Reflowing a BGA?

I have one on the bench as I write. Nice machine with a few design defects. The plastic case is really flimsy and easy to crack along the sides. I have yet to see an X30, X31, or X32 that does NOT have a crack in the case somewhere. Plastic epoxy will fix it if you don't care what the result looks like. Mine resembles Frankenstein:

X30 on the left, X31 on the right.

The X31 uses an ATI Radeo Mobile 7000 video chip.

Before you blame the video chip, carefully inspect the video ribbon cable. I've had failures with that cable that looked much like a video chip problem. They're available on eBay for about $7.

Yep, that's the problem. Hit it with too much heat and it will melt or burn (I forgot which). I monitor the heat with an IR thermometer. Not hugely accurate because it's mostly measuring the temperature of the hot air gun tip, but good enough. It really doesn't take much heat or time to reflow the solder with the "skirt" of PCB material around the BGA. Work fast. This should give you an idea of what to expect:

(Drivel: Not the giant blob of Arctic Silver on top of the CPU to the right. That's about 100 times too much. Oh well).

Incidentally, I just hot air reflowed and fixed 4 out of 6 HP JetDirect J4169A cards, which have the same style BGA chip.

Rosin flux really helps. It largely prevents oxidation (cold solder joint). It conducts the heat to odd places. It explodes if you get it too hot.

In my limited experience, a real hot air desoldering station is a must. You don't really need all the BGA nozzles as a small 3mm nozzle is usually sufficient. I bought mine on eBay for about $80 with 4 nozzles. I suggest you practice on an old PCB before trying the real thing. Getting the temperature right and how fast you move the nozzle, require some practice.

It's worth saving.

Yep. My success rate was about 2 out of 5 motherboards with that configuration. Can't win them all. You have a better chance than most because you can sorta tell where to reflow.

A few hints:

1. Don't push down on the "skirt" while hot. That will cause the solder balls to migrate across adjacent pads.
2. Use flux even if it makes a mess. I messy working computer is better than a clean brick.
3. Build a heat shield out of aluminum foil. The hot air will melt adjacent plastic quite easily.
4. Give it time to cool down.

Good luck.

I discounted the ribbon cable because it fails video ram test and because it has the same problem at the VGA output connector on the back. Is there something I'm missing?

I watched a bunch of videos, including that one. Difference is that they all have a BGA mounted directly to the main board. That intermediate carrier is the wild card. I don't know what to expect except that it's a thermal insulator and have nothing equivalent to practice on. I haven't taken it apart far enough to try to determine if the chip or the carrier is where the fault lies.

I have three temperature controlled air guns. I've made air nozzles with baffles in the past...way past...to rework gull-wing and J-leaded packages. I've got zero experience with BGA and even less with two-layer stacks of BGA.

I thought I'd build a hollow platform out of bricks and blast it from underneath with a power-controlled heat gun while I watched the pre-heat temperature. Then hit it from the top to reflow it. Sounds like reflow temp is about 260C. Any recommendations on what air temperature I oughta use to get there?

You don't really need all the BGA nozzles as a small 3mm nozzle

Thanks, I gotta go find some flux... mike

Flux turned out to be a much more difficult question than I thought. What flux do you recommend?

Ok. It's not the ribbon cable.

Well, the real test is at what point the solder melts. Try taking small pieces of solder and scattering them onto a PCB. You might have to glue them down with some Cyanoacrylate adhesive. Then play with the hot air SMT rework gun to see what it takes to melt the solder.

I'll remove the kbd from my A31 and see what I can find. I don't recall seeing a video carrier board, but it's possible. Hopefully, you wont have to remove the PCB in order to do the reflow.

Good. You have proper tools. Think of it as using a soldering iron made of air. Practice with any PCB at melting solder and removing parts. It's not a perfect analogy of the X31, but it will help with the temperature and timing. I don't recall if the X31 uses ROHS high temp solder, or leaded low temp.

I don't know if that will work. You're blowing air into a dead end "box" canyon, where most of the air is going to blow back towards the nozzle. It will probably spray hot air in a much larger area than intended. Try doing it very quickly, and check the result with a fast acting contact thermometer (thermocouple and DVM).

Nope, but I know how to check. Same trick with the tiny piece of solder. Put it where it won't do any damage if it melts. Tack it down with some glue. Add flux. When it melts, you're hot enough.

Try blowing hot air at a puddle of flux to give you a clue what it will do. Most use alcohol, which might catch fire.

Lenovo X31 hardware service manual:

Well, here a part with the orthodoxy. Most experts recommend using paste flux, which helps keep things in place, and does not volatize when heated. For example:

My guess(tm) is that the above advice assumes that the component to be reflow soldered is a loose part, where the flux can be smeared onto the part prior to assembly. That's not the case with the in place rework as we're discussing.

I tried paste flux, but found that I couldn't get it to go *UNDER* the BGA, where it was needed most. Same problem when cleaning. The paste flux was hell to remove with mild solvents (alcohol) while the liquid flux came off easily.

Not knowing any better, I just used whatever I had handy, which was GC Liquid Solder Flux 10-4202

Googling a little, I find that the current fashion is no-clean Kester

Many web page claim that 951 was specifically designed for BGA rework, but I see no indication of that in the data sheet:

Anyway, the flux cheap enough to try various potions and compare effectiveness.

More on BGA flux use:

I hadn't thought of bulding a "dam" to keep the liquid flux in place, but I'll give it a try next time.

Rework Fluxes:

etc...

Thanks for the inputs. Trying different stuff sounds good on the surface, but I've only got one shot at this ;-)

I find it annoying, although not unexpected, that the cost of a bottle of flux is 8X the cost of the laptop. Sigh...

mike

Huh? I paid $20 for my X31, but had to replace the HD, add RAM, and upgrade the 2100b wireless to a 2200bg card. My guess is I have about $100 into it. Ebay completed auctions show selling prices of $90 to $180 so this is not going to make me rich.

Incidentally, there are motherboards for sale for about $45 which is probably too high to use as a replacement or practice board.

If the price of flux is a problem, you could also make your own.

I've actually done this and find that it somewhat works. The problem was the sticky mess it created. For pine sap, I just went to the local lumber yard and got permission to "sample" the sap oozing from the cheap pine lumber. Very little sap is required. My guess is about 5% solids in solution. I found that I had to add some HCL acid, which made it "highly activated" flux and required cleaning after use.

I had better luck buying some rosin paste flux from the local hardware store and dilluting it in denatured alcohol. It worked about the same as the home made variety, but did not require filtering out the sap solids, bugs, wood debris, dirt, etc.

I buy computers when they're a buck and I think I can fix 'em up. I do it mostly for the challenge and to give me something to do.

Price of flux isn't a "problem", it's an annoyance. Making your own is interesting. Wonder what my neighbor would say if he caught me gnawing on his pine tree? I happened by a parts store today, but they didn't have anything I thought would work. I'll just order some from ebay.

Thanks for the inputs. Flux arrived. I practiced on a TiVo board. Had to get the air temp over 350C to get enough heat to desolder a BGA. I then took a shot at the laptop. The intermediate board curled up on the corner when I heated it. I feared I'd lost connection on that corner. Probably shoulda dropped the temp cause of the thinner intermediate board.

When I tried to run it, I got no video. My heart sank... I didn't think I needed to plug in the boards for wifi, firewire and modem, but I took a shot and reassembled the whole thing. IT WORKS.

Got any suggestions for a blower for a hot air gun. This Leister is a 600W element and temperature regulator at the end of a 10-foot air hose. They ran the power wire down the center of the air hose and it provides a lot of back pressure. It's designed to run off shop compressed air. My 3/4HP compressor won't supply as much flow as I like. I haven't found anything that can give me more volume against the back pressure. I even tried a 14" blower designed for blow-up advertising devices. No luck. Back pressure just stalls the impeller and the flow drops to nearly nothing. Can't really justify a bigger air compressor and a new circuit to run it for this.

Does it make sense to put fans in series to get better flow under pressure? I gots lotsa fans.

Ideas? Thanks,mike

Argh. Too hot. It should about 220C for leaded and about 230C for lead free BGA.

This article also covers some other issues (mixing solder types).

Again, too hot and possibly not moving the hot air gun fast enough. At that temperature, if you stay at one position for too long, you'll burn the board. I've reflowed similar sandwiches on JetDirect boards, and didn't have the edges curled.

Hold on. Have you tried flexing the board? You may have a mechanical contact connection, but not a soldered connection. You might also break some other BGA connections flexing the board, so you decide if it's worthwhile.

The back pressure doesn't matter much. I use a little air as possible. The only thing the air does is move the heat from the air gun heater, to the PCB. Too much air results in premature cooling. Too little air doesn't move enough heat or heats too slowly. If there's some back pressure, and the reflected air remains fairly cool, don't worry about it.

Ummm... I hope it wasn't designed to run directly off a 150 psi manifold. Got a URL for this thing? One of these?

I couldn't find anything that matches your description. Perhaps if you supplied a model number?

Assuming a piston type compressor, 3/4HP should give you about 5 cubic ft/min. That should be enough to peel parts off the top of the board if you get too close. No way do you need that much air for desoldering. You're not trying to blow hot solder balls all over the board.

What size nozzle are you using? That's not normal. Looking at the various Leister models, it appears that they were not intended for use with a small diameter nozzle.

Dunno. Offhand, I don't think so.

Well, I asked you about this before. I used an IR thermometer to monitor the chip temperature and stopped heating when it got to 220C. I didn't time it, but it seemed like it took a long time to get there with 350C air temperature.

When I practiced on the tivo, I tried air at 260C and could never get the chip over 150C. 350C worked nicely, but it didn't have the intermediate substrate.

The thing is still working. Good enough for me.

Consensus seems to be that uncontrolled reflowing is a temporary solution at best. Reballing and reworking with proper equipment is discussed as the only reliable solution. Remember, we're talking a dollar laptop. Not like it's the end of the world if it quits. I hate that darn eraser mouse, so probably won't use it anyway. I just like to fix stuff. I can part it out for more than it's worth.

Labor 7 S

Rated 50-150 l/min at 500mbar static pressure. I set the regulator at around 10psi, no idea how accurate the gauge is. After about a minute, the tank pressure equalizes somewhere below 10psi and that's all the flow I get.

It's designed for plastic welding with a small tip.

That 10 foot hose really does restrict air flow when you use the whole half-inch opening..

When I dug up the spec, I found lotsa graphs of volume vs back pressure for fans. So, I've looked at this in detail back in 2005 and gave up.

I had an NVidia 8500 that the gpu was BGA. I cooked it in the oven at

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Recently there was a thing about high volume low pressure air for paint guns. I bet you could find something surplus or yard sale for cheap.