Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Inverted Chip Resistor

John S


Inverted Chip Resistor | 26 September, 2001

This will probably sound like a dumb question, but...

I have a specific 1206 chip resistor that routinely ends up placed upside down on the pcb. We use Juki 750 placement machines. I normally run the machine with the auto-correct for the pick position turned off to keep the machine gang picking. This allows the pick position to "wander" some, resulting in several pcbs with an upside down resistor in every run. I can turn the auto-correct back on and the problem will stop, but eventually the machine's logic stops allowing it to gang pick. I've been looking through my IPC standards and cannot find one that states that there is a problem with this. Is anyone aware of a standard that prohibits this condition?

Thanks in advance John

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Inverted Chip Resistor | 26 September, 2001

John, you mention yourself that this problem is component related. Is the 1206 presented out of a plastic tape?. The tape could be more slippery than the paper tape and the cover tape may pull the tape out of position.

I am not familiar with the Juki, but can you adjust the tension on the cover tape peel back? Are there any other adjusting elements on the feeder to keep the component in line with the others for simultoneous pick up.

Are you sure the component is not inverted in the pocket during tape transport? Stefan

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Inverted Chip Resistor | 26 September, 2001

Don't hold me to it but... Class 1-process indicator, varify value (cap, resistor) Class2,3-failure (rework required)

This is what we used at my former job when i took over QA responsibility.

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Michael Parker


Inverted Chip Resistor | 26 September, 2001

Electrically, the part still works, even if upside down.

When upside down, you cannot see the part identifier. If you are an OEM and your QA/QC people don't freak out because they can't read the part, let it go.

If you're a CM, your customer would probably find cause for rejection.

Make a command decision based on pratical logic, not just spec's. Save yourself rework if you can.

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Inverted Chip Resistor | 26 September, 2001

Placing a component the correct side up: * May affect heat dissipation. [Umm, that sounds like stretch, but who knows what designers think about?] * Allows reading the markings on those components that have markings, however cryptic the notation of the markings may be.

Stefan raises the interesting point: What�s going on that causes this?? Are you saying that when the pick position wanders, that it picks on the component edge and that allows it to get turned upside down? Er what?

In response to your question: Look to A-610C, 12.3.3, which says something like: Mounting Upside Down * Class 1: Acceptable * Class 2, 3: Process indicator

Commenting: It�s possible that this �no requirement� in A-610C is influenced primarily because bulk feeders are indiscriminant.

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John S


Inverted Chip Resistor | 27 September, 2001

The feeders on the Juki 750 machines have about 0.060" slop in the x-axis. Which allows the machine to try to pick up the part on the edge,inverting it. With the auto-correct feature enabled, the machine locates the feeder pocket based on its pick results. However, it stops gang picking, slowing production significantly. I'm trying to find a way to rigidly locate the feeders as a permanent fix. Juki has attempted to remedy this with the 2000 series machines, but retrofitting our machines and feeders is cost prohibitive.

Thanks John

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