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IndustryArena Forum > GENERAL MANUFACTURING PROCESSES > CHUCKING and MEASURING > 3D Probe - Tri-balls type accuracy & DIY
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  1. #41
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    For prototypes & proof-of-concept tests, vigorous application of the KISS Principal is always a good idea. And in any case, the first iteration has already been sent off for PCB fabrication.

    Just curious... which microcontroller are you using? An AVR of some sort? And from the images... is that in a QFN package?

  2. #42

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    KISS indeed... huge fan of the concept here. Only when the simple stuff werks correctly, that I start adding candies

    Correct. That would be the ATTINY85-20MURCT-ND in a QFN20 package. The smallest I've found (4x4x0.5), its minuscule. A dab of paste and it sits by itself (weightless).
    https://www.digikey.com/product-deta...8aAoscEALw_wcB

    Edit: just noticed the url ^ is wrong. Following one is correct:
    https://www.digikey.com/product-deta...RCT-ND/2774367

  3. #43
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    SOIC? QFP? SOT? I can do those all day (well, or until my back gives out from being hunched over the microscope).

    But I hate soldering QFNs... I can't ever seem to get a good connection on all the pads; hot air likes to blow them away, I can't effectively touch them up with an iron because I can't get under the device; and I can't probe it either because the lands on the device are under the package (and just probing the trace doesn't tell me what the device is actually seeing - i.e, if the pad on the PCB didn't make good contact with the land on the package).

    If you've got any tips for handling them... I'd love to hear it!

  4. #44

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Quote Originally Posted by __Britt View Post
    If you've got any tips for handling them... I'd love to hear it!
    1. Put paste over the pads (only the pads), melt this with your iron and spread that over the pads (*only the pads*, keep the center ground plane free of solder, for now)
    2. Flux the area and do one pass on each pads with your iron, clean your tip regularly i.e to ensure all the pads have an equal amount of solder basically (clean tip required)
    3. Clean the area with acetone, wipe clean. You should now have solder on the pads and a clean/flat ground plane free of anything.
    4. Re-flux the pads, and now place a drop of paste on the center ground plane. Stick that QFN in place (it should stick to the paste and remain in place until the paste melts -datrick!)
    5. Re-flow at your lowest air flow, 325dC.
    6. Gently poke it with your tweezers once and a while. As soon as that ground plane's paste melts, that QFN will go sit in its place automatically<and that's why QFN are better haha

    Probing/testing is carried out the same way as any other packages. There is always solder popping out from the edge of those QFN... that's why there are pads/tin on the package walls. Although with something as minuscule as this 4x4x0.5, you might need to fabricate yourself a test probe... that DMM probe will be too fat (I often use a copper wire tapped onto my DMM probe for small packages like those). That's a whole lot of probes isnt it lol

    Have fun!

  5. #45
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    4. Re-flux the pads, and now place a drop of paste on the center ground plane. Stick that QFN in place (it should stick to the paste and remain in place until the paste melts -datrick!)
    Ahh HA! I knew there had to be a trick to it. I've previously tried tinning the pads with my iron, applying paste flux, and hitting it with the hot air gun (er... it's a real rework station, not a heat gun like you'd use to strip paint) but I haven't tried using solder paste...

    I'll have to give it a try again sometime... thanks!

    I wouldn't use regular DMM probes for something that small... I'd either be trying to hit it with my o-scope; or I'd use super-sharp DMM probes. However, for most of the kinds of stuff I'd be probing that was in a QFN package; I'd probably be more interested in the waveform anyway, so it'd probably be o-scope probes... and if possible, I would have designed in test points or a connector.

  6. #46
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Solder paste makes all the difference in the world.

    My last board had 0402 resistors on it together with a little ARM QFN. Hand soldered a half dozen with 100% success rate - wasn't even game to think about doing it with solder wire like the bigger jobs.

    With paste, no need to tin prior. Be sparing with the paste and heat evenly - the surface tension of the solder when it melts will pull everything into alignment and wick away inter-pin shorts.

  7. #47

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    0402 by hand, yikes. Respect my friend. I'll do those 0805 easy, starting to struggle and talk to myself at the 0603, but certainly can't do 0402 by hand (stencil mandatory). I actually hate those 0402 so much I don't even keep them in my EDA library here just to make sure I'm not tempted in using them. I've used 1206 on this PCB. Not because they are more robust than the smaller ones but because I have an industrial quantity of those here and constantly looking for projects to, well, get rid of them ;-)

    Quick Update: Machining/turning half-way done! Struggled a bit on the precision thread mating the two bodies together so I'll have to re-do one of them - missed that odd 0.08 tip radius on those new uncoated thread inserts I recently got. Thread fits but its just way too tight. I obviously plan on anodizing the kit when done, and so are those threads. Anyone familiar with anodizing will know that it grows oxide and so are the dimensions so... those threads won't fit after that little surface treatment :/ No biggy, off to the lathe later this evening and I'll finish this up, like-a-pro this time lol PCB: mfg sent me an email telling me its in the mail already. Only a few hundred miles from my place so I'll have this in hands tomorrow or latest the day after tomorrow I guess.

  8. #48
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    The 0402 weren't too bad with hand syringe and lots of magnification. But I'm certainly not going to try 0201s without stencil and robotic pick and place! And I know what you mean about using stuff up - I do the same usually but still have reels of old 1206s sitting on the shelf that just won't run out

    Really like how your probe is coming together. Mine's a plastic hack job in comparison. Nice to see someone doing it properly.

  9. #49
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    I do like the way you have joined the top and the bottom parts.

    The trouble with SMDs is that they come on reels ...

    Cheers
    Roger

  10. #50
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Not only on reels, Roger - rsonline, element14, mouser, digikey, altronics and Jaycar all sell strips of small quantities cut off the reel. Pretty handy for one-offs and RS (much as I love to hate their pricing) seems to have gotten better, especially when they will ship TNT to you door next day for free regardless of order amount. And yes, I've taken delivery of a single $2 thyristor before

  11. #51
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Yeah, on strips too - but a lot of my stock is on reels.
    Err - I got them for free...
    And yes, I too have an RS account.

    Cheers
    Roger

  12. #52

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Really doesn't take much to be exited sometimes lol Look who just shown up!

    Fairly happy with the accuracy (deliveries are as per gerber). The only downside is... everything is minuscule and requires microscope work later on.
    You'll noticed from the vias I've temporarily moved the mosi/miso/sck pads on the back side, for that prototype only. Ideally this should be on top and accessible in a prod probe. Again, if this tri-ball probe type screams the max required <0.02mm I'll then give it my best shot on the V2.0 and design a final pcb. Possibly with IR comm ;-)

    I'll get this kit reflow this evening and run switching/timing tests on it as soon as its got its vcc live!

  13. #53

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    I think some of you were waiting to see how those balls sets in the PCB and how good of a job that solder paste/reflow did sitting those balls dead flush and solid.

    Pretty happy with the result and now anxious moving to the next step(s) -assembly! I'm out of town between Thurs and Friday so I won't have time but I'll try to keep a few hours dedicated to the home shop this weekend.

    Done. Chip is flashed and alive! Time to probe.. I guess

  14. #54
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Oh you gotta be happy with that

  15. #55
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Looks nice. That is one bright LED.
    I was curious how you wired everything up so I was looking at the traces. Did you mean to put the 1k resistor in series with the LED? Cause it looks like PB2 is driving the LED anode directly. If your LED has an integrated resistor this will work great, however if it doesn't you may have some trouble programming the UC with the LED installed or the driver for that pin will burn out.

  16. #56

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Quote Originally Posted by dharmic View Post
    Oh you gotta be happy with that
    Ridiculously small set-up, but feels as big as the sun lol

    Just tested it with a 'home-made shank/probe' (hmm) and it is pretty damn sensitive (OD0.5mm music wire spring). The feeling I'm having is... this will end up being way below 0.01. More like 5um or less.
    Not yet done making that test jig where I'll have it fixed to test the accuracy e.g. by pushing on the ball with a micrometer on one side and measuring the motion with 1um resolution mitutoyo digital indicator on the other side.
    I'll have the 360deg data plotted. I'll report as soon as this comes in.

    (waiting for that Renishaw 50mm probe tip... not sure what takes so long for the vendor to let it go. Maybe if I complain here it'll go faster!)


    @Max - got the 1k in circuit for both the led and the pin so it shouldn't pull much. You think that'll be an issue? I'll place the 1k on the LED's gnd leg in V1.2... just to make sure lol
    (you successfully petrified me when I read the word 'burn'. Well spotted btw, unfortunate the silly mistakes you can do when doing 120 different things at the same time. I blame it of those testpoints... if you'd look at how I've wired this in the schematic you'd understand where that mistake came from, routing late a night neither help. Fixed, thanks)
    Attached Thumbnails Attached Thumbnails 3DProbe_V1.01_trace.jpg   3DProbe_V1.01_led_gnd.jpg  

  17. #57
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Mistakes on Electronics is so easy. It is always good to have a second pair of eyes reviewing a design.
    You could use a LED with an integrated resistor. https://www.digikey.com/products/en?...s=WP710A10ID5V
    One less component requiring space.

  18. #58

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Quote Originally Posted by maxspongebob View Post
    Mistakes on Electronics is so easy. It is always good to have a second pair of eyes reviewing a design.
    You could use a LED with an integrated resistor. https://www.digikey.com/products/en?...s=WP710A10ID5V
    One less component requiring space.
    I didn't do mistakes?! the software did(lol). I manually route my circuits (normally) but for this little guy I've pressed the auto-route button thinking "bah there are only 3 wires". It didn't liked the testpoints for some reason. You know, I'm just the guy with the solder iron, gotta love auto-routing.

    Another one you didn't spot (yet!) is the floating pin for the probe switch. That's easy to get going for the prototype by just enabling the chip's internal pull-up, but none the less, another auto-route/testpoints grande. I'll get that fixed in the V1.2. Perhaps V1.3 from the look of things LOL

    Never seen or worked with an integrated R led, interesting, I'll have a look

  19. #59
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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Quote Originally Posted by Mecanix View Post
    Another one you didn't spot (yet!) is the floating pin for the probe switch. That's easy to get going for the prototype by just enabling the chip's internal pull-up, but none the less, another auto-route/testpoints grande. I'll get that fixed in the V1.2. Perhaps V1.3 from the look of things LOL
    I can’t think of a reason I wouldn’t just use the internal pull-up if there is one, especially on a design where real estate is limited.

  20. #60

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    Re: 3D Probe - Tri-balls type accuracy & DIY

    Quote Originally Posted by dharmic View Post
    I can’t think of a reason I wouldn’t just use the internal pull-up if there is one, especially on a design where real estate is limited.
    Hope you guys will be around to help when we'll put in the LORA comm, or IR, or that wheatstone bridge for that strain gauges array... because those tri-balls didn't cut it at the end. That'd be funny... not lol

    Anyway. All up for inputs or even criticism. You guys are top class, thanks again!!!

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