[time-nuts] soldering QFN (was: GPS down converter question)

[paul swed]

Attila sorry flipped some letters.

On Thu, Dec 3, 2015 at 10:06 AM, paul swed <paulswedb at gmail.com> wrote:

> Atilla,
> Thanks you have read what I have written and further your experience
> aligns with mine for hacking these chips at least into the GHz range. I
> suspect it really falls apart in the 2-3 GHz and above region. But I have
> built a lot in the 1.296 GHz region so have that experience at least.
> Regards
> Paul
> WB8TSL
>
> On Thu, Dec 3, 2015 at 5:34 AM, Attila Kinali <attila at kinali.ch> wrote:
>
>> Salut,
>>
>> On Wed, 2 Dec 2015 18:39:55 -0500
>> paul swed <paulswedb at gmail.com> wrote:
>>
>> > Just adding that this is home brew so no real boards. At the IF level
>> thats
>> > both large enough and easy enough to add to a ground plane. So its
>> > reasonable to build the basics and add stuff as needed.
>> > The LNA front end is cheap so will get that just to try. Have to look at
>> > the hot air suggested above to see what that might cost.
>>
>> The Leister one costs IIRC 300-400EUR. I.e. not the thing you'd buy
>> for a single project. There might be cheaper ones though. All you
>> need is something that is small enough that you can confortably
>> fit into your hand, has a small nozzle and temperature control between
>> 200°C and >400°C.
>>
>> But if you are not building a board anyways, there is an even "simpler"
>> way to go: Dead-Bug! :-)
>> For 0.5mm QFN/DFN i usually use AWG30 wirewrap wire or 0.08mm^2 tinned
>> copper wire. Enamelled wire should work too, but I am generally to lazy to
>> tin the tips and make sure that no blobs of enamel residue were left on
>> the wire. The way to ensure that you dont get any shorts is to spread the
>> wires out, such they gain enough distance. As you will be soldering RF
>> chips,
>> which have a ground pad in the center that needs to be soldered, i
>> recommend
>> using solder wick. Use 2 wide strips and solder them first (before any of
>> the pads) onto the ground pad, such that they point to opposide
>> directions.
>> Make sure you do get solder on more of the wick than necessary. After
>> you have finished all the pads, solder the wicks to your groundplane at an
>> as short distance as possible.
>>
>> This is of course not optimal, but the inductance of the wick should be
>> small enough, thanks to the width and the braiding. And you have the
>> advantage
>> that you can rework if something doesn't work out.
>>
>> As for equpiment, you will need a soldering iron with an as fine tip as
>> possible
>> (0.5mm is absolute maximum, 0.3mm is what you should get, if you can get a
>> smaller one, take that one). 0.3mm solder (use leaded, it's easier to
>> work with).
>> I do not recommend using thinner solder. With those the core gets so tin
>> that
>> you dont get enough flux. Oh.. and be carefull about stretching the
>> solder wire.
>> The metal part can be stretched quite easily with such thin wires, but
>> the core
>> doesn't. So if you get this speckled look, cut of that part with some fine
>> side cutting pliers. You will also need at least some kind of optics with
>> an
>> magnification in the range of 10 to 20 to check the solder joints. It
>> would
>> be best if you had access to a stereo microscope (with an 10-20
>> magnification)
>> but if you have good eyes you can do without and instead using some
>> magnifing
>> glass (i recommend line tester/weaver's glass) to see whether the joint is
>> ok and doesn't have any shorts.
>>
>> HTH
>>
>>                                 Attila Kinali
>> --
>> It is upon moral qualities that a society is ultimately founded. All
>> the prosperity and technological sophistication in the world is of no
>> use without that foundation.
>>                  -- Miss Matheson, The Diamond Age, Neil Stephenson
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>