Picture of Extreme Surface Mount Soldering
So you're thinking of building a super-widget and wanted to use the latest QFN / MLF (micro lead frame) package parts. But then you actually LOOKED at one, realized how tiny it really is (Picture 1), and decided no way can I solder that! Think again! This instructable will show you how to design and build a circuit using truly tiny SMT devices. Not only will I show you how to build your own Hot Plate Soldering System capable of soldering the tiniest surface mount components using lead-free solder, you will learn to design the footprints, stencil on solder paste, and solder the components. I'll also point you to cheap sources for design software, PC boards, solder paste, and stencils.

This instructable is about two things: How to build and use a Hot Plate Soldering System, and general guidance on how to design circuit boards using surface mount parts. All the information you need for successful surface mount design and construction. Throughout this Instructable, many sources will be cited: like Newton, I truly stand on the shoulders of giants! (That's another way of saying others have already worked most of this out.) What I'll do is explain the methods I've used successfully to build tiny surface mount circuits. The focus is on specifics, not generalities. I believe the method and tools I'll describe are the most economical available which will yield satisfactory results.

So let's get started. Successful design and construction with those Extremely Tiny devices you've been dying to use is just an Instructable away!

UPDATE February 2010: Closed Loop Control has been added! Have a look at this Instructable.

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dscanner2 years ago
Xcellent project, although just starting. Question on the hot plate. I have seen a lot of different versions similar to the Elite, most are rated at apprx 1000W/115vac. Is this wattage adequate to get to 450 degrees per discussions in this instructable? And what temp does the solder paste actually melt at? I am actually seeing higher temperatures for some types of solders.
doctek (author)  dscanner2 years ago
Great question! Your basic hot plate (any one will do) will easily glow a dull red at high heat. That's about 900F (480C) - well beyond melting point of most any solder intended for electronics use that I know of. The exact melting temperature of a particular solder depends on the exact metals used in it. Most melt in the range of 180C to 220C; consult the data sheet for your solder for the specific temperature. Know that the temperature you want to use is slightly above that value by 20C or so to allow for heat transfer through the circuit board.

BTW, the easiest way to convert from F to C or C to F is to add 40, multiply by 9/5 (C to F) or 5/9 (F to C), then subtract 40.
orboneer doctek5 months ago

An even easier way to convert F to C, or C to F, is to type into the URL box of the Chrome browser. Type "900f=c" without quotes and do not hit enter. Try 180c=f or 220c=k. Sometimes you can just type one unit. Examples: 1ml= 3mi= Equations of volume, area, etc. including units also work. If you do hit enter, then Chrome loads a page with an online calculator or online unit converter.

AmandaS57 months ago

Nice tips! I have a surface mount component with 16 pins to connect. My question is (just out of curiosity), could the circuit work if I did not solder the surface mount to the board but simply lay it in the correct position?

doctek (author)  AmandaS57 months ago
Thank you for your interest in Surface Mount Soldering. Glad the info was of use to you.

Just setting the part on the pads will almost certainly *NOT* work, certainly not reliably! Solder is used to make the electrical connection between the pads and the part and is an absolutely essential component. (Conductive epoxy might be used, but won't work in all circuits. It is conductive, but not as conductive as solder.) If you want to work with surface mount components, you'll find that learning to solder them will be an essential skill.
salmansheikh9 months ago

I initially built a box like Figure 13 with a solid state relay like this instead of the SCR circuit. I was able to turn on the SSR which activated the ac outlet which my hot plate plugged into.

But then decided to embed all my SSR and terminal block inside my hot plate for compactness So, now I have it wired like the attached photo. Before I had the hot and neutral going directly into the ceramic block shown as two lines (red and blue). Now, I have the hot and neutral going to a terminal block and then to the SSR and from the SSR to the ceramic block. But now, when I plug in the hot plate its on all the time w/o nothing hooked up to the digital inputs.

What am I doing wrong?


doctek (author)  salmansheikh9 months ago
I can't really tell what your circuit does. What is the "ceramic block"? What does your new circuit look like? Perhaps you could draw a proper diagram of your circuit with some labels. Maybe I could help you then. Sorry. I just don't get it.

The SSR should break the hot wire. That is, the hot wire from the wall should come in to one pole of the SSR and the other pole should attach to the hot plate. The neutral wire should just connect directly to the hot plate. Then the PWM signal will turn on and off the SSR and hence control the voltage in the hot wire. HTH.
I don't know what the ceramic block does..I think its just a terminal block but not sure what the part in the 3rd set of terminals is for. Perhaps a fuse or something if things start drawing too much current?  Its an Aroma brand hot plate from WalMart..maybe I could look up some schematics. Here is my hookup. Like I said, its on as soon as I plug in...I am probably doing something real stupid that I can't figure out w/regards to the AC hookup. 
What precautions and is it possible to do this AC control unit on single-sided copper pcb instead of the perf board?
doctek (author)  salmansheikh2 years ago
Yes, a single sided board is certainly possible.

- Make sure the traces can carry the current.

- Make sure the traces follow the spacing rules for the AC voltage you use.

Note that the wire and insulation used on the perf board version takes care of these problems.

Probably an even better solution is to simply buy a solid state rely off Ebay. Suitable units are available for less than $10.
May I use 220 ohm resistors instead of the 180ohm?
Can you use an Arduino to get your PWM and not need the I2C expanders?
doctek (author)  salmansheikh4 years ago
Sure, you can use Arduino and not need any of this. This Instructable is for those who want to learn about the AVR processors above and beyond the Arduino.

Whatever works for you.
doctek (author)  doctek4 years ago
Oops - I thought you were commenting on my I2C instructable. Ignore what I just said.

A better answer is: See the Follow-Up to this Instructable that uses the IR sensor for feedback and a PC to enter and track the temperature.

Basically, it uses Arduino for the microcontroller portion.
dausmus4 years ago
Comment on Lead Free issues-

I use lead solder due to the tin whisker problem. I will switch to lead-free once that is really solved, otherwise anything I build without lead-based solder that needs long-term reliability will require inspection on a regular basis, especially if the board is under thermal or mechanical stress. References:



http://nepp.nasa.gov/WHISKER/ (This one has some great pictures of whiskers!)


I think metallurgists will eventually solve the problem, but for now I am sticking with lead-based solders and non-ROHS components unless I have to use lead-free for other reasons. And, my volume is very low.

Is it possible to substitute the MOC3042M-ND for the MOC3043M-ND?  the electrical properties seem to be slightly different... The only reason i would want to is the 42 is on backorder.  Any thoughts or is it safer to wait for the 42 to come in?
doctek (author)  aterhune19845 years ago
The 3043 will substitute perfectly. The only difference I can see is that the current required to trigger the part is only 5ma instead of 10ma for the 3042. It'll work just fine. Cost is about 10 cents higher for the 3043 - I don't expect that's a show-stopper.
jimk30386 years ago
Hey, Checkout this Non-Contact Laser Thermometer at Harbor Freight - it's only $30 bucks and it has a range up to 520 degrees C. For $30 bucks you can't go wrong. Plus, I wonder if it could be hacked so that it could be connect to a PC. Mine is already on order! Jim
doctek (author)  jimk30386 years ago
Great find! Perfect if for this application. Thanks for the pointer!
doctek (author)  doctek5 years ago
Have a look at my update to this Instructable here: www.instructables.com/id/Closing-the-Loop-on-Surface-Mount-Soldering/

In it, I show how to use an IR sensor from Harbor Freight to build closed loop control for this process.
jimk3038 doctek5 years ago
 Very nice.

Someone else has also reverse engineered the Cen-Tech 96451 handheld unit I bought. Here is a link to that discussion too:


Here is a link to the Cen-Tech thermometer I used:

The model I used has more range (up to 500C) and the spot size is 8:1 instead of 6:1. But, my model cost 1/3 more at $30 bucks. Sounds like either model will work.

Thanks for all the info,
It is important to know that most noncontact pyrometers are calibrated for 80% reflective objects. IE, grey to black. Just so you know. Lighter objects read as a lower temperature than they actually are. A dark green PCB may read correctly or a little low. Tshirt pressers often stick a piece of black high temp tape (looks like masking tape) onto a white or natural aluminum press when testing the temperature.
ewertz jimk30386 years ago
Grrrrr. It's $60 now.
snarfer6 years ago
Great instructable! I like to get my stencils from Ohararp.com, supposedly kapton can be laser cut slightly more accurately than mylar. Also, might want to note that when you need to replace those QFN parts you're going to need some sort of rework station with a hot air gun, unless you want to put the entire board back on the hot plate... I got a nice one for 90 dollars, but there were cheaper ones available for half that. Finally, just wonder if you've had any trouble with uneven heating on your hot plate, any ideas on how to address that. I was soldering one board recently that was kind of long and thin, the ends never melted but the middle overheated. Maybe I will try putting a piece of aluminum underneath next time.
doctek (author)  snarfer6 years ago
Great input! Thanks for adding to the discussion. Think I'll try Ohararp.com next stencil. Sounds like a good product at a fair price. Pololu has been very good however. Yes, for rework you need a hot air gun. In fact, some places (like curiousinventor aka Scott Driscoll) suggest two of them, one front and one back. I mostly have avoided rework by using cheap parts and small designs. I know I'll have to deal with this someday. The plate I have seems to give even heat, but I've used only small designs. If you're trying a new design for the first time, then plan to get at least one or two extra boards to experiment with. The aluminum plate idea is one I've seen mentioned in other places. I think it's a good one, but you'll have to work out the correct solder profile if you use one on your hot plate. Again, thanks for the input.
doctek (author)  doctek5 years ago
I no longer recommend Pololu - there prices are through the roof! See my post above about this.
SMTstencils6 years ago
hello there,

Since you your discussion involves SMT stencils, I thought you may want to know that now Applied Electronics provide both Mylar and Kapton SMT stencils. Starting this coming Thursday (June 25th), we will take order for Kapton too. You can choose either Mylar or Kapton of size 8.5x11 inch (actual size for Kapton is 8.5x12) without any restriction on the area or number of components.

Mylar comes in thickness of 3 and 4 mil.

Kapton comes in thickness of 3 mil only.

Visit the following site for detail


Applied Electronics
doctek (author)  SMTstencils5 years ago
This looks like a good option. Kapton has been recommended to me for this application since it is tougher than mylar and can have cleaner edges. Besides applied electronics, I have also heard good things about

I no longer recommend Pololu. Not only do they use mylar, their prices have gone sky high!
adelsmud5 years ago
Hi, there I was wondering where it would be ok to apply small 'blobs' of solder paste on the pads instead of getting a custom stencil made up. Also will a pcb without solder mask work? Thanks and great tutorial by the way.
doctek (author)  adelsmud5 years ago
Applying small blobs is certainly possible. The solder paste often comes in syringe tubes, and needles are available just for what you suggest. Another way to use such a tool is to apply a thin line of paste across several pads. In fact, some people have reported success simply using an Xacto knife to apply a thin layer of paste to the pads (without trying to separate each pad's paste from the ones next to it). Once the paste is on, the part is placed on it, heat is applied, and capillary action / surface tension does the rest. So this is certainly possible. Be careful not to smear the part around as you place it!

Trying this procedure on a board without solder mask is more risky, but might work. I can't say it won't; only that the risk goes up with each move away from using a stencil and solder mask. The risk also increases as pad spacing decreases. So the tinier the part, the more important solder mask and stencil become.
jensenium5 years ago
You're a good man, and thorough.
cgo6 years ago
Hi again. I completed your tutorial, it works great ! However, I'd like to point out this part: Sharp S116S02. It can replace the MOC+the SSRs+diodes+1W resistors, all in one $5 part. It needs a compatible heatsink, too. Regards, Charles.
doctek (author)  cgo6 years ago
Thanks for the suggestion. Looks like a real nice part! Here's two thoughts: 1 - Since it's a triac, it needs a snubber circuit as discussed in the Sharp apps note. One of the reasons I chose SCRs was to avoid needing a snubber. Not a big deal, just a couple of extra parts. 2 - The heat sink tab is not isolated, so you'll need an insulating washer on the external heat sink. Watch out for that. The Digikey part number is 425-2399-5-ND and the price is $6.05.
musick7 doctek6 years ago
Hi Doc! This is Awesome! I would like to make my own and I was wondering if you had a YouTube Video of this in ACTION? I would love to see it working. Not that I don't believe you after all seems many have made one from your Tutorial in all the Reply's. I guess what I'm getting at is, How difficult is this to make? I am very confident in my Soldering Skills and would love to add this to my tools. Is this expensive to make? I have quit a few different MicroChips, Resistors, Caps and so on... If I had to purchase all the Parts needed and I did Bargain shopping online getting the best price and giving each distributor a Max. of 10 days to receive parts ordered from them. What would be the total Cost? And if you don't have a YouTube video where is another great demo of something just like this one? Does anyone else have there Plate on YouTube that they made from this Tutorial?
ewertz doctek6 years ago
Can you safely pass on the snubber if you're sure that your load will only be resistive (like, for this?) ? I'm asking because I've already got a small handful of triacs around... Great write-up. Thanks!
doctek (author)  ewertz6 years ago
IF your load is purely resistive (like this hot plate), then you can skip the snubber. This fact is discussed later in the project for the SCR circuitry used.
tundrawolf6 years ago
This is fantastic! I used to work with used test equipment and related equipment and wave soldering always fascinated me. I would like to see more steps and WAY more pictures. It is a lot for me to digest. But it is great nonetheless.
Gilius6 years ago
Instead o using solder paste can I apply solder to the board instead? (like tinning) The solder would then re-melt and secure the components to the board.
doctek (author)  Gilius6 years ago
Yes, I suppose you can do that. If you do, be sure to put additional flux on the board before your reflow it (Scott Driscoll discuss this on his site which is mentioned in the Instructable).

Now here's why I'm not keen on this approach.
- Getting solder on all those tiny pads is a lot of work. The whole point of using a stencil and solder paste is to avoid that work.
- Making the solder reasonably level is nearly impossible, so some pads may not start off touching. This may or may not be a problem, but if there's too much solder on a central pad, then the resulting pillow could keep the other pads from ever touching. Paste and the correct footprints avoids this problem.
- It's really easy to lift a pad from the board with a little too much heat when you're tinning them. Tinning the part itself is a better plan, but I still don't like it.

Hope that helps.
Gilius doctek6 years ago
It's an alternative becuase I can't seem to get my hands on any paste. :(
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