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OSHW - 24bit ADC measurement system for voltage references
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branadic:
My board is designed with the opportunity to cut the reference part of the pcb and replace it with a flexible substrate, such as 100µm FR4. I had that in mind when I designed the board, but my pcb manufactor doesn't offer 100µm substrates and I don't have such a thin substrate for home-processing. I wouldn't use capton, it's expensive and there is no need for it.
The method of Andreas using "dead bug" is a way, but I wanted to avoid such solutions.

A complete board made of ceramic would be very expensive I guess and you'll never now what ceramic the package is made of to match the CTEs as close as possible.

Edit: In addition to the linked publication, I wonder why they used AD587 (10V) instead off AD586 (5V) and why they have used LTC6655BHM (MSOP8) instead of LTC6655BHLS8. I would expect somewhat better performance of that devices.
Andreas:

--- Quote from: branadic on July 06, 2014, 08:23:23 am ---The method of Andreas using "dead bug" is a way, but I wanted to avoid such solutions.

A complete board made of ceramic would be very expensive I guess and you'll never now what ceramic the package is made of to match the CTEs as close as possible.

--- End quote ---

I can understand this: this mounting method needs much time in assembling.

I did not think about a complete board: but what about a small ceramic with 4-5 pins (mechanical decoupled from PCB) on one side (upright mounting) together with a small temperature controller for the reference on the back side.

Note that I have also a influence of the PCB on the reference on ceramic references like VRE3050AS when I solder all PINs around the ceramic case to the PCB.


--- Quote from: branadic on July 06, 2014, 08:23:23 am ---
Edit: In addition to the linked publication, I wonder why they used AD587 (10V) instead off AD586 (5V) and why they have used LTC6655BHM (MSOP8) instead of LTC6655BHLS8. I would expect somewhat better performance of that devices.

--- End quote ---

Edit:
AD587 and AD586 should not differ much. (in LQ or UQ option).
For the LTC6655BHM I think that they simply started the study before the LS8-Option was available.
On the other side I have large hysteresis with the BHM package. I do not think that the same chip with similar die attach will behave much better in LS8 housing. (would be a interesting test).

With best regards.

Andreas
SeanB:
You can get flexible boards made cheaply now, so probably you can get a sheet made with multiple small adaptors, screen the solder paste on them and mount multiple devices then reflow them, then afterwards simply cut them out of the sheet when needed for use.  Easy to have the connections on one side with the space for a thermistor and decoupling caps as well, then simply have some larger pads with a large solder ring on them ( probably on a 0.2in pitch so you can either solder the board to the board direct or use a pin header) so you can mount them. You can even include a guard trace around the unit  and a copper trace for a cutting guide. Assemble with ordinary kitchen scissors.
branadic:

--- Quote ---For the LTC6655BHM I think that they simply started the study before the LS8-Option was available.
--- End quote ---

Could be the reason, yes.


--- Quote ---On the other side I have large hysteresis with the BHM package. I do not think that the same chip with similar die attach will behave much better in LS8 housing. (would be a interesting test).
--- End quote ---

I would expect better results even in the  lower 0.1Hz region as the die is glued with only the bottom side to the package, while in the BHM package the die is surrounded by the thermoset and glued to the lead frame. But this is all speculation.


--- Quote ---You can get flexible boards made cheaply now
--- End quote ---

This is true only for manufactors outside of germany ;)
While complete devboards are offered by Asian you wouldn't even get the board fabricated nor the parts from a distributor for a comparable price here. And 100µm substrate is called to be "special" not standard and you have to pay for something "special".
branadic:
Added the files for the 2:1 Resistor Divider with LT5400-1 in the first post. Finished the assembly for this board today. Still to do: layout the 2:1 divider with LTC1043 for the Hammond case.
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