Electronic – What initial orientation do pick&place machines use when applying the “rotation angle”

The machine will detect failure to pick a part up to the point where the vision system sees it, but not usually afterwards. The normal process is for PCBs to be visually inspected, either manually or automatically as a seperate process after placement, to detect misplaced or dropped parts. Most P&Ps will probably not know they have dropped a part after it has been imaged, although it is possible some might sense placement pressure and/or vacuum pressure to detect drops, however if set up properly, drops shouldn't really happen.

The IPC-7351 standard defines a coordinate system origin for surface mount parts, as well as a standard orientation. There is a summary of the orientations on the last page of this document: http://landpatterns.ipc.org/IPC-7351BNamingConvention.pdf [Update: archived link], and illustrations in the full standard.

For most surface mount parts:

• The origin is at the centroid of the part's body
• The standard orientation is with pin 1 at upper left, except:
  • two-leaded components, where it's to the left
  • components where pin 1 is in the middle of an edge, where it's at top center

The reason for the origin being at the centroid of the part body is that pick and place machines use a suction cup to pick up the part at that point. Orientation on the reel can vary, so you have to tell the machine which way they are rotated when you load the reel.