One of the assembly companies that I usually work always complains about my pos generated files. They say that SMT position coordinates on bottom layer must be mirrored in order to program their P&P machines
ā¦and what I always end up doing is editing the file to meet their requirements.
Iāve checked the KiCad Generated Placement Files options and Iāve found the āUse negative X coordinates for footprints on bottom layerā checkbox. This just change the X sign so does not solve the problem.
Can this be done via scripting?
A feature request maybe?
English āshouldā is ambiguous and therefore I āshouldā have been more careful with the wording. If I remember correctly there is an option in the dialog.
Iām not sure but it seems that Altium has this option but along the y-axis instead of the x-axis. In this case, I really donāt understand why flipping can only be activated along the y-axis and not for the x-axis. Mirroring? Flipping? I hope it is not another language ambiguity
My first thought here is that you have a weird assembly house, but I donāt have much experience here either. For the PCB itself it is normal to use coordinates as if viewed from the front for all layers. Iām guessing this is standard too for position files (I donāt read much about problems for this on this forum).
I do find it curious that there are settings for: PCB Editor / File / Fabrication Outputs / Component Placement / Use negative X coordinates for footprints on bottom layer PCB Editor / File / Fabrication Outputs / Drill Files / Drill File Format / Excellon / Mirror Y axis
Why X axis for the placement, and Y axis for the drill?
The first setting is relevant here.
I wouldnāt tamper with the second one, itās relevant to Excellon CNC PCB drilling machines and very old. I doubt that itās still used.
Totally agree but it is the most cost-effective company in my area for series. Iām not an expert on this subject either but Iām sure that an ā¬80K insertion machine would have no problem to mirror the bottom layer coordinates.
I donāt think it is worth asking for this feature. Especially if hardly anyone uses it.
I guess that anyone with a bit of experience in programming can write a script that does this coordinate modification in a few hours. It is just a bit of text manipulation.
Does your assembler have a web preview to test whether such a script would work for them?
Hereās my workaround. For example 2 layers mount PCB with R1 on TOP and R2 on BOTTOM. Grid and Drill/Place File Origin are placed in the right bottom corner of the board
For the assembly company this is wrong because X coordinate should be -9.83mm instead -2.17mm
To fix it and make them happy I insert this formula in the PosX column: - PCB_x_width + PosX_value = -12mm + 2.17mm = -9.83mm
Then I copy the formula for the rest of the references and voilĆ . No more complains
IMO, your P&P subcontractor is nuts.
In any mechanical design, you have a reference point for all coordinates.
Often at the lower left corner as X,Y= 0,0.
Moving to the right will increase the X-value, moving up will increase the Y-value.
Now, letās flip the board left to right to expose the bottom side.
This will not change the Y-values
But the X-values will change.
If the defined reference point is kept (X,Y=0,0, itās now at the lower right corner of your board. To manage that, the X-values need to be negative, and thatās exactly what KiCAD does.
Fully correct to any machinst doing drilling, milling, engraving, whatever.
What your supplier wants to do is to take the X-dimension of the board, creating a new reference point in the lower left corner, and compute new X-values from that new reference.
Itās a no-go, and to a machinist not acceptable. With a new reference point based on a milled X-dimension, tolerances start to accumulate.
Find a new board stuffer, or tell him to rethink the workflow. He probably has a fixture thatās only calibrated in one corner. Perhaps fiducials could help?
KiCad has a Drill / File place origin which you can place anywhere on your PCB and then use as the (0, 0) reference for the artwork outputs. I still donāt know what is the best way to handle this part. In theory any location works, I guess that the center of pin 1 of an important footprint on your PCB is a good location for this origin.
But āBoard Stuffersā sometimes have weird wishes. Some need positive coordinates for all parts for example, and the weird mirroring that your fab house desires.
Opinions about fiducials also vary a lot. They used to be considered important but apparently they are becoming obsolute. I guess that faster computers and better picture analysis makes it easier to use the actual pads as orientation marks for placing footprints. With high density PCBās there is also not much room to place fiducials. But there probably are still many assembly houses which use fiducials.
But the problem is apparently, that the board stuffer has either old machines, or machines with limited capability (and zero capability for double sided mounting).
This means mounting one side (and perhaps soldering), and then manually flipping the board to do the other side, needing a new āmirroredā reference point.
Modern machines do not have that limitation.
I see no need for a KiCAD feature here. If someone want to write a plugin or a script, fine.
Apparently gschelotto is happy with with his spreadsheet. Iād also espect that if a board stuffer has old machines, heād have plenty of experience to do some coordinate magic himself.
My last post was partially just to mention the options that are available in KiCad for others searching the forum and reading this thread later.
Well, thatās your opinion. I prefer to think that he has very little time to modify different setups and needs fabrication data to be the way he wants it in order to save time/cost as I use their EMS for long series fabrications.
I have to say that, of all the assembly houses I work with, it is the only one that gives me these āproblemsā. However it is super fast and very affordable price.
I personally prefer to tweak the P&P spreadsheet as I have explained before. I wouldnāt know if KiCad should have this feature but I can live without it.
