Author Topic: Some times, things work out the way they should  (Read 2864 times)

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Offline Rick Law

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Some times, things work out the way they should
« on: January 11, 2015, 01:01:48 am »
Hey, allow me to share with you my success – my first venture into repairing (replacing) small SMD.

My Adafruit ADS1115 and Adafruit MCP4725 were killed by over-volt.  I got the replacement chips from Mouser.  The MCP4725 is SOT23-6, 0.95mm pitch.  The ADS1115 is VSSOP at 0.5mm pitch.

A few months back, I practiced with SOT23-6, VSSOP/ MSOP I found on an old dead cell phone.  I was estimating I had a 50/50 chance of doing it right and may even melt a leg out cleaning up solder bridges as I did during practices.

Reality worked out better.  Practice makes perfect and the dead cell phone really helped.  I had to do a good bid of solder-bridge cleaning.  BUT they both work the first time!  Neither fix look great, but they works!

That feels good.  Looking at the VSSOP, I really was not sure I would succeed...
 

Offline ConKbot

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Re: Some times, things work out the way they should
« Reply #1 on: January 11, 2015, 02:07:11 am »
 :-+ Glad it worked out well.  In the future, if you have to do it again, make sure you have a small chisel tip for your iron, (none of that point/conical nonsense! ) Good solder wick (chemtronics, soder-wick, or any other good brand, deal extreme cheap stuff cant be hit or miss, even with flux added )  Extra flux (flux pens are great for this kind of thing)  and obviously tweezers, and solder thats 1-2x the width of the pad your working on. With all of that, and enough magnification while you work, you can be pretty confident you'll get it done  :)

The worst thing Ive ever worked on is a 0.4mm pitch connector, that had 'blade' style leads instead of the usual formed type of lead.  The big parallel blades that went up into the connector would bridge together super easy, and you couldn't use flux and a 'dry' iron to clear the bridge, you had to use wick and suck out all the solder, and then attempt to solder the pins again because there wouldn't be a good enough fillet to the pad.  0.5mm connectors of the same style werent anywhere near as problematic. Dropping that 0.1mm made all the difference in the world.
 

Offline dannyf

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Re: Some times, things work out the way they should
« Reply #2 on: January 11, 2015, 02:18:02 am »
two things really helped me in situations like this:

1) use generous amount of solder paste. they really helped keeping the solder in place;
2) use a bulky solder tip. I actually bent one of my pointy tips in to a tiny "J" at the end and it helps with soldering tremendously. Cleaning is a little bit tougher, however.
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Offline Rick Law

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Re: Some times, things work out the way they should
« Reply #3 on: January 11, 2015, 02:39:04 am »
:-+ Glad it worked out well.  In the future, if you have to do it again, make sure you have a small chisel tip for your iron, (none of that point/conical nonsense! ) Good solder wick (chemtronics, soder-wick, or any other good brand, deal extreme cheap stuff cant be hit or miss, even with flux added )  Extra flux (flux pens are great for this kind of thing)  and obviously tweezers, and solder thats 1-2x the width of the pad your working on. With all of that, and enough magnification while you work, you can be pretty confident you'll get it done  :)

The worst thing Ive ever worked on is a 0.4mm pitch connector, that had 'blade' style leads instead of the usual formed type of lead.  The big parallel blades that went up into the connector would bridge together super easy, and you couldn't use flux and a 'dry' iron to clear the bridge, you had to use wick and suck out all the solder, and then attempt to solder the pins again because there wouldn't be a good enough fillet to the pad.  0.5mm connectors of the same style werent anywhere near as problematic. Dropping that 0.1mm made all the difference in the world.

You are absolutely right.  During the  "cell phone practice", I used a 1.2mm chisel to (re) solder-on the SMD's, but I do use a conical for removal when I don't really care about if the part survives.

The wick is a must - I can't imagine how else I would remove the bridges and I was getting a lot more bridges than during practice.  I was using cheap Chinese flux during practice which made the solder a good bit more fluid.  I was using Radio Shack rosin today and I don't like the way it works.

Getting the VSSOP done was really good.  Now I should loose my phobia on working with things that requires magnifier instead of just my reading glasses.

two things really helped me in situations like this:

1) use generous amount of solder paste. they really helped keeping the solder in place;
2) use a bulky solder tip. I actually bent one of my pointy tips in to a tiny "J" at the end and it helps with soldering tremendously. Cleaning is a little bit tougher, however.


I love the J-chisel.  My old iron has that and I was looking for that for my hakko clone.  Bending one is a good idea.

I do have to find better flux.  The Radio Shack rosin turns too dark to quick and I have problem seeing what is where with the dark brown stuff all over the place.
 

Offline devanno

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Re: Some times, things work out the way they should
« Reply #4 on: January 11, 2015, 07:46:55 am »
Since you're working with already once-wetted surfaces, try some good no-clean flux.  It's not as aggressive as the highly activated or RA fluxes.  I get mine in syringes as a liquid (not the paste flux, but I have that too).

On a whim, I bought an inexpensive hot-air rework station (an Aoyue).  I found that my first attempts proved that I needed practice, but after a few components, I got the hang of it.  (I'm not suggesting you go out and buy one of these, but if you get into enough SMD rework, you might consider it.)

Images below are of a lighting board in a model RR car... the first (Image 9) is the manufacturer's installed LED and questionable soldering work.  The second, (Image 10) is my replacement of a similar LED using hot air.
Free Electrons - Just one, please.
 

Offline Psi

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Re: Some times, things work out the way they should
« Reply #5 on: January 11, 2015, 08:26:32 am »
imho the 2nd pic needs a bit more paste.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline Rick Law

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Re: Some times, things work out the way they should
« Reply #6 on: January 11, 2015, 07:08:21 pm »
imho the 2nd pic needs a bit more paste.

Thanks!  Pins on the left side do look dry and not enough solder either.

Noting what you said, I tried to recall what I did - I wrap the wick around the solder tip to clean up the solder bridge.  I avoided putting flux on the chip's leads as I was having difficulties with the "brown stuff" covering up what I need to see.  In hind sight, I think I should have flux the wick.  I wish I had video it so I can review my mistakes.

More practice required...  But I feel good having cross the threshold.  Practicing with the old cell phone chips did not allows me to see if the chips I soldered still work.  But with this two first tries, I know they do work so I feel a bit more confident now.
 


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