Anthony Burch asked:




Before you start to hand solder a quad flat pack (QFP) to a printed circuit board, you will need several tools and items. This article describes what is needed for the process, including safety items, consumables (materials that are “used up” during the process) and tools.

Whenever doing any soldering, the first thing to consider is safety. In particular, the protection of eyes, hearing, lungs and skin.

The first safety item that I recommend is a face respirator. You can get a face respirator at your local hardware store. There is a selection of filters that you can buy for these, including ones for dust and paint fumes, and so on. I recommend getting the filters that are for agricultural use because they provide good general purpose fume and chemical filtering. They will help to protect your lungs from soldering fumes.

Another way to deal with soldering fumes is to use a bench-top fume extractor. These are great, but personally I just use a face respirator, which is effective and low cost.

Still on the subject of air safety, it is important to make sure that your work area is reasonably well ventilated so that there is not a build up of solder fumes where you are working.

Eye protection is a must at all times. If you use a head magnifier, this will protect your eyes and give you magnification at the same time. When you are not wearing a head magnifier put on a pair of safety glasses.

You must also protect your hearing, especially when using an air compressor during the circuit board cleaning process. Air compressors can definitely be a hearing hazard while they are running. I like to use yellow foam ear plugs for hearing protection. Alternatively you can use ear muff type hearing protectors. For extra hearing protection you can use the foam ear plugs and the ear muffs at the same time.

For protection of your skin, I recommend using latex gloves. Make sure you get the powder-free ones so that you don’t get any talcum powder from the gloves floating onto your boards and solder. You can buy these gloves at the supermarket. They may be labelled “powder free latex gloves for food handling”.

Now we will look at consumables. Consumables are the materials that are used up during the process, such as flux, solder and cleaning solvents.

One of the real secrets of doing quad flat pack and other types of surface mount soldering successfully is to use “gel flux”, not “liquid flux”. Liquid flux doesn’t have enough solids content, or rosin content, for this process.

It is also important to get the “no-clean” type flux, which is inert and non corrosive. Don’t buy the water soluble type flux because it is corrosive and can damage your board if you aren’t able to wash it all off properly after the soldering process.

Any brand of electronic soldering gel flux will do a good job, such as AIM or Multicore. One way to buy gel flux is in a syringe package. This is the most convenient way to buy it. Alternatively, you can buy it in a tub and load it into a syringe for dispensing.

For cleaning the boards after the soldering you will need some methylated spirits (also called “metho”) and a plastic container of some kind. The plastic container can be a lunch box, a food container or an empty ice cream container. Choose the size of the container depending on how big your circuit boards are and how many you want to put in to wash or soak at one time.

And of course you will need some solder. You can get a reel of tin-lead rosin cored solder from your local electronics shop. Any kind of wire type tin-lead electronic solder is fine.

As a side note, if you want to do lead free soldering then of course you will use lead-free solder instead. The process for lead-free soldering is exactly the same, except that the temperature of your soldering iron needs to be higher. You can use the same gel flux as for normal tin-lead soldering. In general, I recommend that you stay with tin-lead soldering unless you specifically need to do lead-free soldering for a project.

Next we are going to discuss the tools that you need.

First of all, just a quick note – you don’t need to buy a “hot air rework station”. They are expensive and you don’t need one for this process. What I recommend that you do get is a soldering iron with a “reservoir tip”.

A reservoir tip means that the soldering iron tip has a concave cavity where you feed the solder in and it stays there, by the magic of surface tension. Then when you place the iron onto the circuit board, the solder in the cavity flows onto the pads and pins of the chip.

The reservoir tip is the best type to use for this kind of soldering but you could also use a normal wide chisel tip on the soldering iron. As long as the wide chisel tip can hold a little volume of solder for the soldering process.

The next tool is a vacuum pickup tool. This is simply a little suction cup with a squeeze bulb attached. You can use different sized suction cup fittings depending on the size of the component that you are picking up.

You will also need some kind of brush. My favorite is a horse hair brush, which is a brush made specially for brushing circuit boards. However, you can use any other kind of natural fibre or nylon brush. For example, a small automotive parts cleaning brush, a toothbrush, or maybe a cosmetic nail brush.

Another item that I have found invaluable is a hypodermic needle. It’s a needle that is normally used with a syringe for intravenous injections. It is extremely useful to have one of these on-hand to fix any problems with quad flat pack bent pins, in case you have a little accident and drop or bump your chip.

To turn the hypodermic needle into an extremely useful tool, simply use fine pliers to make a small 90 degree bend on the end of the needle to make a little hook or grabber for the pin legs.

You can get hypodermic needles at your local pharmacy. Just ask at the counter.

I recommend getting an air compressor. Personally I have a 1500 Watt, 24 litre air compressor that I got at a hardware store for less than a hundred dollars. An air compressor is a great investment for anyone doing electronics work. It is useful for cleaning boards and components. It can blow away dust and also move flux residue.

I also recommend using an in-line separator and nozzle with your air compressor. A separator is simply a cylindrical device that connects in-line with your air hose and nozzle. It separates out any moisture from the air that is coming out of the compressor, so that the air that comes out of the nozzle is relatively dry.

Finally, it is important to consider anti-static handling. Anti-static handling means making sure that any static electricity build-up in your body is not discharged through the chip or board. There are various ways that you may build up a charge in your body, including going for a short walk across a carpet.

To prevent from zapping your chips with a discharge through your fingers or hands, you can wear a grounded anti-static wrist strap, or at the very least make sure that you dissipate any static charge in your body first. You can do this by touching a grounded metal object on your workbench, such as the exposed metal screw on a grounded metal equipment case.

That covers all the items that you will need for soldering a quad flat pack, including safety items, consumables and tools.

Juan Uflerbaumer asked:




Are you using the most convenient tools? If you use tools to get your job done you can find a very good option in the use of air tools, this tools use compressed air to work.
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