Bad solder under SMD electrolytic caps

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Hello ! I've noticed some hardening and partial non-melting... - May 03, 2025 by madisreivik

I have absolutely seen boards come out of the oven with grea... - May 06, 2025 by ProcEng1

Add theromcouples to the area in question & run a profil... - May 08, 2025 by Carl_P

madisreivik

#91977

Bad solder under SMD electrolytic caps | 3 May, 2025

Hello !

I've noticed some hardening and partial non-melting in one project, under SMD electrolytic caps. All other components and solder joints are fine on this board. I use Interflux LMPA solder paste (low melting point).

I have a theory. The caps are located in board area, which has no planes on top/bottom layers. And the pads are small and mostly hidden under the cap. Could it be that the cap is shielding the heat and there is not enough to melt all the joint ? Also, maybe the lack of heat disturbs the flux flow ?

I think I have to make pads bigger so there will be more heat coming in..

Has anybody seen similar behaviour / problems ?

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ProcEng1

#91981

Bad solder under SMD electrolytic caps | 6 May, 2025

I have absolutely seen boards come out of the oven with great looking solder joints, and the paste on the Electrolitics didn't even flow. I assume the internal plates are just heatsinking and the leads don't see the heat. If you don't want to make zone temp increases, one thing I have had limited success with if the design allows is to position the boards going through the oven so the the large CAPS are on the trailing end. That way the rest of the board starts getting heat-soaked and they have a little more time to heat evenly.

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Carl_P

#91985

Bad solder under SMD electrolytic caps | 8 May, 2025

Add theromcouples to the area in question & run a profile.

You will have the data to fully understand the issue then?

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