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SMD module moving during reflow

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SMTA-David

#82830

SMD module moving during reflow | 18 June, 2019

Hi, I have a SMD radio module that has castellated Pads along one edge of the module. The pick and place machine appears to place them very well but when the boards come out of the reflow oven then up to 20% of them have either rotated a few degrees right or shifted down just enough so the castellation shorts out 2 pads on the PCB. What could case this sort of issue and how could I fix it? Can too much solder case things to slide around in reflow? Would less solder and/or a drop of glue under the part prevent this?

Thanks

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#82832

SMD module moving during reflow | 19 June, 2019

Drop of glue should prevent module from moving, but is not really a solution.

What about pad design? Are pads on PCB themselves much larger then the ones on the module?

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#82835

SMD module moving during reflow | 19 June, 2019

In my opinion, fault lies in printing or reflow.

With printing - it's either too much solder paste or bad print, though I would assume that would be caught.

With reflow, it could be that ramp up rate is too high.

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#82841

SMD module moving during reflow | 19 June, 2019

Here is a link of an article regarding the SMD rotation during reflow issue, you may find it useful. http://www.circuitnet.com/experts/86914.html

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#82844

SMD module moving during reflow | 19 June, 2019

Does the part have a ground/thermal pad underneath or are all terminations on the perimeter?

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SMTA-David

#82850

SMD module moving during reflow | 20 June, 2019

How can I upload image to this forum? I can show you the pad layout.

I am thinking maybe too much solder. I used 0.16mm thick stencil but notice many us 0.12mm thickness.

Also, cream layer is 100% of pad surface, I know for fine pitch parts it is recommended 95% cover, wonder if I need to reduce? The pads are on 1.27mm pitch

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#82851

SMD module moving during reflow | 21 June, 2019

Many aspects cause such problem, stencil windows and thickness, thermal pad and crowded PTH vias on PCB, the castellated pad size and pcb pad size. Do you have picture for reference?

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SMTA-David

#82867

SMD module moving during reflow | 24 June, 2019

Yes, I have images but how do I upload them to the forum? I am new here

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#82871

SMD module moving during reflow | 24 June, 2019

I have not added images in quite some time but the "Attachments" feature below the window where you type your post will steer you through it. You just have to have the image hosted someplace that you can point to. Just for fun, I'll try one here....

My experience with the problem of rotation of parts during reflow has been about 90% due to incorrect design of the stencil for parts with large thermal/ground pads.

Attachments:

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#82872

SMD module moving during reflow | 24 June, 2019

I believe you have to log in at the SMTNET.net directly in order to attach an image file.

Attachments:

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SMTA-David

#82891

SMD module moving during reflow | 26 June, 2019

Thanks, I'll take a look.

Something else I found was the Z height for the module was set to 1.7mm but I am picking up the part on the PCB surface which is only 1.0mm from PCB being loaded, therefore the part must have been let got 0.7mm above PCB and not pushed into the paste and maybe sliding around on top? I will adjust this before next run and see if it fixes the issue

This message was posted via the Electronics Forum @ SMTASMTA

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