SMD reflow plate for soldering - A capacitor jumped out of place

[m_g_s_g]

Hi. New member here, and only starting with SMD soldering. Sorry if such a question was asked before.

I bought one of these cheap GDCHP USB-c PD 65W reflow plates. I checked temperatures with a Fluke multimeter and it seemed to mark within 5 deg C at 183 deg C (I'm using Sn63Pb37 mechanic solder paste).

With my first test board everything looked fine. When soldering my second board, the sole capacitor in it "jumped" out of place. It's a ceramic smd0805 100nf https://www.yageo.com/upload/media/product/productsearch/datasheet/mlcc/UPY-GPHC_X7R_6.3V-to-250V_25.pdf, not supposed to be polarized.

I heated first the plate to 150 deg C, left it 30 secs there and then increased temp to 185 deg C. This happened when the display marked aprox. 170 deg C.

Can somebody please help with some questions:
1. What happened with the capacitor? Static from the silicone mat?
2. Is it Ok to solder different components in several attempts? I understand that it's better to completely populate the board, but it makes more complex to pay attention to component moving out of place


Thanks.

[m_g_s_g]

(Sorry, the GIF file lost the animation when uploading _ This is the C6 capacitor after "jumping")

[janoc]

Probably moisture in the part. It gets hot, develops into vapor and the part "pops" out of place. That's why you get the warnings about moisture, reels are shipped with desiccant bags and moisture indicators. And you are supposed to bake every reel that has been opened for longer than some time before use to get moisture out.

BTW, none of the parts on that board are properly soldered. That paste doesn't look like it has reflowed at all.

Your temperature is too low. You can't follow the reflow profile intended for a reflow oven with a hotplate! Oven heats from both top and bottom and is enclosed, so the thermal losses are much smaller than with a hotplate. Your hotplate heats only from the bottom, through the FR4 which is not a great thermal conductor. So you need higher temperature.

You probably could try to reflow multiple times for a DIY board but you would need to clean off the old paste because the part wouldn't lie flat for new reflow otherwise. However, to fix a capacitor like this it is rather pointless - just rework it using an iron. Much faster and simpler.

[m_g_s_g]

Thank you for your help. Yes, moisture could have been!

The pictures sent were from BEFORE the reflow happened. I think the soldering went Okish.

[woody]

Probably moisture in the part. It gets hot, develops into vapor and the part "pops" out of place. That's why you get the warnings about moisture, reels are shipped with desiccant bags and moisture indicators.

I thought that an MLCC cap like that would most likely be MSL-1 so I would not expect moisture to be a problem? Then again, the jump would make an Olympic record for tombstoning    So maybe some contamination in the solder?

[selcuk]

You should populate all the parts and solder all of them at once. That is the purpose of reflow soldering for prototypes. Your parts are not that small. Doing them one by one is easier with a soldering iron.

Was your solder paste old and dry? Did you add some chemical to thin it? Some chemicals (i.e. butanol) used for thinning solder paste has low vaporizing temperature. If you add to much thinner, those smd components will fly like rockets. Because the thinner is trapped inside the solder paste and become gas and expands before solder melts.

[m_g_s_g]

The solder paste was not expired, but it was too dry, so I thinned it with some drops of JBC flux (FL-15), that is supposedly "especially for SMT and rework". It contains some water, so maybe this was it.

[Leiothrix]

Solder should flash to a bright silver once it has actually flowed, so it should be pretty easy to see if it is done or not.

I use a hot plate as a preheater and hot air on top to actually melt it.

Probably not an ideal setup but it works.