Calling all Electronic Engineers... need some soldering gear

[halik]

So my 50" plasma recently fried out and the repair folks gave me the part # for the stuff that needs to be replaced. The good news is the part is $40, the bad is that I need to surface solder it on there. pics

So for this job my 15 dollar radio shack soldering iron just won't cut it. Whats a good place to buy decent (digital) soldering iron with a fine, fin tip? Relatively cheap would be nice too.

 

[malbojah]

Being that small, with probably close to 100 pins, I would call a tv repair person to fix it onsite...but thats me and I have fat fingers

 

[Cattlegod]

1 - get a 6w soldering iron
2 - remove old chip
3 - make sure there were no bridged connections with your removal
4 - place new chip on board
5 - heat pins and use existing solder on the board. do corners first to make sure it is lined up, then just drag your iron across the pins.

6 - if you did bridge connections during the soldering process, use an exacto knife to split them.

edit: Please note that I have never actually done this, but I don't see why it wouldn't work.

 

[Antisocial Virge]

Yea, you can't do that pin by pin. There is ways to do it professionals would know.

This link shows the way I saw it done once. He ran the soldering iron over the pins pretty fast. The whole job took less than 30 seconds. Feel up to that?

http://www.howardelectronics.c...quik/instructions.html

 

[Shawn]

I am pretty damn good at soldering but even I could not do that. Good luck.

 

[halik]

Originally posted by: Antisocial Virge
Yea, you can't do that pin by pin. There is ways to do it professionals would know.

Actually you can, but thats why i need a good soldering iron (fin point). Ill see if i can get the old one off with hot air, that would make it easier

edit: im talking about tacking it - i'll need to hit a pad in the corner to set it down and then just ran along the length of it to do it

 

[Cattlegod]

here looks like a good tutorial

http://dlharmon.com/solder/smd.html

"then line the device up and tack solder the corner pins. All that matters at this point is that the compent is oriented correctly. I then apply flux over the devices leads then place a small amount of solder on the tip of the iron. This amount of solder will need to be determined by trial and error. The tip used should cover 3 or 4 pins. The flux will cause the pins not to bridge. I Start with one end and drag the tip gently to the other end. If the correct amount of solder is on the tip, all the pins should be well soldered and there will be no bridges. In the case of shorts remove some solder using solder wick. If there is not enough solder on the joints, repeat the preceedure. I find that a bent soldering iron tip is helpful."

 

[engineereeyore]

Originally posted by: halik

Originally posted by: Antisocial Virge
Yea, you can't do that pin by pin. There is ways to do it professionals would know.

Actually you can, but thats why i need a good soldering iron (fin point). Ill see if i can get the old one off with hot air, that would make it easier

Dude, not trying to discredit you, but surface mounting a component with that many pins almost requires a great deal of experience even with a small soldering iron. I honestly wish you luck and truly commend you if you're able to do it, but I'm not sure I'd take the risk. Odds just aren't good.

Sorry I can't think of a good place to get a small soldering iron, but I would recommend that you not go cheap. JMO, take it or leave it. Regardless, good luck!

 

[Molondo]

I found using a hollow tip solder iron works great on SMT small chips. Just run the baby down the side at a constant speed. But its trickier than it sounds. Good luck.

 

[helpme]

http://www.engadget.com/2006/0...-mount-soldering-iron/

 

[halik]

score!

 

[RU482]

DO NOT use an exacto knife to cut solder bridges. You'll likely cut more than you intend to, causing even more problems

While this job would be easy for a seasoned pro, it's not a job for amateurs

If you insist on doing it yourself, find some junk electronics boards to practice on before attempting to do the repair on your TV

 

[Eli]

Oh man. Have you ever soldered before, or not?

If not, you're going to need to practice for like a week before you attempt this.

Why would a chip go out though? Is this a common problem or something? Does it need better cooling?

 

[MrDudeMan]

no way you are going to be able to do that with on prior experience. i soldered TQFP packages for almost a year at my old job, so i feel like i have a lot of experience with this compared to most people.

first of all, the finer the tip, the more chance you have of failing. you want a big fat tip and leaded solder. completely clean off the pads with either a solder sucker or braid. do not use any type of knife to separate bridged pads...that is the worst idea ever. if you bridge pins, you need to put MORE solder on them, then suck it off with a solder sucker or braid. MORE SOLDER. NOT LESS. i soldered well over 2,000 of these things just so you know where i stand.

the chip you have there is a TQFP-100, and ive soldered TQFP-144 and higher (far more dense pin arrangement). if you want more advice, just ask. im waiting to see where this thread goes before i waste more time typing.

 

[edfcmc]

Out of curiosity, MrDudeMan what kind of tools did you use?

Here is a link with more soldering tools.
http://www.web-tronics.com/sol...ipment---supplies.html

 

[MrDudeMan]

nothing on that page looks familiar. i can do it with a really cheap iron, but the tools i used at work were way nicer than most of that.


in the spirit of this thread, here are a few pictures of things ive done in my spare time. the first 2 pictures are of a laser communication system - this is the master board out of the entire configuration. the IC shown is a mega128 microcontroller in the TQFP-100 package like the OPs. the second pictures are just for fun - first a picture of 4 smd LEDs i used as status leds for TX/RX activity on 2 channels. the second picture is a cropped 100% view of a single led. it just so happens that my other hobby is photography...this was taken with a 60mm macro.

edit: i left two of the pics huge so you could zoom in and look around. the boards look ultra dirty but you cant see 99% of that with your naked eye.

full board
close-up of mega128

4 leds
ultra close-up of smd led

all of those are pre-flux removal. all solders on the dense pin arrangements were done in a single pass and no parts were broken from heat. which brings me to my next point about where people go wrong with this...HEAT KILLS.

by using an itty bitty soldering tip, you pass a significant amount of heat into the parts. by using a big fat tip, more heat is distributed through the solder and onto the pins, but it only takes a fraction of the time to finish the solder. as a result, with a big tip you transfer less heat into the part and the solders are much more even. with little tips, there is hardly any surface area to use for thermal transfer, which means not only does it take longer, but the heat can work its way into the part, which is much less heat tolerant than the pins.

if you have no prior experience or less than a months experience, you need good tools to do this effectively and efficiently. you can certainly make it happen in less time than a month, but you almost certainly overheated a part or broke something. in some applications, heating up any of the pins for longer than 1/4 of a second renders it completely useless. speed is extremely important because the transfer of such intense heat right into the guts of an IC changes all of the properties of the diffusions and junctions.

 

[CallMeJoe]

For a job like this, call for a technician, not an engineer. You want someone who can actually do the work, not design the circuit.

First, get a good Antex 15 watt iron, and a needle point (the 1/64" gold tip on that page is ideal). A good flux pen and some fine gauge solder are next. Hot air is the preferred method for removal, but if you don't have the equipment, you will need some precision tip cutting pliers (sorry, no handy link) to cut the individual leads, then remove them one-by-one with the iron. If you try to desolder all the leads with an iron and then lift the chip off, you will surely trash the board. Clean the solder pads on the board with some solder wick, then lightly tin one pad on each corner, place the IC on the board, apply liquid flux to the pads and briefly touch each lead to melt the solder. Spread flux across the remaining leads and solder the leads one by one, being careful to limit your dwell time on each lead to not more than one second, and allowing a brief cooling period before proceeding to the next pad. Work patiently, and examine each pad carefully with a magnifier when you are done. If you find and solder bridges, clean them off with the iron and some solder wick. As stated previously, clearing bridges with an exacto knife is likely to do more damage than good.

If all this sounds tedious and difficult, it is. I work in an avionics shop with three other techs, each with more than 30 years electronics experience, and they all leave jobs like this to me (factory trained and certified by a major manufacturer in SMD repair)

 

[MrDudeMan]

Originally posted by: CallMeJoe
For a job like this, call for a technician, not an engineer. You want someone who can actually do the work, not design the circuit.

First, get a good Antex 15 watt iron, and a needle point (the 1/64" gold tip on that page is ideal). A good flux pen and some fine gauge solder are next. Hot air is the preferred method for removal, but if you don't have the equipment, you will need some precision tip cutting pliers (sorry, no handy link) to cut the individual leads, then remove them one-by-one with the iron. If you try to desolder all the leads with an iron and then lift the chip off, you will surely trash the board. Clean the solder pads on the board with some solder wick, then lightly tin one pad on each corner, place the IC on the board, apply liquid flux to the pads and briefly touch each lead to melt the solder. Spread flux across the remaining leads and solder the leads one by one, being careful to limit your dwell time on each lead to not more than one second, and allowing a brief cooling period before proceeding to the next pad. Work patiently, and examine each pad carefully with a magnifier when you are done. If you find and solder bridges, clean them off with the iron and some solder wick. As stated previously, clearing bridges with an exacto knife is likely to do more damage than good.

If all this sounds tedious and difficult, it is. I work in an avionics shop with three other techs, each with more than 30 years electronics experience, and they all leave jobs like this to me (factory trained and certified by a major manufacturer in SMD repair)

your first statement is so :roll:

i am an engineer, and i can do this quite easily. also, leave the iron on each pin for no longer than 1 second? and you say you have 30 years of experience? the soldering specs for the vast majority of ICs say no more than 260C at 5-10mm for 3 seconds. MAX, and that is a total, as in combined. so you think it would be appropriate to leave the iron on this part of 1 minute and 40 seconds? i know what you meant, but come on. there is a reason those specs are in place - heating up a part more than that changes the properties of it. you can no longer go by the manual for electrical properties such as input/output impedance/capacitance, and those are extremely important for circuit design.

 

[potoba]

Originally posted by: Cattlegod
1 - get a 6w soldering iron
2 - remove old chip
3 - make sure there were no bridged connections with your removal
4 - place new chip on board
5 - heat pins and use existing solder on the board. do corners first to make sure it is lined up, then just drag your iron across the pins.

6 - if you did bridge connections during the soldering process, use an exacto knife to split them.

edit: Please note that I have never actually done this, but I don't see why it wouldn't work.

I was soldering for 3 years and i wouldnt do this. I dont think i'm skillful enough.

 

[CallMeJoe]

Originally posted by: MrDudeMan
your first statement is so :roll:
i am an engineer, and i can do this quite easily.

Most engineers I have known have some experience in prototyping, little or none in repairs. You may be an exception.

also, leave the iron on each pin for no longer than 1 second? and you say you have 30 years of experience? the soldering specs for the vast majority of ICs say no more than 260C at 5-10mm for 3 seconds. MAX, and that is a total, as in combined. so you think it would be appropriate to leave the iron on this part of 1 minute and 40 seconds? i know what you meant, but come on. there is a reason those specs are in place - heating up a part more than that changes the properties of it. you can no longer go by the manual for electrical properties such as input/output impedance/capacitance, and those are extremely important for circuit design.

With this iron and tip, you will expose each lead to a temp of approx 200C, with an intermittent application and cooling period between cycles. I think the heat spec you cite is for assembly soldering or full component hot air soldering, where the entire component is exposed to soldering heat. Different situation.