Need help reading a schematic.

[stj]

Re: Need help reading a schematic.

pretty good,

[Spork Schivago]

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.

[Spork Schivago]

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.

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.

[stj]

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.

[Spork Schivago]

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!

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!

[Spork Schivago]

Re: Need help reading a schematic.

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.

[stj]

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!

[keeney123]

Re: Need help reading a schematic.

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.

[Spork Schivago]

Re: Need help reading a schematic.

why would you need flux to remove something???

It was something that was suggested on a forum. I didn't actually look into the reasoning behind it. This was the post:

I am working with SMD for a while and I suggest you use leaded solder to treat the oxidized solder joints with flux before you get to the hot air stage. After solder mixture process, preheat the board close to 200C and continue with hot air station. I use analog hot air stations because I don't want to turn around and look at the temperature. I know where I have to set the hand dial without looking and I think that is between 7-8 on Hakko 852 station (around 420C). Preheat the chip from distance and can feel when it is enough to start. I count to 5 and viola pull the chip out without any problem. The hard ones are BGA chips and need precision timing and good BGA preheater. Average ICs are rated to 380C/10Sec I think but I am not sure.

Also, I remember when I was looking at videos on how to remove the 360 GPU's / CPU's, for some reason, they were squirting a lot of flux under the BGA type components. I just thought it helped the solder flow a little more easier and that it'd help it melt all at once, instead of maybe a little of it melting here, a little still solder there.

Was this incorrect and the flux isn't actually needed for desoldering?
As for soldering with the hot air, I think I remember now. The flux was to help hold the component into place. I watched many videos on how to use the hot air station when I first got it. Some people would use flux to hold it in place and then put the solder paste on top of the pins, not on the pads. Others would put solder paste on the pads and then put the chip on. I wish I could find the video but I can't. Maybe it's my memory just remembering it wrong?

say i want to remove a 144pin chip - because i do them by hand.
(yes, i do!)

i heat the chip with the handheld air unit, till it lifts off the board.
no flux used.

then i paint the pads with flux and re-heat them to make the solder flat and smooth

then i paint the pads wih flux again,
and the pins on the new chip

then i place the new chip and re-heat the pads/pins till the solder flows.

then i inspect it and if it's all aligned and o.k. i clean off the flux with ipa and get a beer.

btw, when i refer to "painting" the pads/pins, my flux is water-thin liquid and i'm using a brush.

Okay, thanks. My flux is a bit thick. The paste is really thick too unless I warm it up a little (like preheating the board and then touching the tip to the warm board. That seems to make it liquid like).

[stj]

Re: Need help reading a schematic.

why would you need flux to remove something???

say i want to remove a 144pin chip - because i do them by hand.
(yes, i do!)

i heat the chip with the handheld air unit, till it lifts off the board.
no flux used.

then i paint the pads with flux and re-heat them to make the solder flat and smooth

then i paint the pads wih flux again,
and the pins on the new chip

then i place the new chip and re-heat the pads/pins till the solder flows.

then i inspect it and if it's all aligned and o.k. i clean off the flux with ipa and get a beer.

btw, when i refer to "painting" the pads/pins, my flux is water-thin liquid and i'm using a brush.

[Spork Schivago]

Re: Need help reading a schematic.

practice on something scrap.

btw, you dont use flux with solder-paste.
solder paste is flux already with powdered solder in it.

You sure about that Stj? Is the flux just for desoldering and I mistakenly thought it was for soldering as well?

One product is ChipQuik Lead-Free SMD291 Tack Flux N/C for rework & reflow. The other product is ChipQuik Lead-Free SMD291SNL10 N/C Paste SAC305 L/F for rework & reflow.

What's usually a good temperature / air flow to get the stuff working? I tried, unsuccessfully, to replace a really small IC. It had a lot of pins, like 48 or something. Really small. I ended up using wwwwayyyy to much paste. But I tried putting just a dab. I found that if the tip of the syringe was a bit warm, the paste would come out really smooth like and I could just use a dab. I couldn't get the paste to melt without using a higher air speed though. It ended up pushing the paste out of the way. I took the temp and increased it, trying not to push the paste. In the end, I burned the board and a trace lifted up and broke. I suck at this hot air stuff, unless it's removing components. I'd love to nail down using it though.

What's the best way to get the paste on? I know it's probably using a stencil or something but I don't got one of those and I have no way to make one. I tried using some stencil cutter thing but it couldn't go small enough (we borrowed it from a friend). I could probably get a custom one built, but I'm sure there's an easier way.

[stj]

Re: Need help reading a schematic.

practice on something scrap.

btw, you dont use flux with solder-paste.
solder paste is flux already with powdered solder in it.

[Spork Schivago]

Re: Need help reading a schematic.

if you flux them and heat them with hot air they will float and re-align with the pads.

OKay. I'm not very good with the hot air. I'm afraid I'm going to fry one of the boards. I usually use the hot air rework station for removing components but perhaps I should give it a shot. Perhaps I'll try throwing some flux and solder paste on the pads and see what happens.

[stj]

Re: Need help reading a schematic.

if you flux them and heat them with hot air they will float and re-align with the pads.

[Spork Schivago]

Re: Need help reading a schematic.

No it would be for tuning coils etc. in radios, like this

http://www.rf-microwave.com/en/shop/...1-CT-4192.html

It can be anything that is small enough to put pressure down on the resistor without getting in your way of tacking down the resistor with the iron. Preferably something a flat surface that contact the resistor with a straight handle. I picked fiberglass because you can put a look of pressure on it without damaging the resistor. I assume you are using flux core solder? If you are not then you will need to put a little flux down before you tack it down and a little flux on the tip before you tin the tip.

Thanks. I haven't been using a flux core solder. I've been using a silver bearing solder and I have various types of flux. What seems to work okay is this liquid no-clean flux. I wasn't putting any on the actual tip though. Haven't really had any trouble with the solder sticking. Only problem seems to be getting those little buggers lined up just right.

[keeney123]

Re: Need help reading a schematic.

Here is another company that carry the fiberglass TV alignment tools.
http://www.minute-man.com/acatalog/T...ent_Tools.html

One more company look under soldering tools
http://www.gcelectronics.com/order/c...y.asp?CatID=16

[keeney123]

Re: Need help reading a schematic.

Would this be one of those fiberglass screw drivers?

http://www.hardwarestore.com/fibergl...er-283754.aspx

No it would be for tuning coils etc. in radios, like this

http://www.rf-microwave.com/en/shop/...1-CT-4192.html

It can be anything that is small enough to put pressure down on the resistor without getting in your way of tacking down the resistor with the iron. Preferably something a flat surface that contact the resistor with a straight handle. I picked fiberglass because you can put a look of pressure on it without damaging the resistor. I assume you are using flux core solder? If you are not then you will need to put a little flux down before you tack it down and a little flux on the tip before you tin the tip.

[Spork Schivago]

Re: Need help reading a schematic.

Would this be one of those fiberglass screw drivers?

http://www.hardwarestore.com/fibergl...er-283754.aspx

[Spork Schivago]

Re: Need help reading a schematic.

Okay! Thanks guys. What I've been doing is putting solder to one pad, then using tweezers, I've been putting the resistor over the pad that I soldered, then I heat that solder a little bit, move the resistor in place. It's hard because they're so small and even a little movement throws it out of alignment. I will try your suggestion though Keeney123 and see how it works.

Any idea how I can figure out what package these SMD resistors are? They're really small. About 2mm long by 1mm wide. Would that make them 0805's? I see 0805's are 2mm by 1.25mm. I see DigiKey have a few different things that have 0805 in them.

They have a category called Package / Case which has Wide 0805 (2012 Metric), 0508 then they have 0302 (0805 metric) then 0805 (2012 metric). They also have a section called Supplier Device Package. For that section they have 0805 and then 0805 (2012 metric). I don't know the difference between Package / Case and Supplier Device Package. I'd also like to know what's the difference between the various 0805 stuff so when I go to order SMD components for the count down timer PCB, I can try to get the same package for all of them. Thanks and Happy Thanksgiving everyone!

[keeney123]

Re: Need help reading a schematic.

You can use like a Blunted fiberglass screwdriver to hold down the resister. First tin your iron then hold the resistor down with the instrument and tack one side of the resistor. After that is done you will have two free hands to solder the other side of the resistor. Wait till that side cools and finish up soldering the side you tack down. So, you could go down tacking all the resistors and once finished start at the first one as that should be cool and start soldering the other side.