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Old 11-27-2015, 02:01 PM   #121
stj
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Default Re: Need help reading a schematic.

you dont need flux to desolder with hot air if you can see the pins.

BGA is a completely different situation, your using the flux to transfer the heat under the package.
using a nitrogen gas-flow system would be better, but seriously expensive!
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Old 11-27-2015, 03:04 PM   #122
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Default Re: Need help reading a schematic.

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The flux is to transfer the heat from the iron to the solder joint. It allow a even flow through the joint and helps to get rid of oxygen in the joint. If you have no flux in your solder, flux will be needed to unsolder a joint with a solder iron. With a hot air gun, I do not know. I would think the flux would aid in a uniform heat. You do not need a lot of flux. With Surface Mounted Components they usually use a small flux bottle that has needle is attached and use just enough to wet the pads. This would be a liquid not a paste. I would think paste would be messy and harder to control.
I got flux in that needle / syringe type thing but I also have solder paste. It's silver in colour. I "paint" it on the pads / terminals and when I heat it up, it melts into a silverish type solder. It's actually kinda cool and is real good for SMD components. Just that the only time I've successfully used it was when I had a stencil for the component. Just can't seem to judge how much paste to use.

Thanks for the info on the flux. I remember reading something about it having to do with providing a nice clean joint. I too thought that it would help in providing uniform heat, when it came to removing stuff, specially BGA type components.
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Old 11-27-2015, 03:07 PM   #123
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Default Re: Need help reading a schematic.

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you dont need flux to desolder with hot air if you can see the pins.

BGA is a completely different situation, your using the flux to transfer the heat under the package.
using a nitrogen gas-flow system would be better, but seriously expensive!
Oh! That's where my mistake was! Watching the videos on the BGA and just assuming the flux was the same for SMD components! Duh! Man, wish I had a nitrogen gas-flow system. Also wish I had one of those nitrogen systems for wine. My wife likes wine but doesn't drink it very often. The reds tend to turn a bit vinegar-e-ish if they're not drank quick enough. Friend of mine works at a country club (a real fancy one for rich people) and he says there, they have a nitrogen system that replaces the air in the bottles with nitrogen so it doesn't turn. I guess even for the wine bottles, they're real expensive!
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Old 11-27-2015, 04:00 PM   #124
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Default Re: Need help reading a schematic.

red wine - mmmmm...

after 24hours is good, after 48 it starts to go downhill.
just kill the bottle the first day - problem solved.
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Old 11-27-2015, 06:11 PM   #125
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Default Re: Need help reading a schematic.

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red wine - mmmmm...

after 24hours is good, after 48 it starts to go downhill.
just kill the bottle the first day - problem solved.
Yeah, never really meant anyone like my wife before. She'll pour a glass of wine and just drink a 1/4 or maybe 1/2 a glass and just leave the rest. When I used to drink, I always drank until I couldn't drink anymore. I drank on a daily basis for a while there. Once Jess and I found each other though, I gave all that stuff up.
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Old 11-28-2015, 02:27 PM   #126
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Default Re: Need help reading a schematic.

So, what do you think of the solder job using solder paste and a hot air rework station? I think it isn't too shabby. I had a little trouble. The only problem was trying not to put too much paste on the pads. I had to wipe it off once or twice because too much came out. I checked every resistor to make sure there were no shorts or anything. Everything tested good. Two of the resistors ended up lifting off the board and staying straight up in and down instead of laying flat on the board. But I just used a pair of tweezers to push it back down.

The preheater really seems to be the key for this stuff. Using the preheater, it only took a few seconds for the solder paste to melt and turn into solder. I used a low air speed, 3 on my system and a temp of around 650F or so.
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Old 11-28-2015, 03:05 PM   #127
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Default Re: Need help reading a schematic.

pretty good,
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Old 11-28-2015, 04:18 PM   #128
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Default Re: Need help reading a schematic.

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pretty good,
Thanks! First time I've successfully used the hot air rework station to actually solder something. It's great for removing stuff. Glad I didn't have much problems.

On a side note, when I clip the leads off the through-hole UV LEDs, the wire snippers I use cut the leads leave them a bit smushy looking. They definitely don't look like a professionally done PCB. Is there a better way to cut these leads? How do they do it at the factories?
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Old 11-28-2015, 04:31 PM   #129
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Default Re: Need help reading a schematic.

So the power supply powers the UV Exposure Time circuit board, which powers the UV LEDs. The power supply should have a fuse in it I'm thinking but is it possible that the power supply would break in such a way where it could fry the exposure time circuit board? Would it be a good idea to add a fuse to that circuit board or don't power supplies usually break like that?
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Old 11-28-2015, 05:48 PM   #130
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Default Re: Need help reading a schematic.

Man, I had a scare! Took me a bit to figure it out. Soldered all the UV LEDs on the board and one whole column (four UV LEDs) didn't light up at all! I thought for sure it was the trace. I went through and touched a soldering iron to each one, hoping it was a cold solder joint or something. No go. I looked at the schematic and board layout and studied how the lights were actually ran for those four non-working UV LEDs.

Then I went back in the work room and tried putting the ground on my PSU to the ground lead on one of the non-working UV LEDs. This got most of them working, except one. But the three that lit up weren't very bright. I started looking at the one that wasn't lit up and realized I put it in backwards! If I had cut the leads off the LEDs before testing it, I probably wouldn't of figured this out as easy like! Works like a charm now.

I went back through and checked the other two boards that I had already finished to make sure all of them actually lit up. One of them is different though. I even remember when I soldering, one UV LED had much longer leads. I want to say it's the same UV LED. It looks like maybe someone else made it. All the other ones glow the same colour but this one is much deeper in colour. Would this make a difference when I go to transfer the picture to the PCBs? Should I replace it with another UV LED? Thanks!
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Old 11-28-2015, 06:02 PM   #131
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Default Re: Need help reading a schematic.

So with the needle and the flux it is easy to use. Just small amount on the pad and solder. With the right tip on the iron one just puts some solder in the tip and just pull it down on the edge of the component leg. One pin after another without stopping. Just add a little solder when it get used up. If for some reason a solder short appears then apply flux and heat up. The solder will go to the pads. A good solder joint on Surface Mount will be on the outside edges of the leg of the component. So it will be from the edge of the component leg to the pad on three sides of the component leg. This is easily accomplish with a hoofer tip or a bent beveled tip that is about the size of the leg being solder. Should be able to solder a 14 pin IC in a matter of seconds.
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Old 11-28-2015, 06:11 PM   #132
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Default Re: Need help reading a schematic.

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On a side note, when I clip the leads off the through-hole UV LEDs, the wire snippers I use cut the leads leave them a bit smushy looking. They definitely don't look like a professionally done PCB. Is there a better way to cut these leads? How do they do it at the factories?
your cutters are making that look, get a pair with a flush-blade on the outer edge.

factory's used to use a saw to trim all the leads years ago,
now the leads are pre-cut before they are auto-inserted.

you can see this with some of the ebay chinese cap sellers who are selling surplus from production-lines.
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Old 11-28-2015, 06:29 PM   #133
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Default Re: Need help reading a schematic.

Quote:
Originally Posted by keeney123 View Post
So with the needle and the flux it is easy to use. Just small amount on the pad and solder. With the right tip on the iron one just puts some solder in the tip and just pull it down on the edge of the component leg. One pin after another without stopping. Just add a little solder when it get used up. If for some reason a solder short appears then apply flux and heat up. The solder will go to the pads. A good solder joint on Surface Mount will be on the outside edges of the leg of the component. So it will be from the edge of the component leg to the pad on three sides of the component leg. This is easily accomplish with a hoofer tip or a bent beveled tip that is about the size of the leg being solder. Should be able to solder a 14 pin IC in a matter of seconds.
I've seen this method done in videos but when I try I mess up horrible! I tip my hat to anyone that can do it that way. It's simply amazing! My hands shake pretty bad sometimes. Usually it isn't that noticeable until I work on smaller stuff. That makes it a bit harder. Eye sight isn't great either so I usually use a magnifying glass while I'm soldering.
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Old 11-28-2015, 06:30 PM   #134
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Default Re: Need help reading a schematic.

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your cutters are making that look, get a pair with a flush-blade on the outer edge.

factory's used to use a saw to trim all the leads years ago,
now the leads are pre-cut before they are auto-inserted.

you can see this with some of the ebay chinese cap sellers who are selling surplus from production-lines.
Okay. Could you link me to the type of cutters you're talking about? Thanks!
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Old 11-28-2015, 06:58 PM   #135
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Default Re: Need help reading a schematic.

cant find a good foto, but you want a pair where the blade is ground on the inside only.

they are usually called "flush cutters"
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Old 11-28-2015, 07:39 PM   #136
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Default Re: Need help reading a schematic.

Thanks! Like these? http://www.all-spec.com/products/801...FUgXHwodAlwOoA

I'm currently uses these from Radio Shack:
https://www.radioshack.com/products/...ant=5717833157

They're okay for cutting wires but for leads, they just more or less smush the metal. Maybe it's because they're not sharp enough?
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Old 11-28-2015, 10:44 PM   #137
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Default Re: Need help reading a schematic.

I just burned myself on this Weller! It's the first time on this iron! 650 degrees F (around 343 C). It left a nice white mark on my finger where the iron touched. It's about 1/4" (6 - 7 mm) long. Boy does it hurt!
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Old 11-29-2015, 12:12 AM   #138
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Default Re: Need help reading a schematic.

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I've seen this method done in videos but when I try I mess up horrible! I tip my hat to anyone that can do it that way. It's simply amazing! My hands shake pretty bad sometimes. Usually it isn't that noticeable until I work on smaller stuff. That makes it a bit harder. Eye sight isn't great either so I usually use a magnifying glass while I'm soldering.
I did not know that. Anyway, you found a way that works for you and there is nothing wrong with that.
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Old 11-29-2015, 12:17 AM   #139
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Default Re: Need help reading a schematic.

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I just burned myself on this Weller! It's the first time on this iron! 650 degrees F (around 343 C). It left a nice white mark on my finger where the iron touched. It's about 1/4" (6 - 7 mm) long. Boy does it hurt!
343' seems high, i solder at 310' with lead-free solder.
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Old 11-29-2015, 12:17 AM   #140
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Default Re: Need help reading a schematic.

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that's the type.
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