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I want replace a SOIC8 SMD EEPROM on my laptop's motherboard. I have both a hot air gun and a soldering iron.

I bought tin-bismuth soldering paste (Tin 42% - Bismuth 58%), but then I saw on most SMD soldering tutorial that clear rosin-based flux is used instead.

From my researches, I came to the conclusion that application wise it comes down to selecting a solder temperature. I have a few questions:

  1. Can they be used interchangeably for my purpose?
  2. Why is flux sufficient to resolder a component on a motherboard? From what I saw on internet it is used alone to clean soldering surfaces but it must be used in combination to metal to perform soldering.
  3. What will it change to solder at the bismuth tin temperature instead of the one needed for rosin-only soldering?
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  • \$\begingroup\$ Hand soldering? Hot air? \$\endgroup\$
    – winny
    Nov 20, 2023 at 14:38
  • \$\begingroup\$ @winny I was planning to use hot air, but I also have a soldering iron if it is better for my application. \$\endgroup\$
    – servabat
    Nov 20, 2023 at 14:41
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    \$\begingroup\$ You don't need solder paste. Use the hot air to take the chip off and then an iron to put it back. You could use hot air to put on but if you're unclear how this works a soldering iron is much safer. A roll of normal solder wire is best for soldering with an iron. Hopefully that makes sense to you. If not, watch tutorials and practice until you feel comfortable. \$\endgroup\$ Nov 20, 2023 at 14:47
  • \$\begingroup\$ @user1850479 just to be clear, should I use rosin flux to remove the chip using hot air or even this isn't needed ? \$\endgroup\$
    – servabat
    Nov 20, 2023 at 14:50
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    \$\begingroup\$ You don't need to use flux to remove a chip but it won't hurt. Especially with hot air people sometimes apply the flux, remove the old chip and then quickly put a new one before the board cools to save time. You should probably go slower, take your time and be careful not to damage anything. \$\endgroup\$ Nov 20, 2023 at 15:22

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When you remove an IC, there will be solder left on the pads. You can often simply apply a little flux and solder the new part in using the solder that was left on the pads.

I'd remove the old part, remove the existing solder with some desoldering braid, place the part, and solder it in by hand. It's only an SOIC 8. That's about the easiest SMD part to solder by hand.

You can remove the IC using hot air or by hand (link to one of my blog posts.)

Here's how you put the IC back on (link to another of my blog posts.)

The bismuth solder just means your hot air doesn't have to be as hot to solder the new part on. You can use it if you like, or just use regular solder with your soldering iron.

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    \$\begingroup\$ Note that if your laptop is old enough that it uses lead solder (unlikely but it should be noted in case this is an early laptop), you should not use bismuth solder. In combination with leftover lead on the pads, it will form a low-melting-point (as in under 100 °C) tin-lead-bismuth phase that will cause it to fall off when the laptop gets warm. \$\endgroup\$
    – Hearth
    Nov 20, 2023 at 16:55

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