In many of today’s equipments components are Surface mounted. Although I'm partially working with Electronics for the last 20 years (since my graduation in 1986), I'm not familiar with these components.

If any body can help me in this subject I’ll be highly appreciate it. My questions are as follows:

* How to identify what is what (Resistor, Diode or transistor),
* How to read their values,
* Is it possible to replace them or not,
* Can I use similar value of typical components (not surface mounted)
* Are there any resources for Surface Mounted Components technology?

Thanks for any help

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Its what your friend in Your mind, what you in your friends mind

 

identifying a surface mount component can be tricky, but once you get used to doing it, it can get easier. SMT devices come in all sorts of sizes and packages. Resistors and capacitors will come in varying sizes: 0201, 0402, 0603, 0805, 1206, 1210, etc. The number correspond to the length and the width. Small signal transistors and diodes can be packaged in SOT-23, so markings on the package may help determine what it is. Diodes can also come in two pin packages as well. Larger transistors can come in SOT223, DPAK, D2PAK and others.

Surface mount resistors can come in a number of different colors (they are not color coded, though). Many times it is black. Package sizes of 0603 and larger may have the resistance value on them. Ceramic capacitors will be a brown color and there really is no easy way of determining what they are.

Replacing them is easy - I'm sure there are tutorials around (not sure if the one on this forum cover smt)

replacing an smt with a leaded device is possible, but you will be introducing extra parasitics which may affect the circuit - depends on the circuit, of course.

 

I would add that given the proper equipment almost anything can be replaced. We regularly replace 144 pin SMTs with 0.5mm pin spacing. BGAs (Ball Grid Array) are a bit problematic from the production standpoint, never mind replacing the damned things, as they require an x-ray machine to verify the solder joints.

D.

 

Identifying SMT parts is pretty much impossible - SOT-23 can be diodes, diode arrays, transistors or even an IC (like a voltage regulator), and the only identifier is usually a 3 letter code. If you know the manufacturer, you should be able to identify the part, but there are no guarantees.

Also, the small ceramic parts can be capacitors, inductors, PTC resistors, and are obviously they are unmarked.

In short, unless you have the original BOM, you won't have much luck replacing the smaller SMT parts.

 

Hi Aljamri,

you please see www.smdin.com who supplies a book for a small price and also sells dummy components,boards and tools incuding an smd soldering station-- few trials will amke you perfect on descrete SMDs. other components our friends have already enlightened you. in addition, there is a cheap HOT AIR soldering gun which helps removals of components. for example, a chinease make SMD rework station can be obtained at around $70/- or so.

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Regards,
Sarma.

 

I recall seeing a web page where they used the air from an aquarium pump and ran it by the heating element of a soldering iron to make a hot air desoldering tool. Maybe someone has the link.

3v0

 

SO Nice an idea. we can simply adopt it to the manual 'Rubber horn' type solder sucker.
and it should work in thre reverse fashion -- blowing instead of sucking, thAT IS ALL.

But, the fish MAY have to wait FOR THEIR OXYGEN needs till we finish our desoldering work or we have to invest additionally.--

i observed that the hot air thrust coming out of a deoldering gun is approximately same as that of an aquarium pump

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Regards,
Sarma.

 

Could not find the web page I was thinking of but found these:

Based on RS desoldering tool and aquarium pump

SMT Hot Air Pencil

 

Resistors are easy to identify as they usually have a set of numbers on it. The last number refers to how many places to move the decimal. For example, a "1001" is a 10.0k, "1002" is 1.0k, "1000" is 100k, "4770" is 477k, get the pattern?

A diode will most likely have polarity marks on the bottom such as "-" and "-|" but it depends on the component.

Refer to the spec sheet of the item in question. If you need the info because you're taking old boards apart, the board is marked for the type of component. C for capacitor, D for diode, Q for transistors, etc. Most can be easily identified by Googling the part number stamped on them but as hjames mentions many parts such as capacitors are not marked.

 

As someone who just built one of these about a week ago, I'll just say "don't get your hopes up too much". Mine does melt solder, but I don't think I can desolder anything but small discretes with it - it can only manage to melt solder in a very small area, nowhere near large enough to be able to melt the solder on all the pins of an IC fast enough to be able to remove it.

I think it's a problem of insufficient temperature - the iron is designed to only get hot enough to melt solder that it touches - whereas the air coming out of it is going to cool off very quickly so it probably needs to be heated to a much higher temperature to be effective. I know the large paint-stripping-sized heat gun that I have glows red hot and heats air way hotter than the temperature of a soldering iron, and it does a great job taking off all components (though of course it's way too big to be very useful) - I haven't personally used a hot air rework station, but I would expect (based on pictures I've seen of the heating elements) that it heats the air a lot more than a these homebrew soldering-iron units.

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I am sorry to have suggested somthing that did not work.
Maybe it could be made to work with some mods? Not sure what you build so it is hard to tell. Do you have the URL for the one you constructed?

I recall that you needed to stuff the area where the air flows past the element with somthing, maybe a metal scouring pad or course steel wool. That would result in hotter air. Too little air would also be a problem. Not all aquarium pumps are, equal maybe yours is too small or not working well.

 

The article I started from:
http://www.engadget.com/2006/03/07/h...oldering-iron/
It seems to be the same as your first link - built out of a radio shack desoldering iron, the one that originally has a bulb. I did stuff the head with varying amounts of copper desoldering braid as well, and tried crimping the nozzle. I tried using just a small amount of copper braid, and also tried jamming it almost completely full, without much added success.

I also have a small valve on the air line that lets me vary the airflow from my aquarium pump. At fully open, the thing won't even melt solder - the airflow seems too much. When I close it quite a bit, the air is hotter, and it will melt solder, but again, only at a very short distance.

I do plan to do some more experimentation, and maybe I'll be able to get it to a more useful state, but based on the way it is now it would take quite a lot of improvement, rather than marginal gains.

Either way, I spent all of $11 on the iron, using an aquarium pump and tubing I already had, and I can still use the iron as a regular desoldering iron with the bulb if this falls through, so it's no great loss no matter what.

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I found the two links I posted while looking for one I had seen a while back.
It was based on a normal soldering pencile rather then a desoldering tool. Could be that they used a larger wattage iron.

It could be the page was pulled because it do not work very well.

 

could be this one you're thinking of:
http://www.instructables.com/id/E28EU7361LEV2ZAACQ/
I liked the idea, but none of the 3-4 soldering irons I had lying around (which ranged from no-brand, to radio shack brand, to weller) were hollow all the way through the heating element like the one the author had - perhaps he got lucky in that regard.

probably the most promising DIY design I've seen is:
http://www.dansworkshop.com/SMT%20Ho...20Pencil.shtml
but it's also the one that would require the most work as it's basically built from scratch, rather than being a quick mod - plus looks somewhat dangerous as the heating element is exposed and all.

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Try steel wool as opposed to the desoldering braid. I saw it on a webpage somewhere and it made a definite improvement.