Hi,
I am looking to work with 4fans but I'dd like to deport the regulation of the fans outside of the arduino. I have found a great component (MAX6620) to perform the task that fit exactly my needs, but unluckily it only exist in TQFN package :'(.
the question is: is there a realistical (pricewise) solution to use chips like that? (I know there's some zif socket, but they seems to worth around 200$ a piece making it totally useless...) something like a site where you can order for not so much a breakboard with such chips soldered for a correct price?
If you're comforable soldering a tqfp, there are generic tqfp breakout boards (example), but they all seem to be surprisingly expensive. It would be significantly cheaper to throw one together in Eagle and have BatchPCB make it for you.
Edit: oops, misread.
Yeah, qfn is more difficult. This was the best I could find: Reverse Surface Mounting of Small Leadless SMT Components – Starlino Electronics
hum, nice way to mount QFN... but I feel that soldering a 28 terminal chip like that will be hard... better go for a custom pcb and try one of the oven methods... it looks dangerous but still easier... wasn't aware of batchPCB, nice site, i'll maybe consider building a pcb for this, i'll also be able to place the driving transistor and the few other component on it...
check out Silvtronics. They make pcbs and they also sell breakout boards for various smt parts. The breakout boards price from $5 onwards.
A hotplate is easy to setup and works quite well.
You can solder these by hand if you create a custom footprint for your PCB. I made a handsoldering footprint for QFNs that extends the copper land pattern about 30mils from the standard. This gave me enough room to hand solder with a 20mil soldering iron tip.
(* jcl *)
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I'm doing a SMT prototype with tqfp-100/48 and SOIC packages using adapters that is going OK. Futurelec, NKC Electroinics and Dipmicro have cheap adapers. But the TQFN part is another story. Show us your custom adapter layout
@bruceKG I am not sure if the question was addressed to me -- My custom QFN footprint (actually was an SON) just extended the length of the mfg recommended pads by 30mils. This enabled me to have enough length beyond the body to hand solder with a 20mil tip. The alignment is a little tricky.
(* jcl *)
www: http://www.wiblocks.com
twitter: http://twitter.com/wiblocks
blog: http://luciani.org
Get a good magnifying glass. Very fine copper wire, desoldering braid, precision tweezers and some flux core solder.
Roll over the package to the pin side
place the wire on a pin and use the soldering iron to solder the fine copper wire to the pin. At Repeat this for all pins.
If any are joined then get your desoldering braid and clean the joins up.
After your done get some hot glue and glue the under side of the chip. This will stop any Crossover during mounting.
Make Copper tracks and your done.
Not the neatest way but it is the cheapest.
place the wire on a pin and use the soldering iron to solder the fine copper wire to the pin. At Repeat this for all pins.
I tried this method on an QT100A SON device and the pads were so small they
lifted off the IC body 
I ended up re-spinning the board with a different footprint
and soldering from the top.
(* jcl *)
Typical of MAXIM not to cater to the hobbyist. All of their packages tend to be as small as they can make them and only for industrial use.
TQFN is usually referred to as simply QFN. Some companies such as Atmel call it MLF. Before tackling QFN you should be comfortable with at least 0.65mm or better 0.5mm pitch parts such as TSOP or TQFP 0.5mm.
I use the QFN version of the FT232R in my om328p Arduino compatible and initially approached the idea with some trepidation.
The key for me was to use a hot air station and an appropriate PCB with solder stop masks. I got a cheap hot air station for $99. It has also been useful for other projects where I needed to desolder SMD parts.
The process I use is as follows:
- Flux the pads
- Put some additional solder on each of the tiny pads on the board
- Put the QFN part on top its pads as best as you can. It may sit at an angle and not quite fit but that doesn't matter.
- Heat up the part and the board with the hot air station. This gives control of the amount of heat and direction.
- The solder melts and the part drops down nicely onto the pads. You can gently push the part around on the molten solder and it jump back into position because of surface tension. You can push it from each direction to make sure it is sitting squarely on the pads.
- If you need to solder the center pad I usually go back and do that from the other side using a hole that I specifically designed into the PCB.
My success rate has been 100%. If the part doesn't work you can always lift it using the hot air station and start over.
Note that the default Eagle parts for QFN do not meet the BatchPCB 8/8 mil requirement. This can be fixed by editing the part and making the pads slightly smaller.
I'm doing QFN32 with a toaster oven, solder paste, flux, and a fat tip radio shack iron with great success! Frankly I was a bit scared of SMT but now I think that all hobbiests should get into it to take advantage of the great parts available, and the price advantages of having small boards. For example, I put the AVR cpu core (328, clock, voltage reg and assorted caps, resistors and leds) on a section of a board that was about half the size of my thumb.
Here I'm blogging about it.
My iron tip is about the size of 6 pins; I never try to solder individual pins.