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PCB Forum First attempt at SMD soldering
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Related

First attempt at SMD soldering

Andrew J
Andrew J over 6 years ago

I bought a practice kit that, in theory at least, lights up LEDs in some sequence.  I say in theory, but as all the instructions (presumably) are in Chinese, who knows??  Anyway, it has components in a number of sizes: 1206, 0805, 0603, 3528, not sure for the ICs.

 

I've spent the afternoon soldering away - 76 components - and what can I take away from the experience?  Well:

  1. forget 0603, I'm not going there again.  Just too small for hand soldering.  I did of course lose a 0603 capacitor to the God of Misery and the kit had no spares.  One day, I expect to find it. Or not.
  2. forget resistor arrays as well (I think that's what they are), especially in 0603.  Seriously, what sadist invents such a thing??
  3. 0805 is likely to be the minimum I go with.
  4. I need a microscope to do this stuff.  At my age, my eyes aren't good enough and I have a bit of handshake too.  See also (1)!
  5. I need more practice at (a) soldering; and (b) keeping care of my tip.
  6. 0.46mm solder is still a bit thick, but just about do-able.  I dare say if I was better at 5a then it would be ok
  7. Still unsure of the best tip to use.  I had a 1.2mm chisel tip which is the smallest that I have, bar a pointy one
  8. Solder wick (decent stuff) is very useful
  9. It's not clear what the markings on a LED are - there were two variants (green marks on one lot, cut corner on the other lot.)  I did search but found the information results confusing: I assumed the marks referred to the Cathode.
  10. The ICs weren't too bad: I can't detect bridging, solder wick helped
  11. I don't think I'd be too worried about it in the future, at least I've taken the plunge right!  I'm not convinced I'd do better with paste and a hot-air gun either.

 

Questions I have:

  1. Is 350c too hot?  I used leaded solder: Sn 62, Pb 36, 2Ag with 505 rosin cores from Multicore.  It has a melting temperature of 179C.
  2. Would I fair better with a thinner tip?
  3. I used flux but my experience was it burnt off immediately and seemed to do nothing - related to questions 1 and 2?

 

I suppose the question on everyone's lips is "did it do anything?"  Well, in short, no.  I tested the resistors and they seemed ok, the ICs were getting voltage to the correct pins so I know they are the right way around.  Perhaps the LEDs are on the wrong way, perhaps the soldering isn't right, perhaps components are not in the right place (no markings on the tapes so I may have deduced incorrectly), perhaps it doesn't do anything anyway, perhaps, perhaps.  I'm not too bothered: it was a test/practice of soldering SMDs which it achieved.

 

I could definitely do with more practice but I expect I'll get better over time.  I also think that these practice kits are a good idea and I would recommend one to someone whose not done this before.

 

Thanks for listening image

 

EDIT: I have a follow up thread as well - https://www.element14.com/community/message/275494/l/second-attempt-at-smd-soldering#275494

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  • Andrew J
    Andrew J over 6 years ago in reply to Fred27 +9
    I can do you a photo, I'm not ashamed . Don't look too closely at the Capacitors though - those were (some of) the evil 0603s, one of which has gone on holiday. This was all done by eyesight as well.
  • jw0752
    jw0752 over 6 years ago +8
    Hi Andrew, I think you did a pretty good job too. With respect to the LEDs I always use a small analog multimeter set to R X 1 to test and verify polarity on small difficult LEDs. In the case of my analog…
  • Fred27
    Fred27 over 6 years ago +7
    No photos? Maybe best not for your first attempt! Of course you can now practice some rework until either the LEDs light up or you destroy it by lifting a track. It won't take long to get used to SMD.…
Parents
  • jw0752
    jw0752 over 6 years ago

    Hi Andrew,

    I think you did a pretty good job too. With respect to the LEDs I always use a small analog multimeter set to R X 1 to test and verify polarity on small difficult LEDs. In the case of my analog meter I have tested it and I know that when it is on Ohms scale the black lead is positive and the red lead is negative. Here is a picture of the polarity test of a small SMD LED. The only trick is, once identified, not loosing the orientation on the way to the board. You should be able to test and verify the polarity of your LEDs using the same trick as the test usually works very well even for LEDs that are mounted and in circuit.The procedure doesn't work with digital auto ranging meters just the cheap analog meters that use (2) AA batteries for the Ohm ranges.

     

    image

     

    John

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  • jw0752
    jw0752 over 6 years ago

    Hi Andrew,

    I think you did a pretty good job too. With respect to the LEDs I always use a small analog multimeter set to R X 1 to test and verify polarity on small difficult LEDs. In the case of my analog meter I have tested it and I know that when it is on Ohms scale the black lead is positive and the red lead is negative. Here is a picture of the polarity test of a small SMD LED. The only trick is, once identified, not loosing the orientation on the way to the board. You should be able to test and verify the polarity of your LEDs using the same trick as the test usually works very well even for LEDs that are mounted and in circuit.The procedure doesn't work with digital auto ranging meters just the cheap analog meters that use (2) AA batteries for the Ohm ranges.

     

    image

     

    John

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  • fmilburn
    fmilburn over 6 years ago in reply to jw0752

    Ah yes, I read about that analog meter trick in your book John image.  On some multimeters such as this inexpensive Aneng selecting the diode function will also turn on the LED and give forward voltage.  I am using tweezer leads / tips that are made for SMD components here but usually I just use regular tips like John above.  The markings on the SMD LEDs I have are inconsistent as to where the cathode is and I don't always have the datasheet so a means of determining polarity is needed..

    image

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  • jw0752
    jw0752 over 6 years ago in reply to fmilburn

    Hi Frank,

     

    Good point on the diode test setting. I have found that due to the energy gap I am not able to use this test on some of the blue and white LEDs with + 3V forward voltages.

     

    John

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  • fmilburn
    fmilburn over 6 years ago in reply to jw0752

    Agree...  The Aneng will light the white ones I have which have a 2.6 forward voltage.  But my Extech will not even light those.

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  • Andrew J
    Andrew J over 6 years ago in reply to fmilburn

    That is interesting.  I did try with my meter on both resistance and diode setting so I’m guessing it doesn’t do that.  I’ll try again with my other meter and see.

     

    No idea what colour they are which may be a reason too.

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  • fmilburn
    fmilburn over 6 years ago in reply to Andrew J

    Another method I have used is to set my bench power supply to say 3 V and limit current to say 5 mA.  Or use a battery source with current limiting resistor.

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