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Topic: How do I solder wires to this incredibly tiny thing? (Read 364 times) previous topic - next topic

PaulMurrayCbr

So, my LPS33HW sensors arrived today. They are ic2, 3.3v, I can immerse them in 50cm of water depth (which is all I am trying to do), everything I could want but hoo boy are these things tiny. I mean, I knew they were small, but I didn't quite get how damn small.

The pads are spaced .6mm - .35mm of pad, and .25 gap between the pads. I mean - I knew I'd have to get the loupe out, but holy soldering irons, Batman! This is going to take some really, really fine wire.

Is there another way to do this?




larryd

How are you going to mount things ?

1.   PCB and then reflow.

2.   Microscope and 30AWG wire wrap wire.

3.   Get someone to do it for you.











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windoze_killa

Good choice of parts.......will surely test your skills.

You will need to get some 30 or 32 AWG wire, pre tin the ends, use a very fine tip, flux (never enough in the core of solder) and a very steady hand. Pre tin the pads as well. Hold the part in a small vice/helping hand and apply as much good luck as you can. If you were here I could have it done for you in a few minutes but we all need to learn.

Once done, clean the flux off with alcohol and then I would test it and then encapsulate the wires and the PCB only in epoxy, the wires will break off otherwise. DO NOT get lux of alcohol in the sensor it self. Use a cotton bud/cotton tip dipped in alcohol to do the cleaning, this will limit the amount of alcohol around the sensor.

There are other ways of doing it but without $'00 worth of tools the above would be the best.

PS. If the joints don't look the best apply more flux and reheat.

PPS. Have fun and good luck.
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

windoze_killa

How are you going to mount things ?

1.   PCB and then reflow.

2.   Microscope and 30AWG wire wrap wire.

3.   Get someone to do it for you.

2. Personally I would use stranded wire as opposed to solid. Much more flexible and less likely to break.
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

larryd

First add solid wire to the device then connect solid to stranded.

30AWG is quite flexible.




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If you are asked a question, please respond with an answer.
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aarg

Your enemies at that scale are surface tension, and hand muscle tremors. Everything wants to join in one big clump, and the iron seems to have a mind of its own. Plan on talking to yourself a lot, make sure there are no sensitive ears around... :)
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

PaulMurrayCbr

#6
Oct 09, 2020, 03:03 am Last Edit: Oct 09, 2020, 03:05 am by PaulMurrayCbr
encapsulate the wires and the PCB only in epoxy, the wires will break off otherwise
All good tips - thanks. The message I'm getting is it's possible, and the only way to do it is to just do it. I'll head out to Jaycar at lunch for the wire and some flux, and attack the tip of my iron with some fine grit wet-n-dry.

The unint is square, with each side holding 3 or 2 pads. I'm thinking of mounting wires on kapton tape with appropriate spacing and a little bit poking out, and soldering 3 at a time with a single swipe.

I'm dangling the sensors in a fermenter. With one sensor near the top and one near the bottom of the fluid, I should be able so see the specific gravity change over time. When the SG stops changing, the beer is done.

So - not soldered to a PCB, they'll be soldered to a length of wire with 4 conductors (power, ground , SCL, SDA) weighted at the lower end (need a food-safe weight). So, a blob of epoxy, and then perhaps a blob of silicone over that to keep the alcohol from attacking the epoxy.

Next issue - the wire. I'm thinking of using shielded 3-conductor audio cable (ground, left earbud, right earbud, microphone), but perhaps that would be too much capacitance between the shielding and the data line? May have to just try it and see, maybe tell everything to use the slowest ic2 setting.

And after that - a little programming. Once done, I should see a website on my home network with a nice graph of the SG and temperature (because why not?). Depends on how sensitive and noisy these barometers are.

jremington

Quote
I can immerse them in 50cm of water depth
Although the data sheet says "water resistant" it does not state that the device is intended for immersion in water. I take "water resistant" to mean that it can be rained upon, once in a while. 

In any case, connections to the device will corrode in very short order if it is powered up while under water, unless conformally coated. The problem will be MUCH worse if there are salts in the solution, as in a fermenter.

windoze_killa

Obviously Australian going to Jaycar.

Another thing I forgot to mention is use leaded solder, lead free solder is harder to use and requires a higher temp.

The wire you are suggesting should be fine.
Engineers design things.....technicians make them work.

I don't need anti-static wrist straps.....an instructor years ago told me I had no potential.

PaulMurrayCbr

#9
Oct 09, 2020, 03:43 am Last Edit: Oct 09, 2020, 03:44 am by PaulMurrayCbr
Although the data sheet says "water resistant" it does not state that the device is intended for immersion in water. I take "water resistant" to mean that it can be rained upon, once in a while. 
Fingers crossed. The sheet says that they are filled with some sort of gel and can be exposed to chlorinated water among other things. The main place you'll find chlorinated water is in a swimming pool, so I'm taking that to mean that an intended application is swimming pool filtration systems. They'll also need to be washed with detergent and sanitised with a phosphoric acid solution.

Hope the yeast don't decide that gel is tasty.

-- edit --

am now the proud owner of a spool if .26mm wire.

HillmanImp

Hello Paul.

Interesting project. I guess you're going to use the pressure reading to indicate the SG. Will changes in atmospheric pressure be enough to disturb your calcs? How are you going to make use of two sensors? will you use the difference?

I've pondered the idea of using a pressure sensor in the headspace above the brew & somehow monitoring the production of CO2.

Will you monitor temp as well? Will you record? That would be interesting.

John.

MarkT

For a DFN style package like this I'd use PCB, solder stencil, solder paste, and a reflow oven or hot-air gun.

Some can solder by hand to these packages, but its a trial of skill.  Reflow is childs play with the right
equipment and gives very professional results.

My reflow oven is a converted ultra-cheap sandwich toaster oven, and it produces great results.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

Paul_KD7HB

Be doubly sure to get a good ground wire to the center pad as it is connected to the internal shielding for the internal electronics.

Paul

raschemmel

#13
Oct 09, 2020, 09:01 pm Last Edit: Oct 09, 2020, 09:03 pm by raschemmel
Google "Yakosun Headset Magnifer"

(the post link isn't working)

PullUp

Is there another way to do this?
There's a $12.50 breakout board for this sensor, if that packages OK for you and you're willing to eat the previous cost as a learning experience of sorts.

https://www.adafruit.com/product/4258

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