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In Reply to: RE: My first clock install. (need help with extra resistor) posted by tweakmenow on October 28, 2014 at 17:41:40
Removing SMD and soldering in replacements isn't that hard actually. I did it with a good Weller iron with a small tip and and a good heat gun. The other key as I have aged is a magnifying light.Practice: find some old SMD boards say from an old computer or where ever and practice removing items with a heat gun and resoldering them in place. If you are removing say just a small cap or resistor a combo of the heat gun and tweezers on the part so you can remove the part the second the solder bond melts is good. A heat gun is not a blow dryer, it needs to be hotter and have fan speeds that can go lower. It is possible with misuse to blow off several components if you're not careful.
The next step after removal is to clean the mounting pads with good solder wick that has flux in it. Now the surface is ready to solder in the new part. Lay the part in place and remember it takes very little solder. Sometimes I use a small tool like a pick placed on top of the part to hold it in place with one hand while I solder the part in with the other. I just put some solder on the tip first, no need to feed solder which would take a third hand.
Unsoldering that 64 pin chip in your photo isn't that hard either. I sure thought those types would be before I did them. Removal with a heat gun is pretty easy. Resoldering one in its place just requires cleaning the pads, placing it in the center so everything lines up and then solder just one pin from each of the four sides to hold it in place. Just solder one from each side even if it is off a bit no big deal. Reheat each of the four pins as needed for small realignments. When you have done that well and the chip is centered then solder in all the other pins. It is easy to oversolder and you may see a solder jump between two or even more pins. Not to worry. Finish doing ALL the pins first. By the way a dab of solder on the iron is often enough to do two or three pins. Keep doing pins until there is not enough solder on the tip before adding more to the tip. When you're done all you need to do is to take solder wick over the excess solder to clean up any shorts between pins. It works well. Take time to practice. I'm older with not the steadiest hand but still can do it.
Email or contact me for more info if needed. I'm sure in my three years as a bench tech I soldered at least a few thousand SMD items. I only messed up a board a couple of times and made 30 gauge wire jumpers to fix those errors.
ET
Edits: 10/30/14 10/30/14 10/30/14Follow Ups:
I'm humbled by your experience. Once, I had to replace seven SMD in a regulation circuit. I worked using a wide angle 10X eyeglass. Much to my amazement, the soldering was a success.
On another note, thank you for the FANTASTIC post...
Thanks pal for the kind words. I'm no great tech, truth be told I'm more of a parts swapper than someone that can properly diagnose circuit problems all the time perhaps even half. I am one that learns very well from repetition and I was surprised I did as well as I did w/SMD. The first time I did a big four sided chip it didn't go so well but then I got better, then good.
"Repetition is the only form of permanence in nature" - George Santayana
ET
Great post with v useful info. Thanks for being explicit.
YW, it took some time but it was OK after a while. Then I started to like it.
ET
A good iron with a small tip, decent heat gun and a mag are paramount to SMT work.
I luckily have access to a research lab that hand-build prototype components for aviation power supplies and instrumentation (heck, I RUN it!). As a result, I pretty much have the ability to bring in anything that needs work done (within reason of course) and do it on down/off time. Of course, I also get some nice viewing equipment (stereo microscope, loupes of different sizes, etc.).
Dman
Analog Junkie
Nice, access is a great thing!
ET
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