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Hand soldering a 28 pin, 6x6mm QFN

rjenkinsgb

Well-Known Member
Most Helpful Member
Not totally impossible, but not something to do on a regular basis!

I'd dab the underside of the pins with a trace of solder paste to assist heat transfer and solder flow - just enough to leave a fine coating, without bridging the pins, so you can still get the alignment to the PCB pads spot on before applying any heat.

The hardest part is trying to get enough heat through to the PCB tracks without cooking the chip itself; once the joints have flowed, removing the excess is not too bad.

Then go over it with a good light source and magnifying glass to check for any failed joints or tiny bridges.
 

narkeleptk

Active Member
I wouldn't worry to much about cooking the chip, I tin them a little like rjenkinsgb suggests and then just use hot air to place them most of the time. Works well enough for me. Even if just using an iron its not bad at all. If your designing your own boards for it give yourself a little extra pad length and you won't have any issue's at all.
 

granddad

Active Member
I have done a 100 pin TQFP with 0.4mm spacing, onto a breakout board , you need fine solder, fine tip ( o.5 mm ) , I used a flux pen on pads also . tack corners then do each side. probably need to secure the chip somehow..
 

nsaspook

Well-Known Member
Most Helpful Member
Easy with the right tools. Flux and tin the pads. Use a magnifying glass or camera to align the chip. Tack the corners with a very fine tip iron and solder, complete the job if the alignment stays good.
IMG_20190414_075927985.jpgIMG_20190610_152119854.jpg
 

DrG

Active Member
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?

Page 654 of the datasheet…
This caused me to think...not about whether it was possible, but rather, could I do it?

I looked up the pad width for the land pattern and it is .37 mm - right?

I did this 24-pin SSOP with the same (or similar) land pattern width over three years ago - I was really proud. I took a long time and I was dragging beautifully - did not have to use any braid at all!
119487

Advance the clock to a couple of months ago and I did this one and made a mess of it! I had to use braid and I was very frustrated. Granted, I did not have the thinner solder as with the first time (I rectified that). Well, it worked, eventually, but ugh.

119489

In both cases I used magnifiers (like this one).

I have one more like this to do and I hope I am as neat as with the first one.

So, could I do it - yes, I think I could IF I was using a breakout board as shown here with those nice long pads. If it were on a circuit board proper, maybe not.
 

DrG

Active Member
DrG, looks like you need more flux and maybe turn your heat up a little (or clean your irons tip)

here is a 9s12 LQFP144 I just did last night
View attachment 119492
My hat is off to you...you could add "younger eyes and hands" to the list as well. More seriously, I always worry about lifting pads with higher heat. Moreover, and frankly, I would simply not attempt what you are showing there....maybe with a hot air gun and paste like is used in those home-made toaster-oven SMT board makers...but that is "on the list". For now, I was successful in both tries...that will have to do...for now ;)
 

narkeleptk

Active Member
I used to could do these with out magnification but not as well anymore. I use a setup similar to spooks with a 20x-100x scope.
I like to solder hot and quick. Usually around 320-360c. Long as you don't spend to much time in one area you shouldn't hurt anything.

Pick up a cheap hot air rework station. You can get ones at around $50 that work just fine for light duty/hobby work. Your second photo would have cleaned up beautifully with a little reflow using flux and hot air.
 

DrG

Active Member
I used to could do these with out magnification but not as well anymore. I use a setup similar to spooks with a 20x-100x scope.
I like to solder hot and quick. Usually around 320-360c. Long as you don't spend to much time in one area you shouldn't hurt anything.

Pick up a cheap hot air rework station. You can get ones at around $50 that work just fine for light duty/hobby work. Your second photo would have cleaned up beautifully with a little reflow using flux and hot air.
Yeah, I have something like this https://www.amazon.com/F2C-853d-Supply-Soldering-Station/dp/B018LFTWTK/ref=asc_df_B018LFTWTK/?tag=hyprod-20&linkCode=df0&hvadid=312128028232&hvpos=1o1&hvnetw=g&hvrand=18161481416376117201&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007812&hvtargid=pla-571443016695&psc=1 and yes, it is quite cheap (I think there is an old trashing review on this site for a similar or earlier unit). So far, I have only used the hot air for de-soldering components from old boards.

As far as the second photo and cleaning up...I mention this because reading what you wrote, reflexively, I was thinking..yeah let me take the hot air to it...and then I thought &^%$ no. It works and has been working just fine. I always inspect the solder connections with a jeweler loup and I don't want or need to mess with it at this point...but it is good to know. I have some 8-pin SOIC chips and similar carrier boards and I may try the hot air with some low-temp solder paste - I have a syringe around here somewhere.

I am happy with the magnifying lens' that I linked to and would recommend them., they are surprisingly comfortable although they have a limited focal length which is adjustable a bit. I am used to wearing glasses or goggles while soldering and they don't bother me at all.

All-in all, I think it is a pretty good thread, especially for the OP. There is already a range of responses and, most importantly, they include actual experiences...and of course, practice with techniques and so on is an important aspect. -Thanks
 

DrG

Active Member
Do you have one? What's the mag power? Cost? I'm always interested in upgrades. Philosophically, I am often torn between - start cheap until I have proven to myself that I have earned a better one (IOW I know how to use it and I am using it) and - get the best quality tool you can afford because it will turn out to be the best value.
 

granddad

Active Member
I found , solder braid ( mop ) essential to remove excess solder and bridges .. I have a desk mounted magnifier and lamp ... on 4 sided chips after a corner tack I do one side at a time , and wait till chip cools, i dont have a temperature controlled iron just a Antex 12 watt ... with .5mm point
 

ronsimpson

Well-Known Member
Most Helpful Member
Do you have one? What's the mag power? Cost?
What I have is toooo much money and very old. I like that I can have the magnifier up out of the way then by shaking my head the glass falls down over my eyes. My problem is that it takes one hand for the solder, one hand for the iron, one hand for the solder wick, I hold the part down on the board with my tail, then just as I get near the part I need to hold the magnifier glass. All slightly above my pay grade.
 

Flyback

Well-Known Member
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?
 

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