SMT the old fashioned way

[Mariss Freimanis]

Hi,

Part I)

I've had a request to describe how to mount and dismount SMT (surface mount technology) components using manual tools only. We regularly manually assemble prototypes of our drives using a soldering iron and optionally, a hot air hand-piece rework station. No specialized equipment is necessary except for the optional hot air station.

Why do it manually instead of using a pick-and-place machine? Because it is faster when assembling a one-off prototype. It takes over 4 hours to set up a parts trolley and to program component data into a pick-and-place machine. An average drive board of ours has about 150 SMT components; the machines can populate the board in 50 seconds and they are indispensable if you are building 500 drives a day.

With the right manual technique and a few inexpensive hand tools (some homemade), it is possible to place and solder 6 SMT components a minute. A 150 part board can be manually populated (150 parts placed and soldered) in about 30 minutes. Manual setup time is about 30 minutes; the parts you are going to use have to be selected from their carrier tape. That is 4 times faster than a high-speed pick-and-place machine when setup time is included (by hand = 60 minutes; by machine = 480 minute setup, 1 minute run time).

The manually assembled results look just as good, clean and precise as what you get from a production machine. You cannot tell them apart when you use a hot air hand-piece (highly recommended).

In succeeding parts I will take pictures of this process and maybe a few short videos where necessary. Let me know if this is of any interest.

Next: Part II. List of equipment.

Mariss

[Arquibaldo]

Dear Mariss:

Thanks a lot. I'm already sitting on the stands...

Nelson

[Mariss Freimanis]

Part II)

Equipment list:

1. Pencil type soldering iron.

We use JBC Tools BD-1BA soldering iron stations
http://www.howardelectronics.com/jbc/BD-1BA.html
These are expensive at $375 but they are the best you can have. We use the 0.4mm tip cartridges (C245-032) for SMT work. These are usable with even 0.5mm pitch surface mount ICs. Again, pricey at $29 a solder tip cartridge but they are very good.

A cheaper ($99) alternative is the Xytronic LF-1600 with the 44-510603 0.4mm tip ($7.50). I haven't used it but it looks serviceable.

Don't cheap out on a soldering iron station when you work with SMT. It has to be temperature controlled and it has to have a very fine (0.4mm) tip diameter. Anything else is like doing brain surgery while wearing mittens. Run the iron at 250C when using lead solder; this isn't a Tooltime Tim project, hotter isn't better.


2) Optional but very highly recommended. Hot air rework station.

We use Xytronic 852D hot air rework stations. They cost $350 but here $350 is a bargain. Once you use it, you will wonder how you ever managed without this a tool. You flat out cannot properly desolder SMT parts without a hot air station. You will either damage the part, damage the board or waste an awful lot of time trying to avoid damaging either.

It takes 3 seconds to solder or desolder an 0805 or 0603 passive, 15 seconds to work an SOIC-16 and about 45 to 90 seconds to work a VQFP100 package. The results are absolutely clean and unstressed going on or coming off. If you are going to spend money, spend it here.


3) Solder.

Use lead solder (Pb63Sn37) for prototypes. It melts at 178C and is far easier to use than lead free solder at 228C. Lead solder wets better and gives much better quality solder joints than lead free solder. Use 0.025" (0.63mm) diameter rosin core solder. Kester "44" is a quality wire solder. Go to www.digikey.com and get a 1lb roll (KE1109-ND) at $30.23


4) No clean solder paste.

We use AIM www.aimsolder.com no clean solder paste (NC257). Get a 500gm tub and it will be a lifetime supply. Make sure you keep the tub cover screwed shut at all times and store the tub in your refrigerator. This will insure it never dries out.


5) Tweezers.

Get some needle tipped stainless steel tweezers. The tweezers tips will be at molten solder temperatures and you don't want solder to wet the tips. Get a couple because they are cheap.

The tips should be sharp enough to draw blood if you accidentally stab yourself. Which tweezers to use is a personal choice, I like the miniature kind that offers almost no resistance when you close them. Never drop them on the floor; there is nothing worse than a pair of tweezers with misaligned or slightly bent tips. They are 0603 part size catapults.


6) "Homemade" tool.

Almost all surface mount components can be picked up with a magnet. Chip resistors and capacitors, SOT-23 diodes and transistors, SOIC 8, 14 and 16 pin ICs, chip LEDs, even QFN and VQFP packages. They are all ferrous and a magnet will pick them up from their paper tape and plastic carrier trays.

A magnet beats the heck out of using tweezers to pick them out of their carriers or turning the carriers upside down to dump the parts.

There is only one thing better than a magnet and that is an electromagnet. You can turn it on to pick up a part, turn it off to drop the part where you need it. Downside is you can't buy one so you have to build it.

Start with a small Phillips screwdriver. Pick one with a shaft diameter of 0.05". Grind the Phillips end off on a grinder until you have a 0.05" diameter shank with a flat end on it (cylinder). Wind about 500 to 1,000 turns of #30 gauge magnet wire on the shaft. I found some nylon bobbins (1" long, 0.05" ID) to wind the wire on. Wire an SPST surface mount switch (found some in some old TV remote controls) in series with the winding. Epoxy the switch on the screwdriver where it's easy to reach with your thumb while holding the screwdriver. Use an alkaline C-cell on 2' feet of wire to power the picker-upper.

Hover over the part you want, press the switch and pick it up, place it where you want and release the switch. The part releases. Repeat as needed. Far faster and easier than using tweezers to remove parts from paper tape carriers. I wonder why inexpensive pick-and-place machines don't use this method instead of using vacuum pneumatics. My picker-upper is enhanced with a de-gaussing circuit that activates every time a part is released. This for keeping the screwdriver shank from acquiring residual magnetism. I'm a EE so I have to get fancy.:-)


Next: Part III. Prepping the printed circuit board and parts.

Mariss

[kewlkiwi]

Originally Posted by Mariss Freimanis ....Next: Part III. Prepping the printed circuit board and parts.

Great series Mariss, please continue.

Bob

[phomann]

I guess I should add my 2 bits worth. I've made many hundreds of smt boards by hand.

I've tried a number of different tweezers. I find the needle point ones, occasionally slingshot parts accross the room. I now only use the following;

CK-2334 These have small flats on the ends whick are ideal for 0805 and 0603 chip resistors. capacitors, SOTs and other small parts.

ideal-tek SM108X These are a scissor configuration and have small flats on the end. I use them for SO-8, SO-16 , PLCC and larger parts.

I find that tweezers with flats on the end provide better gripping pressure.

The soldering iron I use is a Hakko FX951. I used to have a Weller magnastat. The Hakko is in a different league. I use a 3mm chisel tip. If the tip is too small you don't get the heat transfer happening quick enough.

As to solder, lead is better than lead free. For prototype work I use low melting temp solder. It has 2% silver and is more expensive. But it is great for reworking prototypes.

Another essential is a syringe of gel flux. I makes a breeze when soldering fine pitch stuff.

I also find the PCB holder essential. Mine is from Zephtronics. I use the slab of aluminium as an arm rest. It is necessary to provide stabilisation

Cheers,

Peter.

[TOTALLYRC]

Great stuff.
I will keep watching.

[raymondg]

Mariss,

Thanks for sharing, you're posts are always a pleasure to read. Just letting you know there is plenty of interest here, especially for the pix and vids if you can find the time.

Regards,
Raymond

[eSilviu]

I've used an aquarium pump to pick and place SMT components.
You will say that aquarium pump is blowing air,... but I made-it to suck air - by mirror the rubber seals (or whatever the small piece of rubber are named)
If you want pictures... tomorrow or monday.

1. get PCB's
2. apply solder paste with a stencil
3. place components by type and value
4. owen
5. check for errors

I've made this in batch of 10 to 20 (until my table was full of PCB's).
As quick as can be.

[epineh]

Hi Mariss, just wondering if there is going to be a part three ?

Great reading so far.

Russell.

[vger]

A friend of mine has a pick and place machine for production runs, but always puts one together by hand first for testing. He has 3 toaster ovens that have controllers operating the heating profile. He uses a thermocouple stuck into a hole in one board in the oven to monitor / control the temp of the boards.

[bill south]

Mariss;
I'm sure you are appreciative of others wadeing in but I sure would like for you to finish your small tutorial. I'll have a bit of surface mounting coming up in the near future and I'd sure like to learn from the tried and true master.
Many thanks for all you have contributed over the years!!! I use your drives in all my machines.
Bill

[nerginer]

Mariss;
can you give some information regarding your de-gaussing circuit?,

regards,
Nuri Erginer