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Stencil printer

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Marco:
Are those ~100$ electronic dispensers on ebay any good?

mikeselectricstuff:

--- Quote from: tggzzz on October 05, 2014, 07:07:54 pm ---
--- Quote from: joshhunsaker on October 05, 2014, 06:49:18 pm ---
--- Quote from: zapta on October 04, 2014, 12:22:39 am ---
--- Quote from: tggzzz on October 03, 2014, 11:45:44 pm ---... place the solder paste with a toothpick or jewellers screwdriver.

--- End quote ---

I tried it with 0.5mm pitch and it was very difficult.

--- End quote ---

You can buy a very cheap set of syringes to use to dispense solder paste extremely accurately:
http://www.ebay.com/itm/10CC-Syringe-SMT-SMD-PCB-Solder-Paste-Adhesive-Glue-Liquid-Dispenser-EFD-Loctite-/221234842565

They have some very small tips for it.  Mess-free.

--- End quote ---

My very limited experience of hand placing paste through a small (0.5mm) needle is that it was a pain; I preferred the screwdriver/toothpick technique for small prototype boards.

The principal problems were that a "high" pressure was required, and the paste continued to flow after pressure was removed. Which wasn't surprising since I didn't have a vacuum to remove the pressure and halt the flow.

--- End quote ---
As long as all the pressure is released (i.e. vented) quickly , as opposed to just closing  a valve to the pressure source, flow will usually stop quickly - I don't recall seeing a suck-back option on any dispensing systems, but not looked very hard

tggzzz:

--- Quote from: mikeselectricstuff on October 05, 2014, 08:23:16 pm ---
--- Quote from: tggzzz on October 05, 2014, 07:07:54 pm ---
--- Quote from: joshhunsaker on October 05, 2014, 06:49:18 pm ---
--- Quote from: zapta on October 04, 2014, 12:22:39 am ---
--- Quote from: tggzzz on October 03, 2014, 11:45:44 pm ---... place the solder paste with a toothpick or jewellers screwdriver.

--- End quote ---

I tried it with 0.5mm pitch and it was very difficult.

--- End quote ---

You can buy a very cheap set of syringes to use to dispense solder paste extremely accurately:
http://www.ebay.com/itm/10CC-Syringe-SMT-SMD-PCB-Solder-Paste-Adhesive-Glue-Liquid-Dispenser-EFD-Loctite-/221234842565

They have some very small tips for it.  Mess-free.

--- End quote ---

My very limited experience of hand placing paste through a small (0.5mm) needle is that it was a pain; I preferred the screwdriver/toothpick technique for small prototype boards.

The principal problems were that a "high" pressure was required, and the paste continued to flow after pressure was removed. Which wasn't surprising since I didn't have a vacuum to remove the pressure and halt the flow.

--- End quote ---
As long as all the pressure is released (i.e. vented) quickly , as opposed to just closing  a valve to the pressure source, flow will usually stop quickly - I don't recall seeing a suck-back option on any dispensing systems, but not looked very hard

--- End quote ---

Well, I can assure you my finger stopped pushing and the paste continued flowing. The only way to quickly stop the past flowing was to "pull back" on the plunger until the internal pressure in the paste was the same as atmospheric pressure.

mikeselectricstuff:

--- Quote from: tggzzz on October 05, 2014, 08:47:16 pm ---Well, I can assure you my finger stopped pushing and the paste continued flowing. The only way to quickly stop the past flowing was to "pull back" on the plunger until the internal pressure in the paste was the same as atmospheric pressure.

--- End quote ---
Sorry I thought you were referring to a compressed-air system.
Hand dispensing is a pain as you have to use enough force that it's hard to keep the needle in the right place.
Foot-pedal operated compressed air is the way to go.
 

tggzzz:

--- Quote from: mikeselectricstuff on October 05, 2014, 09:11:49 pm ---
--- Quote from: tggzzz on October 05, 2014, 08:47:16 pm ---Well, I can assure you my finger stopped pushing and the paste continued flowing. The only way to quickly stop the past flowing was to "pull back" on the plunger until the internal pressure in the paste was the same as atmospheric pressure.

--- End quote ---
Sorry I thought you were referring to a compressed-air system.
Hand dispensing is a pain as you have to use enough force that it's hard to keep the needle in the right place.
Foot-pedal operated compressed air is the way to go.

--- End quote ---
Re-reading my comment, it was indeed ambiguous.

Actually you can just about let off the finger pressure, relax and position the needle - while the paste slowly erupts. But I found the real aggro is that there was no way stop the eruption when sufficient paste had been deposited. That would continue to be true with any positive-pressure-only mechanism.

I have assumed, without checking, that the foot operated machine stop the eruption by sucking the plunger for a short time.

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