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SMD at home
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SiliconWizard:

--- Quote from: tautech on April 15, 2019, 04:27:56 am ---There's a bit of good info in this thread:
https://www.eevblog.com/forum/beginners/so-surface-mount-it-is/

This vid from member paulca impressed me:

https://youtu.be/rgcupYOnvBo

--- End quote ---

Yeah, this is cute but it won't work for fine-pitch parts, especially when there is no solder mask between the pads. Of course 1.27mm pitch will be no problem. Many low-cost PCB manufacturers don't have the ability to add soldermask between pads for pitches <= 0.4mm, or sometimes even <= 0.5mm (and quite a few not-so-low-cost ones)... and those that can, this is often a costly option. So just take a look at your PCBs with a microscope and see for yourself. No soldermask between pads is a recipe for solder bridges unless you have managed to dispense just the right amount of solder paste on each pad. Doing that manually is difficult. And even so, you may get occasional bridges.

As to hot air... yes due to local turbulences (just consider what happens when you blow air onto a surface), very small/light parts will tend to move around, even at the lowest air flow settings. Pure hell. Pre-heating the board will help, but I really suggest using a reflow oven if you're gonna deal with very small parts.

I recently had to hand-solder UDFN-6 parts (0.4mm pitch, 1.2x1.0mm case) and it was no fun, even if there were only 6 pins. :-DD
Finally managed to do it, but I tried different approaches. I didn't manage to get the hot air approach right. It was atrocious. The parts were either blown away outright, or if not, tended to "surf" onto the flux (and thus get misaligned) before the solder balls had a chance to reflow. I eventually did it with a soldering iron (JBC 210) and a very small chisel tip (one of the smallest I think). And since the pads were designed for reflow assembly, they were not quite long enough to get reasonable access for hand soldering, so that was really no fun. (Had to do it quick and had no access to a reflow oven at the time.)

mayor:
OK, so it's not just me :-)

I have an IR toaster oven, but never finished a reflow controller project. For home stuff, do any of you eyeball it ? I could stick a thermocouple in there and be the controller!
Psi:

--- Quote from: mayor on April 15, 2019, 02:19:56 pm ---I did wonder about how much pressure to apply when putting the parts on. So it sounds like just a bit of pressure, then. Maybe I've been pushing them down too hard.

--- End quote ---

It's more important to push them down when you have applied paste with a syringe and have a blob on the pad.
If using a stencil the paste coating is usually thin enough that you don't have to push down much.
Pushing down a little is good because it makes more contact between the part and the paste and locks it into a depression in the paste.  This makes it less likely to tombstone or 90deg rotate during reflow.


For getting the stencil flat on the pcb i usually trap unpasted pcbs around the one to be pasted. Like 0-9 on your numeric keypad where 5 is the one to be pasted.
If the blank pcbs are the same design and were manufactured at the same time they will be exactly the same thickness and give a perfectly flat surface to use.
pix3l:
You could also try using a thinner stainless stencil in order to get less solder paste on the pads. For example PCBWay has four different thicknesses (0.1 , 0.12 , 0.15 and 0.2 mm).
Kjelt:

--- Quote from: pix3l on April 16, 2019, 06:34:26 am ---You could also try using a thinner stainless stencil in order to get less solder paste on the pads. For example PCBWay has four different thicknesses (0.1 , 0.12 , 0.15 and 0.2 mm).

--- End quote ---
The possible problem with that choice is that you can get too little paste on the normal component pads.
So in order to facilitate the few  "problem" components you take a chance of creating issues with the majority of normal components.

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