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parts popping off during reflow



parts popping off during reflow | 13 September, 2001

We've had several instances of parts (1206R, SOT-23) popping off of their location during reflow. Parts placement is OK, paste brick is aligned and compact before oven. But we get random parts off their location just lying somewhere else on the board after reflow.(parts just jump up and land somwhere else) Checked for mechanical obstruction but found nothing. We don't use nitrogen on our 5 zones conceptronics oven. We use WS609 water soluble alphametals paste. I'm baffled. I'd appreciate any help.

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Dave G


parts popping off during reflow | 13 September, 2001

Too much Convection Airflow in the Reflow Oven blowing parts around ? Moisture Contaminated Parts out gassing ? Board out gassing?

Just some thoughts, DG

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parts popping off during reflow | 13 September, 2001

You're correct. It is curious.

Possible angles to look at are: 1 WS609 loves moisture in the air. In high humidity shops, this paste hakes-on liquid. If this is the case, you should also see slumping, resulting in fine pitch bridging, and solder balls before cleaning. If so, consider reviewing your: * Paste storage and handling processes to reduce opportunities for moisture in the air to condense on the paste. * Process flow to reduce the amount of time between paste print and reflow. * Environmental controls in the SMT processing area to reduce the humidity. 2 Specific plastic encased components may have absorbed moisture and are pop-corning from the board due to rapid boiling and release of the moisture within the plastic case of the component. 3 Could your blowers be getting spikes of electricity that is increasing their air flow? 4 When checking for mechanical obstructions, did you check the operation of your conveyor?

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parts popping off during reflow | 14 September, 2001

please check the following also. in one of the cases we came across the second point was the problem.

1. the parallelisum of the conveyor. 2. the warpage of the board. 3. the stencil.(the differential height in the paste deposition of the two pads may also be cause)

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Kevin Simpson


parts popping off during reflow | 27 September, 2001

Hi, What does your profile look like? I have two 5 zone ovens and to reach the desired time of 4 1/2 minutes sometimes you may ramp the board temp up to fast not allowing for it to stabalize.??? Is the components poping off out from other components etc... not near any large components? That portion will heat up faster. >>> try a linear ramp to allow the entire pcb to heat up evenly. What is your conveyor speed?

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parts popping off during reflow | 28 September, 2001

Just had a similar phenomenon 2 days ago. May relate to your issue --- or not.

Like you, I did a once over looking for mechanical obstruction & couldn't find any.

Ran a thermal profile on the offending PCB & all checked out.

Looked in end of oven with flashlight where PCB exits reflow area (while PCBs were there) & noticed a thin fiber (barely visible) that had frayed from the flexible shroud that seperates the reflow and cooling area. It was dragging across parts while solder was molten & caused skewing & moving of parts off their pads.

Trimmed the fiber & all was well.

Check one more time for mechanical obstruction. It doesn't take much!

Good Luck....

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