Getting started with SMT soldering

[TomWS]

I settled on the reversed aquarium pump + syringe & bended needle method which is cheap and the fastest you will ever get with hand placement, I can guarantee that.

Felix, I saw your blog on this (I LOVED the discovery of reversing the valve! EXCELLENT!) and explored it but didn't find a source for bent needles.  I did find lots of straight ones in all kinds of sizes.  Where did you get yours and what size/gauge is it?

Tom

[Felix]

Bent by me
Just take a thicker needle, saw it down to about 1/2-3/4" length and then bend it gently to avoid it collapsing/creasing.
And by the way since I wrote that post I found (others did it) that the valve is very easy to reverse instead of making a hole and rerouting the output (the way I originally did it). Just flip the valve in the pump and now the output pump nozzle will suck air instead of push air (ie vacuum).

[OSHStencils]

Tom,

You can send us 2 file formats.  Either A)  An Eagle .brd file  or B)  A RS274-X Gerber file.   Board outlines are not required, but are recommended for visual reference of how big your stencil will be.  You should send us your cream/paste layer (some EDA software calls it paste, some call it cream, it's the same thing).

In most cases using our 3mil product, with the standard shrink amount for your EDA software is recommended.

If you have any additional questions, don't hesitate to email us.

-Brent

<..snip> But you can also order them from oshstencils but the downside is the wait.

Felix, would you be willing to provide some insight on what files you recommend sending to oshstencils?  They have so many options that it's pretty overwhelming. I know for the etching you shrunk the SMT pads by some fixed amount.  Would you do this with these stencil files as well?

<..snip> Back in manual SMD days I used a small toaster oven that I insulated with tinfoil which made it much better and used a K thermocouple to watch it reflow, that's the best thing before a real reflow oven.

After watching one of your videos on using a toaster oven I purchased one, fiddled with the timing while measuring the temps, and now have a Moteino (non-wireless) controlled reflow oven!  All automatic (except opening the door for the cool down phase).  I'm not sure I would have tried this without your sharing your experience.
Thanks!!!

Tom

[ColinR]

I hand apply and use a toaster oven with a Pi. Works fine with a steady hand.

http://www.cupidcontrols.com/2013/12/home-reflow-soldering-on-a-budget/

[TomWS]

Tom,

You can send us 2 file formats.  Either A)  An Eagle .brd file  or B)  A RS274-X Gerber file.   Board outlines are not required, but are recommended for visual reference of how big your stencil will be.  You should send us your cream/paste layer (some EDA software calls it paste, some call it cream, it's the same thing).

In most cases using our 3mil product, with the standard shrink amount for your EDA software is recommended.

If you have any additional questions, don't hesitate to email us.

-Brent
<snip...>

Wow! What service!  Answering my question on our forum!   

I use Eagle so no problem there, but I do have a question: If I send a .brd file, does your ordering system understand if there are only SMT devices on a single layer or will it want to charge me for two stencils anyway?  A related question (since this does occur on one of my boards), if I have SMT devices on both layers but only want a stencil for one of them (bottom layer is just a few large caps - easy to hand solder these), is that possible?

I have a new board going out in a couple of days.  I'll get a stencil from you as well.

Thanks!
Tom

[Felix]

Wow! What service!  Answering my question on our forum!   

Indeed, pleasant surprise. OSHPark and OSHStencils are providing a very valuable service to the electronics enthusiasts and maker community and to all those that just need a quality and prototype from a dependable service.
I use OSHPark all the time for my prototypes. Haven't tried OSHstencils since I etch my stencils on my laser machine from mylar but I saw some first hand. I did notice the OSHstencils are kapton that come from a roll which leaves them curvy, almost cylindrical , so they probably need to be framed to be kept flat, otherwise it might be difficult to apply the paste especially with larger PCBs, I'm sure they have some guidelines around that, but otherwise very nicely etched apertures and resolution.
Also 3 mil might be a little thin for some components like USB connectors or large footprints, but again this is prototyping, as long as there is a bond it's good to go.

[TomWS]

A curved stencil might be a problem unless the concave side is up where the curve would help press the stencil against the PCB...

The good news is that I'm not smart enough (any more) to design any "larger PCBs"   

Tom

[Felix]

A curved stencil might be a problem unless the concave side is up where the curve would help press the stencil against the PCB...

The good news is that I'm not smart enough (any more) to design any "larger PCBs"   

I think everyone who got used to Eagle designs boards smaller than 80x100mm which is plenty for most things. I think designing small and efficient takes more smarts (and time!) than throwing components in a large area and calling it a day.

[OSHStencils]

Tom (and Felix),

If you upload the .brd file, we will extract out the tCream and bCream layers automatically and display them.  Then there is an option to ignore a layer, so if you don't have components on the bottom side, just set it to "Not Used" and it'll only produce renderings of the top side, and thus you can order just that one side.

Felix:  As for the stencils "rolling", yes that's true, our film does come on rolls, however we're about to make an announcement about that next week   I've been working with our manufacturer for 6 months to produce a process that they are no longer on rolls and are completely flat.  We've ordered our first production run of the material in flat form, and it should be here at the end of next week.  We'll release a more formal announcement about it once the material arrives and we've validated that the material integrity has not changed with the new manufacturing process.  That said, you can just counter-roll our film with your hand and it'll lay fairly flat, and for most projects just taping a second side does the job nicely.

Let me know if you have any additional questions, and thanks for considering us for your stencil needs.   More announcements are coming this quarter too... stay tuned!

-Brent

Tom,

You can send us 2 file formats.  Either A)  An Eagle .brd file  or B)  A RS274-X Gerber file.   Board outlines are not required, but are recommended for visual reference of how big your stencil will be.  You should send us your cream/paste layer (some EDA software calls it paste, some call it cream, it's the same thing).

In most cases using our 3mil product, with the standard shrink amount for your EDA software is recommended.

If you have any additional questions, don't hesitate to email us.

-Brent
<snip...>

Wow! What service!  Answering my question on our forum!   

I use Eagle so no problem there, but I do have a question: If I send a .brd file, does your ordering system understand if there are only SMT devices on a single layer or will it want to charge me for two stencils anyway?  A related question (since this does occur on one of my boards), if I have SMT devices on both layers but only want a stencil for one of them (bottom layer is just a few large caps - easy to hand solder these), is that possible?

I have a new board going out in a couple of days.  I'll get a stencil from you as well.

Thanks!
Tom

[TomWS]

@OSHStencils, thanks again for the reply.  This is perfect, thank you!  I'll be sending my board in soon.

Tom

[TomWS]

I've received my first stencil from OSHstencils.  FAST turnaround!  I sent it in in the morning and it was mailed that evening!  As Felix warned, there is a bit of curl in the stencil but it should be fine.  Now if I only had the PCBs to try it out!   (I JUST hit the Chinese New Year window      sigh...

They even included a solder paste spreader with the order - kinda looks like the room key from the last hotel I stayed in and 'forgot' to return... 


Tom

[Felix]

I am not sure why OSHStencils would not use mylar instead of kapton. I used mylar to laser etch stencils with excellent results. Maybe they experimented more and it's better for extreme fine pitch because of the heat won't create rings around the fine apertures. But for most other 0.5mm+ pitch i think mylar is great as long as the laser settings are tuned right.

[TomWS]

I FINALLY got a chance to use the stencil I received from OSHStencils as it took 4 1/2 weeks to get my board from Seeeds...

Bearing mind that I haven't used a stencil before, I found that using this stencil made all the difference in the world in getting a nice even paste on the pads.  This particular board wasn't all that challenging.  It was mostly SOT23, a couple of SOT323, and then a few large ones, a JST connector, and a bunch of 805 resistors & a few 1206 LEDs.

The curl Felix mentioned was annoying, but relatively easy to deal with because the PCB was small.  It would have been a royal PITA if it was a larger board.  I also purchased a set of 1/16" ell guides from OSH stencil and this turned out to be a wise decision.

I set the guides on my paper cutter's board (nice and square, flat, and stable), taped the stencil to the top most guide and pasted my first board. The paste thickness seemed uniform and, after reflowing, the SOT packages and JST connector were soldered to perfection.  The resistors, on the other hand, were soldered reliably but it seemed as if they had too much solder - odd.

All in all, as my first stencilling experience, I'd say it was successful and certain will pay off the next time I do a TQFP or DFN chip.

Tom

[EloyP]

Hello,

Thanks to all for all the thoughts and suggestions on this topic. Since my original post here I've made what I consider to be great progress in my SMT soldering capabilities at a hobbyist  level. I plan to do a writeup on my experiences but I wanted to summarize what I've done based on recommendations received here and what I've read elsewhere -- I modified a toaster oven and added to it a reflow oven controller that I bought, I bought some solder paste, applied it with a toothpick, and assembled an Arduino shield-sized board that I had designed a couple of years ago (SOT-23s, 603s, SOICs). Everything worked right out of the oven; the result was fantastic -- shiny joints without the mess of solder flux everywhere, unlike the manual soldering method I had tried previously. I can't wait to try a solder stencil in the future but for assembling a couple of boards applying solder paste with a toothpick was not too bad for me and the results were very good.

All in all, after this experience, I draw two conclusions:

1. With the right tools (e.g. a small reflow oven, good solder paste, good soldering iron, etc.) SMT soldering is really easier than through-hole soldering, even for a hobbyist. It's hard to believe but now I'm convinced it's true.

2. My manual soldering SMT skills do not seem to be as bad as I thought they were -- my initial failures seem to have caused by the Kester flux that I used and my failure to properly clean the flux residue after I was done with manual soldering. This caused severe corrosion of traces, which in turn produced malfunctioning circuits that were really hard to troubleshoot, i.e. is it software? DoA components? components damaged during manual soldering? incorrect design?, etc. Had I cleaned the boards to remove the flux residue I think my circuits would have worked just fine.

Thanks again for all the suggestions. I'll try to do a more detailed writeup about my experiences soon.

Cheers,

Eloy Paris.-

[WhiteHare]

The Dangerous Prototypes guy did this youtube comparing different fluxes:

He makes it seem as though with a good quality PCB and with a high quality flux, the solder almost automatically flows right where you want it to go.

The flux he appears to love the most is this one:  http://www.newark.com/edsyn/fl22/flux-soldering-syringe-5ml/dp/35M3870?ost=EDSYN+%09FL22++FLUX
which, in addition, claims to be a "No Clean" flux. 

In contrast, he thinks the Kester flux he tested was "worthless."