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SMD soldering techniques? 
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QFP80 - Contributor

Joined: Fri Jun 14, 2013 12:49 am
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Location: Gibsons, BC Canada
Is there a consensus on the best way for DIY SMD soldering? I'm OK with through hole but my old eyes are getting dim so rather than a magnifying glass and shaky fingers I'd probably be better off to build a reflow oven.

Opinions?

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Mon Sep 09, 2013 5:18 pm
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Flood and soak up works pretty well if you're careful and don't cook things. FTDI is dangerous to do like this, high thermal conductivity from legs to silicone. Burns easily. Per pin with a fine tip and fine solder works too.

An existing forum link: viewtopic.php?f=24&t=166

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Mon Sep 09, 2013 5:44 pm
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LQFP112 - Up with the play

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Load and drag method. Tack opposing corners down, then Liquid flux entire row of pins and load up solder on tip of iron. Then you drag tip over pins at a rate that only you can determine, maybe 1/8 inch per Second. You want an equal amount deposited on each pad, the flux is the key. You can do maybe 10-15 pins at a time with this method depending on how much you can load up on iron. Use a tip thats broad enough To provide the heat, not pencil sharp but more like a chisel Tip. This is for fine pitch chips, smt components like resistors and caps need a 45 degree tip (well, more like a 90 as in 2 45's) so as to contact the pad and the end of the component at the same time, then touch some .020 solder to it and bam, your done. Smt is fast fab, just make sure you got magnification or loupe, very fine solder, liquid flux and a smallish tip.

This is great vid on processes.
http://www.google.com/url?sa=t&rct=j&q= ... 3540,d.cGE


Mon Sep 09, 2013 9:36 pm
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my flood and soak = your load and drag.

I do it without flux, just feeding in rosin core at the right rate. But yes, tack the corners first either way.

+1 on big tip for this. I use a fine pointy tip for other parts using the end of it as one of the surfaces in your 45/45 setup.

Cheers for input :-)

Fred.

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Mon Sep 09, 2013 11:46 pm
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TO220 - Visibile

Joined: Mon May 30, 2011 5:59 am
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Best way i have found is just using some solder paste and paste all the pads individually if they are big enough, or if you do small stuff, lay a thin bead across the pads of the IC. Then place the component on top, making sure the legs touch the solder paste on the pads. Align it to a reasonable standard (the bigger the chip the better the alignment must be) and the use a hot air gun to reflow it instead of an oven (if you dont have an oven or are just doing a few bits and dont wanna oven everything)
If the component is small enough (like an 0805 resistor, SOT23 or even a soic8) it will pull the component straight when the solder paste reflows between the pad and pin. Big components like 40+ pin ICs are a little harder to evenly heat up and often wont pull straight at all so the initial alignment is quite important.

Use the correct size tip on the solder paste syringe though to get the right amount of paste. If the paste is a bit thick and its hard to get a nice even amount on the pads, blow some hot air onto the board before placing the paste and component. This will let the paste flow nicely as it gets less viscous when warm and will spread quite nicely and evenly.

If you dont have a hot air gun, you can touch the pads/pins/paste with a fine tipped iron as well. I like it better than the load and drag/flood and soak methods as the finish is much cleaner.

If you do a lot of this, getting a cheap solder paste dispenser from ali-express or something isnt a bad idea.


Wed Sep 18, 2013 1:32 am
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Joined: Wed Nov 11, 2015 8:31 am
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Recently, I started designing a PCB that has lots of LEDs, lots of rotary encoders, and lots of outputs to relays. Trying to pack this board with through-hole components like resistors and transistors was challenging and resulted in having to increase the board size larger than I would have liked. The increased area of the board also drove the cost of the board up, very high. If only there was a way to make the board smaller, but still get the functionality that I needed. But of course! Use surface mount components. Surface Mount Devices (SMD) are very small and take up less space! I had never considered using surface mount components before, but since I had the resources available to do so, the time had come to learn.

There was still one problem though, how to solder the SMD components. I didn't want to have to solder each component on by hand. That would be very tedious and time consuming. I needed to be able to apply solder paste quickly and easily. I needed a stencil. At [my company], we use metal stencils. They are strong and last for thousands of builds. They're expensive though. Not very practical for building one or two boards. Especially if they are prototypes and their design could change.


Last edited by Fred on Fri Jan 29, 2016 9:38 pm, edited 1 time in total.

Suspected spam, replaced URL with "my company" and let go.



Wed Nov 11, 2015 9:02 am
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