LED Misalignment

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Hello I experiencing major misalignments. I am using a Nichi... - Apr 22, 2022 by sweng365

You could try putting a dot of adhesive like Loc tight chip ... - Apr 25, 2022 by DWL

It's difficult to diagnose without the LED specs. Is the spa... - Apr 25, 2022 by SMTA-64387687 SMTA

I didn't look into the two pad layouts and what they look li... - Apr 26, 2022 by ProcEng1

Thanks ... - Apr 26, 2022 by sweng365

sweng365

#87875

LED Misalignment | 22 April, 2022

Hello I experiencing major misalignments. I am using a Nichia LED package size@ y=.086,x=0.33mm, with recommended solder pad pattern x.086mm, y=.033. Note here is the kicker the PCB pattern does not meet this requirement. The PCB pad landing is based of a Cree LED with the dimension of x=0.65, y=1.20 larger than the Nichia led pads. The question is there anything I can do at this time to stop the Nichia Leds from shifting and drifting (misaligning)?

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DWL

#87877

LED Misalignment | 25 April, 2022

You could try putting a dot of adhesive like Loc tight chip bonder or similar between the pads. The adhesive will cure before the solder paste hits the reflow temp and hold the LED in place.

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SMTA-64387687

#87880

LED Misalignment | 25 April, 2022

It's difficult to diagnose without the LED specs. Is the spacing between the pads the same? Your pads seem too large for the Nichia part. Try reducing the stencil apertures to deposit less paste and closer to the inside edge. Depending on your oven, you might have to reduce blower speed.

This message was posted via the Electronics Forum @ SMTA SMTA

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ProcEng1

#87884

LED Misalignment | 26 April, 2022

I didn't look into the two pad layouts and what they look like, but here is what I tell my operators.

When the solder goes to liquidous, the surface tension will pull on the part from each pad, essentially centering the part. Assuming that the pads are laid out correctly. I have operators that try to place the part to one side (for whatever reason) and wonder why the part doesn't stay to the side after reflow. One issue we had with NICHIA LEDs was that one pad is way larger and when reflowed, the solder was thicker on that pad, so the LEDs would not lay level. SO we had to play with apertures to get an even thickness after reflow.

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sweng365

#87887

LED Misalignment | 26 April, 2022

Thanks

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