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How does surface mount soldering even work?
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How does surface mount soldering even work?

by Ben321 on Mon Jul 01, 2019 7:56 am

I've seen modern boards with lots of SMT components, but how are these soldered? There are no pins or leads coming out of the components to go through holes to keep them in place on the board while you touch the soldering iron to them. And I know that to get good heat transfer for a soldering iron, you need to definitely apply some pressure. That will work with through-hole components, but any SMT component will be instantly pushed off of the solder pads that you were trying to solder it to. How is it even possible for SMT components to be soldered? It seems like magic.

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Re: How does surface mount soldering even work?

by adafruit_support_bill on Mon Jul 01, 2019 8:54 am

Solder paste is screened onto the solder pads of the boards with a stencil: https://blog.adafruit.com/2019/06/10/ho ... day-video/
Components are placed robotically in the 'pick and place' machine: https://blog.adafruit.com/2016/04/25/pi ... ingmonday/
Then it all goes into a reflow oven which melts the solder paste: https://blog.adafruit.com/2013/02/08/sc ... flow-oven/

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Re: How does surface mount soldering even work?

by Ben321 on Mon Jul 01, 2019 5:47 pm

adafruit_support_bill wrote:Solder paste is screened onto the solder pads of the boards with a stencil: https://blog.adafruit.com/2019/06/10/ho ... day-video/
Components are placed robotically in the 'pick and place' machine: https://blog.adafruit.com/2016/04/25/pi ... ingmonday/
Then it all goes into a reflow oven which melts the solder paste: https://blog.adafruit.com/2013/02/08/sc ... flow-oven/


Doesn't the heat of being in an oven damage the components? I mean when you solder, you try to just heat the leads of the components, with normal components at least.
And also that sounds like you are describing an industrial process. How do hobbyists solder with SMT components? Since more and more components are SMT now, and fewer and fewer are through-hole components, it seems that hobbyists are probably finding ways now to solder SMT components. What kind of techniques would a hobbyist use though, since they don't have access to industrial equipment (nor would all that stuff fit in a normal house, as it is normally large enough to need a whole factory building).

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Re: How does surface mount soldering even work?

by adafruit_support_bill on Mon Jul 01, 2019 6:15 pm

Doesn't the heat of being in an oven damage the components?

Overheating will damage components, so oven temperatures do need to be controlled. If you study the datasheet for any SMT component, there will be recommended heating profiles for reflow soldering.

How do hobbyists solder with SMT components?

Mostly with hot-plates or hacked toaster ovens.
https://blog.adafruit.com/2011/11/14/ha ... soldering/
https://blog.adafruit.com/2012/05/02/di ... flow-oven/
https://blog.adafruit.com/2009/03/09/so ... rying-pan/

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Re: How does surface mount soldering even work?

by adafruit_support_mike on Tue Jul 02, 2019 12:34 am

It's also possible to solder SMT parts by hand. I build most of my prototype circuits that way.

SOIC chip packages (20 pins per inch) aren't much harder to solder than DIPs (10 pins per inch), and 0805 passive components (0.080" by 0.050") have roughly the same pad spacing as though-hole capacitors. There are some tricks to holding things in place long enough to make the first solder joint, but they aren't hard to learn.

Once you've gotten comfortable with those, you start wondering if you can handle chips in SSOP packages (40 pins per inch) and 0603 components. In general, the answer is yes. Keeping the pins aligned to the pads while you make the first joint is a little harder, but the actual soldering is pretty easy.

The dominant forces at SMT scale is the surface tension of the molten solder, and the strength of any joints that have already been made. Components are specifically designed to make the right kinds of joints in a reflow process, so for hand soldering it's really just a matter of getting molten solder close enough to the terminals and letting physics take over.

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