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Old Mar 22, 2006, 05:15 PM
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Freeforming SMT Circuits

I'm really looking to cut down weight on a project I'm working on, and as such I'm trying to freeform (i.e., no PCB) a simple circuit out of surface mount parts. I was wondering if anybody had any advice or experience with this before I dive in. Now, before you say "my advice is, don't use SMT parts," I know, I'm feeling that, but I really don't have much choice because of the size and weight constraints. So, thoughts? Thanks!
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Old Mar 22, 2006, 05:27 PM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
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Quote:
Originally Posted by bobb9000
I'm really looking to cut down weight on a project I'm working on, and as such I'm trying to freeform (i.e., no PCB) a simple circuit out of surface mount parts. I was wondering if anybody had any advice or experience with this before I dive in. Now, before you say "my advice is, don't use SMT parts," I know, I'm feeling that, but I really don't have much choice because of the size and weight constraints. So, thoughts? Thanks!
My advice is ...

Watch the heating temp and times. Without a PCB to sink the soldering heat, damage might come faster and easier in freeform. I've made a few freeforms too. It's not that bad.

Gary
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Old Mar 22, 2006, 05:48 PM
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Thanks :-). I've done some before too, but just on through-hole type components. I'm just looking with fear at those tiny little resistors...By the way, would CA glue be ok for attaching them to things/each other? I've heard that silicone glue might be better, but that's not readily available to me.
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Old Mar 22, 2006, 05:53 PM
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Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
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Quote:
Originally Posted by bobb9000
Thanks :-). I've done some before too, but just on through-hole type components. I'm just looking with fear at those tiny little resistors...By the way, would CA glue be ok for attaching them to things/each other? I've heard that silicone glue might be better, but that's not readily available to me.
DON'T use CA before soldering things together! The CA when heated with a soldering iron will give off very bad fumes. You know that 'stinging eye' thing when you get when thin CA kicks off real fast? Multiply that by 10. If you want to CA things after all the assembling is done, that's ok.

Gary
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Old Mar 22, 2006, 06:02 PM
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You can get some very very thin pcb material. Probably as thick as card stock paper. Would that be to heavy too? Another thing you could do is have all the area between components routed out.

-Rocko
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Old Mar 23, 2006, 05:22 AM
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crewe england
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in the electric a/c -indoor and micro there's a sm rx made by glueing dead-bug sm bits and point 2 point wiring. it worked.
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Old Mar 23, 2006, 06:12 AM
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I used small modified crocodile clips, flattened the front end to hold the SMD device and draw the heat away. The modified clips are put into a hands free (helping hand) device to hold parts in place while soldering +- 1 2sec. contact time.

markmi
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Old Mar 23, 2006, 12:17 PM
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Thanks everybody! I avoided the CA (thanks for the tip, that could have been disasterous), found myself some silicone glue. Seems to have worked pretty well, and I like the fact that it takes longer to cure than CA. I needed the time to get the positions right with those little parts. Smells like vinegar, though - that could be interesting when I solder. As for using a milled PCB, it might be light enough, but space-wise, it's really much better this way. Thanks markmi, I might try that helping hands setup. How did you stick your parts together?
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Old Mar 23, 2006, 01:52 PM
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Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
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Quote:
Originally Posted by bobb9000
Thanks everybody! I avoided the CA (thanks for the tip, that could have been disasterous), found myself some silicone glue. Seems to have worked pretty well, and I like the fact that it takes longer to cure than CA. I needed the time to get the positions right with those little parts. Smells like vinegar, though - that could be interesting when I solder. As for using a milled PCB, it might be light enough, but space-wise, it's really much better this way. Thanks markmi, I might try that helping hands setup. How did you stick your parts together?
Silicone glues can have a corrosive effect on some parts metal leads. What should be used is RTV. Works the same but does not have the vinegar smell and takes longer to setup. Don't worry about it on your project, just file the information for the next project.

Gary
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Old Mar 23, 2006, 10:43 PM
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Actually the electronics grade RTVs are quite a bit more expensive than the normal (vinegar smell) RTVs. But they aren't likely to cause problems with electronics. We use both kinds where I work. I think the last purchase I made, the regular were about $5.00/tube, and the electronics grade (Non-Acetic Acid) about $17.00/tube. They definitely take almost twice as long to set up.
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Old Mar 24, 2006, 12:27 AM
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Joined Apr 1999
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Originally Posted by 50+AirYears
Actually the electronics grade RTVs are quite a bit more expensive than the normal (vinegar smell) RTVs. But they aren't likely to cause problems with electronics. We use both kinds where I work. I think the last purchase I made, the regular were about $5.00/tube, and the electronics grade (Non-Acetic Acid) about $17.00/tube. They definitely take almost twice as long to set up.
Yup... RCA's 2.5 ounces is about $17.00. Expensive stuff! But I make several thousands dollars per tube - so, it's worth it.

Gary
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