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SOLDER-IT SILVER BEARING SOLDER PASTE - anybody use it?

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bob332

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decided on a project and a atmega328 is on the board in the 32 tqfp package. i thought i could do it, but honestly, after receiving the parts, i think a solder stencil on a hotplate (ghetto way) would net better results.

now my question is has anybody used this solder-it stuff? it is at mouser - https://www.mouser.com/ProductDetail/Wahl/7459/?qs=wT7LY0lnAe2r5UPJoeJJnQ==

i can't find a data sheet for it but have found some info online line that it is liquid @ ~385F, which doesn't seem much higher than 60/40 solder. it is cheap and thought i would give it a try if you guys think it would work. i will be monitoring the hotplate (w/ 1/4"-1/2" Al plate on top for heat distribution due to coil temp irregularities around the surface and 2 temp probes).

my thought process is that w/ this setup, it will be heated up until flow, then turned of. w/ me soldering by hand, i see multiple heating cycles clearing bridges. what says the hive?

tia,
bob
 

Rob B

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I just typed a long reply and realised that you have a TQFP and not a QFN (which I've also managed to replace by hand :)).

I would recommend draw soldering for a TQFP part. This is a subtractive soldering method where you tack the part in place with two or three blobs of solder and then flood the legs and pads with solder. With practice you can pull the solder along without leaving bridges and then remove any excess using desoldering wick.

I have replaced various TSOPs and even TQFP208 at 0.5mm pitch but it requires a bit practice. Find some old scrap boards to try it on.

You may find that placing the component by hand would cause the paste to smudge. I think using your method is definitely possible but it is not too difficult to do it using solder wire and desoldering wick.
 

    bob332

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dksoba

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I solder TQFP packages by hand all the time. Yes, the draw soldering method is the way to go. Also make sure that your tip is sufficiently large. IDK why but this method doesn't work well with a fine tip for me. MOST IMPORTANTLY, make sure to use a good flux on the pcb pads and on the pins. I can't stress how important this is. Lastly, use as little solder as possible to avoid bridges. With a bit of practice, you can solder these no problem w/out bridges. If you do get bridges, just use solder wick to wick off excessive solder.

Of course, investing time/effort into a solder paste/hot plate method might be better in the long run if you want to solder leadless packages.

By the way, I use flux pens that were given to me. Can anyone recommend a good flux, especially one that is easy to clean off?

Matt
 

    bob332

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Rob B

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I usually use a Chemtronix CW8100 flux pen.

Surgical Spirit (Rubbing Alcohol) is good for cleaning most fluxes including the ones commonly found in solder wires. It evaporates slowly giving you plenty of time to get the residue off.
 

    bob332

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