10V ,
PANASONIC , $0.1174 , 1000.0 , @EACH, DIGIKEY

Cheers

Phil

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com

John Larkin
Guest

Mon Feb 11, 2019 10:45 pm   



On Mon, 11 Feb 2019 13:18:24 -0800, John Larkin
<jjlarkin_at_highland_snip_technology.com> wrote:

Quote:
On Mon, 11 Feb 2019 13:14:08 -0800, John Larkin
jjlarkin_at_highland_snip_technology.com> wrote:

On Mon, 11 Feb 2019 15:59:28 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:

On 2/11/19 12:07 PM, John Larkin wrote:


I was wondering what might be the thermal effects of lumping a heap of
glob-top epoxy on a surface-mount part.

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. That's pushing things a bit even by my standards.

I might be able to push stuff around to fit a 1210 or even something
bigger, but not much. The entire board is 0.77 square inches and there
are some big parts wasting space already.

The board will be glob-topped, so maybe the epoxy will spread the heat
around some.

Experiments may be required. I could glob-top a 1206 platinum RTD and
let it self-heat and measure itself maybe.

This is nice epoxy:

https://www.dropbox.com/s/jmhyros7en61tnd/T852B_Glob_2.jpg?dl=0

PANACOL STRUCTALIT 5891 C

but the thermal conductivity is only 0.4 w/mK, still a lot better than
air.



There are 1-W 0612 resistors. I'm using these ones:

R15-100H-00, RES,, FIXED, 100.0m, 1.0%, 1.0W, 100.0p, THICK, 200.0,,
Wide 1206 hi pwr , 0612 , ERJ-B2CFR10V ,
PANASONIC , $0.1174 , 1000.0 , @EACH, DIGIKEY

Cheers

Phil

That only comes in 0.1R. The 0612 orientation does allow better
conduction cooling, hot spot to end caps.

Susumu has a 1 watt 1206

https://www.digikey.com/product-detail/en/susumu/HRG3216Q-20R0-D-T1/408-1893-2-ND/5762557

but it looks like they just have more pad area. I can do that with any
1206.

There are some 0612s in my resistance range, rated 3/4 watts.

https://www.digikey.com/products/en/resistors/chip-resistor-surface-mount/52?k=&pkeyword=&sv=0&pv2085=u19.6+Ohms&pv2085=u20+Ohms&pv2085=u20.5+Ohms&pv2085=u21+Ohms&pv2085=u21.5+Ohms&pv2085=u22+Ohms&pv2085=u22.1+Ohms&pv2085=u22.6+Ohms&pv2085=u23.2+Ohms&pv2085=u23.7+Ohms&pv2085=u24+Ohms&sf=1&FV=ffe00034%2C142c199b%2C142c0367&quantity=&ColumnSort=0&page=1&pageSize=25


Now I'm thinking that two 0805s in parallel will be a lot better than
one 1206.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Winfield Hill
Guest

Mon Feb 11, 2019 11:45 pm   



John Larkin wrote...
Quote:

Now I'm thinking that two 0805s in parallel will be
a lot better than one 1206.


Or series. Maybe you can separate them.
I'm using CRCW1210-HP e3, rated 0.75W.


--
Thanks,
- Win

John Larkin
Guest

Tue Feb 12, 2019 12:45 am   



On 11 Feb 2019 14:06:28 -0800, Winfield Hill
<hill_at_rowland.harvard.edu> wrote:

Quote:
John Larkin wrote...

Now I'm thinking that two 0805s in parallel will be
a lot better than one 1206.

Or series. Maybe you can separate them.
I'm using CRCW1210-HP e3, rated 0.75W.


Good idea, series: less capacitance.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

John Larkin
Guest

Tue Feb 12, 2019 1:45 am   



On Mon, 11 Feb 2019 16:08:59 -0800 (PST), whit3rd <whit3rd_at_gmail.com>
wrote:

Quote:
On Monday, February 11, 2019 at 9:07:59 AM UTC-8, John Larkin wrote:

I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. .... The entire board is 0.77 square inches and there
are some big parts wasting space already.

A watt for a square inch is troublesome. Surely the board MOUNTS to
something, can you position the hot thing near a (heat-conductive) structural
element?


It will be a baby board that surface-mounts on a bigger board.

1 watt isn't bad for the whole baby board. It is a potential hot spot
on the little board.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

whit3rd
Guest

Tue Feb 12, 2019 1:45 am   



On Monday, February 11, 2019 at 9:07:59 AM UTC-8, John Larkin wrote:

Quote:
I have an interesting circuit that unfortunately dumps 0.8 watts into
a 1206 resistor. .... The entire board is 0.77 square inches and there
are some big parts wasting space already.


A watt for a square inch is troublesome. Surely the board MOUNTS to
something, can you position the hot thing near a (heat-conductive) structural
element?

Tim Williams
Guest

Tue Feb 12, 2019 1:45 am   



"John Larkin" <jjlarkin_at_highlandtechnology.com> wrote in message
news:a8b36eh36mmlr00rtblhgmjv66vv8tok12_at_4ax.com...
Quote:
PANACOL STRUCTALIT 5891 C


It even has its own Youtube show.


Good tunes, too. Panacol The Disco!

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

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