Solder paste dispensing

[scsi]

Is anybody using solder dispenser for their short runs and prototypes? Any luck with 0.5mm pitch components?

I'd like to find a live person who has used or still using dispensing methods to ask a couple of questions. What kind of paste do you use, auger or time/pressure, what nozzles etc.

I'm building a low cost auger dispenser here and want to clarify several things before I close on the design. Here's the most recent results: http://www.youtube.com/watch?v=HoT4s2wY17k

-scsi

[adafruit]

ooo cool

[charliex]

I've got one of these, http://www.zeph.com/zt-5100.htm , unfortunately i haven't used it yet since i hadnt had time to hook up the air…. it uses their needles and their solder paste. sorry thats not much help

and cool on the auger!

[mikeselectricstuff]

I'm just about to start looking into converting an old X-Y plotter into a paste dispenser for low-tech PCBs. I was thinking of just using a standard air dispensing system with controlled air times - I assume the auger head has a screw type element inside - do you have any info on the design of your head?

I assume the main issue with air based systems is uncertainty due to changes in viscosity versus temperature/paste age.
From the point of view of simple engineering, I wonder if there would be any mileage in something like a very small peristaltic pump, using small -bore silicone tube. A nice advantage of this is that when it clogs you just replace the tube.

As regards auger type dispensers, I wonder if you could use something as simple as a woodscrew as the drive element?

I'd think that if you can dispense 0.2mm dots then 0.5mm pitch parts would be doable, although the dots may splay sideways when the part is placed. Perhaps if the head dragged along the pad while dispensing you could elongate the dots?

[scsi]

I'm just about to start looking into converting an old X-Y plotter into a paste dispenser for low-tech PCBs. I was thinking of just using a standard air dispensing system with controlled air times - I assume the auger head has a screw type element inside - do you have any info on the design of your head?

That's right, it's got a screw inside driven by a small stepper motor. Weights around 250g and has a very small footprint, smaller than a regular auger dispenser. I think a plotter should be able to handle it no problem. Shoot me an email if you want to beta test one.

I assume the main issue with air based systems is uncertainty due to changes in viscosity versus temperature/paste age.
From the point of view of simple engineering, I wonder if there would be any mileage in something like a very small peristaltic pump, using small -bore silicone tube. A nice advantage of this is that when it clogs you just replace the tube.

For the time-pressure dispensing, change in viscosity is an evil but not the biggest. The amount of air necessary to build up the pressure in the barrel varies as the syringe empties. This and the reduction of friction forces with time make the whole system severely non-linear and hard to control. Peristaltic pump is something I have been looking into. There is one major drawback that has to do with pulsing of the fluid you are pumping. Also, the flow is interrupted at a certain point in the rotation cycle. It's basically a dead end for microdispensing.

As regards auger type dispensers, I wonder if you could use something as simple as a woodscrew as the drive element?

This was the very first thing I tried and it worked to some degree. Didn't last long though because the flux was attacking the screw... Here's one of the the first prototypes that was pumping grease successfully. Looks very ugly because I hacked it together in under one hour. See that metal screw on the bottom?

[mikeselectricstuff]

I'm just about to start looking into converting an old X-Y plotter into a paste dispenser for low-tech PCBs. I was thinking of just using a standard air dispensing system with controlled air times - I assume the auger head has a screw type element inside - do you have any info on the design of your head?

That's right, it's got a screw inside driven by a small stepper motor. Weights around 250g and has a very small footprint, smaller than a regular auger dispenser. I think a plotter should be able to handle it no problem. Shoot me an email if you want to beta test one.

Not sure my plotter would manage 250g! - I'd be interested to see the shape of the screw etc. and the general mechanical arrangement, e.g. how do you segregate the paste from the motor? A magnetic coupling might be nice if you could make it work.
Regarding auger type drives, I was thinking more along the lines of a small gearmotor to reduce size and weight compared to a stepper - maybe use the motor and box from an RC servo as a nice small light gearmotor, probably with an encoder for feedback.

I also wonder if there may be scope for something really crude - a simple (high-res) leadscrew into a syringe, like an infusion pump - this would eliminate the air volume issue. Maybe use a fairly small-bore syringe to reduce the 'gearing' between piston and paste movement. I also wonder if hydraulics may have advantages over pneumatics.

For the time-pressure dispensing, change in viscosity is an evil but not the biggest. The amount of air necessary to build up the pressure in the barrel varies as the syringe empties.

I wonder to what extent you could reduce this effect by upping the pressure and having precise timing (although the latter may get difficult). Or maybe have closed-loop control of pressure to effectively compensate for volume changes.

For what I need, I think pneumatic would work - I've done it by hand with a manually-timed foot- operated dispenser in the past - slightly under 1mm dot size would be OK - I don't mind hand-soldering the odd fine-pitch part.

As regards auger type dispensers, I wonder if you could use something as simple as a woodscrew as the drive element?

This was the very first thing I tried and it worked to some degree. Didn't last long though because the flux was attacking the screw...[/quote]
Stainless screws are readily available, and even if corrosion is a problem, if you could figure out a way to use an unmodified screw, you could just treat it as a consumable.A hex socket, torx or hexagon bolt head comes to mind, or maybe something like this

[scsi]

Not sure my plotter would manage 250g! - I'd be interested to see the shape of the screw etc. and the general mechanical arrangement, e.g. how do you segregate the paste from the motor? A magnetic coupling might be nice if you could make it work.
Regarding auger type drives, I was thinking more along the lines of a small gearmotor to reduce size and weight compared to a stepper - maybe use the motor and box from an RC servo as a nice small light gearmotor, probably with an encoder for feedback.

I'm currently using NEMA14 motors and the plan is to move on to NEMA11, it's quite small already and much more reliable than gear motors. In my design the motor with ball bearings plays crucial role and the auger screw is machined directly into the stainless shaft. There is an o-ring to segregate the paste from the motor.

I also wonder if there may be scope for something really crude - a simple (high-res) leadscrew into a syringe, like an infusion pump - this would eliminate the air volume issue. Maybe use a fairly small-bore syringe to reduce the 'gearing' between piston and paste movement. I also wonder if hydraulics may have advantages over pneumatics.

Yes, simple linear motors are being used for coarse dispensing. For example http://www.fishmancorp.com/download/LDS_Technology.pdf. These cannot do microdispensing though. The resolution is not there.

I wonder to what extent you could reduce this effect by upping the pressure and having precise timing (although the latter may get difficult). Or maybe have closed-loop control of pressure to effectively compensate for volume changes.

Closed loop pressure control is quite difficult to acheive in very short intervals (milliseconds). Some advanced time-pressure do exist. Martin Clever Dispens is one example: http://www.martin-smt.de/en_p_d_cd.php

Stainless screws are readily available, and even if corrosion is a problem, if you could figure out a way to use an unmodified screw, you could just treat it as a consumable.A hex socket, torx or hexagon bolt head comes to mind, or maybe something like this

Screw corrosion was not the only problem. Precise positioning and centering of the screw was challenging. For solder paste dispensing the auger screw cannot touch the walls and some stable gap has to be maintained. Otherwise, it will squish solder balls and weld them together which will eventually clog the nozzle.

[frankmurch]

I think I am nearly an alive person and I know a little about dispensing

You want to find a paste with a powder size at least 7 times smaller than the opening you are using. I think you will find a Type 4 powder will do this. You also want to use a dispensable grade solder paste. The difference is the amount of flux (85-86% metal loading, the balance is flux vs 90% metal loading for printable). This lowers the viscosity and increases lubrication. The last thing you want is to use a conical nozzle – not a needle. That allows you to avoid trying to force the solder paste down a long narrow path where is clogs. These are the basics to get a good dispense

As for trying to design your own auger valve – interesting, perhaps educational, but in the end, there are a bunch of them out there and they are going to take a lot less time, frustration and money to use. There is a need to get the depth of cut in the screw – tightly toleranced and the sleeve to screw gap right. Also run out is a killer – This is really a machine show issue, and beyond your average engineer (beyond many machine shops too)

If you want – you can email me at frank@ocinstruments.com and I will try to answer your questions. A lot of these are answered on my web site – www.dispensetips.com

Frank

[adafruit]

thats a very handy site! do you have any tips/guides on selecting stainless steel stencil thicknesses?

[frankmurch]

I am writing a printing guide and a segment on solder paste tack, but - as of right now - no stencil guide, sorry

[isozee]

Solder paste stamping feature is added to 7722 series.
Silver paste stamping feature using 2 pin stamping nozzle is already in 7722 as LV = 2 but now it is expanded to solder paste stamping using 0.3 to 0.4mm dia single stamping nozzle as shown.

0.3mm pin with solder paste

dippingimage.jpg (16.82 KiB) Viewed 7010 times

This feature will be useful for low volume assembly.
To use this feature,
1.stamping nozzles
2.additional nozzle nest
3.solder paste applicator disk to be installed in tape feeder bank.
4.new software
are required.
Some dispensing dots are shown.
Transistor

Transistor

StampTRauto.jpg (46.59 KiB) Viewed 7010 times

256 BGA thou it takes time!

256 BGA

BGA256right.jpg (48.38 KiB) Viewed 7010 times

[f.murch]

Well, I worked at a dispensing company for 10 years and a solder paste company for 10 years. I sell the paste and I designed dispense tips for the application. What cha want to know? frank@ocinstruments.com www.dispensetips.com