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Offline EEVblog

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EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« on: January 25, 2013, 08:56:49 AM »
Dave shows you how easy it is to do surface mount SMD reflow soldering with a stencil and a hot air gun:
http://astore.amazon.com/eevblogstore-20

Hints and tips for quick and easy component placement, solder paste application, and reflow soldering using cheap easy to get tools.



Dave.
 

Offline ceecrb1

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #1 on: January 25, 2013, 10:06:49 AM »
not too much of a shame that it doesnt go past the focus wheel..
If you did place it further back then the actual focus wheel and lens surround would cause a shaddow in the centre of the image when doing closeup work... its better for a ringlight to be right up the front of the camera.
Just bodge some sort of holder... eppoxy it onto a cheap ebay wide angle lens or filter with the glass removed.. then you can just screw it onto the front...

One of these would be Idea! it would give a nice big surface to glue onto.. or even scews & bolts.
http://www.ebay.co.uk/itm/NEW-58mm-Adapter-Ring-for-Cokin-P-Series-Square-Filter-Holder-/271140713442?pt=UK_Photography_CameraLenses_Lens_caps_hoods_adaptors_ET&hash=item3f213ef3e2

Thanks for the reflow video, was a goodn.. its something Ive never seen!
« Last Edit: January 25, 2013, 10:09:34 AM by ceecrb1 »
 

Offline HardBoot

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #2 on: January 25, 2013, 10:07:43 AM »
That lead solder paste makes DIY look better than commercially done lead-free.
 

Offline free_electron

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #3 on: January 25, 2013, 11:55:07 AM »
That rubber spatula is waaaay to soft. Credit card works better. Or use those disposable spackling or plaster applicators.

Excellent video.

Two bits of background info of which the 'why' was not explained :

1) solder paste in the fridge.
The reason for that is to avoid separation of flux and solderpowder. if you let the syringe or cannister sit at room temperature the solderpowder will slowly float to the top ( believe it or not but the granules of solder are so small and the flux so dense that that stuff actually floats on the flux. So the emulsion is now no longer an emulsion and this gives problems. it becomes impossible to squirt it out of the syringe and if it comes out of the tub you have to re-stir it to homogenise it. Throw it in the fridge : problem solved.

2) Capping the paste container air-tight. Fluxes can be hygroscopic ( especially the water soluble ones ) and part of the flux evaporates as well. Leave that tub or syringe open and the flux will slowly evaporate and absorb moisture from the air basically destroying it.

So there you have it. Close the pot and throw in the fridge. Especially the syringes. If that stuff settles you won't be able to squirt it out anymore. If it's a tub you can stir it. Solder paste properly stored airtight can be used well past its 'expiration' date.

a couple of things to watch for in the video

Time index 24:00 : as Dave is applying circular motion : you first see the solder paste 'sag' it goes from a nice 'sharp' edge to a puddle. The surface is nice and shiny 'wet' because of the flux . At 24:16 the 'shiny' portion has gone away completely and the solder paste turns dull. This is the point where all flux has evaporated and we are now left with pure solder powder. A fraction of second later the solder starts melting. That is what you are looking for.
If the solder starts melting while there is still flux it will 'spatter' and little droplets of solder may get flung all over the board and form tiny little balls..
if there is too much tie between full evaporation and solder liquifying the solder will oxidize and the wetting will not be good.


As for the LED marking deviating from the explanation in the book : White and blue LED's have two bond wires. In a normal LED ( red green yellow ) the substrate is the cathode and the bond wire the anode. it is the anode that emits light. the substrate is conductive so they just silver-glue that on the pin and done. This stuff also only applies to 2 pin LEDS.

 The Cree LED is not a PLCC-2 but a PLCC-4 package. The notch simply indicates pin '1'. consult datasheet to find out how the A/K assignment is done.

White and blue led's are built on an isolator... so they need two wires coming from the surface. High efficiency red LED's are also like that.
The drawing in the book is only applicable to LED's with a single bond wire. With others : all bets are off. 

That's why one of the projects in the book is an LED tester. ( the strangely shaped little board inside the ringlight.) you simply prod the LED with the tester and the tester tells you where the anode sits. The tester has no polarity. I produce an alternating current. when the LED under test conducts it turns on the indicator LED. one indicator per phase. and they are positioned on the board so they indicate which pin is 'positive'. you can use two pogo pins or simply drop the led on the board.

The vacuum-pen Dave shows is really only useful to manipulate stuff like TQFP packages where you would need tweezers with a large opening and even then it is annoying to precise position it on a pasted board. i use em only to take parts out of trays or put them back in trays or in/out of zif sockets. for soldering .. never. too cumbersome. Unless it is a vacuum pump driven pickup. That's a different animal.

Another tip. Watch closely as Dave puts the parts down. He pushes them slightly into the paste. This will avoid tombstoning as well. just dropping them 'on' the paste is not enough. Parts really need a bit of a 'tap' so they sink in the paste. Not all pastes are created equal and there is a big difference between them some pastes are designed for a long working time ( they stay 'thick' long and evaporate slow ) such pastes may not release well from the stencil in fine structures. So there you have more liquid pastes that contain a solvent carrier for the flux , but that evaporates quickly so boards need to be reflowed immediately after placement. you can't let them sit for a few hours. Paste manufacturers will specify the intended purpose for the paste.
for this kind of 'hand-pick-n-place' get a 'rework-paste'. It can sit long , has slightly higher flux content and is medium in term of 'rigidity'. the drawback is : it separates easily so throw it in the fridge.

As for the size of the ringlight : i made the hole so that it fits over an x6 SLWD lens from the original mantis as well as the macro lens of my 4:3 Olympus PEN camera.
The three mounting holes on the ringlight allow you to zip-tie it . works better than the original bulbs that always burn out on the most inconvenient time.
« Last Edit: January 25, 2013, 12:19:13 PM by free_electron »
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Offline kyndal

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #4 on: January 25, 2013, 12:14:19 PM »
am too late!  Doh!   but ya... you dont want the ringlight any further back than really.. the front of
your optics..  will cause shadows.

im currently building one using an array of xenon bulbs from discarded single use cameras..
not for video ofcourse.

/Kyndal
« Last Edit: January 25, 2013, 12:16:29 PM by kyndal »
 

Offline The_Penguin

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #5 on: January 25, 2013, 03:39:49 PM »
That rubber spatula is waaaay to soft. Credit card works better. Or use those disposable spackling or plaster applicators.

Excellent video.

Two bits of background info of which the 'why' was not explained :

Indeed excellent video.  And excellent post! Thanks for the additional details.
 

Offline Bloch

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #6 on: January 26, 2013, 12:01:27 AM »
I did try search "cheep" stencil Dave talks about. But did not find any.


Anyone with links preferably from a EU country then pls post them.
 

Offline JuKu

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Offline JuKu

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #8 on: January 26, 2013, 12:27:53 AM »
Some more hints: The spatula should be a hard (steel)  one, as noted. If you tape the stencil down, one side only, you gain:
- a nice jig to do that particular board again
- easy to lift the stencil away cleanly
- you can use both hands when putting paste. That gives you one pass only and applying even pressure, very good results. (Better than on Dave's video; sorry Dave!)

Really, buy the oven. A controller for one can be bought with €129 (maybe even less) and a pizza oven is much cheaper.

I wrote about my experiences at http://www.eevblog.com/forum/manufacture/beta-layout-reflow-kit-first-try/.

IMO, this is the way how electronics really should be built. So much better results, much easier and much cooler than through-hole. :)
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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #9 on: January 26, 2013, 05:34:09 AM »
Thanks. This was very interesting. I have to admit that's not too hard soldering that way and the work looks very professional. The only problem I have it's about the solder paste... where can I get one of those?

And, also can the solder paste be used whit trough hole components?
 

Offline Fliz

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #10 on: January 26, 2013, 05:42:13 AM »
IMO, this is the way how electronics really should be built. So much better results, much easier and much cooler than through-hole. :)
Yes, all that, but when you want to cross from "thrugh-hole" to "SMD" world and you don't have anything of equipment ... it is pretty expensive step to do ...
 

Online mikeselectricstuff

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #11 on: January 26, 2013, 05:46:49 AM »

Really, buy the oven. A controller for one can be bought with €129 (maybe even less) and a pizza oven is much cheaper.

You don't really need a controller, just a way of limiting the power - variac or triac control.
Just turn it on, watch til it flows then open the door.
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Offline Scrambler

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #12 on: January 26, 2013, 06:40:19 AM »
Good job, Dave!

But you skipped these 2 inner double-side loaded boards. How would you reflow solder them? In particular I am interested in the second side, when first side is already soldered.
Probably, components from this first side could be desoldered by heat while you reflow solder the second side. How to do this properly?
« Last Edit: January 26, 2013, 07:48:26 AM by Scrambler »
 

Offline uwe

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #13 on: January 26, 2013, 08:08:33 AM »
Two questions:

1. Dave can you do one of the other boards with lead free solder? It would be nice to see how it works...
2. Are there any problems in mixing lead free solder paste and using lead solder with the thru hole parts?

I ordered the book and the kit a second ago :).

Thanks

Uwe
 

Offline free_electron

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #14 on: January 26, 2013, 08:13:48 AM »

Probably, components from this first side could be desoldered by heat while you reflow solder the second side. How to do this properly?

nope. the parts' wont fall off , even if the solde rmelts.

here is how you approach this one: you do the same like what dave did but you begin by placing 2 blocks of metal or wood on the bench and taping them down. then you put two pieces of scrap board down with the board inbetween.
Code: [Select]

====              ====
-----            -----
     |          |
     |          |

= : scrap board
- : wood or metal block

I just left a small 'lip' exposed simply drop the board in

Code: [Select]

==== BBBBBBBBBBBBB====
-----            -----
     |          |
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see how it rests at the edge on the blocks ?

then go on by placing stencil etc..

when you reflow the solder on the bottom will liquify but the cohesion forces ( is that the right term ? hmmm ) of the solder will keep the pins or pads of the parts trapped and the parts will not fall off. Even a TQFP will not fall of the board. ( unless you thump the board of course. )  let it cool down and done.
« Last Edit: January 26, 2013, 08:16:32 AM by free_electron »
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Offline PChi

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #15 on: January 26, 2013, 09:02:07 AM »
Thanks for the Video showing the technique. I also found it difficult to get the solder paste to fill the holes in the stencil. Either it was dragged out by the spatula or it migrated under the stencil. I ended up cleaning everything and trying a second time. I have only tried once and was only partially successful, not helped by the PCB being very small. I guess practice is required to learn the craft.
 

Offline ee851

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #16 on: January 26, 2013, 09:06:28 AM »
Would this work if I just used an ordinary hot air gun?   Not a professional thermostatically-controlled one like Dave's, just a 2-speed heat gun  without a nozzle.
 

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #17 on: January 26, 2013, 10:30:47 AM »
Thanks for the Video showing the technique. I also found it difficult to get the solder paste to fill the holes in the stencil. Either it was dragged out by the spatula or it migrated under the stencil. I ended up cleaning everything and trying a second time. I have only tried once and was only partially successful, not helped by the PCB being very small. I guess practice is required to learn the craft.
One non-obvious thing is that the consistency of paste for printing is less runny than that used for dispensing.
As you say, it is mostly down to practice - you ideally want to be able to do it in one pass to avoid it going under.
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Offline EEVblog

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #18 on: January 26, 2013, 11:35:15 AM »
But you skipped these 2 inner double-side loaded boards. How would you reflow solder them? In particular I am interested in the second side, when first side is already soldered.
Probably, components from this first side could be desoldered by heat while you reflow solder the second side. How to do this properly?

Double sided boards are done exactly the same way. Solder one side, let cool, apply paste to other side and reflow again. The bottom parts won't fall off, except for very heavy ones like say an SMD transformer or large choke perhaps. In which case you can hand solder those or glue them down first.
You need chocking blocks along the edge to lift the board up to paste the 2nd side, and you may need an extra support block in the middle to prevent your board warping when you apply pressure with the squeegee.

Dave.
 

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #19 on: January 26, 2013, 03:07:58 PM »
Would this work if I just used an ordinary hot air gun?   Not a professional thermostatically-controlled one like Dave's, just a 2-speed heat gun  without a nozzle.
Plug it into a heavy duty light dimmer (the kind often used to control theater lighting prior to the common availability of dimmable fluorescents) and it will work like a charm.

Offline Mikey

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #20 on: January 26, 2013, 08:38:03 PM »
I got the same hot air rework station (got it because I saw the review here long ago), and I love it! :-+

Been reflowing multiple boards with it already and haven't had any problems with it yet.
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Offline T4P

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #21 on: January 27, 2013, 12:01:25 AM »
About the Atten 858D <- At least, the Yihua 858D is a POS
i just got 1 the other day, it's an rebadged version but i don't care, the temperature is spot on when about 1cm away from the nozzle.
Of course any further and all bets are off, about 2cm away it drops off by about 5-10C
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Offline vk3yedotcom

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #22 on: January 31, 2013, 07:45:20 PM »
Plus an honourable mention on Southgate AR News on 26/1   http://www.southgatearc.org/news/january2013/electronics_engineering_video_blog.htm  including on their main page http://www.southgatearc.org/   :-+
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Offline psycho0815

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #23 on: February 01, 2013, 08:36:05 PM »
Just got my weekly elektor newsletter, They Mention you too. Also I'm guessing most elektor readers propably know your blog already.
If you like, check out my blog (german):
http://h-reg.blogspot.de
 

Offline daves.toolroom

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Re: EEVblog #415 - SMD Stencil Reflow Soldering Tutorial
« Reply #24 on: February 08, 2013, 10:15:16 PM »
Great video Dave!
An extra reason why you let the solder paste warm up to room temperature before using it is that cold solder paste will tend to absorb moisture from the warmer air in the room.
Then when you reflow the solder paste, the moisture trapped in the solder paste can rapidly vaporize and cause bits of solder to be ejected from the solder joint and form 'solder balls' scattered around the PCB.
This is probably not a big problem with hand reflowed boards like this, but can be a real pain in full scale production.
 


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