Any way to force placement order?

Started by Mike, October 16, 2011, 10:42:38 AM

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Is there a way to force placement of parts in a particular order - I tried moving the blocks of parts in the job file but it made no difference. It doesn't seem to be doing anything clever like sorting into increasing height - anyone figured out the logic of what order it decides to place in?


I thought it takes its placement order from the top-down order of parts in the BOM file, with the following extra considerations:

1) The tool number for the part takes precedence, to keep tool changes to a minimum of course. I think the tool order is 1,6,2,[7],3,[8],4,[9],5,[10]. Numbers in brackets are guesses as I have not used tools from those locations. Therefore all parts using tool 1 are placed first.

2) This is also a bit of a guess, but I think it places all the same parts together, so that as soon as it comes across the first instance of a part in the BOM, it then places all other instances of it regardless how much further down in the BOM they are. Eg if you have the following order in the BOM:
C1 = 100nF (0603)
C2 = 47pF (0603)
C3 = 100nF (0603)
C4 = 1uF (0603)
C5 = 47pF (0603)

Then the placement order would be C1, C3, C2, C5, C4.

3) If a part becomes skipped because of feeder errors then of course that changes things.

4) Also if you stop a run and restart it, that changes things too.

Does that help?


So the answer looks like there isn't an easy answer - the immediate problem I had was 0603 Rs very close to caps, and the nozzle was sometimes hitting the caps when placing the Rs.
As a quick fix I just put tool 6 in the tool 1 position. Will remember to leave a bit ore space on the PCB next time....
BTW  something that appears to take precedence over all of the above is if the CDF run-time test is enabled, which make sense. 


I use a 'tool 6' for all 0603's - its in the tool 1 position.

And yes, missed that about "run time test", which does always come first. Several components with run time test enabled probably follows the same priority rules as above.


load 2 identical tools (positions 1 and 6 perhaps) and set your CDF's so the device you want placed first uses the appropriate one, you lose some time because of the extra too, changes and you better hope you never interrupt the job because lord knows what its logic is when that happens.

Alternatively set biases on the compenents concerned so they are offset by 25% of the pad or so away from each other (assuming they are not sandwiched and there are no via waiting to swallow them) and they should self correct back to where they belong.