Replacing components on a PCB

Discussion in 'The Projects Forum' started by djsfantasi, Mar 20, 2016.

  1. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
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    Hello! I need to replace/change values on four resistors. I've successfully removed the originals with a soldering pencil, solder wick and a few tools.

    But the through holes still have solder in them. How do I insert the new resistors?

    Any and all tips and techniques are welcome.
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    Either use a solder sucker, or add solder to the holes and rewick it out. Or, you can "walk" a new resistor in by placing on the solder, the flowing it while pushing the resistor down. A little on one side, then a little on the other. Ultimately, your new resistor will be in place and you can trim the leads and go to the others. Once the resistors are in place, add fresh solder to the pads so that there aren't any cold solder joints.
     
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  3. magnet18

    Senior Member

    Dec 22, 2010
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    Be VERY careful with this, I can't count how many times I've ripped off a copper pad trying this or something similar, especially with ground/power planes that don't want to heat up.

    Your best bet is the solder sucker, heat on one side and suction the other
     
  4. #12

    Expert

    Nov 30, 2010
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    Melt the solder and poke a dental pick in the hole. Solder won't stick to stainless steel or tool steel.
     
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  5. John P

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    Oct 14, 2008
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    Or heat up the pad while holding the iron in one hand and the board in the other. Then very quickly, rap the board on the edge of your bench so that the solder is flicked out of the hole. Only do this with boards that do not have fragile components on them!

    Or clip off the leads of the old resistor so that there are stubs left standing. Then solder the new resistor to these. Yes, it looks funny, but it works.
     
  6. djsfantasi

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    Apr 11, 2010
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    Now that's an idea! Unfortunately, I've already removed the components.
     
  7. jpanhalt

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    Jan 18, 2008
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    I effectively do what SLK001 does with solder braid and rarely have to add more solder. Never had to use a solder sucker on typical holes. There are differences between braid brands. Some seem to suck the solder much better than others. I stick to just one of two brands I trust. Also, I find the braid that is one step up from finest (i.e., size #2 or B) works well. It is thin enough to be deformed just a little by the iron's tip to get into the hole and suck the solder. And as SLK001 said, if you can't reach the solder with the wick, add a little more solder and repeat.

    Another tool I use is a fine piece of music wire. My usual use for that wire is to hold smd parts in place while I solder one end or pin, but it is fine enough to go into most TH's. Solder doesn't stick well to it, and you end up with a hollow casing of solder. It is definitely my second choice, but comes before the sucker.

    If the hole is not through plated, you many have to work from both sides.

    John
     
  8. djsfantasi

    Thread Starter AAC Fanatic!

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    @jpanhalt
    Music wire! What a concept. Particularly since I think I have some. Or I can get some old guitar strings from my son.
     
  9. jpanhalt

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    Jan 18, 2008
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    For my uses, I grind the cut ends to a cone. Shape is not critical. The reason I like it for holding parts is that it is just a little springy. The size I use most often is 1/32" (0.034"), which is probably a little large for a guitar; although, I have no idea. There are many sizes available, as you know.

    John
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Add a bit more solder and rewick it out.. repeat if necessary..
    It will come right out when you do it properly..

    Or yes just heat the pad/solder and plunge the resistor into it while hot..

    The "smack it on a desk" trick is a bit dangerous (use safety glasses for sure) and highly frowned upon/not allowed in any professional company..
     
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  11. SLK001

    Well-Known Member

    Nov 29, 2011
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    You also have no control as to where the molten solder ends up. It can (and has) resolidified across pins on an IC. You're then left with a "gee, how did that get there" look on your face.
     
  12. #12

    Expert

    Nov 30, 2010
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    In a much more complicated look at the matter, "suck" is merely the opposite of, "blow". Compressors are way easier to find than vacuum pumps, and aquarium stores sell valves for low pressure applications. You might find a cheap way to change this from a suck job to a blow job.:rolleyes:

    I did a vacu-former for a wooden leg store which involved a pedal to on-off the vacuum. The pedal is pretty expensive at Graingers. Then a 5 gallon compressed air tank from Western Auto. Still, I expect you don't want to spend a couple of hundred dollars for a Rube Goldberg contraption. Just, if you have some of this stuff laying around, it might be easy enough and cheap enough to rig up some amateur hack job to remove solder. The problem with hooking up a wet&dry vac is the huge waste of power and the "annoying to unbearable" noise it causes.
     
  13. mcgyvr

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    Thats what I was referring to with the "dangerous" aspect..
    You never know when its going to fly up into your eye or burn other parts of your face/body/surrounding furniture,etc...



    Wicking is easy but as I stated sometimes it works much better if you add some solder back to create more of a "mass" that transfers the heat around better.. Too little solder and you just can't pass the heat around well enough to consistently get that last bit out..
     
  14. djsfantasi

    Thread Starter AAC Fanatic!

    Apr 11, 2010
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    Ahhh, the old "do it properly" story. That approach sounds the cleanest to me (if not intuitive).

    I'll try it tonight. Thanks for all your suggestions.
     
  15. djsfantasi

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    Apr 11, 2010
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    Worked like a charm! Added more solder and then wicked it out. For 7 of 8 holes... That last one, I took a sacrificial resistor and heated a lead and pushed it through the hole... I drew it back a hair (drawing out the solder) and let it cool. Then, I used the wick, reheated the joint and pulled the resistor out. Ta Da!

    Thanks again.
     
  16. John P

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    Oct 14, 2008
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    Technique, my friends. Skill. But no, it's not a method for the professional environment.
     
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