Hand soldering a 28 pin, 6x6mm QFN

[ronsimpson]

I think we will just have to end up trying to solder it without soldering the centre pad

I use a oven to heat up the entire board at one time. The center pad will solder well that way. I payed $5.00 at the used appliance store for the oven. It takes about 10 minutes to solder a board. Bring up the temp slowly and watch the heat level.

 

[narkeleptk]

Hot air-gunning i think is best if you actually aim it at the dead centre of the chip and try and "burn" it on through to the tinned solder pads?

I usually use a circular motion around the outside of chip (nozzle pointed in ward a little) instead of dead center. Might help to slowly heat the pcb a little first and then place the ic. If you tin it lightly and flux it well it will probably pull itself into alignment as long as you place it pretty close.

 

[granddad]

Louis Rossmann , ( utube) uses a heat gun on these chips ..( and bad language !!! ). and gallons of flux..but think it takes some practice..

 

[kubeek]

Hi,
Thanks for all these great replies, I think we will just have to end up trying to solder it without soldering the centre pad, as some of the small pads of the QFN achieve a ground connection anyway.

The footprint pads emerge 0.3mm outside the QFN body outline all the way round.

We have got a hot plate but I am not convinced a great deal of heat will conduct through the 4 layer FR4 PCB. Some other components on the top side are already placed, as we needed to run the board manually (without the micro) first.

Hot air-gunning i think is best if you actually aim it at the dead centre of the chip and try and "burn" it on through to the tinned solder pads?

The usual way is to preheat the board to around 100-120°C, use some solder paste on the pads and the power pad, then use hot air to get the solder flowing. After it melts and the IC is positioned correctly, I use a tweezer to push the part to be flush with the board. Let it solidify, wick away excess solder, and reheat with air and additional jelly flux to finish the soldering and/or correct any shift.

 

[Flyback]

Thanks, and i like the idea of the bella oven to actually do a reflow , having stencilled in a solder flux pattern on the footprint.
This video seems to encapsulate what the kind contributors here have said....

i wish he had said what he cleans the burnt up flux off with.....i always use IPA but dont know if its best.
I like the look of that "clear jelly" type flux he uses.....i have no idea where you buy that....(any ideas appreciated)
It seems that "water soluble" and "no-clean" flux's arent very good...it has to be the "rosin" type flux(?)

Also, i reckon we will need to clean up quite a bit, as i am anticipating ruining about 5 or 6 QFN chips before i get this right.

We will put kapton over surrounding components so they dont melt off.
The video says we can just leave off doing the center pad so we will not solder the centre pad.

 

[tvtech]

This really works!
View attachment 119502

We had a guy here many years ago. The guy that got himself fired for beating up a fellow worker.

He used to love walking around town with this thing on his head lol.

Hahaha.....locals thought he was a Professor of TV'S lol.

 

[narkeleptk]

i wish he had said what he cleans the burnt up flux off with.....i always use IPA but dont know if its best.
I like the look of that "clear jelly" type flux he uses.....i have no idea where you buy that....(any ideas appreciated)
It seems that "water soluble" and "no-clean" flux's arent very good...it has to be the "rosin" type flux(?)

I just use IPA as well to clean. As for flux itself I do not care much for the paste types and prefer liquid fluxes. My favorite one is kester 959t. Its meant for wave soldering but it works good for rework and is very clean. Its alcohol based and uses a small % of rosin. If that ones not working then I use kester 186 which is a bit messy and needs cleaning. There is a guy on ebay "joelouis2000" who sells small quantities (and does not dilute them) if you don't need a lot or want to test it out.

here is the 959t, you can easily clean up with ipa and a brush usually if even needed.

 

[hyedenny]

Hi
Do you think its possible to hand solder the 28 pin , 6x6mm QFN version of the PIC16F18856 by hand soldering? Eg…dragging solder along the pins, then mopping the excess up with braid?

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• #29

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I've done it a bunch of times. The secret is to use plenty of good flux, good quality solder, and a soldering pencil at the CORRECT temperature. You shouldn't even have to use braid to clean it up. There are many demonstrations on YouTube.

 

[hyedenny]

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EDIT -- Sorry, double post!