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  1. #1
    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?
    Last edited by HankMcSpank; 24-12-2011 at 11:12 PM.

  2. #2
    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...

  3. #3
    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.?

  4. #4
    Quote Originally Posted by JAZZCNC View Post
    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!

  5. #5
    Quote Originally Posted by Jonathan View Post
    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.

  6. #6
    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.

  7. #7
    Quote Originally Posted by HankMcSpank View Post

    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.

    Quote Originally Posted by HankMcSpank View Post
    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.

  8. #8
    Quote Originally Posted by JAZZCNC View Post
    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.
    There's no need to auto probe to get the cnc machine to find the SMD pad centre , my pcb software can either give me those coordinates or I can export the smd pad as a gerber file & import into a cad program & get the cad software to mark the centres of each SMD pad. (which I can then use cam software to use this coords with)

    Ok so using this brain melarkey....my z plane lowers & once at say 0.2mm, a trigger happens....but what is the output here? Mach 3 has control of the printer port, presumably once the 0.2mm threshold is breached a nominated pin will change state?

  9. #9
    Quote Originally Posted by HankMcSpank View Post
    Ok so using this brain melarkey....my z plane lowers & once at say 0.2mm, a trigger happens....but what is the output here? Mach 3 has control of the printer port, presumably once the 0.2mm threshold is breached a nominated pin will change state?
    Yes the brain or script watch's the designated Axis DRO and while ever it's at the commanded position it will trigger the pin state of which ever pin you choose, So say output pin 11 will turn ON and activate the dispenser or relay that controls it. Then when axis starts to move the pin state changes back OFF untill it reaches the commanded height again so on and so forth.

    The script or brain can be as simple or complex as you want and really for safety sake you would want it to do some simple error checking IE: only change the pin state if the X & Y axis are not moving etc but in it's simplist form it's a very simple thing to do. Go to the artsoft site and watch the vids on scripts and brains it will give you a quick run down and idea just how simple.

  10. #10
    Ok, thanks I'll go have a read.

    The video I was referring to earlier was this one...

    http://www.youtube.com/watch?v=HdqVt..._order&list=UL

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