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SMT Tip for Velleman VTSS5U
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SMT Tip for Velleman VTSS5U

by epalaima on Fri Feb 09, 2018 11:23 am

Hi, I am looking for a soldering iron tip I can use for SMT soldering (specifically TSOP), which will fit the Velleman VTSS5U iron that I have. Can anyone recommend anything?

This is what the regular bit looks like:

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Re: SMT Tip for Velleman VTSS5U

by adafruit_support_mike on Sat Feb 10, 2018 12:47 am

I'm afraid we don't carry anything that size, but you can use a fairly wide range of tips to do SMT soldering.

SMT is all about capillary action, and the joints pretty much form themselves. My favorite tip is the hoof type:

Because it has a good balance between mass and precision. In my experience, narrow-point conical tips lose heat too quickly and make it hard to control the way the solder moves. The hoof has plenty of metal to hold heat, but you can turn it to work with the point or the edge in tight spaces.

The main technique for soldering SMT parts is drag-soldering, where you gather a blob of solder on the tip and literally drag it along the pins on one side of the chip. As long as the solder is hot and well-fluxed, each joint will form as the tip moves past, but will only retain enough solder for a proper joint when the tip moves away. If you do end up with a few bridges, you can use a bit of solder wick to pull the excess metal away.

Start by applying a blob of solder to one pad at a corner of the footprint, set the chip on the board, and reheat the solder to make a tack joint that holds the chip in place. You can reheat the joint a few times as necessary to get the chip's pins well positioned on the pads. Then move diagonally across the chip and tack the pin at the far corner. You can do fine adjustment by melting one joint and using the cold one as a pivot to rotate the chip slightly.

Once the chip is where you want it, drag-solder the rest of the pins on each side. That part only takes a few seconds, and you have to do it a few times to stop being surprised at how easy it is.

Keeping the solder well-fluxed is critical though. As long as the surface tension of the metal stays low, the joints will form almost by magic. If the solder starts to oxidize and get pasty, everything stops working. At that point you need to stop, apply some more flux to the area where you're working, clean the tip, and start again.

It helps to run the iron a little hot, but not crazy-hot. I prefer to work at about 460F to 470F for small SMT joints, and about 550F for large mechanicals. You'll develop your own preferences as you work though. A hotter iron makes the metal flow more smoothly, but there's a point where the joints get starved for metal and you have to move fast to keep the heat from causing secondary problems like melting other nearby connections. That's the point where you want to turn the heat back down a little.

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Please be positive and constructive with your questions and comments.