On 2/15/2014 12:21 PM, John Larkin wrote:
> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 2/15/2014 11:30 AM, krw@attt.bizz wrote:
>>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk
>>> <joseph_barrett@sbcglobal.net> wrote:
>>>
>>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold
>>>> <gherold@teachspin.com> wrote:
>>>>
>>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote:
>>>>>> On 14/02/14 02:51, Tim Wescott wrote:
>>>>>>
>>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote:
>>>>>>>> Transistor as heater/ temp sensor.
>>>>>>> Using it as a temperature sensor would be complicated by the fact that,
>>>>>>> due to its recent service as a heater, it would be warmer than its
>>>>>>> surroundings.
>>>>>>
>>>>>> But you have time - measure the temperature curve after a heating pulse
>>>>>> and correlate that with a thermal model. Using a thermal model is the
>>>>>> only way of calculating how much of your heat has reached the target at
>>>>>> a given point in time, so you have to do it anyway.
>>>>>>
>>>>>> Clifford Heath.
>>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor.
>>>>>
>>>>> George H.
>>>>
>>>> Ya know George, the longer i think about this the less i like trying to
>>>> get a specific power for a specific duration with a transistor, and the
>>>> more i like SMD resistors, perhaps mounted "upside down".
>>>>
>>> How do you get pick-n-place to place them upside down? What sort of
>>> manufacturing process hoops do you have to jump through to do that?
>>>
>>>
>> Might have to re-reel them, but you don't need to. Indium-solder them
>> to the anodized Al, top down.
>>
>> Cheers
>>
>> Phil Hobbs
>
> To get the heat out, just mount them normally, soldered to biggish copper pours
> and then vias to copper on the opposite side of the board. Most of the heat
> flows out of the end caps.
Tends to be slow, though. I'm a big fan of maximizing bandwidth in
thermal systems.
>
> Or use some nice copperclad aluminum nitride.
>
> Inverted resistor mounting is useful at picosecond speeds. The reduction in
> inductance can be dramatic.
Interesting idea, thanks.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
On 2/15/2014 12:21 PM, John Larkin wrote:
> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> On 2/15/2014 11:30 AM, krw@attt.bizz wrote:
>>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk
>>> <joseph_barrett@sbcglobal.net> wrote:
>>>
>>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold
>>>> <gherold@teachspin.com> wrote:
>>>>
>>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath
wrote:
>>>>>> On 14/02/14 02:51, Tim Wescott wrote:
>>>>>>
>>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote:
>>>>>>>> Transistor as heater/ temp sensor.
>>>>>>> Using it as a temperature sensor would be complicated by the
fact that,
>>>>>>> due to its recent service as a heater, it would be warmer than its
>>>>>>> surroundings.
>>>>>>
>>>>>> But you have time - measure the temperature curve after a
heating pulse
>>>>>> and correlate that with a thermal model. Using a thermal model
is the
>>>>>> only way of calculating how much of your heat has reached the
target at
>>>>>> a given point in time, so you have to do it anyway.
>>>>>>
>>>>>> Clifford Heath.
>>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I
was hoping to be just able to wait ~5 time constants or so. I must
admit I thought it might be fun to watch the heat leak out of the
transistor.
>>>>>
>>>>> George H.
>>>>
>>>> Ya know George, the longer i think about this the less i like
trying to
>>>> get a specific power for a specific duration with a transistor,
and the
>>>> more i like SMD resistors, perhaps mounted "upside down".
>>>>
>>> How do you get pick-n-place to place them upside down? What sort of
>>> manufacturing process hoops do you have to jump through to do that?
>>>
>>>
>> Might have to re-reel them, but you don't need to. Indium-solder them
>> to the anodized Al, top down.
>>
>> Cheers
>>
>> Phil Hobbs
>
> To get the heat out, just mount them normally, soldered to biggish
copper pours
> and then vias to copper on the opposite side of the board. Most of
the heat
> flows out of the end caps.
>
> Or use some nice copperclad aluminum nitride.
>
> Inverted resistor mounting is useful at picosecond speeds. The
reduction in
> inductance can be dramatic.
>
>
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net