I took this op-amp IC out of an electronics kit. It's on a PCB and soldered to some longer leads. There's some yellow/brown goo on the back of the board, and I'm not sure what it is.

You can see it in a stripe through the middle, and partially covering some solder joints:

Sorry, no amusing XKCD hovertext for you.

I can scratch it with my fingernail, and it feels kind of like rubbery plastic, much like hardened glue.

What is it? Will it interfere with soldering/desoldering?

  • \$\begingroup\$ I don't know what the flux that is \$\endgroup\$ – infixed Oct 4 '16 at 15:33
  • \$\begingroup\$ Not sure it's flux - wax(often used to fix adjustable components) or hot melt glue are both possibilities. \$\endgroup\$ – Brian Drummond Oct 4 '16 at 16:17
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    \$\begingroup\$ @BrianDrummond infixed was making a play on words =P \$\endgroup\$ – DerStrom8 Oct 4 '16 at 19:32

I'd guess it's quite heavy flux residue.

It should not interfere with soldering or desoldering (it helps there in the first place), but it can interfere with the operation of the circuit. Especially if you try to build some low power / high impedance circuits...

Clean it with some ethanol or isopropanol.

Based on the comments it seems to be glue, so in that case:

It will interfere with soldering or desoldering. It will likely burn (or boil) and create some toxic fumes. It can also attack the tip of your iron and make it unusable because the tin won't wet it anymore (maybe you can clean the residues off, but if you are unlucky you need a new iron).

In this case you should definitely try to clean it off before doing soldering near that stuff. Hardened glue might need some special treatment to come off though. Some require heating (up to 150°C) and then you can wipe them off, others will come off with some solvent.

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  • \$\begingroup\$ Could be flux, but "rubbery plastic" doesn't fit any flux I've used. I'd guess it is a wax or glue used to fix down a heavy or mobile component on the other side - a mechanical rather than electrical process. \$\endgroup\$ – glen_geek Oct 4 '16 at 15:55
  • \$\begingroup\$ @glen_geek depends on how long you have the flux on there it can change its properties over time, the description "opamp IC" made it sound like an opamp breakout board, so I didn't think of any big component which needs to be fixated. \$\endgroup\$ – Arsenal Oct 4 '16 at 16:03
  • \$\begingroup\$ I just noticed that the PCB was apparently glued to the inside of the kit, so it looks like it may actually be glue. There's much less or none of it on the other PCBs in the kit, so I assumed that it was something unintentional. I guess whatever it is, cleaning with alcohol is the likely solution (no pun intended). \$\endgroup\$ – Kendall Frey Oct 4 '16 at 16:06
  • \$\begingroup\$ @KendallFrey if it's glue, you might need something different than alcohol, I've updated my answer a bit. \$\endgroup\$ – Arsenal Oct 4 '16 at 16:18

It appears to be rosin flux which supports the solder, but that's just from what's visible in the photo. If you scratch a bit off an it comes off as light yellow powder, it's very likely to be rosin which many technicians use in soldering.

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