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I received some boards back from the PCBA fab and noticed that one 0402 resistor is flipped onto its side (R25):

enter image description here

This site tells me this is a pick-and-place error. But the footprint happens to be one where I increased the space between the pads very slightly, so that I could run a trace in-between. Other instances of the same footprint were correctly assembled by the fab.

Question: is this defect always caused by an incorrect pick-and-place setup, or can it happen during reflow in a phenomenon akin to tombstoning?

In that case, could the modified footprint be responsible?

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    \$\begingroup\$ I don’t have an answer for that, but it may still be allowed under IPC class 2 if it makes the correct electrical connection. \$\endgroup\$
    – winny
    Feb 21 at 17:17
  • \$\begingroup\$ Is the resistor now higher than the IC? So if you wanted to mount a heatsink onto the IC, it could be in its way? \$\endgroup\$ Feb 22 at 20:18
  • \$\begingroup\$ @ThomasWeller no need for heat sinking on this ADC chip. The main concern is that it is somewhat more vulnerable to being ripped off the board (the board is a test article and won't be inside a case). \$\endgroup\$
    – DamienD
    Feb 23 at 11:22
  • \$\begingroup\$ Sorry, my formulation was not good enough: I wonder whether I need to consider this "billboarding" when designing my own circuits which might need a heatsink. Given your IC needed a heatsink, would the resistor now be in the way and potentially prevent proper mounting of the heatsink? I'd never have thought of this in advance \$\endgroup\$ Feb 23 at 11:42
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    \$\begingroup\$ @ThomasWeller in this particular case the chip still clears the billboarded 0402 resistor, which sticks out about as much as a 0402 capacitor. \$\endgroup\$
    – DamienD
    Feb 23 at 12:07

3 Answers 3

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As stated in vir's answer, the issue is called billboarding.

is this defect always caused by an incorrect pick-and-place setup, or can it happen during reflow in a phenomenon akin to tombstoning?

It's totally a pick & place issue but there are different causes:

  • Before picking up the component, the P&P machine rotates the reel mounted to the feeder by one step and peels off the protective tape at the same time. During peeling, if the component is stuck to the tape, it may flip over or flip on its side, or even be removed by the tape.

  • If the slot on the reel is too big for the component, during the rotation of the reel and peel-off, any unnecessary vibration can cause the component to flip.

  • If the slot on the reel is too big, an off-centre pick with a mismatched nozzle may result in a flip by the nozzle itself or a flip during the placement.

Preventing billboarding is important, of course. But more importantly,

  • Isn't there an optical/photographic check during placement? Almost all p&p machines perform a photographic check before placing a component and if they detect a mismatch then they simply don't place the component and put it into a bin-like thing then re-try in the next placement cycle.
  • Isn't there any person who performs a visual check of the final board? One can easily detect that billboard by just looking at the board even from miles away.
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  • \$\begingroup\$ Good to know! I would indeed have hoped that the fab would have noticed this, especially considering they cost 3 times as much as those in the far East. \$\endgroup\$
    – DamienD
    Feb 23 at 11:20
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It's called "billboarding". The IPC standard is mute on the precise reason, but it notes that billboarding may occur during assembly. That condition is acceptable for all three IPC classes if the width of the device is less than twice its thickness. The IPC standard notes, however, that any billboarding might not be acceptable for high frequency or high vibration applications.

Edit: after poking around, it looks like the consensus is that billboarding is a pick and place issue, not a reflow issue which makes sense because tombstoning is usually a consequence of pads heating at different rates.

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    \$\begingroup\$ I did not know the term "billboarding", that's helpful! \$\endgroup\$
    – DamienD
    Feb 21 at 18:20
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The extra pad spacing could be a contributing factor: it would decrease the tolerance for pick-place. If the lead to solder paste contact area is insufficient you would get this problem.

Did your board get run through a DFM check (e.g., Valor or similar)? What did the report say?

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  • \$\begingroup\$ On my side no, only the DRC which passed. Not sure if the fab ran their own checks; they're an expensive, western europe fab, and I'm a bit surprised that they did not flag or detect this. \$\endgroup\$
    – DamienD
    Feb 21 at 18:23

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