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Getting started soldering SMD components

November 16th, 2010 Leave a comment Go to comments

In this post I’m going to give some Soldering hints for soldering SMD components, and which tools you need to get started

 

Temperature-controlled soldering station

Velleman Soldering Station (VTSSC40N)


You need a good iron for soldering SMD components, especially when using small/thin tips. I’ve chosen to get a temperature-controlled soldering station because this will help keeping the tip-temperature constant, whatever tip size I’m using.

 

Bevel and Cone tip

Bevel and Cone Tip


When soldering I mostly use two different tips:

  • Cone tip: 0.5mm diameter
  • Bevel tip: 3mm diameter

 

Solder and Solder Wick

0.4mm Solder and Solder Wick


Of course you need some solder, and my recommendation is 0.4mm Leaded solder (64/36/2 Ag). I find it easier to use thin solder when soldering SMD components, because it’s easier to control how much to apply. I use Leaded solder as it melts at a lower temperature, and the gasses made from soldering with leaded solder are not that poisonous as soldering with LeadFree solder.

 

Grease Flux and Flux Pen

Grease flux and Flux pen


When soldering regular SMD components like resistors, capacitors and IC’s with a few pins, I use a Flux pen to flux the pads before soldering. When soldering fine pitch SMD IC’s like QFP or TSOP I use the Grease Flux, which I add after I’ve placed the component.

The Grease Flux is a gel substance, while the Flux Pen contains liquid flux. You could, of course, also use liquid Flux instead of the Grease Flux. That’s something you have to decide for yourself!

 

Angled Tweezers, Magnifying Lamp, 15x Loupe and Tip Cleaner

Angled Tweezers, Magnifying Lamp, 15x Lupe...


Theese 3 tools are VERY necessary when doing SMD operations.

  • The Tweezers are used to grab and hold the components in place while soldering
  • The Magnifying Lamp is used when soldering
  • The 15x Loupe is used to check the connections after soldering
  • The Tip Cleaner is a metal-grid ball which “drags” the solder off the iron while also fluxing it

 

Soldering two leaded SMD components like resistors and capacitors

Two leaded components are mostly the easiest to solder, and I’ve done 0603 resistors with my magnifying lamp only. You have to prepare everything, install the chisel tip, turn you iron on, and set it to 330 degrees (626 fahrenheit) when using leaded solder as I do.

Then use your Flux Pen to Flux the pads where you are going to solder the components. Take your iron and tin the tip, clean it, and place a small drop of solder on the iron again. Place this small drop on one of the pads, but touching the pads gently and holding the iron on the pad for a couple of seconds.

Next grab the component with the tweezers, while you are still holding the iron with your other hand. Heat up the pad where you placed a solder drop before, and push the component against the soldering iron while pressing it down to the PCB, too. Remove the soldering iron while still holding the component in place with the tweezers. After a couple of seconds, remove the tweezers, and one side should be soldered.

Finally heat up the other side of the component and the pad beneath it, and if required add a small amount of solder.

 

A “Solder Ball” was created – what do I do?

If a “Solder Ball” appears while soldering SMD components, you either haven’t heated the pad enough or you have added too much solder. You have to make sure that a connection is made with the pad, as not enough heat will make the solder just “lie” on top of the pad.

So to fix this, Flux the pad with your Flux Pen, and then heat up the component and the pad. If the “Solder Ball” gets smaller after a couple of seconds, you haven’t added enough heat to the pad the first time you soldered the component. The connection to the pad has now been made, and you can go on.

If the “Solder Ball” doesn’t get smaller, you have probably added too much solder. It’s recommended to remove some of the excess solder by using the “Solder Wick”.

 

Notice for LEDs and other Diodes

SMD Polarity (seen from the bottom)


Most of the times LEDs and other Diodes have two leads, like all the other passive components. But as you probably know LEDs and Diodes are polarized, so they have to be mounted correctly. That is why we have to take a look at the bottom of the SMD LED or Diode to see where the anode and cathode are. The image above shows the two markings that will indicate the polarity.

The thing I noticed was that on a PCB where you have a line to mark the cathode (negative), you have a line to mark the anode (positive) on the SMD component itself!

 

Soldering SMD ICs with a few pins

When you are going to solder a SMD IC with a few pins, like a TSOP or SOT23, I recommend using the same method as descriped above. You start by fixing a corner pin, and then you flux the rest of the pins with your Flux Pen, and finally you solder them one by one.

However, you could also use the same method as for soldering Fine Pitch ICs (described beneath), to solder theese. I just recommend using the method described above when you are not soldering 0.5mm parts or parts with >16 pins

 

Soldering Fine Pitch SMD ICs, and ICs with a lot of leads

Fine Pitch ICs and ICs with a lot of leads are pretty easy to solder, if you are using the right tools. When I solder Fine Pitch ICs (0.5mm spacing), I use the Bevel Tip and the Grease Flux.

To start with you have to prepare your soldering iron by changing the tip to a Bevel Tip. Then you turn it on and set it to 330 degrees (626 fahrenheit). When the iron is heated up, tin the tip, and clean it.

Now you have to place and align the IC. I use a Vacuum Tool to pick up the IC, so I don’t bend any leads. Then I carefully use the tweezers to align the part on the pads. This can be a tough task and you might need the 15x Loupe to check if the alignment is correct. When the IC is aligned properly, fix it with tape or solder a couple pads in the corners. I find it easier to hold it in place by using tape.

Next you have to add the Grease Flux to a row of leads. It’s better to add too much than to little. You could, of course, also use Liquid Flux instead of the Grease Flux, and maybe that will work better for you. When you have fluxed a row of leads, grab your iron and add a lot of solder, so it makes a kind of drop/ball on the beveled tip.

Now you have to move the flat side of the beveled tip across all the fluxed leads. By doing this slowly enough, you will be able to drag the solder drop across all the leads, but still get every lead soldered.
When you come to the last couple of leads in the row, slow down even more, and lift the iron slowly away from the leads. NOT by lifting upwards, but by lifting across – as if the row had more leads. This keeps the solder drop on the iron, instead of the last couple of leads.

If it happens that the solder drop stays on the last couple of leads, or if any other Bridges occour, then just take you Solder Wick and remove the solder. You do this by placing the Solder Wick on top of the Bridge, and then heat up the Solder Wick and the Brigde on the same, by touching the Solder Wick with your iron. After a couple of seconds the solder Bridge will be “sucked up” into the Solder Wick.

This soldering method is called Drag Soldering, and I find it very easy to do, after I tried it a couple of times. With this method you will be able to solder 144-pin TQFPs in no time. For me it takes about 30 minutes to solder a 100-pin TQFP (Xilinx VQFP). Practice, and you will find it easy and fast, too.

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  1. burn fat
    August 11th, 2011 at 08:11 | #1

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