Author Topic: Getting started with SMT soldering  (Read 36741 times)

EloyP

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Getting started with SMT soldering
« on: February 01, 2015, 03:37:41 PM »
Hello,

I am pretty frustrated with my first SMT project -- I designed a board, had it made at Seed Studio, and manually soldered all the components (I have a decent Hakko FX-888 soldering iron). Parts of the board works and some other parts don't work. I've soldered a couple of boards and there is always some issue that I need to troubleshoot. The worst part is that I am wasting a lot of time troubleshooting, which prevents me from focusing on the firmware, or to move on to the next project. It's frustrating to not know if a problem is caused by a bad component, a bad PCB, or a cold joint. The same subsystem (a latching solenoid driver) is duplicated four times on this board, and it works on both the breadboard and on other parts of the board, so I think the design is good. I am even having problems tracing with a multimeter signals within the board (sometimes I have continuity and some other times I don't).

I used liquid flux to facilitate soldering of all components and that seems to always make a mess (pads seem to get corroded over time, the board looks dirty, etc.).  If the design has problems it is really difficult to diagnose because pads look corroded so it's hard to make good contact with the multimeter. Pads are very small to put there the multimeter probes. I used 603 resistors, SOICs, SOT-23 transistors, etc. Nothing too tiny I guess but it is being difficult for me to solder all these components by hand and have everything working without some serious troubleshooting.

I know there are better ways to finish these boards but I'm not sure which one to choose. I don't mind making a small investment to buy a small toaster over or an electric skillet. Anything to avoid the frustration or getting discouraged from working on my electronic projects (which is currently the case). I do not intend to do mass-produce any boards; I just need to produce a couple of boards of each project for personal use. I don't know why this is being so hard; these boards are not complex; I'm not talking about creating a Raspberry Pi-like board.

I've heard good things about the electric skillet method (https://www.sparkfun.com/tutorials/59)... Should I go this way as my first attempt to do better than the manual method that is causing me so much frustration? Recommendations for a good starter solder paste to use with whatever method you recommend would also be appreciated (bonus points for a Mouser part number as I need to place an order with them soon).

Thanks in advance!

Frustrated,

Eloy Paris.-

Felix

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Re: Getting started with SMT soldering
« Reply #1 on: February 01, 2015, 07:16:40 PM »
For anything SMD I recommend using solder paste and a stencil, it will be much much faster than hand placement of paste and tweezing the components. I used to make all Moteinos by hand by making stencils out of soda cans, read those links for more details. These days I have a laser cutter so I etch my stencils out of mylar which is much faster and cleaner etc. But you can also order them from oshstencils but the downside is the wait. The flux is very important for rework, and the ebay and chinese market is full of junk flux and paste just watch this video of my experiece with solder paste bought from Sparkfun which I believe they now replaced with brand name paste after realizing it was indeed garbage. I recommend a good brand sac205 lead free no-clean solder paste. Keep it refrigerated. 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.

TomWS

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Re: Getting started with SMT soldering
« Reply #2 on: February 01, 2015, 07:59:45 PM »
<..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

Felix

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Re: Getting started with SMT soldering
« Reply #3 on: February 01, 2015, 09:18:05 PM »
For making stencils you have to send the CREAM layer. Every maker has their own spec of how to process that layer before sending (if at all) or they process it for you, so its fab specific. The thickness of the stencil also matters a LOT depending on what you are placing on the board/panel. There are a lot of ins and outs to making a good placement and a good reflow. It's a huge learning experience especially after owning a pick and place machine. It's hard to explain it all in a blog post or here. It's just a matter of practice and observation of what works best. These kinds of things you will probably never find on any blog post or from companies like adafruit or SF regardless how "open" they claim they are. This is more like insider knowledge that will never be shared because it's more like IP and it costs thousands in fabrication/materials and man hours to tweak and develop a process technique and set of parameters that work best. It probably costs a fortune to train someone to understand how this works. Fabrication and assembly are really hard things to master and do well. I am still learning by mistakes. Also notice how adafruit is not really open hardware any more since they became huge haha...

TomWS

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Re: Getting started with SMT soldering
« Reply #4 on: February 02, 2015, 07:29:35 AM »
For making stencils you have to send the CREAM layer. Every maker has their own spec of how to process that layer before sending (if at all) or they process it for you, so its fab specific. The thickness of the stencil also matters a LOT depending on what you are placing on the board/panel. There are a lot of ins and outs to making a good placement and a good reflow. It's a huge learning experience especially after owning a pick and place machine. It's hard to explain it all in a blog post or here. It's just a matter of practice and observation of what works best. These kinds of things you will probably never find on any blog post or from companies like adafruit or SF regardless how "open" they claim they are. This is more like insider knowledge that will never be shared because it's more like IP and it costs thousands in fabrication/materials and man hours to tweak and develop a process technique and set of parameters that work best. It probably costs a fortune to train someone to understand how this works. Fabrication and assembly are really hard things to master and do well. I am still learning by mistakes. Also notice how adafruit is not really open hardware any more since they became huge haha...
Thanks Felix, this is helpful. I'll look at the stencil maker's website to see if they have a DRC/post processor like Seeed has.  I should have done this in the first place...  :-[

Tom

Felix

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Re: Getting started with SMT soldering
« Reply #5 on: February 02, 2015, 08:04:02 AM »
I think your best bet is oshstencils, its cheap and probably pretty fast and I'm sure they know how to deal with edge case stencils apertures. But I'd check their rules to be sure you're getting what you expect.
And I meant to say congrats for making a Moteino controlled reflow oven, I've never taken it that far, I'm such a dork not using my own hardware to pimp my toaster oven. But these days I very rarely use it, only for prototypes, all production boards get reflowed in the conveyor oven, pop in and pop out, perfect reflow, no stress.

TomWS

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Re: Getting started with SMT soldering
« Reply #6 on: February 02, 2015, 09:16:08 AM »
I think your best bet is oshstencils, its cheap and probably pretty fast and I'm sure they know how to deal with edge case stencils apertures. But I'd check their rules to be sure you're getting what you expect.
And I meant to say congrats for making a Moteino controlled reflow oven, I've never taken it that far, I'm such a dork not using my own hardware to pimp my toaster oven. But these days I very rarely use it, only for prototypes, all production boards get reflowed in the conveyor oven, pop in and pop out, perfect reflow, no stress.
Thanks Felix, I've re-read their website and didn't see any DRC but did indicate which files they need so I'll give it a shot.

The reflow oven came out very well, thanks you your tips about when to turn off the element.  The controller was very easy to build on a perf board and I hacked the SSR into the heating element wiring so that the rest of controls still work.  I used a MAX31855 Thermocouple module with a K type probe and that works very well.  I've attached the temp profile I'm getting with it.  Good enough for anything I'm going to throw at it.

I've been doing hand pasting and it's come out ok, but had some issues around Christmas time trying to solder some 14 pin LGAs (ADXL345 accelerometer).  Uh, I had to do three passes to get one of two boards working - not very good.  I'm hoping stencils will allow me to do this kind of work.

We'll see.  Thanks again.

EloyP

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Re: Getting started with SMT soldering
« Reply #7 on: February 02, 2015, 12:55:11 PM »
For anything SMD I recommend using solder paste and a stencil, it will be much much faster than hand placement of paste and tweezing the components. I used to make all Moteinos by hand by making stencils out of soda cans, read those links for more details. These days I have a laser cutter so I etch my stencils out of mylar which is much faster and cleaner etc. But you can also order them from oshstencils but the downside is the wait. The flux is very important for rework, and the ebay and chinese market is full of junk flux and paste just watch this video of my experiece with solder paste bought from Sparkfun which I believe they now replaced with brand name paste after realizing it was indeed garbage. I recommend a good brand sac205 lead free no-clean solder paste. Keep it refrigerated. 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.

Thanks Felix. Right now I am not too concerned about using a toothpick or syringe to apply the solder paste -- I just need to assemble for personal use a handful of boards of each project I make. Not sure it's worth to create my own stencils (or have them made) when I will only assemble a couple of boards. But I do see the benefit of using stencil when one has to assemble more than a handful of boards.

At this point in my journey into SMT I am more concerned about how to solder components once solder has been applied and components been placed. You mention a small toaster over. Would you recommend that over the electric skillet method described in that Sparkfun tutorial? And on a related note, is there some open source project I can use for controlling the reflow process using a toaster over?

Thanks again.

Cheers,

Eloy Paris.-

Felix

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Re: Getting started with SMT soldering
« Reply #8 on: February 02, 2015, 01:08:01 PM »
how to solder components once solder has been applied and components been placed .. ?
I think you mean reflow phase, just get a cheap toaster oven and insulate it with tinfoil and kapton tape. It's much better than a skillet.
There are countless tutorials online how to do the different phases of SMT and how different people do it different ways.
Also many open source control methods. I haven't used any, I just sat there for a few minutes every time I reflowed, thinking to myself I am such a dork wasting my time looking at a temperature reading, glad that phase is over now. If making your own stencils is not worth it for you then making a reflow oven controller is much less so.

EloyP

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Re: Getting started with SMT soldering
« Reply #9 on: February 02, 2015, 01:18:54 PM »
how to solder components once solder has been applied and components been placed .. ?
I think you mean reflow phase, just get a cheap toaster oven and insulate it with tinfoil and kapton tape. It's much better than a skillet.
There are countless tutorials online how to do the different phases of SMT and how different people do it different ways.
Also many open source control methods. I haven't used any, I just sat there for a few minutes every time I reflowed, thinking to myself I am such a dork wasting my time looking at a temperature reading, glad that phase is over now. If making your own stencils is not worth it for you then making a reflow oven controller is much less so.

Yes, sorry, I meant the reflow phase.

Not sure I understand your comment that if making my own stencils is not worth it for me then making a reflow over controller is much less so. Unless you are talking about the *controller* and not the oven itself? I mean, I still have to solder my boards (small quantities, just for personal use, at least for now) and hand-soldering is not cutting it (perhaps I am lacking skill, but the bottom line is that I seem to damage components, create cold joints, etc.). This is why I'm looking into another solution (oven or skillet). Just wanted to know if you meant that the over (not the controller) is not worth it if I will not be using stencils ;-)

In any case, if going the toaster oven route, is the temperature reading a must? Can I just not watch through the over window when the solder reflows? Apologies for the dumb questions but I am so new to this!

Cheers,

Eloy Paris.-

Felix

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Re: Getting started with SMT soldering
« Reply #10 on: February 02, 2015, 01:31:45 PM »
If you have to ask .. do it in this order :)

1. Put it in toaster oven and watch for solder to reflow, then count to 10 and stop/open door and blow air gently on the boards to cool them down.
2. Use a ktype thermocouple with a multimeter (this is what I did) and watch the temperature rise, stop the oven after soak zone, then once temperature stabilizes start it again and watch it raise towards reflow zone, stop it before it reaches that and oven should still heat up to allow reflow. This takes practice.
3. Get fancy and buy a reflow oven controller.

EloyP

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Re: Getting started with SMT soldering
« Reply #11 on: February 02, 2015, 01:38:41 PM »
If you have to ask .. do it in this order :)

1. Put it in toaster oven and watch for solder to reflow, then count to 10 and stop/open door and blow air gently on the boards to cool them down.
2. Use a ktype thermocouple with a multimeter (this is what I did) and watch the temperature rise, stop the oven after soak zone, then once temperature stabilizes start it again and watch it raise towards reflow zone, stop it before it reaches that and oven should still heat up to allow reflow. This takes practice.
3. Get fancy and buy a reflow oven controller.

Haha, okay, that works. I'll give the toaster over a try then. Okay to assume that pretty much any oven I can find at Target or Walmart will do?

Cheers,

Eloy Paris.-

Felix

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Re: Getting started with SMT soldering
« Reply #12 on: February 02, 2015, 04:10:48 PM »
Probably, look for one that looks easy to insert/remove the tray. If you can find one with 4 elements that's even better (more even heating). But even the cheapest should be ok.

Lensdigital

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Re: Getting started with SMT soldering
« Reply #13 on: February 04, 2015, 10:17:18 AM »
Fun thread! I never heard about OSH stencils before, wow they are cheap!
Also just found this and wanted to share: DIY Manual Pick and Place machine. Fascinating!

Felix

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Re: Getting started with SMT soldering
« Reply #14 on: February 04, 2015, 12:30:12 PM »
I was fascinated about that machine also until I realized anything in between hand placement with a nozzle tool and a real pick and place is too expensive/too slow/hopeless/useless.
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.
Read this post which explains why this machine you included is not something I ended up using. The ONLY advantage of that machine is placing on very large PCBs which are hard to reach in the middle with a stable hand. Also looking away from the PCB to a monitor for placement of a component will make it about 10X slower than it already is, it's essential that your eye is looking at your hand when placing manually, and not away to a monitor.