surface mount soldering techniques

[Guest]

Has anybody got some surface mount soldering techniques

The first way I was taught to replace surface mount parts some years ago (like 10 years ago).

How to replace surface mount parts.
(1) Take off the old part,
(2) Simultaneously heating and rubbing tined copper braid known as solder braid using a standard hot iron to soak up any old solder,
(3) Clean up tracks with isopropyl alcohol and tooth brush,
(4) Then apply a thin trace of solder paste over the copper tracks from a small syringe of paste,
(5) Then put the surface mount IC on top and blow hot air over it until the paste melts and solders the part in place.

WARNING
One problem when you take off a part for the first time some people make is they pull too hard and the tracks come away
THE PARTS ARE NOT HEAVY you just need the tiniest effort to remove the part when the solder has melted.



One of the disadvantage of using hot air is some times you can easily "blow off" other nearby components.
and found that one idea might be to use "solder paste & soldering iron"

[Guest]

thanks for that Eric but arent't the methods you describe pretty well established. None the less, useful for those just starting out with SMDs.


GzR

[Guest]

Interesting that is not what I read in Elektor magazine a few months ago, or what I found on the web via google, and then there are the jokers at work who never did any electronics training and they "know everything"

There was a question was going to appear on part two posting on trying to find a suitable syringe to fill with paste,
but due to the long response time the question has gone away.

[maxa]

sorry error!

[maxxypane]

Only suggestions to soldering or desoldering chips is to not solder consecutive leads. This can lead to overheating & damaging the chip. Whenever possible stagger pins & sides of the chip to allow heat to go dissipate rather than keep build.

Gold Contact Repair Kit'

[Guest]

Let me share what I know by practice (and after having read quite a few posts on this topic)

For soldering and de-soldering SMD, one thing you need to be careful with is whether you are dealing with a lead-free solder or not. Lead-free solder needs to be heated to higher temperatures. I typically adjust to about 330 degC (or sometimes higher) for no-lead solder. For leaded solder 250 to 290 degC will be enough.

On desoldering:

Using a thin nozzle for hot air gives you a good control over the directivity of the hot air you are blowing to the components. When you first start the desoldering, the component will be cold. So I suggest you warm it up from a distance of about 10 cm first. After about 5 to 10 seconds, bring the nozzle closer to the component you are trying to remove. This will rapidly increase the temperature of the component and you will see the solder melting away. It is also a good idea to grab hold of the component with a pair of tweezers while the hot air is directed towards it. Once you observe the solder melting away, you can "gently" pull the component out. DO NOT EVER move and force the component BEFORE the solder melts otherwise you can easily damage the circuit board pads, which will cause a lot of headache afterwards. If that happens, you will not be able to replace the component with a new one (if you need to in the future).

Although most people are adamant to use hot air desoldering, it is a great way to work. The devices are generally strong enough to withstand the hot air they are exposed to for a reasonable amount of time. Don't be afraid to experiment. I suggest you get yourself an old circuit board with SMD on it so that you can comfortably practice on that before moving to the boards you intend to use after desoldering and reworking.


On soldering:

Soldering SMD is (in my opinion) easier than desoldering. I always find it tricky to apply the required amount of solder paste to the pads. I often put more than what is required. First of all make sure the pads on the board are clean. My measure of cleanliness is that the pads have a silver shine to them. I use solder wick and alcohol to clean the pads and these work pretty well. Once the pads are clean put a little bit of solder paste to each pad and heat them up to bond the solder to the pads first. Then hold the component you wish to solder with a pair of tweezers on the target pads and start to heat it up with the hot air. Start from 10 cm and slowly bring the hot air gun closer to the component. You will notice that the solder on the pads will start to melt at some stage. At that point "gently" push the component towards the pads so that the pins sink into the molten solder. Then slowly move the hot air gun away from the component which will already be held in place. After you complete the soldering, be sure to clean up the pads and the excess solder around the component. I always find inspecting the quality of the soldering with a magnifier afterwards. Sometimes tiny balls of solder may be left between the pads which will cause various types of failures. So inspection before a power up is definitely worth it (especially if you are a beginner in this technique).

After soldering if you find that some of the pins do not look like they are in place or have sufficient solder on them, re-apply the hot air to the component to melt the solder again to give it a chance to move around and fill the gaps between the pins and the pads. This will be similar to the desoldering I explained above without physically removing the component.

I hope the above practical pointers will be useful.

Regards...