CNC solder paster dispenser - how do I approach this.

[HankMcSpank]

Ok, so I'm always knocking out SMD surface mount circuit prototypes....most end up in the bin (!), but nevertheless a significant time overhead, having either etched or isolation milled the circuitboard is actually applying the solder paste!

I have a pneumatic dispenser (like this - http://www.ebay.com/itm/Solder-paste...item27a93935b6) a compressor & can therefore do solder paste syringe dispensing by hand, but my hand/eye doesn't have the accuracy for smd SOT23 pads etc ....it's not worth making a stencil for a one off proto...so that has got me now looking at using the cnc machine itself to dispense the solder paste.

As ever, google was quite helpful....this guy in particular has a good pdf & video...http://ciciora.com/picknplace.html (which has a cool video of his cnc doing what I want mine to do too!)but he still leaves a bit of investigative work.

Ok, my questions mainly relate to one of procedure (vs hardware). Here's what I think I need (hw excluded, because like I say I have the hw to dispense)...

1. A way of locating the centre of every smd pad

2. A way off getting g-code to send a signal to my dispenser (it has a foot switch so any output signal could easily be converted to trigger this - the solder dispenser can be made to work manually....the amount of 'dispense' related to how long the switch is pressed, or it has a timed 'shot' feature)

Re issue 1 ..... the guy in that link above uses eagle (so do I) & a ulp called smd-coordinates.ulp ....it seems to output text info...he then used that info into a program called labview. I've never heard of/used labview...I'll check it out, but in the meantime if anyone can think of alternative (fast) way of getting the smd pad centre coords that would be cool.

Re issue 2 ....this is the bit that I have to hold my hands up & say right away...not a clue. I'm looking for a way using a CAM/CNC program to be able to map an 'action' to a coord. eg goto x1,y2 and output a signal (the signal I use to drive my dispenser)...so I need an output signal (coolant/mist? ....something like that which can be used to trigger my dispenser)

Any ideas or tips?

[Jonathan]

Perhaps make the code for the paste just engraving and link the paste feed to the Z-axis direction pin? Have it so if the Z axis is moving down the pin will be high, so the paste switches on, and vice versa. Mach3 latches the direction pins, so it should stay on until the 'tool' is retracted. Might be awkward at the beginning and ends, but a bit of fiddling with the distances and feedrate should sort that? You could link it to coolant / mist or something, but then you've got to find a way to add those commands into the Gcode ... to be fair find and replace + notepad (find Z moves) should be sufficient.

To get a suitable line on each pad select them and contour inside half the width of the pad. Should be feasible as I doubt there's many different size pads.

I've often wondered if you could attach a soldering iron (just the heater+tip) to the router and get it to solder accurately...

[JAZZCNC]

RE Issue 2. If using Mach then I would look to using a brain or macro pump.
If used in combination with G0/G1 and G4 (Dwell) (which you could easily make your CAM program insert G4 by altering/making the post processor special for this job type) and setting the dwell time needed to dispense the correct amount of paste. Then building a simple macro pump set to watch when the X & Y axis are NOT moving which then triggers your output connected to the switch.

Could go some thing like this. G1 X11,Y20 F900 G4 P2 (pause 2 seconds) the Brain will see this pause then turn the pump ON untill either X or Y axis start moving again or set amount of time which you can set in the brain.

There will probably be other simpler ways but I'm pritty sure you'll end up using either a bit of VB in a macro or a brain. Macros and brains are very powerfull and can really make your machine do pritty much anything you want.

RE Issue 1,

Dont the smd chips come on tape or strips that have pre-determined spacing.? If not then build a special holding jig that you know the coord's of the centre of each bay.?

[Jonathan]

Dont the smd chips come on tape or strips that have pre-determined spacing.? If not then build a special holding jig that you know the coord's of the centre of each bay.?

The paste goes on the PCB not the ICs!

[JAZZCNC]

The paste goes on the PCB not the ICs!

I was refering to finding the centre of the chip not paste.! With a jig to hold the chips he would know the exact centre coord.

[HankMcSpank]

Thanks for the input.

Jonathan....re Z move triggering ....but I need those Z moves too?

Sequence will be like this...

1. Machine moves to first coord
2. Z lowers
3. Once Z is at +0.2MM abovez0 (or similar), the 'trigger' happens.
4. Z raises

rinse repeat.....so I don't see how I can link the solder paste dispense to a z move, else the paste would be dispensed as the z plane is descending.

Jazzcnc ...not sure I'll be using mach3 (I'm warming to the CNC software called USB CNC...and will likely jump over to that .that software allows scripts though, I've coded pics in PICBASIC, so it should be within my ability to lash something up). Not sure I'm understanding you point about the smd components and the reel...I'm not doing pick & place, I just want to get a dab of paste at the centre of each smd pad.

[JAZZCNC]

rinse repeat.....so I don't see how I can link the solder paste dispense to a z move, else the paste would be dispensed as the z plane is descending.

This is easy with a brain just tell it to watch Z Axis DRO and while ever equal to 0.2 then turn on dispenser.! . . could easily be done with a VBscript as well using something like a While-wend loop.

Not sure I'm understanding you point about the smd components and the reel...I'm not doing pick & place, I just want to get a dab of paste at the centre of each smd pad.

Ok didn't realise that.! . . . If theres something to probe against then It's very easy to find the centre of a square or circle.

[mocha]

Lateral thought... would it work to make all the pads on the PCB the same size?

[JAZZCNC]

Have you used the dispenser before.? Like the guy in the Vid I would think you will need a pressure dump other wise the airline and cyclinder will still be under pressure so seepage could happen.

Regards the different pads amounts then this would be done using the G4 pause command. It could maybe done using the tool numbers.? So T1= Sot23-3 and T2=PLCC LED and so on. . . . . . . . . . . Then I don't think it would be to hard to write a script that reads the code and looks for the T number value then changes G4 P value to time required for that pad. Little like replace in note pad but more controlled.

Edit: Actually thinking about it.!! . . I bet If you altered or built a purpose post processor then it could insert the correct time into G4 P value.?

[Jonathan]

Does USBCNC include the equivalent of 'brains' in mach3 as I can't see any mention of it on their website (www.planet-cnc.com)?
If not then it looks like you'll have to generate code which has a line, or point, for each pad and use dwell commands/adjust the feedrate. What I suggested originally with using the direction pin would work enable you to set the time the axis is down for. Can add a delay with a 555 or a pic or something...might be worth trying as it's quick to set up.

Doing it in the Gcode allows better control though.

Then I don't think it would be to hard to write a script that reads the code and looks for the T number value then changes G4 P value to time required for that pad. Little like replace in note pad but more controlled

I could write a quick program to do that, but find and replace will be fine. I use that all the time to edit the code when I accidentally put the wrong feedrates/retract height in.