Soldering a crystal, ideas ?

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Noodle Twister
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Soldering a crystal, ideas ?

Post by Noodle Twister » Mon Jan 06, 2020 10:18 pm

In the absence of an isolator disc, what's your preferred method of soldering a crystal ? They aren't normally supposed to be flush with the pcb.

They are usually the low profile type and through hole.

Think I used blu-tac and maybe a piece of removable card previously. Anyone got a better idea or technique or is it simpler to just buy a bag of isolator discs ?

How thick are these discs normally ? I guess about 2mm ...

Thanks for any replies.

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Re: Soldering a crystal, ideas ?

Post by guest » Mon Jan 06, 2020 10:25 pm

i dont think ive seen a crystal on standoffs before, is it to keep the case from contacting traces? you could use some small nylon washers, one on each leg.
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Noodle Twister
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Re: Soldering a crystal, ideas ?

Post by Noodle Twister » Mon Jan 06, 2020 10:40 pm

Ah, found the reference. It's from the build guide for the penrose quantizer. Wondered if these are commonly used, certainly looks a bit simpler.

Yes , I think it's to keep solder joints clear of the case. Probably heat resistant material ?
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Re: Soldering a crystal, ideas ?

Post by guest » Mon Jan 06, 2020 11:17 pm

yeah, there is a questionably tented via right on the ridge of the crystal outline. pretty much anything would work here, you could cut a small bit of cardboard as long as youre quick with the soldering. or cut up an old platic bottle.
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Muff McMuff
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Re: Soldering a crystal, ideas ?

Post by Muff McMuff » Mon Jan 06, 2020 11:38 pm

I soldered one the other day. I bent the legs so it wouldn't fall out of the holes and this positioned it about 5mm above the board after soldering. Is this method not recommended?

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Re: Soldering a crystal, ideas ?

Post by bobsynth » Tue Jan 07, 2020 2:37 am

Hi,

I just cut a piece of PVC electrical insulation tape slightly larger than the footprint of the crystal and stick it to the PCB. Push the crystal legs through and solder. If you are worried about melting the PVC (probably applying far too much heat to the crystal anyway if that happens) you could use kapton tape if you can lay your hands on some.

Not really a good idea to bend crystal leads if it can be helped, also mounting above the board looses some mechanical stability and runs the risk of damaging it if it gets accidentally knocked.

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Re: Soldering a crystal, ideas ?

Post by Grumble » Tue Jan 07, 2020 10:26 am

I just put a narrow piece of paper that would fit between the legs under the crystal while soldering and removed it when I'm done. After soldering you could add a bit of hot-glue to keep the crystal in place. (I never did that, just the paper thing)

The best is just create the pcb in a way that no traces are running on the pcb top-side under the crystal.

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Re: Soldering a crystal, ideas ?

Post by Noodle Twister » Tue Jan 07, 2020 1:50 pm

Thanks for the replies. Did a search and the convienient 'bag of isolators' seems to not exist. It's possible that they are provided with some crystals and mostly not. Didn't know if using the discs was an accepted norm or not. It seems not.

The kapton tape is out there about £3 for a roll of 10mm wide. Think I will just use the blu-tac and card for now, going to go with 2mm clearance and go easy on the solder.

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Re: Soldering a crystal, ideas ?

Post by Schlumpfhut » Tue Jan 07, 2020 2:20 pm

When i build a MIDI/CV converter that employes a PIC and a corresponding crystal i did not solder the crystall at all. Instead i got my hand on a special crystal socket which i soldered to the PCB. Then i cut the legs of the crystal and stuffed it into the socket. It maybe not the most stable solution but it never failed to me

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Re: Soldering a crystal, ideas ?

Post by fitzgreyve » Wed Jan 08, 2020 4:04 am

As long as there are no exposed tracks or vias etc on the PCB suraface below the xtal, I've always just soldered flat to the PCB - no insulator or spacer.

Never had any problem.
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Re: Soldering a crystal, ideas ?

Post by EATyourGUITAR » Wed Jan 08, 2020 4:29 pm

I never heard about them being sensitive to soldering heat. that spacer must be there to cover a via or maybe to allow the PCB to flex during shipping?
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Re: Soldering a crystal, ideas ?

Post by Noodle Twister » Thu Jan 09, 2020 1:15 am

EATyourGUITAR wrote:
Wed Jan 08, 2020 4:29 pm
I never heard about them being sensitive to soldering heat. that spacer must be there to cover a via
Indeed, it looks like it. I'm not currently building the penrose but have other builds with crystals involved so having seen this I posted for general advice as I remember a previous build where it was required for the crystal to not be flush with the PCB.

Here's the grab from the build guide , guest and EATyourGUITAR are correct. I circled the via in red.
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Re: Soldering a crystal, ideas ?

Post by KSS » Thu Jan 09, 2020 7:10 am

In the 60s-70s it was not unusual to find glass beads used on the legs of components to lift them free of the PCB. Beads of the kind hippies used to make native American style headbands and bracelets. Wasn't seen as cultural appropriation back then. Since beading is still a common and popular craft activity, many craft or bead stores will have these colorful beads inexpensively.

Prior to more widely used automated through hole assembly in the PCB industry, many components were not designed to stand clear of the PCB as are nearly all modern parts, both TH and SMD. This was one reason the glass bead kludge came into being and also why it disappeared once parts incorporated their own means of standoff.

The advantages of glass for dealing with resistivity, inductance, temperature and humidity would be great compared to using blu-tac or cardboard.

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Re: Soldering a crystal, ideas ?

Post by Altitude909 » Thu Jan 09, 2020 7:30 am

why not just flip the board around and solder the crystal in so its off the board a bit

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Re: Soldering a crystal, ideas ?

Post by Noodle Twister » Thu Jan 09, 2020 4:24 pm

fitzgreyve wrote:
Wed Jan 08, 2020 4:04 am
As long as there are no exposed tracks or vias etc on the PCB suraface below the xtal, I've always just soldered flat to the PCB - no insulator or spacer.

Never had any problem.
So in this case the above is true. This is 'Arpie' by 64 pixels. Looks pretty flush. The other case is covered by the sonic potions penrose with the via. Well thanks for clearing that up :sb:
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