First SMD soldering attempt

Discussion in 'General Electronics Chat' started by spinnaker, Jan 20, 2013.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    I am about to try and solder my first SMD chip. It is a SOT89-5 so not awful bad. I bumped up the size of the pads to make it more forgiving.

    Here is my plan.

    1. Apply flux to pads.

    2. Tin pads.

    3. Place the chip and apply heat to each pin / pad with soldering iron with the smallest tip I have (I think it is the smallest made for my iron 0.3MM)

    Is this a good plan?

    How do I keep the chip in place while soldering?
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    For one-off soldering like that, I tin the pads then remove ALL excess solder with wick, or if it is a commercially made PCB the pads will already have tinning without excess.

    Then hold down the IC with a pointy metal thing on top of it, and just tack a leg(s) with the freshly tinned iron.

    Then inspect it to make sure position is right, if not, heat the tecked legs and reposition it.

    Once it is in the right position solder the other legs, don't worry too much about shorts, just get fresh solder on those legs so they are all soldered even if joined. With a SOT89/5 you will get shorts between legs for sure.

    Then freshly tin the tip again, and wipe off excess from the tip, then when you touch the tip to the legs it should suck off any excess solder from the legs onto the tip, leaving the legs soldered properly but not shorted together.

    It might take a couple of gos if you are not experienced but basically you use the surface tension of the solder on the legs and tip to transfer the excess solder to the tip.

    If you find that hard, you can always resort to using some clean fresh wick to help remove the excess solder between the leg shorts.

    Another tip is to tilt the PCB up, solder is heavy and this will help determine whether the excess solder moves from legs to tip or vice versa.
  3. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    Thanks for the tips. Maybe not the neatest job in the world but not too bad for first try and better than a lot I have seen.


    It was not as bad as I first thought. My hands can shake a bit but I was able to get it under control.
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  4. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    Hey and it actually worked! It is a PT4115 which is a current regulator. I grabbed two 10Ω resistors I had on had and put them in parallel. My target current was 20ma to light an LED and I am getting 24ma open circuit. Not too bad.

    This is just a prototype for a <500 ma regulator I have in mind. Currently, I have the prototype lighting a single led.
  5. vrainom

    Active Member

    Sep 8, 2011
    Are you a wizard?
    just kidding.
  6. WBahn


    Mar 31, 2012
    Not bad for a first go. I would say that you have a lot of excess solder on there, but that shouldn't cause any problems.

    I do mostly the same as The RB, but I try not to get shorts and bridges or have to go back over any more pins than is necessary. I haven't sodered any SMD to a homebrew board for a very long time and those were all pretty large pitch stuff so it didn't take a lot of care. For stuff on fabbed boards (i.e., tinned), for two-terminal parts I put a tiny bump of solder on the right hand (I'm right handed) pad of all horizontal components and the bottom pad of tall vertical components (with exceptions if proximity to other components favor the other pad). I then start with the horizontal components and put a pile of all of the components (no more, no less) of a given value in the middle of the board and then pick one up with a pair of tweezers, hold it in place on the board, and then touch the junction of the solder bump and the component lead and settle the component down on the pad. This almost always results in a good solder joint with just the right amount of solder (in part because I have gotten pretty good at judging how much of a solder bump to use. Once I have all of the horizontal components in place, I turn the board ninety degrees and do the rest of them. By counting out the exact number I need, I can more easily prevent missing a component or putting a component in the wrong place. I also generally highlight a copy of the PCB silkscreen as I mount components. Once I have all the components mounted I turn the board ninety degrees again and solder the other side of the horizontal components, rotate ninety degrees and solder the other side of the verticals. I keep count as I go so that I have some confirmation that I got them all and I also visually inspect the entire board to make sure the joints are (1) present and (2) good, touching up any that need it. For multi pin parts, say a 240-pin FPGA on a 0.5mm pitch, I position the part as best I can and tack one corner leg while pressing the part down gently with a pair of tweezers to keep it from sliding. On most PCBs you don't need to put an initial solder bump and can either rely on the residual solder on the tip or even the solder from the board tinning itselff - you are only looking for a tack joint. I then go to the opposite corner and tack that pin down. I then look at the alignment of all the pins and, if necessary, retack one or both corners. If the overall alignment is good, I may still have to tweak a few pins into alignment individually. Then I proceed to solder down all the pads, including the ones that were just tacked, by touching the tip and the solder (as fine a solder as I can get, which right now is some 0.008" stuff) and a very quick on-off motion. I genreally deal with any bad joints or excessive solder jissues on the spot. I've gotten so that I can (or at least could) put down a 240 pin part in under five minutes. As I said before, I prefer to avoid bridges, but they do happen from time to time and usually a touch with the tip will solve it. Occasionally I need to sweep the bidge out with the tip of the tweezers or a dental pick (dental picks are great electronics tools!). If I have to, I will use solder wick. I've gotten in the habit of using some thin rosen paste flux that I spread across the pins before I start soldering -- I'd guess the volume of flux I use is roughly comparable to the volume of the pins that contact the pad, perhaps a bit more. That seems to rusult in much cleaner joints that require only a very short hit with the iron and almost never any bridging.

    For smaller pin count stuff, I generally still tack opposite corners (or two widely separate pins if "corners" doesn't apply) and follow the same general process even if some other technique might be more appropriate, in part because if I do everything that I can the same way, I get good at that one thing.
  7. nerdegutta


    Dec 15, 2009
    Nice job!

    Have you tried/considered using solder paste, and a kitchen stove/oven?
  8. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
    Solder paste has a short shelf life. I have some around here but didn't even bother looking for it.
  9. WBahn


    Mar 31, 2012
    It has a short life for production work, but I wonder how short it is for hobbyist work. Has anyone here had any experience trying to use solder paste that is many years past its shelf life for hobbyist type stuff where you can spend some one-on-one time with the board?
  10. kubeek


    Sep 20, 2005
    I saw some videos on youtube (i think it was something from sparkfun) where they said that you simply need to mix the dried past with a bit of liquid flux to refresh it. And that was for stenciling, if you apply it manualy I wouldn´t see a problem.
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Yep, I've got some paste that has been used for about 9 years. It's kept in the fridge, and you can "revitalise" it to some extent by heating to 50-60'C for an hour which softens the flux and gets the balls re-lubricated. Mixing helps, mixed when warm of course.

    The problem with paste is not that anything "goes bad" but is a settling and surface tension problem.

    The reason the fridge helps in storage is that it makes the flux very thick so it takes much longer for the balls to settle out.
  12. SPQR


    Nov 4, 2011
    A few months ago I was looking at all those tiny little things on computer boards, and said to myself "those are waaaaay to high tech for me".

    A month ago I was shopping at Jameco and noted some SMD parts on sale and bought a few resistors and capacitors.
    After learning how to read them, I made a PCB for capacitor replacement, and started soldering.

    Since then, I've starting using more and more - no ICs yet, but I've got some drivers and regulators that I'll use over the next few months.

    I used 0.033 solder and did OK.
    Tinning one end of copper, soldering the SMD to the little "lump".
    Pushing down to make it flat then soldering the other end.

    Last weekend I found some 0.015 solder at All Electronics and tried it.
    It works very nicely, and probably will work well for the fine legs on the IC SMDs.
    I'll be using SMDs more and more...
  13. vortmax


    Oct 10, 2012
    Metalmann and SPQR like this.
  14. Metalmann

    Active Member

    Dec 8, 2012
  15. Dreso12

    New Member

    May 19, 2013
    I have been using an toaster oven and a controller for soldering SMD components in pcbs for some time and the results are not bad at all.

    The most difficult thing is to dispense the right quantity of solder paste in the pads but it can be done with a syringe or better with a stencil with a little bit of practice. I have found this video in youtube which is similar to what I do

    The other difficult thing is to set up the oven an find the right temperatures an times but after some tests with an old pcb you can get the right settings and it will work without much problem.

    For the solder paste I just buy small quantities and I store them in the fridge to it lasts longer.