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I have a PCB in front of me with a surface mount 5V voltage regualator. I'm wondering how I got about soldering this with just solder (I don't have paste).

I have heat paste, but I'm wondering if pre-tinning the pad and heating it up afterwards from the side with the regulator will be equally effective if this is possible.

enter image description here

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    \$\begingroup\$ What package is it in? Just "buck" up and solder it down by hand. \$\endgroup\$ – Some Hardware Guy Feb 20 '15 at 13:33
  • \$\begingroup\$ @SomeHardwareGuy It's a triple pin TO-263, Texas Instruments LM1086. \$\endgroup\$ – MikeFoxtrot Feb 20 '15 at 13:36
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    \$\begingroup\$ Yeah def just put it down on the board and hand solder the pins and the tab. Nothing special about this part, use the largest tip you have for the pad. \$\endgroup\$ – Some Hardware Guy Feb 20 '15 at 13:38
  • \$\begingroup\$ @SomeHardwareGuy should I pre-tin the heatsink pad? Or sort of just 'connect' it along afterwards on the exposed edge \$\endgroup\$ – MikeFoxtrot Feb 20 '15 at 13:46
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    \$\begingroup\$ No just going to make it more difficult, use flux if you have it \$\endgroup\$ – Some Hardware Guy Feb 20 '15 at 13:47
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No need for solder paste.

I use an RMA rosin flux pen (it works like a Sharpie) to coat the pads (especially the big one) with flux and then solder. Liquid flux with a brush works well too. Heat the big pad and tab from the side and introduce enough solder to get it thoroughly attached. If the board is reasonably fresh it will suck the solder in under the large pad quite readily. Liquid flux and flux pens are a bit of a pain because they can't be shipped by air, so they're easiest to buy locally. Liquid flux in large quantities even attracts a Hazmat shipping surcharge.

enter image description here

Make sure the part is quite flat before soldering with essentially no gap before introducing the solder.

If the part does not need to dissipate much power (for example, a regulator where you don't expect more than a few hundred mW) you can just tack the end of the tab rather than flowing the solder right under. Make sure the connection is solid- especially on the DPAK package (the one you show is a D2PAK) because a lost ground on a 3-terminal regulator can have unfortunate consequences.

If, for some reason, you have to remove the part and replace it, clean the pads thoroughly by sucking up the solder (for example, with fresh solder wick) and make sure the new part sits dead flat on the cleaned board before attempting to solder it on.

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Thermal conductive paste is pretty useless for this. In fact, I think it's sole consequence would be trouble.

  1. Place part on pads.
  2. Solder pads.
  3. Enjoy.
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  • \$\begingroup\$ But can/ should I try to solder the heatsink to the PCB after the pins are down? \$\endgroup\$ – MikeFoxtrot Feb 20 '15 at 13:38
  • \$\begingroup\$ @MikeFoxtrot Yes. And no pre-tinning is required/recommended. \$\endgroup\$ – Dzarda Feb 20 '15 at 13:47
  • \$\begingroup\$ Ouch, hopefully he was talking about solder paste. Thermal grease would make a miserable mess! \$\endgroup\$ – Spehro Pefhany Feb 20 '15 at 15:09

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