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I want to know about the SMT requirement documents. When I make a partlist and XY-coordination data from PCB software that shows me rotation angle like R90 or MR270. I know that R90 means rotate it 90 degree and MR270 is mirror and rotate parts. enter image description here

But I'm curious how to know the direction? R90 can be either clockwise or counterclockwise? and I think If the pin position is opposite, so it may cause confusing.

For example, If I make a capacitor which is left to right pin number are 1 and 2. But other people make a capacitor which is left to right pin number are 2 and 1. Those are opposite way.

In that case How the SMT manufacturer know the direction of parts?

(add one more picture for a question)

enter image description here

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  • \$\begingroup\$ Gerber files contain all information regarding this \$\endgroup\$
    – Sorenp
    Oct 24, 2019 at 7:35
  • \$\begingroup\$ @Sorenp gerber files do not. ODB++ files do. \$\endgroup\$
    – Jeroen3
    Oct 24, 2019 at 7:55
  • \$\begingroup\$ I added one more picture what I'm curious. Please help me out! Thanks \$\endgroup\$ Oct 24, 2019 at 9:36
  • \$\begingroup\$ @Jeroen3 GERBERS do, GERBER-v3 includes this information \$\endgroup\$
    – user16222
    Oct 28, 2021 at 10:54

3 Answers 3

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In that case How the SMT manufacturer know the direction of parts?

In short they do not. What there is is a convention for a given footprint to place pin1 in the top-left corner and ensure the centre of rotation is the middle of the part. This is captured in IPC-7351 and eCAD librarians are expected to follow some standard. Kicad's library convention stipulates such orientation.

If a footprint was captured following such convention then the position file contains the centre and the rotation and in theory all that would be required at the assembly site is the orientation of the components within the ribbon to align the two datums so that a 90deg rotation on the PCB means something to the PnP machine (eg -90deg) based upon the physical orientation of the part.

However... not all footprints are captured following such a convention and thus a CAM engineer must painstakingly check each components orientation to ensure their datums are aligned (time,money and error prone). Likewise there is still the missing information with regards to the orientation of the card.

The more advanced fileformats aim to solve this

  1. GERBER-X3
  2. ODB++
  3. IPC-2581 (DPMX) by including assembly information (and additional information to help with testing)

Below is a screenshot of a GERBER-X3 generated output. Top silk, Top paste and Top Components are shown. You can see the component layer (pink) has a circle marker for the centre of rotation and a diamond for pin1. This information is what is required by CAM software to align to the orientation from the tape

enter image description here

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For components that have no polarity, like resistors and ceramic capacitors, the pin definition is irrelevant.

For components that do have polarity, like electrolytic capacitors, diodes, ICs, etc., you have to provide polarity information on the silk screen. For instance, draw a line on the silk screen next to the pad corresponding to a line in the component marking (typical in capacitors), use + and/or - symbols, write letters A and K next to the correspondent anode and cathode pins in a diode, etc. For ICs the convention is to mark the location of the pin 1 or A1 in case of a ball grid array. Through-hole ICs or connectors sometimes use a square pad for pin 1 and circular pads for the other pins.

If your board has no silk screen you have to provide polarity information in assembly drawings to clearly define the polarity of components that may present orientation ambiguity.

Based on this information, the production line technicians will properly program the pick-and-place machine to place these components correctly based on the orientation that they come inside the reel.

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  • \$\begingroup\$ thanks for your kind. but If I draw footprint rotated for example, first pin is rotated in my footprint 90 degrees, then in the board, 0 degree is not the real 0 degree of the parts, because actually it is rotated in the footprint in that case how they can know? I think the 0 degree which has diversity of footprint because it can be varied for each people who is drawing footprint. I add one more picture for explain it. \$\endgroup\$ Oct 24, 2019 at 9:26
  • \$\begingroup\$ You have to make sure that your footprint library is consistent with your schematic symbol library. Double-check everything. \$\endgroup\$
    – joribama
    Oct 24, 2019 at 17:22
  • \$\begingroup\$ Yea, the tech's will have to program this. Different types of reels may have different orientations, and can even be fed into the pick and place from different directions. There is no chance that the person doing the layout can know how much the part has to be rotated from the reel to the PCB, so this has to be programmed as an offset for each type of package based on information in the silk screen or assembly layers. \$\endgroup\$
    – Arcatus
    Feb 25, 2021 at 8:25
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Upon submitting your board to the manufacturer you can ask them to first assess the board for any irregularities such as wrong component rotation, misalign pin 1 to top copper.

You can help the technician/engineer to understand your board by providing cue marks such as a dot on pin 1 or a line for cathode part.

Some fabricators also provide a gerber file viewer online, you can use this to see if your board looks good and align before fabrication. If you see that some parts are rotated or misfit, you can manually fix them in the pick and place file

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