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Advice for soldering wires to QFN48 (6x6)

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Mickster

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I have recently purchased one of these kits:
http://www.banggood.com/100KHz-1_7G...Radio-Frequency-Modulation-Kit-p-1120249.html

There is a link to assembly instructions, just at the bottom of the "Specifics" section. ( http://img.banggood.com/file/products/20170109215514SKU472022.pdf )

I have done most of the soldering, the caps, SMD passives, link wires etc. have been no problem, just have the transformer left to make and solder the wires to Q+ and Q-, connections 4 & 5 respectively, of the RTL2832U QFN48 6x6. The Q+ & Q- part is what I am looking for advice on.

As the QFN is so small and I do not have a stereo microscope, I imagine that I will be suffering from solder bridges when trying to make connections to this device with a soldering iron, along with moving the fine wires when trying to remove bridges. Therefore, what I am thinking of doing, is to Kapton tape the surrounding area, tin the wires and trim the ends, then tape the wires on top of the QFN with some Kapton and form the wires with tweezers so that they touch the connections, apply flux and then try to use hot air to make a joint. I have a USB microscope to aid in this process.

For those who work with such small devices on a regular basis, would you think this approach will be suitable, or can you offer a better solution. I do not have a small enough iron tip and I don't think my hand is steady enough if I did have one.

Thanks in advance.
 

Mickster

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Finally got the wires joined to the QFN!
I didn't go with the hot air route, as I didn't want the 0402's getting blown off the board and not being able to find them.
Instead, I turned down an iron tip to a needle point and re-tinned it, then persevered under a magnified desk light.
It took a few goes to get in between the QFN and what looks to be an inductor, to attach to pin 5, but that turned out to be the easy one!
Pin 4 was much harder to solder, as although I had a bit more room, it allowed Shakin' Stevens (me) to move the wire around a bit too much and end up with the wire offset to one side, or the other. This one probably took close to a dozen attempts, as it also came off a few times when cleaning with a Q-tip.

1.jpg

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Not too bad in the end.
 

dr pepper

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I built the same kit, the sdr, its pretty good for what it cost.
I did it with a standard soldering station with a fat bit, I wrapped some copper wire around the end and used that as the tip, it was bloomin hard to do but it worked, and I used a cheap head mount magnifier with both maximum mag lenses.
Its only for the brave thats for sure.
The problem with this receiver is that the lower freq input is not all that sensitive, if you listen to some, but I've found it to be really good, I get lots of stations on Vlf with a miniwhip.
Do you use Sdr# with it?
 

schmitt trigger

Well-Known Member
Mickster;
I'm totally awed at your perseverance and patience..... My sincere admiration.

I've attempted similar tricks in the past, but have never been successful. And as you mention, hot air will blow away any component 0402 and smaller.
Lead-free solder actually makes the task even harder.

But at least the component had visible terminals. Had it been a leadless package or even worse, a BGA..............then it is impossible.

Small wonder than younger engineering generations shun hardware and go for the software route.
 
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