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mass soldering techniques

Discussion in 'General Electronics Discussion' started by Danneskjold, Apr 16, 2010.

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  1. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    Hello Everyone,

    Just registered and happy to find this place!

    I am working with a friend on an electronics project that we intend to produce ourselves while the numbers are small. Then of course we'll farm it out to a stuffing house.

    Our new board consist of both through-hole and surface-mount parts, including a FPGA. We are not quite sure about how to go about soldering everything efficiently.

    and obviously we don't want to buy a wave solder, especially here in California!

    I have read some of the posts about using solder paste for through-hole. Unreliable, is what I took away from it.

    So, how would you go about doing this soldering job? Right now we are looking at hot air rework for the smd parts and with a special nozzle for the FPGA. Then, manually soldering the throug-hole parts. I hate to think of that kind of labor, form a number of perspectives!

    Are we sure that the shole thing could not be assembled with generous dollops of solder paste on the through hole parts, and run it through a convection oven for reflowing?

    Or, has anyone tried to do some kind of DIY pseudo wave soldering, wherein the board is heated and sprayed with flux, and dipped into a bath of molten solder for a very short time? I have read about folks trying this in other parts of the Intrnet, and no one can really offer anything that works.

    I was thinking of some kind of enclosure that is devoid of oxygen (by N2 purge or the like) to avoid the dross problems.

    OK that's a lot for my first post. Looking forward to your responses!


    Cheers,
    Danneskjold
     
  2. NickS

    NickS

    367
    0
    Apr 6, 2010
    Hello

    I work in a fairly small firm that does our own production work too. Are any of the SMT parts leadless(is the FPGA a BGA package)?

    We just implemented a solderpaste delivery mechanism that uses fixed amount of pressurized air(from a small compressor and external trigger/regulator). It works great for fast consistent delivery in quantities too small to justify making a paste screen.

    Anyhow this may be a working solution for your through hole stuff. After the through hole parts are inserted into the board you could distribute the paste where you want it (fairly rapidly). And then reflow the solder.

    For reflow we use a board warmer that brings the entire board up in temp but not to the melting point of solder so that after we apply the paste we just brush quickly over with the hot air pencil and the solder is flowed.

    Just a thought.

    Welcome to the forum.
    -Nick-
     
  3. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    Induction soldering

    I saw a youtube video of an induction heater used to solder a board. Any thoughts as to how this might affect certain board components?

    Barring that, It seems like an ideal method--induction heating only heats conductive objects. I am sure that the heating could be controlled so that traces aren't lifted, but not so sure what would happen to ICs or even capacitors.

    Anyone?


    Danneskjold
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    I've seen people use frying pans! (I am not recommending this)
     
  5. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    Moderator,

    C'mon. I am new here but I expect better.

    I know, it's Friday night!


    Danneskjold
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    Saturday afternoon here Danneskjold.

    I would invest in a small reflow oven (I'm presuming all components can be done this way). I use a "home made" oven and a rework tool for very small things. An oven will give you the consistency you can't get with a rework tool.

    You *want* consistency, especially with BGA that are next to impossible to inspect without expensive equipment (X-ray I believe).

    How much through-hole is there? What quantities are you doing? Is hand-soldering a possibility? I'm not sure I'd like to use a reflow technique with through-hole stuff except in some fairly unusual cases.

    How are you laying down the solder paste?

    Oh, and for wave soldering or similar... How are you gluing the components to the board?
     
  7. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    Thanks for the thoughtful reply, Steve!

    We are still in the design phase of the board, so I can't say what the respective parts counts are. I do know that there will be the FPGA and ATM-90 on the surface mount side, and a large poly cap and toroid inductor on the through hole. Those can easily be added after reflow of course.

    I can try to convince my engineer to use more smd parts, but I am slightly at his mercy as his eyesight and dexterity are challenged. But I may press him regardless as a matter of necessity.

    Is glue necessary with reflow? I thought just with wave solder. Out of interest, what is generally used for that?

    Reflow ovens: I have not done one lick of research on these, so please forgive my ignorance. I have built numerous conventional, convection and infrared ovens for my glassblowing business, so I am aware of the basic concepts.

    What principle do reflow ovens operate? If I had to guess I would say convection. If I were to build it today, I would probably use an infrared burner or electric element to irradiate the bottom of the board, and also use a fan to transfer the secondary heat to the top side. A small conveyor belt would be cool.

    But again, I know less than nothing about how this is actually done. Thanks in advance for your help!

    Danneskjold
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    If you're going to use surface mount and hand solder the rest, then I would strongly advise you to use as much surface mount as possible. Laying down the solder mask and placing components is faster (with practice) than soldering, and reflowing in an oven is not only really cool to see, but produces an amazingly professional result.

    I would be testing my ability to reliably solder any BGA package, and if your engineer is not familiar with their use, I'd use another package that allows visual inspection.

    Reflow ovens either use heated air, IR or a combination of both. There are published temperature profiles that basically heat the board for a while, then increase the temperature to a point which melts solder, then reduce heat again at a controlled rate.

    Depending on your budget, you can spend thousands. the "cheap" ways are summarised here. I would tend to recommend an oven with good temperature control as I don't lile the idea of the temperature profile the skillet idea involves (see, I wasn't joking!)

    That article actually points out some important points. The thermal inertia of components can make a difference. In that case I *may* have opted to run the oven once with just the large USB connectors, then place all the smaller components. It means you can minimise the amount of heat applied to sensitive components. This may be an issue for you if you have any large components.

    Another point to watch is that some components may melt in an oven and you will need to add them manually later. This is *generally* not a problem for surface mount components,

    Glue is only required if you're using a solder wave technique or you're soldering both sides at once. If the board is double sided, you can theoretically solder one side with a high temperature solder, then later the other side with a lower temperature solder, but obviously your temperature control needs to be really good. Dispensing glue is it's own issue because you want something that is stable at 250C and isn't going to lift the components from the board. It's really easier not to use it.

    For a while a colleague and I used a variation on the skillet technique. We had a hot air blower that the boards sat above which was set to approx 150C and then used a hot air rework tool above the board. The heating of the board to a relatively safe temperature made reflowing much faster with the rework tool.

    Reflow ovens (in our experience) completely eliminate some problems with very small components (0603 and 0402). Manually reflowing these occasionally causes them to stand on end when the solder at one end melted before the other. The melted solder has strong surface tension and can impart quite a force on components. Normally this is a good thing, bringing components into alignment as if by magic, but if you're using a rework tool to do a whole board and you happen to cause one end of a resistor to be melted well before the other, bad things can happen. This happened on test boards more than in real life (when we were testing the limits of technique) but it is a thing to watch out for.
     
  9. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    The answers to all your questions will be different depending upon how many components there are on the board and how many of the boards you expect to produce.

    Before you decide that you need to buy or make an automated system, step back and really look at your requirements. For really small quantities, you can hand solder everything except BGAs. For anything more than small quantities, you can farm out the assembly to a place that specializes in doing that. It is the zone between "really small" and "small" where the heartache lies.

    Given a choice, I would get whatever I can in surface mount. Other than certain connectors and very large power devices, everything else can be had in in surface mount.

    ---55p
     
  10. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    Thanks for the advice, 55p.

    I was talking about this with another friend, and he had something interesting to say: that when solder is placed in an iron container, it forms a meniscus. With a board-sized bath, one could pre-heat the board, and dip it in the solder. the meniscus would ensure that the solder travels from the center of the board to the outside edges.

    These are small boards, about 4" x 4".

    Anyone seen or heard of this? Thoughts?



    Dananeskjold
     
  11. 55pilot

    55pilot

    434
    3
    Feb 23, 2010
    You sound like you are a solution in need of a problem. You have decided that you want a wave soldering system and now you are looking to justify that "want". A better option would be to avoid putting yourself in a position where you can even use a wave soldering machine. It is easily done.


    ---55p
     
    Last edited: Apr 20, 2010
  12. Danneskjold

    Danneskjold

    23
    1
    Apr 16, 2010
    solder bath

    Hello All,

    Just thought I'd update you on this topic, and what I have learned.

    Our new board that has a ton of smd parts on it now, is going to be made by e-teknet. with two 100-pin chips, we decided not to pull our hair out. (as if I had any to spare!)

    We still have a couple of through-hole only boards. What I ended up doing was making a solder pot that's big enough to fit our largest board. I mount the through-hole parts, and cut the leads. brush with rosin flux, and put into the toaster oven to warm up and activate the flux.

    then, with some tongs I made, I grab the board by the edges, and dip it in the solder bath. I use a slight rocking motion, and one second later, over 100 solder joints are done.

    The solder 'holidays' I had in the beginning were all due to insufficient flux. the boards come out perfectly now. I have a new membrane nitrogen generator I picked up from eBay for about $125, so soon I will have some inerting as well, to cut down on the dross.

    Anyone else ever try this?


    thanks for all the tips and suggestions!


    Danneskjold
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    I don't suppose you could supply some photos could you? And give us some idea of the temperature profiles you're using?
     
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