Heat Gun/Solder PAste SMD soldering

[Govmnt_Lacky]

Does anyone have a good tutorial or know of a good video of the process using a heat gun (NOT a hot air reflow station) and solder paste to do SMD work?

I know some of you on here have the experience. Just trying to find out who. I have the paste and an adjustable Stinel heat gun ready to go. 

I only have 1 PCB though and don't want to ruin it with my SMD noob-ness. 

[m-Kresol]

Hi Greg,
there are tons of videos on youtube, I saw that one and a few others before doing the nomojo fuzz:

Anyhow, it is easier than it looks. You'll need good tweezers and most likely have to use some kind of magnification. I used a regular heat gun with a 4 cm wide nozzle, so it really works with very crude tools too. The only problem I had is that one of the resistors flew away never to be seen again.
Good luck

[selfdestroyer]

I found this really interesting also, its for a SMD toaster over but the temps and times will work for a heat gun also.

This is the solder profile for the Easy Profile 256 paste:


Taken from http://www.openhardware.net/Misc_Stuff/ToasterSMD/

Cody

[alanp]

Hi Greg,
there are tons of videos on youtube, I saw that one and a few others before doing the nomojo fuzz:

That was really interesting -- this works with normal heat guns, not just SMD soldering stations? I tried it once with normal, solid solder and my heatgun, and the parts went flying off, never to be seen again.

Video was kinda funny -- "you want not too much, or too little", proceeds to slather luvverly huge gobs over the IC pads... that man needs tweezers and a toothpick.

[wgc]

Got your PM, very glad to see someone else taking a crack at this!

I actually don't recommend using a heat gun, but that said, it should work.  (You might try an old frying pan on the stove and an infrared thermometer if you want a little more control.)   Can't really beat reflow in a calibrated oven with computer control though.  But I just use an iron these days.  I still have on my to-do list a demo video, didn't watch the one posted yet.  Chuckbuick did an awesome write up not too long ago too.

You're looking for something around 400F, much like the graph posted by Cody. 

The problem with a heat gun and a hot air station for that matter is that you can't really control the ramp, soak, and reflow times and temps.  It will happen to some extent naturally, but I do see a lot of partially reflowed solder joints by people using hot air.  Not the end of the world, you can always touch up later.

Anyway, your problem is finding the right balance of air flow, temp, dwell, and distance. 

• Too much air, you blow your parts off the pcb before the solder flows.


• Too much heat, you can delaminate the pcb (double sided should still be ok, but if there's lots of vias you might have wrecked the pcb).  Or wreck an ic.


• Too far or too close, and you change the amount of air and/or heat.

A secondary problem is getting the right amount of solder paste on the pads.  You'll probably need less than you think, a diy stencil will work wonders.

You can practice on some copper clad pcb for etching with some extra resistors and some paste before you do the real thing on a pcb.  Don't worry too much about getting it perfect, you don't even need pads. 

You just want to get a feel for how long, how hot, how far you need to be with your heat gun.  If you don't have any copper clad, you can use a piece of glass or something relatively flat and flame proof.

You also want to be sure to keep the gun moving and not stay in one place for more than 10-15 seconds.  I move the air around in small circles about 1-2" in diameter, center outwards, without concentrating too much on one area but not moving away from it so fast that it cools off too much.  This movement helps prevent delamination and shocking your parts.  If you feel like you need to hover for longer than that, then you need to adjust at least one of your other three variables.  If you are reflowing quicker than that, then you need to move a little farther away.

With a little practice, you can find what works best for you, but really, don't sweat it too much.  Almost anything can be fixed or reworked, and you might be surprised at how easy it is.

Good luck, and send a pm if you need more info.  Looking forward to seeing a great build report!

[Govmnt_Lacky]

Thanks for the inputs, tips, and videos 

I'll be using a Stinel heat gun and MG Chemicals Leaded solder paste. I suppose I can try out some temp and distance checking on a piece of copper clad.

@wgc

I have read about using a frying pan for reflow. I can grasp the process however, the only question I have is how the PCB is placed in the pan itself? Wouldn't it burn/melt/etc. if it was placed directly on the pan bottom?

[rullywowr]

Thanks for the inputs, tips, and videos 

I'll be using a Stinel heat gun and MG Chemicals Leaded solder paste. I suppose I can try out some temp and distance checking on a piece of copper clad.

@wgc

I have read about using a frying pan for reflow. I can grasp the process however, the only question I have is how the PCB is placed in the pan itself? Wouldn't it burn/melt/etc. if it was placed directly on the pan bottom?

I use an electric skillet.  Just make sure you don't use it for pancakes later    Sparkfun dubs the process a "reflow skillet".  By far this is my favorite way to do SMD.
LINK:  https://www.sparkfun.com/tutorials/59

With a skillet you increase productivity pretty nicely.  With a skillet, panelized boards, and a stencil...the sky is the limit.  You basically are running a pick and place machine with you being the pick and place. 

The PCB doesn't melt...as the FR4 itself is heat resistant and so is the solder mask.  Check out the tutorial and there are plenty vids on the subject on youtube.

I agree... a regular hot air gun will "work" but it's hard to control the temp, parts can blow off the board, and its is very possible to roast a component or PCB in a bad way.

[Leevibe]

Thanks for the inputs, tips, and videos 

I'll be using a Stinel heat gun and MG Chemicals Leaded solder paste. I suppose I can try out some temp and distance checking on a piece of copper clad.

@wgc

I have read about using a frying pan for reflow. I can grasp the process however, the only question I have is how the PCB is placed in the pan itself? Wouldn't it burn/melt/etc. if it was placed directly on the pan bottom?

I use an electric skillet.  Just make sure you don't use it for pancakes later    Sparkfun dubs the process a "reflow skillet".  By far this is my favorite way to do SMD.
LINK:  https://www.sparkfun.com/tutorials/59

With a skillet you increase productivity pretty nicely.  With a skillet, panelized boards, and a stencil...the sky is the limit.  You basically are running a pick and place machine with you being the pick and place. 

The PCB doesn't melt...as the FR4 itself is heat resistant and so is the solder mask.  Check out the tutorial and there are plenty vids on the subject on youtube.

I agree... a regular hot air gun will "work" but it's hard to control the temp, parts can blow off the board, and its is very possible to roast a component or PCB in a bad way.

Now THIS gets me interested in SMT

[Govmnt_Lacky]

@Ben

Now THAT is awesome! I always heard of using a skillet or hot plate but wondered what would happen to the PCB is placed directly on it. I guess it will survive huh 

Looks like I need to start looking for a secondhand hot plate/skillet! 

They mention using Kester solder paste. I will be using MG Chemicals leaded paste. Shouldn't be much of a difference right?

[pickdropper]

I've always preferred the Kester paste but I assume that the MG should work fine (but check the data sheet for reflow info).

It's important to know that solder paste does have a shelf life.  We use it for prototyping at work and the stuff we use is less effective after about 6 months.  You can bring it back a little bit by adding liquid flux to it, but it's not quite the same (but usually still works).  Also, store it in the freezer when not in use.

[davent]

I have read about using a frying pan for reflow. I can grasp the process however, the only question I have is how the PCB is placed in the pan itself? Wouldn't it burn/melt/etc. if it was placed directly on the pan bottom?

To test acrylic painting of pcb's to see what would happen to the paint in contact with an overheating component i took a torch to the painted boards, boards were unscathed, paint job not so much.

[Govmnt_Lacky]

To test acrylic painting of pcb's to see what would happen to the paint in contact with an overheating component i took a torch to the painted boards, boards were unscathed, paint job not so much.

Yes but... did that board have soldermasked trace runs and vias? I am more worried about damaged traces, vias lifting, or solder mask melting 

[davent]

I was solely addressing your stated concern with the burning/melting/etc. of the pcb in direct contact with the pan.
dave

[Govmnt_Lacky]

If I am going to be using a new PCB... and clean the pads... Would I need to use flux on each pad prior to laying down the solder paste OR can I just put the paste down on the pads and start placing components?

[m-Kresol]

I didn't add any additional flux to the pads myself. Just the paste and adding the components worked just fine