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Question about the pic soldering

  1. Dec 29, 2014 #1
    I am learning SMD soldering. Probably need to solder a pic microcontroller with lot of pins. I found this tutorial. https://www.sparkfun.com/tutorials/101
    Not sure if any of you try out that method before. Thank you.
     
  2. jcsd
  3. Dec 29, 2014 #2
    a follow up question. do you think if it is worthwhile investing in one of these soldering stations for serious smd soldering? http://www.whichsolderingstation.com I am thinking about buying Hakko-FX888d (least expensive one) but never heard it before. sorry a lot of questions. Thank you.
     
  4. Dec 30, 2014 #3

    berkeman

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    Staff: Mentor

    If you can afford it, I'd recommend getting a Metcal soldering station. They use RF heating of the tip, so they heat up very quickly and regulate the tip temperature very well (even for heavy thermal loads like soldering to ground planes). You may also end up needing a Hot Air Rework/Soldering station if you do a lot of SMD work.
     
  5. Dec 30, 2014 #4

    Averagesupernova

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    Science Advisor
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    It makes a huge difference on the quality of the PCB to start with. I have replaced many many many SOICs with a soldering iron and a heat gun. Getting the device off the board is always the most difficult part. I have done this by flooding each side of the device and the part sticks to the iron and lifts off. An extra iron, one in each hand, works better. After this a good quality solder wick cleans the pads up. Then use an iron and build up just enough solder on each pad. Lay the device on the pads and apply heat from above with the heat gun. Watch closely and you will see the solder melt and the device starts to pull into place when all pads have become molten. Tap the board and the vibrations help the surface tension of the molten solder pull the device into place. Remove heat and you are done.
     
  6. Dec 31, 2014 #5
    Thank you for the advice. I heard a lot of good things about Metcal station. It is my ideal station. But, it is a bit above my budget for now... Yes, the hot air station is on the buying list too. But, I will get a cheap one first.
     
  7. Dec 31, 2014 #6
    It will take a lot of time for me to practice and get comfortable with SMD soldering. I will get a heat gun. Appreciate your input.
     
  8. Jan 3, 2015 #7
    Either the Weller or the Hakko are good products, though I suspect the Hakko has superior comfort and tips. I still use a Weller, because I'm just that way...

    (1) The soldering tip must be very clean so that solder likes to wick onto it and make excellent thermal contact. Even a tiny bit of oxide or scale, and you won't be able to transfer heat effectively. A wet sponge is a great means for rapidly cleaning the time, and applying a little extra solder to the tip helps as well. If the tip is so contaminated that it requires harsh cleaning, it's better to get a new tip than use harsh chemicals (saves time).

    (2) Solder actually penetrates into the metals to be joined at the surface to form an intermetallic bond. If either metal has contamination (i.e. oxide), the solder doesn't have any interest in the metal.

    (3) Metals to be soldered should be clean before hand. Keep materials in a dry bag. If corrosion is present, clean it off and clean it well. Avoid oils in the solder area - especially silicon based oils. Solder wick also corrodes, so store it in a sealed, dry bag when not in use.

    (4) Even clean metals will have oxide on them, solder flux will leach away thin oxide layers to allow the solder in. Both solder and flux are presented at the same time, but the flux quickly becomes overheated and loses it's cleaning ability. So, be prompt about solder joints lest they corrode from the air around them.

    (5) This is touch, but here goes... Lead free solder is awful to work with. It requires higher solder temperatures, tends to be tacky, and doesn't show good capillary action. My favorite solder is Ersin Multicore 63/37 Pb/Sn with rosin activated flux. No clean flux means you can't get rid of it, and once the circuit sees humidity, you'll have tiny leakage currents through the flux. Water clean seems to work out if you have the right baths, but I don't. The old rosin flux is messy, but I kinda like the smell and I know I can always get it off with alcohol.

    (6) About lead solder - Using lead solder means committing to discipline. You must segment your time, and enforce required

    behaviors. There is a time to solder and a separate time for eating, going on break, handling babies, etc... You must always put away the solder and residues and wash your hands thoroughly afterwards. You must keep the solder in a place that is safe from kids and animals - especially cats. This stuff is a slow, irreversible toxin, so you need to give it respect. When your done with a roll due to old age (very old age, LOL), be certain that it goes to a reclamation center. The same holds true for any old circuit boards.

    (7) About lead solder paste - Lead solder paste is incredibly bad for the environment - and you. By breaking the lead into millions of tiny spheres, it becomes very effective at dissolving into ground water and contaminating your skin. It is very difficult to use lead free solder as a hobbyist, but this stuff is bad enough to make you cross the line.

    (8) Design your boards to be soldered - Think seriously about how you're to solder a part when designing it's PCB decal. Make the pads about .05" longer to have access with a solder tip. Be careful of chips that have pads underneath - it's difficult to solder those pads. Smaller pads underneath with a large plate through hole allows you to solder from the backside. Don't run traces directly from one pad to another. Route them out and then back to the chip. Don't make massive routes when you can avoid it. These require a lot of heat to solder.

    (9) HASL - SMT parts are easier to solder on a board that has a fine layer of solder on the pads. Thus HASL (Hot Air Solder Leveled) boards are easiest to solder.

    (10) Resistors and Capacitors - Start by wetting the pads with a thin solder flux (i.e. from a flux pen). Capacitors and resistors are usually placed using fine tweezers in one and and the soldering iron in the other. Some people place a tiny bit of solder on the first pad to be soldered and remove some of the solder with solder wick if it proves to be a bump. Lower the part into place with the tweezers, and heat the pad with the iron after the part is in place. It's important to get the heating time to a minimum, so if you slip, remove the part, and reprep the pad before starting over. Afterwards, heat the opposite end and flow solder into the joint. Be fast, or the first joint will melt! Finally, fill the first joint as you did the second. This method will not work for 0402 parts because they will unsolder too quickly. 0603 parts require skill, but I've had no difficulty with 0805's. Thus I design with 0805's or larger.

    (11) SOT23-3, etc - These are usually a dream to solder. Simply tack or solder the center lead while using tweezers, and then get the opposite leads.

    (12) ICs - Solder SMT ICs comes in various levels of difficulty. SOIC packages are easy. Finer pitches are somewhat difficult but possible. QFN are a nightmare, and BGA's require extra equipment and care. For SOICs, fine pitch, and QFNs (especially QFNs) remember to design your solder pad so that it extends beyond the leads. Much of the work requires transferring heat (and even solder for QFNs) across the pad.
    The first step for all but BGAs is to obtain X-Y orientation and corner tacking. A bit of tacky solder paste is helpful. Lightly apply the paste to the board to aid in holding the IC steady and cleaning solder joints. Align the IC as well as possible in the X and Y orientations, and attempt to tack it into that position be soldering a corner lead. This may prove difficult, but it is important. Afterwards, shift out any tiny misalignments while tacking an opposite pin. Sometimes you may need to go back to the first pin to be sure everything is aligned. Next, tack all corners. Now, load the pins up with tacky flux to about the height of the pins. Clean the soldering tip thoroughly. Apply a small drop of solder to the tip and wipe one row of pins with the solder ball. If your timing was good and all things in your favor, every pin in that row will be soldered in one wipe! For QFN's alignment must be done correctly on the FIRST pin. It will not rotate to allow a correction. Also, QFNs require a lot of care to ensure each pin has had an opportunity to heat and draw solder under the chip. Even after all of that, they often have a pin or two that's unsoldered, but difficult to spot...

    (13) Regarding BGAs - Avoid them... If you're forced to use one, I've found that preheating the board with a hot plate (i.e.125-150C) and then using the hot air tool helps. Yech!

    I hope some of this helps, and I wish you well.

    - Mike
     
  9. Jan 4, 2015 #8
    That is a lot of info to process. Thank you very much for all these tips. Appreciate it!

     
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