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I'm trying to solder the pins on an Arduino nano but the solder won't go around the whole pin. This happens seemingly no matter how much solder I apply. If it's a lot and it blobs it only blobs on one side. Am I soldering incorrectly or is this natural? Are these pin connections still valid?

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    \$\begingroup\$ Not enough heat. You're likely using incorrect technique. Make sure the tip is tinned well, and you're making good contact \$\endgroup\$
    – Shamtam
    Jan 17, 2018 at 4:18
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    \$\begingroup\$ Are you using tin/lead (60/40) solder? You can as hobby projects do not need to meet RoHS specifications. \$\endgroup\$
    – user105652
    Jan 17, 2018 at 4:21
  • \$\begingroup\$ @Shamtam tinning the tip meaning add some solder before making contact to the joint right? I tried that and it doesn't seem to be working, maybe I'm doing that wrong though... I am using lead free solder so maybe that's hurting me? \$\endgroup\$
    – rcplusplus
    Jan 17, 2018 at 4:25
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    \$\begingroup\$ Soldering is hard to describe. Try to find some good videos online, if possible. Could be that you need more heat. It could be that the tip is worn out (oxidized). If the iron has a temperature adjustment, you can try turning it up a bit to see if it helps. You put a little on the tip, touch the tip to the pin and hold it. Gently touch more solder to the pin. If it melts freely, it is hot enough. If it doesn't melt freely, it is not hot enough. \$\endgroup\$
    – user57037
    Jan 17, 2018 at 4:32
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    \$\begingroup\$ @mkeith I've watched so many videos leading up to this (because I had attempted it twice before and was woefully unsuccessful) and yet following the instructions as best as I could, I had no success... What I did is touch iron to the joint, and then drag the tip of the solder from the very tip iron to the pad (if I tried to put solder just on the joint it wouldn't melt). The joints looked nice and clean from my angle, but when inspecting the back side they looked like what I posted above. If I try to tin the tip the solder globs higher up the cone, not at the tip. \$\endgroup\$
    – rcplusplus
    Jan 17, 2018 at 5:00

2 Answers 2

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Get some good quality and fresh 63/37 RMA rosin core flux wire solder (0.8mm is good for through-hole parts).

Preferably use a temperature controlled iron set to the recommended temperature for the solder you are using (600-700F for 63/37).

Put the tinned tip in contact with the pin and pad simultaneously (press a bit harder against the pin, but a light touch overall) and, after a brief pause, apply a small amount of solder to the opposite side at the junction of the pin and pad or directly to where the tip touches the pin/pad. It should almost be sucked into the joint.

If you are still having problems, try another type of header, maybe the gold plating is deficient in some way.

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There are two points :

One you need to make sure the pin is clean - and a flux will help with this, even if you have cleaned the pins, they oxidise as you heat them so you can either use a flux-cored solder or have a separate flux from a tin. Do not get a plumbers flux as it will be too strong and it leaves a corrrosive residue.

When using a lead-free solder the temperature has to be higher - about 40 degrees more iirc, and definitely use a flux - usually I flux the iron and the heat / flux the pin and pad and finally add the solder...

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  • \$\begingroup\$ Would it be easier to just get a 60/40 tin lead solder with rosin core? That way I don't have to deal with adding flux and then cleaning it? \$\endgroup\$
    – rcplusplus
    Jan 17, 2018 at 5:18
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    \$\begingroup\$ @rcplusplus Cleaning off extra flux is less hassle than soldering without enough flux. Sometimes the core flux just isn't enough. \$\endgroup\$
    – vofa
    Jan 17, 2018 at 5:24
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    \$\begingroup\$ Most of the time, once you have had a problem like this, you are going to need to add flux. If you solder a pristine board perfectly, maybe not. But once it is all messy, you need to add flux. Believe me, flux is your friend. You can use a no-clean liquid flux. \$\endgroup\$
    – user57037
    Jan 17, 2018 at 5:36
  • \$\begingroup\$ Just for reference: Liquidus for 63/37 is 183C, for SAC305 (a lead free type) it is 217C. Full reflow is about 25C to 30C above those numbers. \$\endgroup\$ Jan 17, 2018 at 8:15
  • \$\begingroup\$ So 217 - 183 = 34 not bad then... \$\endgroup\$
    – Solar Mike
    Jan 17, 2018 at 8:40

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