Solder cracks on circuit board

I get a little bunch of laptop cast-offs for one reason or another. Often, if they are current enough to be useful, I'll track down whatever parts they
need, within reason, and press them back into service with employees' kids for school or such. Usually I get Dells and have great luck with parts and well documented cures for their ailments. I even had one that required resoldering a surface-mounted chip with solder cracks.
The current one is a Toshiba Satellite 5105-S501 with a known problematic video card. Replacement cards are not available. The problem seems to be from too much heat and too many thermal cycles cracking the joints on the video memory chips.
On the Dell, I made an extension for a pencil soldering iron from 28 ga wire. It worked after three tries but it was like threading a needle with a baseball bat. I've seen reports of resoldering this video card with a heat gun at 750 degrees for a full three minutes. However, some of the people reported melting off the components and blowing them away. At that point you just scrap the whole machine. I'm thinking of making a jig to hold the parts in place or try again with the tip extension. I can't afford to spend any serious money on this but I hate to scrap the laptop just yet.
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Many people have reported success using a toaster oven as a reflow oven...
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That is true, Joe. But not with all the "hand add" parts on the board, such as the connectors, etc.
Paul
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Buerste wrote:

I do this sort of stuff all the time. Not fixing laptops, but building and reworking stuff with our own custom chips. Now, we are using a chip with 0.4 mm lead pitch, which is really getting to the limits of what can be done by hand. I use a stereo zoom microscope, and a couple Weller soldering micro pencils. I use an EC1302B pencil at home on an older soldering station, and a newer WMP at work. For the micro stuff, they have a pointed (conical) tip that is quite sharp. Temperature usually 650 F for tin-lead solder, and 750 F for lead free. After getting too much solder on there, I use the smallest desoldering wick that I dip in GC liquid solder flux to make it work better. I dip a foot or two at a time, dry with a paper towel and let air dry for a minute or two before using to desolder.
You really can't do this fine-pitch stuff without some kind of magnifier, at least a head-mount visor thing.
Jon
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Are these ball mount of lead chips? The ball mounts may not be able to be redone without lots of equipment. The lead chips can be removed with a desolder paste. Chip Quik http://www.chipquikinc.com/ is nice stuff. As someone else says, the really fine pitch leads require a microscope.
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I haven't extracted the card yet, work keeps getting in the way. I've always wanted a good stereo boom microscope/camera...now I can justify it, right?
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Try a very sharp small solder tip, resolder all the pins, dont worry about shorts between pins. Then use solder wick to remove the excess solder. Use a jewellers loupe (I've cut down a second loupe and mounted it on the back of teh 1st one) with some solderwick and remove any excess solder and solder bridges. You may need to clean excess flux between steps using isopropyl alcohol or methylated spirits. This techinique regularly works for me - just go slowly and carefully.
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Preferences vary a lot among techs depending on their experience, vision and fine motor skills. For me an Optivisor with a #3, 14", lens is right. I have the swing-away magnifier on the side of my better eye to inspect but solder without it. You may find a microscope difficult for a while because you lose depth perception, and the flux fumes can condense on the lens unless you blow them away. Look for a microscope with a long "working distance".
I need my wrist supported which rules out Panavise board holders, but placing the board on the static mat is fine. I clamp small boards and connectors in a 1-1/2" drill press vise.
Needle-pointed soldering iron tips don't work as well as slightly larger conical tips for me. Power leads with a short path to internal planes draw the heat away too quickly from fine cylindrical iron tips. I usually have to bump the tip temperature up to 700F unless all the pads connect to fine signal traces, then 650F is enough.
0.015" lead + rosin solder flows better than lead-free with no-clean flux. The isopropyl alcohol I used for cleaning was semiconductor grade. You can get 91% in drugstores.
If you are in a quiet area you can detect unsoldered leads by sliding a needle probe across them and listening to the twang. An unsoldered one sounds duller. You might have to try this on a known loose lead to hear what I mean.
Jim Wilkins
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<SNIP>
I puchased a "black head removal + splinter pick" tool from the pharmacy - with a very fine point its good for finding the leads that are not stuck down.
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    That is where the stereo zoom microscopes win.

    A Rotron muffin fan blowing across the soldering area helps here.

    Hmm ... perhaps another Panavise with a soft wrist support held along the bar?

    I've done work with a copper wire wound around the tip and then extending as a fine tip. Not often, or I would have bought a tip which was right for the task.

    Absolutely. I bought several spools of the ultra-fine Pb/Sn solder a few years ago at a hamfest, so I am now equipped with a lifetime supply. :-)

    Right -- though I have a much higher percentage two gallon bottle saved for such work. (It is seldom opened, so it should still be over 91%. :-)

    That one would almost certainly not work for me. I've got terrible high frequency hearing, and have had it at least since high-school days. (I was not tested before that, and had not realized it on my own.)
    Enjoy,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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I mentioned it because used microscopes can be expensive and you may not be able to try working under one before buying it. Mine has 100mm of clearance below the head.
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Many of the reliable techniques to repair solder faults have already been mentioned.
A hot air iron is very effetive for small spot repairs without involving nearby components. Hot air irons operate with no direct contact, so transferring too much solder from a soldering iron tip to the device pins doesn't become a problem. Many times all that's needed besides heat is a very slight amount of activated liquid rosin flux. Using a toothpick to apply a tiny amount of the liquid flux is generally all that's required.
A desoldering iron with a low air flow coming out of the tip may work as an improvised hot air iron, but the air flow needs to be very limited volume or the tip will get too cold to heat the air to desired temperatures.
FWIW, I have found one of the most useful tools is something that's often thrown away. The round hardwood sticks that long cotton swabs are put on, are very useful for examining and probing for loose pins. I cut the swab off with flush cutting pliers at a low angle to the stick, making a useful sharp tip. These sticks are alo great for screw starters, by jamming a squared end into a phillips recess, the stick holds surprisingly well. A tapered end will work with smaller screws.
Flat hardwood sticks are great for burnishing and cleaning contacts. When used with a deoxidizer solution, the round and flat sticks will clean contacts very effectively without risk of scraping/scratching away thin layers of plating.
With the ends squared off, flat sticks do a very good job for mixing small amounts of epoxy and other compounds.
--
WB
.........
metalworking projects
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You can also buy thicker, stiffer wooden sticks as "orange sticks", or get shishkebab sticks in the grocery store.
Mash the end with pliers or a hammer to make a small flux brush, or pull off some of the cotton.
An old toothbrush is about as good as anything for scrubbing flux residue.
Tweezers fit better if you pull fine sandpaper through the closed tips to cut them parallel.
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Jim Wilkins wrote:

Thec depth and breadth of knowledege in this place is astounding !!!
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I nearly always use lacquer thinner, Jim, for removing flux with cheap cotton swabs which makes it almost effortless.
For tweezers and fine tipped pliers, filing the mis-matched jaw edges to match them up helps improve the grip for things with very little protrusion, like splinters.
FWIW, about a year ago I started using curly stainless steel kitchen/pot scrubbers for cleaning soldering and desoldering iron tips, which works great. It strips off flux and any oxidation with no damage to plated tips. The scrubbers look like wads of thin SS lathe turnings. I poke a wad of it into a small cup-like holder, and just jab the tip into the wad a couple of times.
After years of using damp sponges, the scrubbers are much more effective. Before sponges, I tried using steel wool, but quickly found out that was a bad idea when I didn't notice I had transferred a piece of a fine strand onto the circuit board, followed by a lot of confusion. Braided tinned or bare copper shield from coaxial cable makes a decent tip cleaner, too.
Another practice I got into the habit of is adding a little fresh solder to tips right after turning the iron off. This has been working much better than cleaning them very well before turning them off. The result is a freshly tinned tip every time the iron is turned on for the next use.
--
WB
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metalworking projects
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Buerste wrote:

Could tiny drops of conductive epoxy help in some of those cases?
It's sved my skin a few times.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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Great minds think alike! I was wondering if I could use conductive paint like window defroster repair kits.
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Silver epoxy is really nice stuff when you have rich Uncle to pay for it (space project).
The shelf life is rather short, I kept it in a lab refrigerator and still some of it went bad.
I used it to repair broken 1 mil x 5 mil gold wirebonds to salvage a $40,000 laser diode chip. Don't ask me to try it again.
Jim Wilkins
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The output of a heat gun can be custom tailored by fabricating nozzles, baffles, and shields and by restricting the air intake and using a Variac to control the temperature and speed of the blower. Soldering iron tips can be custom made from copper to reach even around corners. With a custom baffle on a heat gun, many chips can be fairly easily desoldered and replaced. I was once fairly good at it but never did it enough to get really proficient like some people are.
A good heat gun does work good to mass de-solder boards. Just heat carefully till you see the solder melt and whack the board edge against something solid. Nearly all the components will fall off cleanly unless they have crimped leads.
Don Young
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I had a butane powered soldering iron (Portosol, I think), that came with several tips. One of these tips was a hot air tip. For heat shrink tubing and the like. The hot air coming out was VERY hot but the stream was quite small in diameter. Kind of hokey for heat shrinking tubing because it would only heat a small spot at a time. But if held too close to the tubing it would scorch the tubing. I imagine that it might be perfect for surface mount spot reflow. ERS
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