Measuring the pressure inside of a solder paste syringe

Hello,
I need a way to measure the pressure inside of a solder paste syringe that is actuated by a stepper motor in order to precisely dispense solder paste on a pcb. Do you know any ways to measure that. Any sensors and ways to place them.
Any help would be apreciated.
Thank you,
Tudor

A load cell placed underneath the syringe holder could possibly indirectly measure the pressure by sensing the force exerted by the solder paste inside the syringe and not being extracted.

Possibly by calibrating the force to pressure, you could obtain pressure readings.

To be honest, I don't see how measuring the pressure will help you dose the paste precisely. In my opinion, the number of steps on the stepper motor determines the amount of paste. Maybe it's good to have the motor with a feedback loop.

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Indeed - as long as the stepper has enough torque to push the content out at every step.

is it possible that you can use a pressure sensors that would read the pressure applied to the injector maybe.

And as long as the steps of the stepper correlate with a meaningful solder paste dose, which will depend on the physical layout of the system - syringe diameter, stepper to syringe coupling, nozzle, etc.

Btw, solder paste tends to be rather viscous and sticky, and I wonder how well it works to accurately dispense it from a syringe. I often apply it by hand and I don't really see how you could accurately dose it from a syringe onto e.g. 0805 pads, let alone SOP/SSOP/TSSOP or QFN pads. Sounds quite challenging. I suppose there's a good reason why it's usually applied using a paste mask!

good point indeed!

MY former electronic assembly company used dispensing controllers that used compressed air to make the syringe dispense the exact requested amount of paste and then immediately had a short time of vacuum to retract the plunger. A foot switch triggered the operation. They never tried to do more that a single prototype board using a hand powered syringe.
The solder paste must be stored in a refrigerator to keep the particles from separating from the flux. Warmed to room temp before using.
A stencil was only used in mass production boards/panels.

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There is a company called volterra that does this kind of solder paste dispensing very accuratly. I found a link to the sensor they are using

It says on their page that they use "an elastomer window that contacts the fluid" , but i do not know what that can mean.

Thank you for the replies.

It doesn't look like they're dispensing solder paste, though. Going by the description of their Nova system, they print conductive ink to make flexible circuit boards.

@Paul_KD7HB that's interesting - did they use the same solder paste that's also used for mask application, or was it a modified/specific type intended for dispensing it in this particular way?
I can see how the plunger retraction would help prevent the 'stringing' you easily get with the solder paste I'm familiar with. It's a similar approach as seen on 3D filament printers.

It was 100% the same as used for the stencil printers for production work. We bought large jars of solder paste and kept them in the refrigerator. One was removed to warm up before production started.
The person doing work on individual boards would fill the syringe form the jar of paste using a small spoon and then use the automated dispenser to control the syringe.

Added: I looked up the auction web page and we had more units than I remembered. I see one by Ashcroft, two EFD800, an EFD800D, and an EFD 1000XL.

Even if they are not dispensing solder paste, maybe the sensor they are using may be of help?

Maybe some type pf sensor to detect the flow of solder paste?

I think the temperature of the paste and the age of the paste are just as important as pressure. As the flux in the paste ages, it gets stiffer. As the temperature is raised, the paste flows easier.

That period of vacuum is important to stop the flow of solder paste . Without it the paste continues to flow after the pneumatic pressure is released.
I think a stepper motor controlled syringe will suffer from that type of leakage.

Seems to be called "drool"!

Reverse the motor a few steps to "suck back" the "drool".

We used the Pace PRC 2000. An incredible machine. I had no idea the thing cost $8K
https://paceworldwide.com/prc2000-miniature-microminiature-electronic-repair

I never bought such things new. Government forced inflation is a terrible thing!

Ha, I never could afford the nice stuff. I have a cheap crap Asian version without the pump.

I use a 3D printed paste dispenser